Disorders Presenting in Infancy
Disorders of the knee presenting in infancy include hyperextension and flexion deformities. With the exception of patellar dislocation, which may not be apparent at birth, these deformities are usually obvious in the newborn infant. When present, these disorders should trigger a thorough assessment for an associated syndromic diagnosis. Once assessment is complete and the global developmental prognosis defined, rational treatment can produce functional ambulation in children with these dramatic congenital abnormalities.
Hyperextension Deformity
Congenital Hyperextension of the Knee
Few musculoskeletal birth abnormalities are as dramatic as congenital hyperextension of the knee ( Fig. 21-1 ). Those unfamiliar with the condition may describe the extremity as having “the knee on backward.” Clinically, the foot usually presents at the infant’s mouth or shoulder and the femoral condyles may be palpable on the distal thigh. The hyperflexion of the hip is present in utero and should raise the suspicion of concomitant hip dislocation. The incidence of congenital hyperextension deformity is less than 1 per 1000. It has been diagnosed prenatally by ultrasonography.
Classification
Congenital hyperextension deformities of the knee can be classified as congenital hyperextension, subluxation, or dislocation of the knee based on physical examination and radiographic assessment. The degree of passive flexion of the knee also helps determine prognosis and treatment. If the knee will flex and reduce with gentle stretching of the quadriceps, it is classified as grade 1, or congenital hyperextension of the knee (see Fig. 21-1 ). In grade 2, or congenital subluxation of the knee, the knee will not flex beyond neutral, but the femoral and tibial epiphyses are in contact and do not subluxate when flexion is attempted ( Fig. 21-2 ). If knee flexion is not possible and the tibia, which is anteriorly translated in the resting position, displaces laterally on the femur when more vigorous flexion is attempted, the deformity is classified as grade 3, or true irreducible congenital dislocation of the knee (CDK). True CDK is always associated with significant quadriceps fibrosis and shortening. Some consider this the main cause of the deformity. A true lateral radiograph of the knee may help to differentiate between knee hyperextension, subluxation, and dislocation. Fluoroscopy—or even arthrography—may not only increase the quality of the “lateral” radiograph (which may be difficult to obtain because of the deformity, and patient age and size), but allows dynamic assessment of the femoral-tibial relationship ( Fig. 21-3 ).
Etiology
A search should be done for associated anomalies and syndromes at the time of the initial evaluation. Bilateral CDK is almost always syndromic, most commonly associated with laxity syndromes such as Larsen, Beals, or Ehlers-Danlos syndrome ( Fig. 21-4 ). Ipsilateral hip dislocation and clubfoot are present 70% and 50% of the time, respectively. Upper extremity, face, and gastrointestinal and genitourinary systems anomalies are not uncommon. Unilateral CDK may occur as an isolated musculoskeletal condition (with or without ipsilateral hip or foot deformity; Fig. 21-5 ) or may be associated with an underlying neurologic condition, such as arthrogryposis or spinal dysraphism. A person with spinal dysraphism may present with unilateral or bilateral CDK, or he or she may have one hyperextended knee and one knee with a flexion deformity.
Whether isolated or syndromic, CDK is thought to be the result of abnormal fetal positioning. Once the abnormal position occurs, lack of movement because of neuromuscular conditions (e.g., arthrogryposis) or hyperlaxity leads to persistent hyperextension resulting in subsequent quadriceps atrophy and fibrosis. Hypoplasia of the patella and contracture of the iliotibial (IT) band are noted in CDK and may be the result of decreased in utero muscle and joint movement.
Clinical Features
The degree of ligamentous laxity is variable in CDK. Elongation, insufficiency, or absence of the cruciate ligaments is at times a complicating feature of CDK. We believe that cruciate ligament absence is more frequent in bilateral cases associated with laxity syndromes. Conversely, in isolated CDK, which is often unilateral, once the knee is reduced it is relatively stable.
Other pathologic findings in true CDK include anterior subluxation of the posterolateral and posteromedial structures, including hamstring tendons and the IT band. The suprapatellar pouch may be atrophied or obliterated, with adhesions between a hypoplastic patella, the femur, and the IT band.
Treatment
Manipulative
Nonoperative treatment should begin as soon as possible in infancy. The flexibility of the quadriceps can be assessed by applying gentle traction to the tibia and attempting flexion of the knee. The knee with congenital hyperextension can usually be corrected with gentle manipulation of the tibia into a flexed position. Longitudinal traction is applied to the tibia, and pressure is applied to the tibia in an anteroposterior direction to bring it around the femoral condyles. It is important to avoid a hinge type of flexion that will leave the tibia anteriorly subluxated on the femur. The new position is maintained in a cast or splint. Once 30 degrees or more of flexion is obtained, the knee will usually further flex to 90 degrees with one or two more manipulations. Forceful manipulation can produce fractures or epiphyseal injuries and should be avoided ( Fig. 21-6 ). Once 90 degrees of flexion is obtained, a removable splint can be used for a few months to maintain correction. Recurrence is unusual.
When a more severe quadriceps contracture prevents reduction, a block of the femoral nerve using a local anesthetic or a quadriceps block with botulinum toxin type A may allow further correction of the deformity. A trial of nonoperative management, with a neuromuscular blockade if necessary, may be effective if started before 12 months of age.
Surgical
Surgical treatment for knees that do not respond to serial manipulations may be done as early as 6 months of age and probably should be initiated by 1 year of age. The ideal age for treatment depends on the surgeon’s experience, and often on the planned management of other lower extremity abnormalities.
The classic surgical approach to true CDK has been a V-Y quadricepsplasty combined with medial and lateral arthrotomies of the knee, which allow mobilization of the ligamentous structures that are anteriorly displaced ( Fig. 21-7 ). Historically, little attention has been paid to the redundant posterior capsule or the anterior cruciate ligament (ACL) deficiency. Unfortunately, the extensive quadriceps release required to obtain adequate length often results in weakness (which manifests itself in extensor lag) and fibrosis (which limits flexion). These features, combined with the redundant posterior capsule and ACL deficiency, may lead to recurrent anterior instability and even redislocation. In an unpublished review of 22 congenitally dislocated knees in 14 patients treated at Texas Scottish Rite Hospital for Children, we found nine knees treated with V-Y quadricepsplasty without ACL reconstruction that were unstable, had poor quadriceps strength, and required full-time bracing or other assist devices (i.e., crutches, walker, or wheelchair) for community ambulation. Eight of these nine unsatisfactory knees were in patients with laxity syndromes—predominantly Larsen-Johansson. As a result of this review, we have modified our approach to the patient with an ACL-deficient, congenitally dislocated knee and a laxity syndrome to include posterior capsulorrhaphy and ACL reconstruction. In addition, because of problems with extensive quadriceps scarring, we prefer to perform acute femoral shortening and avoid quadriceps lengthening.
Preoperative Planning.
Preoperative planning begins with an assessment of all concomitant lower extremity deformities. The use of femoral shortening rather than V-Y quadricepsplasty allows simultaneous correction of hip and knee dislocations. Hip and knee deformities usually are corrected before any concomitant foot deformity. Patients with “hyperlaxity” syndromes are more likely to develop instability or redislocation. Patients with “neuromuscular dislocations,” such as arthrogryposis or myelomeningocele are less likely to have redislocation but are more prone to postoperative stiffness. We have found that femoral shortening rather than extensive quadriceps lengthening produces weakness and fibrosis of the quadriceps.
Operative Technique.
The knee is approached through a midline longitudinal incision that extends proximally and laterally to facilitate lateral exposure of the femoral diaphysis. A lateral parapatellar arthrotomy is performed to mobilize the IT band and vastus lateralis. The quadriceps tendon, patella, and patellar tendon are mobilized through a medial arthrotomy. The biceps and pes anserinus tendons, which are usually subluxated anteriorly, are identified and mobilized after the medial and lateral arthrotomies. The femur is usually shortened 2 to 2.5 cm at the distal metaphyseal-diaphyseal junction. If a hip dislocation is being treated concomitantly, the femoral shortening may be done in the middiaphysis or the proximal metaphyseal-diaphyseal junction. Once the quadriceps is “functionally lengthened or decompressed” with femoral shortening, the patella can usually be stabilized in the intracondylar notch by advancing the vastus medialis and imbricating the medial capsule. At this point, the knee should be assessed to determine whether capsulorrhaphy or ACL reconstruction is necessary.
Because recurrent instability is common in patients with laxity syndromes, we often perform capsulorrhaphy with or without ACL reconstruction in this patient population. Instability is less common in patients with arthrogryposis, but they sometimes have recurrent or persistent subluxation resulting in limited flexion and may benefit from capsulorrhaphy. Capsulorrhaphy is performed at the posterior corner of the lateral femoral condyle after bluntly dissecting the capsule with the knee flexed. It is usually possible to excise 1 to 1.5 cm of the posterior lateral capsule ( Fig. 21-8 ). Once the posterior lateral capsulorrhaphy is completed, we make a 3- to 4-cm incision behind the medial femoral condyle. This incision is localized by placement of a blunt instrument from lateral to medial, posterior to the femoral condyles, and anterior to the capsule. Medial capsular dissection is carried out with the knee flexed and the gastrocnemius muscle retracted posteriorly. Consideration should be given to shortening of the hamstrings in conjunction with the capsulorrhaphy. At the completion of the capsulorrhaphy, the knee should lack 30 degrees of full extension and should flex to at least 90 degrees. It has been our experience that this flexion contraction will stretch in the first postoperative year.
If the ACL is absent and the patient has a hyperlaxity syndrome, we believe consideration should be given to ACL reconstruction. Our preferred technique for ACL reconstruction is the antegrade IT band transfer described by Insall ( Fig. 21-9 ). The IT band is taken off its insertion on Gerdy tubercle and mobilized proximally. The tendon is then tubularized and distally rerouted “over the top” of the lateral femoral condyle and through the intercondylar notch. The distal reattachment into the proximal tibia can be either through a drill hole entirely within the epiphysis or through a more vertical transphyseal tunnel. The major advantage of this technique is that, left in its anatomic location, the IT band is a deforming force, producing hyperextension, valgus, and external tibial rotation—thus rerouting it may actually prove beneficial. In addition, rather than a simple passive restraint, it is an active transfer. The biggest disadvantage of this technique is the potential for physeal injury. We believe this risk can be mitigated using an entirely epiphyseal tunnel, advancing the tendon through the epiphyseal drill hole and securing it by a button on the skin of the anterior tibia. Care should be taken when drilling the epiphyseal tunnel to avoid damage to the physis (particularly anteriorly) and to ensure that the tunnel is through bone rather than cartilage to facilitate tendon ingrowth.
Flexion Deformity
Congenital Dislocation of the Patella
Whereas patellofemoral instability is a common and diverse condition familiar to all orthopaedists, congenital dislocation of the patella is a rare condition that presents with a laterally displaced, hypoplastic patella. These patients usually have varying degrees of flexion and valgus contracture of the knee, as well as external rotation of the tibia ( Fig. 21-10 ). The most severe forms of congenital dislocation of the patella are associated with a significant knee flexion contracture that is readily apparent at birth. Often the patella is not palpable in these patients because it is both hypoplastic and nearly adherent to the lateral femoral condyle. At the other end of the spectrum are patients with a more mobile patella that actually may be “reducible” when the knee is flexed. These more mildly affected patients may be unable actively to extend the knee from full flexion but have normal ability to maintain knee extension once it is attained and the patella is reduced.
Etiology
Although Goldthwait described surgical treatment of patellar dislocation in 1899 and Conn described vastus medialis obliquus (VMO) advancement in 1925, it was not until 1976 that Stanisavljevic and colleagues attributed congenital dislocation of the patella to aberrant fetal myotome development. They noted that laterally placed thigh structures rotate internally in the first trimester of embryologic development and hypothesized that congenital dislocation of the patella was the result of failure or disruption of this rotation, leaving the patella laterally displaced along the lateral femoral condyle.
Clinical Features
Congenital patellar dislocation presents with a spectrum of severity. The most severe forms have significant knee flexion contractures that make the diagnosis evident in infancy. However, more mildly affected individuals may not present until school age, when relative quadriceps weakness begins to present functional problems. Radiographs may be difficult to interpret because the patella does not normally ossify until about 3 years of age, and this may be delayed even further in the presence of congenital dislocation. In severe cases, radiographic assessment is also complicated by the fact that the patella may become nearly confluent with the lateral femoral condyle.
Treatment
Congenital dislocation of the patella usually requires surgical reconstruction that involves “medializing” the entire extensor mechanism. This is accomplished with extensive lateral release and advancement of the VMO distally and medially. In more severe cases, the IT band may need to be divided transversely and the quadriceps may be lengthened by either V-Y plasty or femoral shortening. Although some authors have advocated a skin incision that extends to the proximal femoral metaphysis, we believe that an extensive lateral release can be performed through a more limited distal incision. In our experience, to achieve adequate medial realignment the vastus lateralis should be mobilized from the intramuscular septum. We believe this can be accomplished without an extensive skin incision. In addition to the lateral release and medial reefing, more severe cases will require medialization of the patellar tendon. In such cases, we prefer the Goldthwait transfer of the lateral half of the tendon rather than complete release and reinsertion, primarily because of the lower risk of physeal injury. Before skin closure, we expect 50 to 70 degrees of flexion without lateral dislocation of the patella. Patients are casted in 10 to 20 degrees of flexion for 6 to 8 weeks. Aggressive quadriceps rehabilitation is necessary after cast removal. Parents should be counseled that an active extensor lag will persist for 3 to 12 months.
The results of quadriceps realignment for congenital dislocation of the patella are poorly documented. Recurrent dislocation has been reported in up to 10%. Persistent extensor lag has also been noted—particularly in patients with an underlying skeletal dysplasia or neuromuscular condition such as arthrogryposis. Both medial redislocation and peroneal nerve palsy have also been reported.
Patients with Down syndrome and patellofemoral instability—whether congenital or acquired—are more difficult to treat because of recurrent dislocation. Patellofemoral instability has been reported in up to 8% of patients with Down syndrome. However, many of these patients are asymptomatic. When considering “prophylactic intervention” in the minimally symptomatic or asymptomatic patient with Down syndrome, it is important that successful results have been reported in 86% of patients who had functional impairments before reconstruction.
Congenital Knee Flexion Contracture
A mild knee flexion deformity is not an uncommon finding in the neonate. These “positional knee flexion contractures” are a benign, self-resolving problem likely associated with intrauterine positioning and can be viewed as a normal finding. Positional knee flexion contractures initially may be up to 45 degrees. If further knee flexion and quadriceps function are normal and there are no other neurologic or dysmorphic features, the parents can be reassured that the flexion contracture will resolve in the first few months of life. Unfortunately, management is more difficult in the child with a more significant knee flexion deformity. Significant knee flexion deformities are most commonly associated with other underlying conditions. These conditions are outlined in Box 21-1 and include primary limb dysplasias, syndromes associated with soft tissue contracture, neurologic conditions, and skeletal dysplasias. Diagnosis of the underlying condition may require the assistance of a geneticist, and more severely involved patients may have significant neurodevelopmental issues.
Lower Extremity Dysplasias
Congenital femoral deficiency
Tibial hemimelia types 1a, 1b
Congenital quadriceps/patellar tendon dysplasia
Congenital dislocation (fixed) of the patella
Syndromes with Soft Tissue Contracture
Arthrogryposis
Popliteal pterygium syndrome
Escobar (multiple pterygium) syndrome
Beals syndrome (congenital contractural arachnodactyly)
Neurologic Syndromes
Sacral agenesis
Myelodysplasia
Skeletal Dysplasia with Bony Flexion Deformity
Diastrophic dysplasia
Metatrophic dysplasia
Miscellaneous skeletal displasias
Etiology
The cause of a congenital knee flexion contracture usually depends on the underlying diagnosis. Although congenital knee flexion contractures may be seen with any congenital limb dysplasia, they are most commonly associated with congenitally short femur or tibial hemimelia. The underlying pathologic process in these patients is a failure of normal musculoskeletal development. Although these patients present with a wide spectrum of deformity and comorbidities, certain factors should be considered in all patients when planning treatment. These include the function of the quadriceps, knee stability, limb length difference, and the status of the contralateral extremity. The status of the upper extremities should also be assessed. Patients who lack upper extremity prehension may use their feet as their primary prehensile mechanism. Surgery to reposition the lower extremities in these patients should be approached with caution to avoid loss of prehensile function.
Related Conditions
Congenital knee flexion contractures perhaps occur most commonly and are most difficult to treat in patients with soft tissue syndromes, such as arthrogryposis, Beals syndrome, popliteal pterygium syndrome, or Escobar syndrome. Arthrogryposis and Beals syndrome are characterized by limited active (and subsequently passive) motion of multiple joints. Presumably this lack of motion is present in utero, reflected by the absence of skin flexion creases across the involved joints ( Fig. 21-11 ). In addition to extensive popliteal webbing, patients with popliteal pterygium syndrome (also known as facio-genito-popliteal syndrome) may have cleft lip and palate, intraoral webbing, intercrural webs that can produce distorted external genitalia, and finger and toe syndactylies with nail abnormalities ( Fig. 21-12 ). These patients usually have normal intelligence and development. In multiple pterygium, or Escobar syndrome, webbing occurs across multiple flexion areas, including the neck (85%) and popliteal fossa (60%). Less commonly affected areas include the axilla, antecubital fossa, and fingers. These patients may also have kyphoscoliosis and short stature. These patients are often “normal” at birth and have progression of webbing with growth. The common feature in patients with pterygium syndromes is a subcutaneous fibrous band that extends from the ischium to the calcaneus. This band is usually intimately involved with the tibial branch of the sciatic nerve. The band is a subcutaneous fascial cord enveloped in a tent of aberrant muscle and fascia that fills the web and is confluent with the lateral intramuscular septa at the thigh and leg.
Knee flexion contractures also are seen in patients with myelodysplasia or sacral agenesis. Many factors influence the decision to release these contractures surgically. The absence of quadriceps function may contraindicate release if there is little likelihood of functional ambulation.
In patients with skeletal dysplasias, knee flexion contractures may be the result of bony or articular cartilage differences rather than soft tissue constraints. Thus their deformity may be better addressed by bony procedures, such as osteotomies or growth manipulations (i.e., physeal stapling/tethering).
Treatment
The decision to treat a congenital knee flexion contracture involves a careful assessment of all lower extremity deformities and the neurodevelopmental status of the patient. One contraindication to treatment is the absence of active quadriceps function because these patients will invariably experience a recurrence of deformity. In general, equinus deformities of the ankle and hip flexion contractures need to be addressed to prevent recurrence. Obviously, patients who have global delay or significant weakness that precludes ambulation may not warrant aggressive treatment. It has been our experience that treatment of severe knee flexion deformities may redirect the arc of knee motion, but it is unlikely to significantly increase the total arc of motion.
Nonoperative Treatment
Patients with mild (30 to 40 degrees) contractures can occasionally be managed successfully with serial manipulations and casting. If soft tissue manipulation does not prove effective in reducing the knee flexion contracture, these patients may ambulate with knee-ankle-foot orthoses that accommodate their knee flexion contracture. We have occasionally used a hinged cast—with or without a soft tissue release—to manage patients with mild or moderate contractures. The Quengel hinge allows both extension and translation ( Fig. 21-13 ).
Unfortunately, few patients with significant knee flexion contracture will be managed definitively with nonoperative techniques. Thus, once it has been established that the patient has enough quadriceps and gross neurologic function to warrant treatment, surgical management is usually required.
Surgical Treatment
Mild Contractures.
Patients with skeletal dysplasias or mild “soft tissue” flexion contractures can occasionally be treated with either distal femoral extension osteotomy or procedures to manipulate the growth of the distal femur (i.e., anterior physeal tethering with staples, screws, or a plate). We reserve these techniques for mild deformities and caution parents that recurrence is common with growth and remodeling of the distal femur.
Contractures Greater Than 60 Degrees.
Correction of congenital knee flexion contractures greater than 60 degrees usually involves complete posterior release and femoral shortening. Not infrequently, there is also a fibrous adhesion in the anterior part of the knee that blocks full extension (similar to a rug under a door); this can be excised through an anterior incision and medial parapatellar arthrotomy, which allows débridement of the patellofemoral joint. We approach these in the supine position, which facilitates medial, lateral, and anterior incisions.
We begin with a lateral incision (Henry approach) that allows identification of the peroneal nerve, release of the biceps and IT band, and posterior capsulotomy. Once the posterolateral aspect of the joint has been released, a blunt instrument can be placed behind the condyles from lateral to medial to localize the medial incision. A 3- to 4-cm medial incision allows release of the medial hamstrings and the medial capsule. At this point (after complete posterior release and capsulotomy), the tightest structure is frequently the neurovascular bundle. Decompression of the neurovascular bundle can be achieved through a femoral shortening osteotomy. The incision can be extended laterally to allow exposure of the lateral aspect of the femoral diaphysis. The femur can be safely shortened up to 3 to 4 cm, if necessary. The fixation plate is most commonly placed laterally; however, if it is placed directly posteriorly, it is in an improved biomechanical position on the tension side of the osteotomy as the knee is extended.
Once the femoral shortening has been completed, knee motion is examined. If there is an “anterior block” preventing full extension, it can be addressed through a midline anterior incision and arthrotomy to remove the redundant tissue that impedes extension. At this point, consideration is given to shortening of the quadriceps or patellar tendon. This may be accomplished by primary excision and repair or reefing using a “rolled anchovy” technique. If there is a significant equinus contracture at the ankle, posterior release should be considered, although care must be taken to avoid a double stretch to the neurovascular structures that occurs with addressing both knee flexion contracture and ankle equinus at the same setting. (Tibial shortening may be performed to further decompress the neurovascular and other soft tissues.) The patient is then placed in a hip spica cast with the knee in maximum extension. If the surgical time has been prolonged and the soft tissue dissection extensive, a bulky dressing may be applied, followed 1 to 2 weeks later by the spica cast. The cast is removed after 6 to 10 weeks. Knee-ankle-foot orthoses may help slow the rate of recurrence, which is common after these difficult procedures.
Contractures in Popliteal Pterygium Syndromes.
The surgical management of patients with popliteal pterygium syndromes is even more difficult than those with straightforward congenital knee flexion contractures. These patients often require Z -plasties of the posterior skin and careful dissection of the ischiocalcaneal cord, which is usually intimately intertwined with a branch of the sciatic nerve. These patients may be best addressed in the prone position.
Gradual Correction Using External Fixators.
Correction of severe knee flexion contractures with external fixators is an attractive option that has been successfully performed with circular and monolateral devices. The sciatic nerve may be more tolerant of gradual correction with a hinged external fixator, and skin problems may be more easily managed. However, recurrence of the deformity is still a frequent clinical problem. There is some debate as to whether soft tissue release is necessary before attempting correction with an external fixator. Distraction arthrodiastasis may induce an increased fibrous tissue response, which may be more pronounced after soft tissue release. We prefer to achieve gradual correction with the frame without a soft tissue release. After applying the frame with the hinge carefully positioned on the joint center, we initially distract across the joint and then begin gradual angular correction. We believe the initial distraction is important to decrease the forces across the joint because articular and epiphyseal cartilage pressure necrosis is a potential complication with this technique.
Results of gradual correction of knee flexion contractures in patients without pterygium syndromes appear to be slightly more encouraging than those with acute correction. Correction of contractures of more than 90 degrees has been reported with the Ilizarov frame, although complications occurred in 4 of 13 patients (3 pathologic fractures and 1 nerve palsy).
Results and Complications.
Despite meticulous and careful treatment, it is inevitable that some patients with severe congenital knee flexion contractures will experience recurrence that impedes function. Recurrence is by far the most common complication after surgical treatment of congenital knee flexion contractures. These procedures are best at redirecting the arc of motion and seldom increase the total arc of motion. Patients with the pterygium syndromes have an increased likelihood of wound problems even when approached surgically through Z -plasty incisions, which expose the ischiocalcaneal tether. Damage to the epiphyseal plate can also occur—presumably from excessive pressure between the femur and tibia when the knee is extended. Adequate femoral and tibial shortening may help to prevent this complication. In some cases, such as the pterygium syndromes, amputation may be appropriate. If there is significant limb length inequality, knee arthrodesis and Syme amputation may provide a more cosmetic and functional result than knee disarticulation. If ankle range of motion and strength are adequate, these patients can also be managed with a resection/rotationplasty that will allow them to be fitted with a below-the-knee prosthesis.
Disorders Presenting in Childhood and Adolescence
Anatomic Conditions
Bipartite Patella
Pathogenesis
The patella normally forms from one ossification center. Occasionally there are two or more centers of ossification, and if they fail to fuse, a bipartite or tripartite patella results. In more than 75% of the cases, the accessory patellar portion is on the superolateral pole, the next most frequent location is on the lateral margin, and an accessory center rarely occurs in other locations. The lesion may be bilateral in up to 25% of cases.
A bipartite patella is often asymptomatic and may be an incidental radiographic finding in approximately 2% to 3% of normal people. Trauma may cause the fragment to separate through a fibrous union, which may then result in patellar pain. The pain is aggravated by activity and is localized around the bipartite fragment. A symptomatic bipartite patella will most often have pain reproduced by direct palpation of the fragment region.
Radiographic Findings
Plain radiographs reveal a separate fragment of patella with a lucent line between it and the remainder of the bone. If there is doubt as to the source of symptoms, magnetic resonance imaging (MRI) may be helpful. An increased signal within the bipartite fragment is often seen in a symptomatic patient. The MRI also may assist in the exclusion of other sources of pain. Whereas a bone scan has been used in the past, increased uptake may be seen in both symptomatic and asymptomatic bipartite fragments.
Treatment
A painful bipartite patella in children should be treated initially with reduction of activities, the use of nonsteroidal antiinflammatory drugs (NSAIDs), and, if necessary, immobilization in a knee immobilizer or cast for 3 to 4 weeks. Chronic and persistent symptoms that restrict activities may indicate a need for surgical treatment.
Open and arthroscopic lateral release has also been reported with good functional result. Unstable fragments should be removed, but stable fragments may be left in place. Union of the fragment may occasionally occur, but may not be required for successful pain relief.
Fragments may be excised with good outcomes. Excision may be carried out arthroscopically, or through a limited direct approach. When activity modification has failed and local fragment palpation reproduces symptoms, we prefer arthroscopic examination and excision ( Fig. 21-14 ). The knee is examined for other pathology and the fragment is excised arthroscopically using a motorized chondrotome and manual instruments. The fragment is removed from the under surface of the lateral retinaculum and vastus lateralis, leaving dorsal expansion of these soft tissues intact in the remainder of the patella when possible. Fluoroscopic control is used when required, and conversion to a direct superior-lateral open approach is performed when lesion size or character dictates. Postoperative mobilization and weight bearing are immediate, and early closed-chain strengthening is employed. Return to sport is allowed when strength is symmetric and the effusion resolves.
Discoid Meniscus
Discoid meniscus is an anatomic variation of the meniscus that may be asymptomatic or may cause mechanical symptoms in the knee. Most reported discoid meniscal structures are in the lateral compartment, but infrequent cases of medial discoid meniscus have been reported.
Pathogenesis
The exact cause of discoid meniscus has not been determined. Initially, it was attributed to failure of an embryologic sequence of degeneration of the center of the meniscus. Further embryologic studies showed that the normal meniscus is not formed from a discoid precursor. Rather, the menisci form from a mesenchymal condensation that occurs between the femur and tibia toward the end of the second fetal month. From the beginning of their formation, the menisci have a semilunar shape. One theory is that the discoid meniscus forms from fibrocartilage laid down in mesenchyme that normally disappears in joint formation. Histologic studies demonstrating abnormal numbers and orientation of collagen fibers within discoid menisci suggest that they are a structural variation rather than a morphologic variant. Discoid menisci have been found in 4- and 6-month-old infants, suggesting an early causal event.
Classically, discoid meniscal findings are grouped into three types as described by Watanabe. The first is the Wrisberg ligament type, in which the lateral meniscus has no attachment to the tibial plateau posteriorly. Instead there is a ligament that connects the posterior horn of the lateral meniscus to the lateral surface of the medial femoral condyle. This is called the meniscofemoral ligament or the ligament of Wrisberg, which is normally found in quadruped animals. The ligament tethers the meniscus so that it is unable to glide forward when the knee is extended. Rather, it pulls the meniscus into the intercondylar notch as the knee extends and returns the meniscus to a normal position as the knee flexes. This motion produces a snap with each excursion of the meniscus and causes the meniscus to become hypertrophic and irregular. Traditionally, this has been reported as the least common type of discoid meniscus. The second type of discoid meniscus is the complete type, which is characterized by a thickened lateral meniscus that has peripheral attachments and is not highly mobile within the joint. When stable peripheral attachments are present, this type may often be asymptomatic, as opposed to the more globular, hypermobile Wrisberg type.
The third type is the incomplete type, which differs from the complete type only in that it exhibits varying amounts of concavity at its central margin and does not entirely cover the lateral tibial plateau.
An unknown percentage of discoid menisci, complete or incomplete, with normal coronary ligament attachments may remain asymptomatic indefinitely. Discoid meniscus is noted by imaging and arthroscopy in asymptomatic individuals. These may be complete or incomplete, but Wrisberg type with peripheral rim instability tends to become symptomatic at a young age. In an unknown percentage of the stable complete and incomplete variants, biomechanical forces through the abnormal menisci are theorized to lead to the development of tears and subsequent symptoms. The differential factors resulting in torn and symptomatic menisci as opposed to preserved and asymptomatic discoid menisci remain unclear.
Clinical Features
Presentation in younger age groups often takes one of two forms. Classically, the presenting complaint is that of a popping or snapping of the knee that is both heard and felt by the child or parent. The popping or snapping may be noticed in early childhood and occasionally in infancy, but most often it is noted in children older than 4 years of age. Most often the snapping is not painful and the child is normally active. Physical findings may be diagnostic. The typical findings are a palpable snapping as the knee flexes and extends. Along the lateral joint line, the examiner feels a bulge as the meniscus seems to protrude beyond the margin of the tibia. As the knee moves, the meniscus snaps into the intercondylar notch and the bulge disappears. Presentation with these signs of hypermobility, and any presentation before adolescence may be correlated with a higher rate of bilateral discoid morphology and should therefore prompt contralateral evaluation and monitoring. A second type of presentation may be one of flexion contracture, with an unclear time of onset, and vague symptoms with activity. In some cases the knee may be locked and lack full extension. This implies a torn or peripherally unstable discoid meniscus, most often with translation of the enlarged meniscus anteriorly causing a mechanical block to extension.
The first symptom in many of the older children and adolescents may be pain, snapping, popping, or locking with or without a history of injury. There is often focal lateral joint line tenderness and an effusion.
Radiographic Findings
Plain radiographs may show widening of the lateral joint space. Widening is most easily seen when both knees are imaged on the same radiograph for comparison ( Fig. 21-15 ). Other findings include flattening of the lateral femoral condyle (giving a squared-off appearance), cupping of the lateral aspect of the tibial plateau, and a relatively high fibular head. Several studies have shown that MRI can demonstrate a discoid meniscus and most tears and therefore may aid in diagnosis. The presence of an anteriorly shifted meniscal segment or an increased height of Wrisberg ligament attachment may predict posterior rim detachment of complete discoid variants. Additionally, an increased measured height of the posterior meniscus on sagittal imaging is suggestive of a torn complete discoid meniscus. The presence of a tear or instability of the discoid may not always be demonstrated, therefore thorough arthroscopic inspection at the time of treatment is paramount.
Treatment
Many children with discoid meniscus may require no treatment. Mild snapping and popping may be present for many years without pain or limitation of function. These younger children may be followed and treated only if pain or loss of motion or function occurs. Surgical treatment of the discoid meniscus is indicated when discomfort, swelling, loss of motion, locking, inability to run, or inability to participate in sports occurs.
Procedure.
Recommended treatment is arthroscopic partial meniscectomy and preservation of peripheral meniscal structure. A standard 30-degree arthroscope is used, with the majority of meniscal evaluation and débridement performed with the knee in the figure-4 position. Because of the volume of meniscal tissue present and varying degrees of subluxation of the meniscus as a result of commonly encountered peripheral rim instability, visualization and access to the central portion of the compartment can be difficult. The use of both standard- and small-joint instruments may facilitate débridement in smaller patients. Miniarthrotomy may facilitate access in smaller joints.
Various techniques of partial central meniscectomy have been described. General principles are stepwise central débridement with hand-held and motorized instruments, preservation of 5 to 7 mm of peripheral tissue, and stabilization of the peripheral rim ( Fig. 21-16 ). Frequent joint repositioning to evaluate peripheral tissue volume and excursion is useful during débridement ( Fig. 21-17 ). Good visualization and meticulous probing for peripheral rim stability are critical to evaluate requirements and strategies for stabilization. In a series of 128 knees, Klingele and colleagues identified peripheral rim instability in 28% of cases. This finding was present in both complete and incomplete morphologic subtypes and was amenable to repair in 31 of 36 cases. Peripheral stabilization requires superficial débridement and preparation of tissue with a rasp or motorized shaver, and suture repair. We apply vertical sutures by both inside-to-out and all-inside techniques. Outside-to-in techniques are used for anterior–one third stabilization. Peripheral meniscal body tears within the zone of planned preservation are repaired by similar techniques.
Postoperative Treatment.
Postoperative treatment depends on the requirement for meniscal stabilization. Patients with partial or complete meniscectomy are allowed to bear weight without restriction and are released for activities at 3 weeks. After meniscal repair, bracing and limited weight bearing are advised for 4 to 6 weeks with early range-of-motion exercises and muscle rehabilitation. No sporting activities are allowed for 3 to 4 months. Patients having a preoperative flexion position may require physical therapy to regain full knee extension.
Results.
The results of arthroscopic partial meniscectomy are good to excellent in approximately 85% of patients. In general, short-term functional outcome may be equivalent with partial and subtotal resection. However, over time, volume of meniscal loss tends to correlate with poorer functional and radiographic results. With follow-up beyond 5 years, meniscal preservation results in decreased radiologic degenerative changes and symptoms of arthrosis. While long-term results of saucerization in conjunction with repair of peripherally torn discoid menisci and stabilization of peripheral rim instability are not available, short-term results are encouraging with good functional outcomes. Finally, early and more severe radiographic deterioration may be seen in patients having symptoms for more than 6 months, preexisting valgus alignment, articular cartilage change at the time of treatment, and in those requiring total meniscectomy. In general, these findings and the large body of literature regarding meniscectomy in the general population reinforce the recommendation for meniscal preservation whenever possible.
Osteochondritis Dissecans
Osteochondritis dissecans (OCD) of the knee is characterized by the presence of an area along the femoral articular surface consisting of cartilage and bone that may be softened or may become loose and separated from the rest of the femoral condyle. Most lesions are located on the lateral side of the medial femoral condyle and range in size from a few millimeters to 2 to 3 centimeters in diameter. The osteochondral fragment may remain in place or may loosen and become an intraarticular loose body. The disorder was first described by Sir James Paget, who called it “quiet necrosis.” The term dissecans should be used because it implies a process of cutting loose. The term is often misstated as desiccans, which connotes a dry lesion.
Etiology
Mechanical.
The exact cause of the osteochondral lesion has not been determined. A biomechanical study of the distal femur using finite-element analysis showed that as loads are applied to the distal femur, the stresses on the subchondral bone are greatest in the medial femoral condyle. These stresses arise from loading forces in the mediolateral direction and from compression forces generated by the patella and tibia in the anteroposterior (AP) direction, and they are the greatest in 60 degrees of flexion. Rehbein was able to produce experimental lesions similar to those of OCD by repeated forced hyperextension of the knee combined with force placed on the femoral condyles through the patella. Mechanical axis deviation within the compartment exhibiting lesions has been demonstrated, further suggesting that increased loading may be related to OCD cause.
Langenskiöld and others postulated that cartilage fractures in childhood result in osteochondritis lesions. He excised a segment of hyaline cartilage from the articular surface of the distal femur of rabbits, leaving a synovial tissue attachment. The fragment was then replaced in its crater. Several months later the fragment had developed an osseous nucleus similar to that seen in the disorder in humans.
Mechanisms that have been shown to cause osteochondral fractures of the femoral condyle include impingement from a tall tibial spine, direct blows causing compaction, rotatory forces, and joint compression forces. Nonunion of an osteochondral fracture produces a lesion that is identical to that of osteochondritis dissecans. Most osteochondral fractures are noted immediately after a traumatic event, occur when the knee is acutely loaded, often in a flexed position, and may be accompanied by a loud snap. It may be that lesser injuries that are unnoticed, or at least unreported, result in OCD lesions. Only one in five patients with osteochondritis can recall a specific injury.
Juvenile and adult lesions behave differently and may well have different causes. Smillie suggested that the juvenile form represents a disturbance of epiphyseal development, with small accessory islets of bone being separated from the main osseous nucleus of the epiphysis. He attributed the adult form to trauma. Histology studies suggest common features of physical separation and fibrous tissue mixed with varying degrees of viable subchondral bone trabeculae within the interposition zone. However, two different patterns of surface cartilage may be seen: an abnormally thick hyaline section, or a relatively normal thin hyaline layer over subchondral bone.
Hereditary.
A number of reports in the literature suggest that osteochondritis is a familial condition. Some of these reports lump osteochondritis lesions of different joints together, which may confound the findings.
There are cases of multiple joint involvement in the same patient and a 13% to 30% incidence of bilateral knee involvement, which suggests some type of predisposition. There are also cases associated with dwarfism, which may imply either a genetic predisposition or a mechanical cause based on abnormal joint configuration.
Ischemic.
Primary ischemia has been proposed as a cause of OCD, perhaps due to some embolic phenomena. However, this theory has been refuted by Rogers and Gladstone, who described a rich blood supply to the lower end of the femur and the lack of end arteries in the region.
Pathology
The characteristic pathologic findings of an OCD lesion are an area of avascular necrosis of bone with a cleft on one or the other side, with varying degrees of ischemia and fibrosis of the overlying hyaline cartilage. Initially, the hyaline cartilage appears normal, but as subchondral bony support is lost it undergoes degenerative changes, including softening, fibrillation, and fissuring. Improvement in the histologic features of the cartilage has been reported following fixation and healing of unstable lesions.
Healing of the avascular bone occurs by revascularization and repair by “creeping substitution.” When healing is incomplete, the interzone between the osteocartilaginous fragment and surrounding cartilage is filled by dense fibrous tissue. These findings indicate delayed union or nonunion of the fracture.
Clinical Features
The most common presenting complaint is nonspecific knee pain. The patient may report aching pain in the parapatellar area that is aggravated by vigorous activities. Pain with stair climbing may also occur. If the fragment has become loose, the patient will note crepitance, popping, giving way, and occasionally locking of the knee.
Physical findings are often minimal. In early cases there may be mild parapatellar tenderness, slight quadriceps atrophy, and slight pain with range of motion. Specific tenderness along the medial border of the patella with the knee flexed may be found, with the lesion commonly located on the lateral aspect of the medial femoral condyle. Wilson sign is said to be specific for the diagnosis. It is noted by flexing the knee to 90 degrees, fully rotating the tibia medially, and then gradually extending the knee. When the test result is positive, there is pain at 30 degrees of flexion; the pain is located over the medial femoral condyle anteriorly. The test has a low diagnostic value because it may often be negative in patients with an existing lesion. When patients do report pain with the maneuver, it may be used to follow healing of the lesion.
With more severe lesions or when a loose body has formed, there may be effusion, tenderness, synovial thickening, and greater quadriceps atrophy. Crepitance is occasionally noted, and rarely the loose body may be palpable. Occasionally the knee is locked. These features are correlated with lesion instability and are usual indications for operative treatment.
Radiographic Findings
The lesion is usually noted on AP and lateral radiographs of the knee and may be seen tangentially on a flexed or “notch” view ( Fig. 21-18 ). The notch view is especially suited to show the lesion in its most common location—on the posterolateral aspect of the medial femoral condyle. Early lesions appear as a small radiolucency at the articular surface. Lesions of varying size may present on the medial femoral condyle in various locations, or the lateral and posterior aspect of the lateral femoral condyle ( Fig. 21-19 ). Historically, medial lesions have a better prognosis for healing, and the larger lesion size is a risk for failure of nonoperative treatment. More advanced lesions have a well-demarcated segment of subchondral bone with a lucent line separating it from the condyle. The presence of this radiographic sclerotic rim may predict failure of nonoperative treatment.
In young children (between 2 and 6 years of age), ossification of the distal femoral epiphysis is often irregular, and small foci of ossification may appear beyond the margin of the main ossific nucleus. These lesions are not thought to be related to OCD. Caffey and associates have classified these irregularities as follows: group I—varying degrees of roughening of the margins and occasionally small separate foci of calcification; group II—larger marginal irregularities with specific indentations; group III—marginal irregularities with an independent island of bone, similar to what is seen in OCD in older children. If there is uncertainty regarding the finding in older children with knee symptoms, MRI may be useful in identifying the nature of the lesion. Lack of bone marrow edema distinguishes the irregularity of ossification from OCD.
MRI is useful in determining the stability of the osteochondrotic lesion and is therefore vital as a guide for treatment in older children. Subchondral cysts and displacement of the osteochondral fragment are clear signs of instability and the need for surgical intervention. Articular cartilage discontinuity with synovial fluid tracking below the lesion is also a sign of instability, but this may be difficult to ascertain. High signal intensity around the lesion on T2-weighted images must be interpreted in the context of articular surface continuity. When the articular surface is uninterrupted, high signal intensity may represent a healing response rather than instability of a lesion in a skeletally immature knee ( Fig. 21-20 ). Because this data suggests that articular cartilage continuity may be a major determinant in healing, techniques for MRI enhancement may improve prognostic value. Emerging cartilage-specific MRI sequences may improve the accuracy of osteochondritis assessment.
Radionuclide scintigraphy with technetium may also be helpful in determining the state of the fragment. One study found that if the scan showed increased activity in a patient with open physes, the lesions healed spontaneously. Another study found that in patients with symptoms for more than 2 months, an increase in blood flow favored spontaneous healing, and a decrease in flow favored failure to heal.
There have been numerous radiographic and MRI classification schemes described for OCD. The failure to agree on a single accepted classification and the fact that most classifications are based on the problematic interpretation of stability make discussion of OCD lesions in conjuction with a grading system difficult. At present, physeal status, lesion size, the presence of radiographic sublesional sclerosis, and MRI criteria for articular continuity are the most useful features for patient stratification.
Treatment
The natural history of OCD is variable and appears to be influenced by age at diagnosis and lesion size. In children and adolescents with clinical and imaging criteria indicating stable lesions, there is an improved prognosis for healing in those with open physes. Patients who are younger at diagnosis, with smaller lesion size, and medial femoral condylar lesions generally have a better prognosis for nonoperative healing and generalized improved outcomes. When the disorder is diagnosed after physeal closure, the long-term prognosis is guarded, with one study demonstrating tricompartmental arthritis in 80% of patients followed for more than 30 years.
Nonoperative Treatment.
In approximately two thirds of patients with skeletal immaturity, healing will occur within 6 months following initial decreased weight bearing and activity restriction. Casting, or range-of-motion bracing, with crutch use for 6 weeks followed by activities of daily living only until union is noted is recommended most often. Unloader braces may be used. Within the immature population, a presenting age younger than 13 has been reported as a beneficial prognostic factor. Presenting symptoms of effusion or mechanical features may be predictive of failure of nonoperative treatment. Additionally, larger lesion size and the presence and extent of sublesional sclerosis on radiographs are predictive of nonhealing at 6 months.
Arthroscopic Treatment.
An ideal lesion classification scheme and treatment modalities remain unclear, but treatment of symptomatic or unstable lesions most often begins with arthroscopic assessment. After a complete arthroscopic examination has been performed to rule out other conditions, the lesion is examined and probed. Guhl has classified lesions as type 1, intact (no fissure or definable fragment); type 2, early separated (articular cartilage breeched, not displaceable); type 3, partially detached (attached partially by cartilage but displaceable, fluid behind lesion); type 4, salvageable craters and loose bodies (loose body in situ or displaced from bed); and type 5, unsalvageable craters and loose bodies ( Box 21-2 ).
Type 1: Intact lesion
Type 2: Early separated lesion
Type 3: Partially detached lesion
Type 4: Salvageable craters and loose bodies
Type 5: Unsalvageable craters and loose bodies
Intact Lesion.
An intact lesion may be drilled to promote healing. Good results have been reported after both antegrade and transarticular drilling. * Drilling brings about healing in most skeletally immature patients but is less successful in those with closed physes. A 1.6-mm Kirschner wire is drilled through the lesion into the subchondral bone at intervals of 3 to 4 mm—either under fluoroscopic control during the antegrade technique, or transarticularly under arthroscopic visualization when the lesion margins are definable. Non–weight-bearing range of motion is allowed after surgery, advancing to full weight bearing at 6 weeks. Unrestricted activity is allowed when the lesion exhibits evidence of radiographic healing.
* References .
Early Separated Lesion.
In the early separated lesion, in situ fixation is preferred. Good results have been reported with metal and bioabsorbable headless compression screw fixation, counter-sunk screw fixation, and in situ fixation with osteochondral autograft transfer grafts. Results of noncompression bioabsorbable devices have been varied. The general reported outcome following fixation of this in situ lesion is union and functional improvement in greater than 80% of patients.
Partially Detached Lesion and Salvageable Crater.
When the lesion is partially detached or when it is fully detached with a fresh crater, the fragment should be replaced and stabilized ( Fig. 21-21 ). The bed of the crater should be curetted down to bleeding bone and cleared of all fibrous tissue. When replaced, the fragment should be flush with the condylar surface. Because hypertrophy of the fragment or subchondral bone may occur, contouring and compression fixation of a displaced fragment may be best managed through a small arthrotomy. Short-term results of lesion salvage are encouraging and improved over excision or leaving the defect untreated. Viability of displaced-lesion cartilage and improvement in histology has been reported following fixation.
Unsalvageable Crater.
If the fragment is not salvageable, the crater may be managed in one of several ways. Microfracture is used to stimulate fibrocartilage coverage of smaller defects (<10 mm) without excessive lesion depth. In this arthroscopic technique, all fibrous tissue is curetted to expose subchondral, bleeding bone. Hand awls are used to fenestrate the bone at 4-mm intervals, with return of fat droplets confirming depth of penetration. Continuous passive motion is used after surgery, with weight bearing allowed at 8 to 12 weeks. Osteochondral grafting can be used to replace larger defects and restore articular congruity. Arthroscopic and miniopen techniques for autologous grafting (from lesser articulating areas of the marginal trochlea) and allograft osteochondral grafting have been used with numerous reports of favorable results. † Donor site morbidity, risk of allograft disease transmission, failure of integration of the graft, and failure of cartilage cell survival are possible complications of these techniques. However, grafting of the lesion has been shown to have better results than microfracture alone.
† References .
Popliteal Cysts
Cystic masses filled with gelatinous material develop in the popliteal fossa in children. They are usually minimally symptomatic and not related to an intraarticular pathologic process. Spontaneous resolution is the usual course. They have also been called Baker’s cysts.
Clinical Features
The usual presenting complaint is that of a mass behind the knee. It often arises gradually and may be fairly large when first noticed. Occasionally it is found after an injury. Complaints of pain are unusual and, unlike in adults, there are no symptoms of internal derangement of the knee.
Physical examination reveals a firm cystic mass in the popliteal fossa, often medially located and usually distal to the popliteal crease. It is most prominent when the knee is hyperextended and the patient is standing or prone ( Fig. 21-22 ).
Differential Diagnosis
Popliteal cysts are most often isolated and benign. The cysts most often occur in normal children without associated pathology; however, they may occur in inflammatory disorders as well, with 61% of children with arthritis having popliteal cysts in one series. Chronic infectious processes such as Lyme disease may also present as popliteal cysts. Pigmented villonodular synovitis may also present as a popliteal mass. Other tumors, such as lipoma, popliteal artery aneurysm, enlarged lymph nodes, synovial sarcoma, and osteosarcoma, have been mistaken for popliteal cysts.
Pathology
The most common site of origin is the bursa of the gastrocnemius and semimembranosus. This bursa extends proximally around the inner border of the origin of the medial head of the gastrocnemius, partially covering the muscle superficially. It extends transversely over the deep surfaces of the gastrocnemius and semimembranosus muscles and then reflects onto the articular capsule over the upper part of the medial condyle of the femur. The cysts often arise in the bursa deep to the medial head of the gastrocnemius ( Fig. 21-23 ). De Maeseneer and colleagues have reported that MRI most often reveals no communication of the cyst with the joint capsule in the pediatric population. A less common site of origin may be herniation through the posterior joint capsule of the knee.
Histologically, the cysts are classified as fibrous, synovial, inflammatory, or transitional ( e-Fig. 21-1 
). Fibrous cysts have a well-defined fibrous wall with a glistening inner surface of hyalinized fibrous tissue. Rice bodies may be found along the surface of these cysts. Synovial cysts have a thicker wall with a villous lining. The lining cells resemble synovial cells. Inflammatory cysts have an even thicker wall and an adherent fibrinous exudate composed of an inflammatory infiltrate. Transitional cysts are intermediate in character. It is likely that these types are not indicative of different conditions but rather are variations on a similar process.
Diagnostic Studies
A simple diagnostic test is transillumination of the cyst. The cystic nature can be confirmed by darkening the examination room and placing a flashlight against the cyst. A cyst brightly transilluminates; a solid tumor does not. Ultrasonography is also useful in distinguishing a solid mass from a cystic lesion. In one study, 11 of 13 popliteal cysts were correctly diagnosed with ultrasonography. Identification of fluid signal in the semimembranosus–medial gastrocnemius tendon interval has been reported to increase diagnostic accuracy. Ultrasonography, however, cannot be used unequivocally to rule out the presence of a soft tissue component lining a cyst wall ( Fig. 21-24 ). Plain radiographs or MRI should be obtained in the less common presentation when atypical history or physical examination findings are present.
MRI clearly defines the cyst and has a good chance of delineating more aggressive soft tissue components.
Treatment
Most popliteal cysts do not require treatment. When the features are typical and transillumination or ultrasound confirms the diagnosis, further diagnostic studies are not indicated. The cyst usually resolves over a period of months to a few years. In addition, surgically removed cysts may recur.
Surgical excision of a popliteal cyst is indicated only when symptoms are severe and limiting, and have not resolved with at least several months of follow-up. Resection without recurrence has been described using a purse-string suture technique at the cyst orifice in the posterior capsule when present, and suturing the gastrocnemius tendon over this closure. Immobilization of the leg for 2 weeks postoperatively is advocated. If any solid mass is present within the cyst, a frozen section should be obtained in the operating room.
Surgical biopsy is indicated when there is evidence of some other pathologic entity and should be performed within the guidelines for biopsy of possibly malignant lesions. Clinical indicators of possible malignancy include systemic signs such as weight loss, night pain, and rapid enlargement. The presence of a solid mass detected on examination or MRI indicates exploration.
Plica Syndrome
The plica syndrome is an uncommon but real condition in which a thickened band of fibrous tissue and synovium impinges on the femoral condyle as the knee moves through flexion and extension. A number of synovial folds, called plicae, have been identified in the knee. One study estimated that 87% of knees had a suprapatellar plica, 72% had a medial parapatellar plica, and 86% had an infrapatellar plica. Plicae have been noted to form in the fetus between 11 and 20 weeks of gestation.
The infrapatellar plica (previously known as the ligamentum mucosum) and the suprapatellar plica rarely cause clinical symptoms. A third plica, the medial parapatellar plica, is the only plica likely to become symptomatic. The syndrome is a relatively infrequent cause of knee pain and should largely be a diagnosis of exclusion. Plica syndrome is less common in children than in adults.
The reason why some plicae become symptomatic is unclear. Chronic irritation from prolonged sports activities may cause the plica to thicken and rub across the femoral condyle. Direct trauma may also cause inflammation of the plica. Farkas and co-workers found higher numbers of neural elements in posttraumatic symptomatic plicae than in plicae without a specific history of trauma. Direct trauma resulting in a bucket-handle tear of the medial plica and resultant mechanical symptoms over the region of the medial femoral condyle has been described.
Clinical Features
The symptomatic plica often presents as activity-related, anterior-medial parapatellar pain. Complaints include aching after activities, a snapping sensation, and pseudo-locking in which the knee seems to “catch” momentarily. Symptoms may begin after prolonged running or sports participation or may follow a direct blow to the knee. These symptoms may mimic those of a torn meniscus. Physical findings include medial parapatellar tenderness and a palpable thickening or band, usually located several centimeters medial to the patella along the surface of the medial femoral condyle. In many cases the band can be felt to roll beneath the fingers as the knee is flexed and extended, and this reproduces the patient’s pain.
Diagnostic Studies
While there are no definitive studies for the plica syndrome, history and clinical examination can be reliable when focal tenderness reproduces symptoms and other specific examination criteria are present. MRI has been shown effective in demonstrating the presence of a plica, but clinical relevance to symptoms should remain dictated by history and examination. Dynamic ultrasound using specific criteria has been reported to be 90% sensitive and 83% specific for symptomatic plica syndrome confirmed with arthroscopic treatment. At arthroscopy, a thickened band with a corresponding area of fibrillation on the femoral condyle is diagnostic. However, arthroscopic evaluation may also be equivocal. Strover and co-workers have described an arthroscopic technique that can demonstrate the plica and its impingement on the medial femoral condyle.
Treatment
Treatment should begin conservatively with rest, reduction of activities, and stretching of the major muscle groups around the knee. In one study, 40% of patients responded fully to conservative measures. Simple release of the plica may be followed by recurrence, and arthroscopic resection of the plica back to normal capsular tissue usually relieves the symptoms.
Overuse Conditions
Osgood-Schlatter Disease
Osgood-Schlatter disease, tibial tubercle apophysitis, is characterized by pain over the tibial tubercle in a growing child. It is probably a traction-induced inflammation of the patellar tendon and adjacent cartilage of the tibial tubercle growth plate. MRI studies have shown changes suggesting tendinitis of the patellar tendon and have not shown evidence of avulsion of the tubercle. The disorder is self-limiting in most patients and resolves with skeletal maturity. In an occasional patient an ossicle developing in the area of insertion of the patellar tendon may become symptomatic in adulthood. The first descriptions were by Osgood in 1903 and by Schlatter the same year.
Clinical Features
The disorder usually manifests in adolescence and is more common in boys than in girls. Regular sport activity and tightening of the rectus femoris, as judged by passive knee flexion in hip extension, are associated with tibial tubercle apophysitis. Pain directly over the tibial tubercle is the usual complaint, and swelling over the tubercle is often of concern. The pain is aggravated by activities but usually persists even when activities have been curtailed.
The examination reveals point tenderness directly over the tibial tubercle and the distal portion of the patellar tendon. There is often enlargement of the tubercle, which is firm on palpation. Pain in the area is produced by resisted knee extension.
The natural history is one of persistence for months to years during adolescence, with subsequent gradual resolution. Occasionally symptoms will persist after skeletal maturity, particularly an inability to kneel comfortably. Fragmentation of the tibial tubercle on radiographs has been associated with prominence of the tubercle and continued symptoms at follow-up.
Radiographic Findings
Plain AP and lateral radiographs are usually the only diagnostic studies necessary. The lateral radiograph may show fragmentary ossification of the tibial tubercle, which is often a normal variant. In late cases ossicles may form on the undersurface of the patellar tendon just as it reaches the tubercle. One study has shown an association of patella alta with Osgood-Schlatter disease.
Treatment
The treatment of Osgood-Schlatter disease should be conservative and expectant. Reassurance is important because some parents fear that the swollen tubercle may be a sign of malignancy. Activity limitations should be left up to the child and family, with the understanding that this is not a progressive or crippling disorder. Thus, activity that can be done with tolerable discomfort should be recommended. NSAIDs may be helpful, and a knee immobilizer may be used for a few weeks in severe cases. As tightening of the rectus femoris has been shown to be associated with the condition, quadriceps stretching may be recommended for symptomatic improvement.
Removal of ossicles from the tubercle may occasionally be necessary in patients with persistent, disabling symptoms. Prominence of the tubercle has been the major complication after surgical management. Combined ossicle excision and anterior prominence tubercle plasty through a patellar tendon splitting incision at maturity has been reported with good results.
Complications
While uncommon, closure of the tibial tubercle with severe genu recurvatum has been reported with untreated Osgood-Schlatter disease.
Larsen-Johansson Disease
Larsen-Johansson disease (or syndrome) is characterized clinically by pain and tenderness over the inferior pole of the patella and may be accompanied by radiographic ossicle formation or apparent fragmentation of the inferior pole of the patella. While similar in presentation to tibial tubercle apophysitis, Larsen-Johansson syndrome may present at a slightly earlier age in late childhood. It is thought to result from traction tendinitis, with calcification developing in a partially avulsed patellar tendon. Most patients seek medical attention after pursuing athletic activities, and the pain is aggravated by running, jumping, climbing stairs, and kneeling.
The diagnosis is usually made from clinical examination and plain radiographs, which may demonstrate calcification at the inferior pole of the patella. Four radiographic stages have been described. In the first stage findings are normal, in the second stage there is irregular calcification at the inferior pole of the patella, in the third stage there is coalescence of the calcification, and in the fourth stage the calcification is incorporated into the patella. Ultrasonography has also been used diagnostically.
Treatment is symptomatic, with most patients becoming asymptomatic with rest and antiinflammatory medications. Occasionally Osgood-Schlatter disease is found in the same knee.
Patellar Tendinitis
Patellar tendinitis, or inflammation of the patellar tendon, usually presents as anterior knee pain in an active adolescent. (It has been termed jumper’s knee. ) Clinically it may be difficult to distinguish from Osgood-Schlatter and Larsen-Johansson diseases, and some patients may appear to have two—or even all three—of the conditions. In fact, similarities in the MRI and ultrasonographic studies of all three conditions suggest that they may represent a spectrum of the same inflammatory process, and the distinctions may be more historical than clinical. ‡
Activity-related anterior knee pain reproduced by palpation at the inferior pole of the patella (best reproduced by palpating in full extension with the tendon fibers relaxed) is the hallmark of the condition. Decreased thigh strength and decreased quadriceps flexibility may be present. Increased length of the distal pole of the patella has also been associated with the condition. Activity restriction, quadriceps strengthening and stretching, and antiinflammatory medication are the mainstays of treatment and are often successful. For recalcitrant cases, operative (open or arthroscopic) débridement of the inflammatory changes within the tendon with or without operative inferior pole resection usually produces relief in these patients. §
‡ References .
§ References .
Pes Anserinus Bursitis
The pes anserinus is the tendinous insertion of the sartorius, gracilis, and semitendinosus muscles. This musculotendinous complex may become inflamed and painful in young patients, particularly those who are athletic and active. Patients have anteromedial knee pain that is worse with activity. They have point tenderness at the pes tubercle. As with the previously discussed overuse syndromes, patients improve with rest and antiinflammatory medication. Pes anserinus bursitis is frequently seen in patients with multiple osteochondromatosis, and it is not uncommon for relatively small osteochondromata on the medial proximal tibia to be significantly more symptomatic than larger osteochondromata elsewhere about the knee.
Proximal Tibial Stress Fracture
Stress fractures involving the proximal tibia are another potential overuse injury in the knee area. Although most common in adolescents and young adults, they have been reported in children as young as 2 years of age. A number of studies have looked at risk factors for the development of stress fractures in athletes and military recruits. These studies have shown that such risk factors include lower bone density, a history of menstrual disturbance, less lean mass in the lower limb, a discrepancy in leg length, a high longitudinal arch of the foot, excessive forefoot varus, acute weight loss, and a lower-fat diet. Ground reaction force, bone density, and tibial bone geometry were not found to predispose to the development of tibial stress fractures in women.
Although stress fractures can frequently be diagnosed on plain radiographs alone, a number of studies have looked at other modalities to assist in making the diagnosis. Both three-phase bone scans and MRI have been used to diagnose stress fractures. Although MRI has been shown to be capable of differentiating between shin splints and stress fractures, bone scans identify more abnormalities in symptomatic individuals. It is clinically important to remember that both bone scans and MRIs have shown abnormalities in asymptomatic control subjects ( Fig. 21-25 ).
Activity modification is the first line of treatment for stress fractures and is successful in the vast majority of cases. However, delayed healing and nonunion have been reported more often in diaphyseal lesions. Those who have prolonged symptoms before a diagnosis is made (>3 weeks) have a longer recovery period. Treatment modalities used for persistent stress fractures include electrical stimulation, arch supports, and open reduction and internal fixation.
Patellofemoral Instability
Instability of the patellofemoral joint may manifest as acute patellar dislocation (see Chapter 31 ), recurrent patellar dislocation or subluxation, habitual dislocation (dislocation each time the knee is flexed), and chronic dislocation. Congenital dislocation of the patella is discussed earlier under the heading of that name.
Recurrent Patellar Dislocation
Recurrent patellar dislocation is defined as more than one episode of dislocation of the patella documented by an observer or clearly described by the patient. The dislocations are almost always to the lateral side of the femur. The history of a dislocation should include a description of a period during which the knee appeared deformed and then suddenly was restored to a normal appearance either spontaneously or by manipulation. Events described as slipping of the knee that instantly resolves without visible distortion of the appearance of the knee should represent subluxations.
Incidence
Historically, the incidence of acute patellar dislocation has been estimated at 43 per 100,000 children younger than age 16 years. Recurrent subluxation and dislocation is reported more commonly in girls than in boys. Most series report 70% or more of recurrent dislocators are female. A history of recurrent instability (two or more episodes) is predictive of future instability. Younger children (<14 years of age) are more likely to experience recurrent dislocations than older children.
Etiology
Stability of patellofemoral articulation depends on the relative contributions of bony and soft tissue constraints. Patella alta, torsional and angular deformity, trochlear dysplasia, muscular imbalance, and ligamentous laxity or disruption may all contribute to lateral patellar instability. The interplay of these factors may be variable, and the abundant literature on the subject has not clearly defined a universally identifiable risk factor.
Patella Alta.
Patella alta is commonly associated with patellar instability. Independent of trochlear anatomy, a superiorly positioned patella engages the bony restraints of the distal femur at a later point during flexion and may predispose to medial or lateral instability. The relationship of patella alta and extensor complex development and function is unclear.
Torsional and Angular Deformity.
Torsional relationships of the femur and tibia, as well as valgus of the knee, may in isolation or combination result in laterally directed vector forces on the patella. The combination of femoral anteversion, genu valgum, and external tibial tubercle position is reflected by the Q angle. This is the angle formed between the patellar tendon and a line drawn along the quadriceps tendon ( Fig. 21-26 ). The difficulty of quantifying these factors by a single examination finding is evidenced by the variable agreement of measured Q angles and patellar instability in the literature. The interrelationships of these torsional and angular factors in the dynamic setting remain poorly understood factors of patellar instability.
