Introduction
Traumatic forces applied to an immature knee result in fracture types that usually differ from those seen in adults. As in other anatomic regions in a growing child, the cartilaginous structures around the knee tend to be weaker and thus more vulnerable to injury than the ligaments and tendons that insert onto them. Fractures involving the epiphyses require accurate reduction to minimize the risk of a growth disturbance that could lead to significant angular deformity or shortening of the limb. As in adults, fractures involving the articular surfaces should be carefully reduced to restore joint congruity to best assure proper long-term function of the joint. As the knee matures, especially during adolescence, adult-type cartilage and ligament injuries become more prevalent and should be considered when the clinician evaluates injuries in this more mature population.
Fractures of the Distal Femoral Metaphysis
Smith and colleagues reported that supracondylar fractures of the femur account for 12% of femoral fractures in children. However, when only displaced fractures in otherwise healthy children are considered, this percentage is closer to 3%.
Pertinent Anatomy
Important neurovascular structures are positioned in close approximation to the distal end of the femur. Awareness of these structures is important when pins are inserted for traction or external fixation so that injury is avoided. The femoral artery in the adductor canal is in close proximity to the medial cortex of the distal femur as it enters into the posterior compartment. It then becomes the popliteal artery as it emerges from the adductor hiatus and enters the popliteal fossa. Within the popliteal space, the popliteal artery gives off the five geniculate arteries: paired superior and inferior and an unpaired middle artery. Although these arteries anastomose with the anterior tibial recurrent artery, they are small and too insufficient to allow continued viability of the lower part of the leg if the popliteal artery is occluded or disrupted. As the popliteal artery enters the popliteal fossa, only a thin layer of fat separates the artery from the posterior surface of the femoral metaphysis. Because the artery is relatively tethered above to the femur at the adductor hiatus and below to the tibia by the fibrous arch over the soleus muscle, it is vulnerable to damage from the metaphyseal fragment of a fracture of the distal femoral metaphysis.
The posterior tibial nerve lies adjacent to the popliteal artery in the posterior part of the knee. The common peroneal nerve separates from the sciatic nerve just above the popliteal fossa and then descends along the lateral border of the fossa close to the medial border of the biceps femoris muscle. The nerve then exits the popliteal fossa between the biceps femoris muscle and the lateral head of the gastrocnemius and becomes subcutaneous just behind the head of the fibula before it wraps around the neck of the fibula deep to the peroneus longus muscle. Because of its location, the common peroneal nerve may be prone to injury by a displaced fracture of the distal femur, especially when the injury results from hyperextension or varus stress. This structure is also at risk when a traction pin is inserted into the proximal tibia.
Mechanism of Injury
A distal femoral metaphyseal fracture is most often caused by a direct blow to the anterior or lateral aspect of the thigh or a fall from a height. In children younger than 4 years, especially those younger than 1 year, child abuse should be considered. The lack of a reasonable explanation for the injury, an unreasonable delay in seeking medical care, or the presence of additional injuries should raise the level of suspicion of abuse. A corner fracture, or bucket-handle lesion, at the level of the distal metaphysis makes child abuse a strong possibility. More recently, Arkader and colleagues reported that 20 of 29 complete transverse distal femoral metaphyseal fractures (75%) seen in children younger than 1 year of age were associated with or were highly suspicious for child abuse. A plastic bowing fracture of the distal metaphysis of the femur has been described and may mimic congenital subluxation of the knee. In older children, nondisplaced fractures or stress fractures may occur. These patients are seen with local pain and tenderness, and radiographs reveal new periosteal bone. The possibility of a pathologic fracture should be considered in these patients. Distal femoral metaphyseal fractures have also been reported in association with certain musculoskeletal conditions, including osteogenesis imperfecta, spinal muscular atrophy, and hemophilia.
Evaluation
Examination
Patients with a fracture of the distal femoral metaphysis are seen with local soft tissue swelling, tenderness, and deformity in the region of the distal part of the thigh and knee. The skin must be inspected for a possible open fracture. Because the femoral artery in the adductor canal is in close proximity to the medial cortex of the distal femur, careful neurovascular examination is warranted.
The presence and strength of the pedal pulses and the function of the common peroneal and posterior tibial nerves should be documented. The use of a Doppler ultrasound may aid in assessing the circulation to the limb. The peroneal nerve is at risk in a distal femoral fracture either by a direct blow to the posterolateral side of the knee (e.g., from a car bumper) or from a stretch injury to this nerve at the time of fracture angulation and displacement.
If the limb is ischemic, a gentle reduction maneuver may restore circulation. An assessment of the ankle-brachial index (ABI) should be considered in adolescents.
Absent or diminished pulses may warrant vascular imaging. If the limb is frankly ischemic, and the location of the vascular injury is clear, vascular exploration and early restoration of perfusion should not be delayed for imaging. Otherwise, ongoing evaluation of the lower extremity is important during the first few days after the fracture so that a developing compartment syndrome may be detected promptly. Compartment pressures should be measured if clinical signs and symptoms of a compartment syndrome are present, even in the presence of intact pulses.
Imaging
Anteroposterior (AP) and lateral radiographs of the distal end of the femur should reveal the fracture. As with any long bone fracture, radiographs of the entire bone should be taken, including the joints above and below the injury. Accordingly, radiographs of the entire femur, including the hip and knee, should be taken when the patient is initially evaluated.
Classification
Fractures of the distal femoral metaphysis in children are generally classified according to the degree of displacement and comminution.
Emergent Treatment
If the limb is ischemic, a gentle reduction may restore the circulation. The patient with a fracture of the distal femoral metaphysis should have the injured extremity splinted in a position of comfort. The neurovascular status of the patient should be carefully monitored pending definitive management of the fracture. An ABI test should be considered in this situation. Traction, either skin or skeletal, may be useful for patients with more displaced fractures.
Nonoperative Treatment
Nonoperative treatment may be appropriate in nondisplaced fractures of the distal metaphysis of the femur. A single spica cast provides the most secure immobilization, especially in more obese children. Fractures treated in this manner must be closely followed for any subsequent displacement due to the muscle forces on the distal fragment.
In patients with displaced or comminuted fractures, traction followed by application of a hip spica cast or cast brace may be indicated.
Traction and Cast Application
Traction and cast application are less commonly used for definitive treatment of fractures of the distal femoral metaphysis than in the past. This option may, however, be useful for temporary immobilization in the polytraumatized patient to maintain length and alignment of the fracture while definitive management is decided.
In this technique, traction is applied to the lower extremity to obtain proper reduction of the fracture until enough callus has formed to allow alignment to be safely maintained in a spica cast or cast brace. In a young child, skin traction can be applied to the lower part of the leg, but skeletal pin traction is preferable in children older than 3 years.
Skeletal traction may be applied through either the proximal part of the tibia or the distal end of the femur. The skeletal traction pin is either a K-wire or a Steinmann pin applied aseptically under local or general anesthesia. If a proximal tibial site is chosen, the pin should be inserted in a lateral-to-medial direction so that the risk of injury to the peroneal nerve is minimized. Care should also be taken to avoid the proximal tibial physis and tibial tubercle apophysis. If a distal femoral site is chosen, the pin should be inserted medially to laterally so that the risk of injury to the femoral artery in the region of the adductor canal is minimized.
Because of the special muscle forces present, the use of a single traction pin may not maintain adequate alignment ( Fig. 15-1 ). Double-pin traction is often needed. A proximal tibial pin allows for longitudinal traction, but it may be necessary to insert a second pin into the distal femoral fragment to provide an anteriorly directed force to achieve satisfactory position on lateral radiographs. Similarly, if the distal femoral fragment is long enough, two pins may be inserted into the femoral fragment proximal to the physis. Staheli described a double-pin traction technique in which one pin is placed through the metaphysis and a second pin is placed through the epiphysis. The two pins are attached to an external fixation apparatus through which traction is applied.
Although a two-pin traction technique may provide satisfactory sagittal plane control, the need to keep the hip and knee flexed in 90/90 traction makes it difficult to accurately determine whether a varus or valgus alignment is present. If this treatment method is selected, the child can be placed initially in 90/90 traction. Once early callus has formed and sagittal plane alignment is satisfactory, the knee can be straightened gradually; lateral radiographs are taken to ensure that sagittal plane alignment is maintained. The patient is removed from traction when early callus is seen on radiographs. With the knee in a more extended position, any residual varus or valgus malalignment can be corrected when the hip spica cast is applied, while the callus is still relatively soft.
The duration of immobilization varies with the age of the patient: it is only a few weeks in the very young and 6 to 8 weeks in older children. After removal of the cast, rehabilitation is begun to strengthen the quadriceps and hamstring muscles. Weight-bearing can be full, as tolerated, but crutches are used for protection until knee motion and thigh strength are adequate to allow the patient to walk safely without assistive devices. Return to regular activities is permitted after the quadriceps has regained normal strength and full range of motion of the knee joint has been achieved.
The main complications that may result from treating a distal femoral metaphyseal fracture with traction and cast application are varus malalignment and premature closure of the anterior part of the proximal tibial physis, which leads to recurvatum deformity of the proximal end of the tibia. Careful traction management and cast application can prevent varus malalignment. When a proximal tibial pin is used, meticulous pin placement can avoid physeal injury to the tibial tubercle area, although some reports have noted that premature tibial tubercle growth arrest can occur in association with femur fractures, even without the use of a tibial pin. Malalignment in the sagittal plane, with apex posterior angulation at the fracture site, may result in an apparent hyperextension deformity of the knee and limited knee flexion. In a young child, this deformity largely remodels with time.
Cast Brace
A cast brace may be used after an initial period of traction in selected older children and adolescents whose fractures do not have excessive posterior angulation. Cast brace treatment can provide an opportunity for early ambulation and avoid much of the knee stiffness and muscle atrophy that occur with spica cast immobilization.
In the technique described by Gross and colleagues, a large (7/64- to 9/64-inch) Steinmann pin is inserted into the distal end of the femur in the operating room with the patient under general anesthesia. The pin is completely covered with cast padding, and a cylinder cast is applied with careful molding at the fracture site to prevent varus angulation. If radiographs show that satisfactory reduction has been achieved, an elliptical section of plaster is removed from the posterior part of the knee. The plaster anteriorly is transected in part, and a bridge overlying the patella is left intact at this point. After hinges are applied medially and laterally, the anterior bridge of plaster is transected so that flexion of the knee can occur. A specially bent segment of coat hanger is incorporated over the tibia to allow traction to be applied. Postoperatively, the patient is sent to physical therapy for standing and gait training. After several days, radiographs are taken both in traction and while standing to assess alignment and shortening. Wedging of the cast is done at this stage, if necessary. Weekly radiographs are mandatory for monitoring length and alignment. After 4 weeks, the cast brace is changed and the pin is removed in the outpatient setting. Use of the cast brace is discontinued when clinical and radiographic union is achieved.
In general, cast braces for the treatment of femoral fractures have been used sparingly. Although other methods may be superior to a cast brace for proximal and middle-third diaphyseal femur fractures, some authors have suggested that fractures of the distal end of the femur are best suited to this technique.
Surgical Treatment
Surgical treatment is indicated for displaced fractures of the distal metaphysis of the femur to control the alignment of the fracture during the healing process. The muscle forces on the distal fragment may present problems in obtaining and maintaining proper alignment of displaced fractures of the distal femoral metaphysis. Generally, the distal fragment displaces posteriorly, often with exaggerated flexion, because of the pull of the two heads of the gastrocnemius muscle. If the fracture line is just proximal to the distal insertion of the adductor magnus muscle, the distal fragment may also angulate into a varus position. Surgical options for this injury include external fixation, percutaneous pin fixation followed by application of a long leg cast, open reduction and internal fixation, and submuscular bridge plating.
External Fixation
External fixation may be effectively used to reduce and stabilize distal femoral metaphyseal fractures (see Fig. 15-1 ). The best situations for the use of external fixation for this injury are in children who have sustained polytrauma, an open fracture, or a floating knee.
In cases of polytrauma with multiple fractures, abdominal injury, or head injury, stabilizing the fracture with an external fixator allows the child to be transported for diagnostic studies or operative procedures. In persistently comatose children, external fixation provides stability of the fracture when spasticity ensues. Tolo has observed that more than 90% of children in a coma for more than 48 hours have excellent neurologic recovery. Therefore it is important to treat all fractures in children with head injuries with the assumption that full neurologic recovery will occur.
In open injuries, especially when skin loss is present, the use of external fixation to stabilize the fracture greatly facilitates care of the wound. In children who have a fractured tibia and a distal femoral metaphyseal fracture, stabilization of the distal part of the femur with an external fixator allows the tibial fracture to be treated more easily.
The use of external fixation for the management of distal femoral fractures may limit the cost of prolonged hospitalization that occurs with the use of traction. In addition, the family may find it easier to care for a child, especially an older child, treated with an external fixator rather than a hip spica cast.
If external fixation is used to manage a distal femoral metaphyseal fracture, the surgeon should keep several technical points in mind. The pins should be inserted from the lateral side under image intensifier control. It is recommended that the distal pin be placed at least 1 cm, preferably 2 cm, from the physis to avoid potential thermal injury during insertion, as well as damage from a possible pin tract infection. The external fixator pins should be applied in parallel while an assistant holds the fracture site in a reduced position. Pins should be placed into uninjured bone and through intact, uninjured skin, whenever possible. In transverse fractures, an end-to-end reduction is attempted; in oblique fractures, bayonet apposition with about 5 mm of overlap should be considered in children younger than 10 years to minimize the effect of limb overgrowth. The use of an external fixation frame that allows some adjustment of varus and valgus, as well as rotation, is preferred. After placement of the frame, final adjustments are made, and radiographic confirmation of adequate reduction is obtained before the child is awakened from general anesthesia.
Pin care is taught to the child and parents while in the hospital, and this pin care is continued at home on a daily basis. If the patient is compliant, partial weight-bearing with crutches can be started early. When radiographs reveal the formation of callus, weight-bearing can be increased. If the fixator requires dynamization, it is done at approximately 4 to 6 weeks after the fracture, when callus has been present for a few weeks.
Once early fracture stability has been gained, the surgeon may choose to remove the external fixator and apply a long leg cast until healing is complete. Alternatively, the external fixator may be used for the full course of treatment. Once healing is complete, typically between 6 and 12 weeks from the time of the injury, depending on the age of the patient, the device may be removed in the outpatient setting. In most older children and all adolescents, it is best to leave the external fixator on for the full 12 weeks to minimize the risk of refracture after frame removal. The fixator should not be removed until there is bridging callus across at least 3 cortices on AP and lateral radiographs.
Potential complications from the use of external fixation include pin tract infection, malunion, and refracture through either a pin tract or the original fracture site. A pin tract infection can usually be avoided by good pin care. A short course of oral antibiotics may be sufficient to treat a superficial infection. The skin should be incised if tension on the skin is present. If drainage persists or if erosion around the pin is seen on radiographs, the pin should be changed and the pin tract should be débrided. Alternatively, if sufficient stability exists at the fracture site, the entire device may be removed, a cast applied, and appropriate antibiotic treatment instituted.
Because the knee may be extended to assess femoral–tibial alignment quite readily, varus or valgus malunion is not common if care is taken in the initial placement of the fixator. However, because of a tendency to apply the fixator with the distal fragment in slight external rotation, rotational alignment should be carefully assessed when the frame is applied.
Refracture of the femur occurs more often with fractures treated with external fixation than by other methods. A fracture may occur through the old fracture site if the frame is removed prematurely. A fracture may also occur through a pin site, particularly in young children in whom 5-mm fixator pins have been used.
Injury to the distal femoral physis is certainly a potential problem for distal femoral fractures treated with external fixation. This injury should be avoidable if the pins are kept at least 1 cm proximal to the physis when inserted. The pins should always be inserted under image intensifier control to avoid transgressing the physis.
Closed Reduction and Percutaneous Pin Fixation
Closed reduction and percutaneous pin fixation supplemented by the application of a long leg cast may be used to treat distal femoral metaphyseal fractures in selected patients. This technique is particularly useful in younger patients in whom the metaphyseal fracture is quite distal ( Fig. 15-2 ).
With the patient under general anesthesia, the fracture is reduced, and smooth pins are inserted in a crossed fashion under image intensifier control. It is preferable to insert the pins through the distal metaphysis, provided that sufficient metaphyseal length is available; if not, the pins may be inserted through the distal femoral epiphysis as described further on for distal femoral physeal fractures. The pins are bent to avoid migration and may be left through the skin for ease of removal. A long leg cast is applied with the knee immobilized in 20° to 30° of flexion. The pins can usually be removed after 4 weeks so that the risk of infection is reduced. After 6 to 8 weeks, when healing has occurred, the cast is removed.
Damage to the femoral vessels on the medial side has been suggested as a potential complication of this method. Butcher and Hoffman have recommended that the lateral pin be started from the posterior epicondyle of the distal femur and directed anteriorly so that damage to the femoral vessels near the adductor hiatus is avoided. Although smooth pins that transgress the growth plate may carry a risk of potential growth disturbance, the small diameter of the pins relative to the physeal area makes this complication unlikely.
Open Reduction and Internal Fixation
Open reduction and internal fixation may be needed for distal femoral metaphyseal fractures that cannot be reduced by other methods or if an arterial injury has occurred at the time of the fracture. The most common reason for failure to obtain adequate reduction by other means is the presence of interposed muscle between the fracture fragments. If repair of an arterial injury is needed, internal fixation prevents excessive motion at the fracture site and protects the repair.
The surgical approach depends on the indication for the surgery. If interposed muscle is blocking reduction, a straight lateral approach allows the quadriceps muscle to be reflected anteriorly and affords access to the distal end of the femur. If arterial repair is needed, the incision should be posteromedial to allow access to the femoral and popliteal arteries, as well as the saphenous vein, if vein grafting is necessary.
Rigid internal fixation, as is commonly used in adults, is not usually necessary in children. Once reduction of the fracture is obtained, crossed pins provide acceptable, provisional fixation that can be supplemented with a long leg cast. The pins are bent to prevent migration and are cut off just below the skin to facilitate later removal.
Compression plate fixation is rarely indicated to treat distal femoral metaphyseal fractures in a growing child, except perhaps in the polytrauma setting. In this situation, compression plating may be a useful alternative and does not cause excessive femoral overgrowth. The plate is generally removed in 6 to 8 months, followed by 4 to 6 weeks of cast immobilization to prevent fracture through the screw holes.
More recently, Lin and colleagues have described open reduction and internal fixation using a pediatric physeal slide-traction plate for fixation of comminuted distal femur fractures in children. They reported excellent outcomes in 16 children treated with this device after a mean follow-up of 36.4 months. They recommended this device as a safe and effective treatment option for children with comminuted distal femur fractures.
Submuscular Bridge Plating
Submuscular bridge plating has recently been shown to provide adequate operative stabilization of distal metaphyseal fractures in children. This technique is especially advantageous for managing comminuted and unstable fracture patterns ( Fig. 15-3 ). The procedure is performed with the use of an image intensifier. A precontoured plate is tunneled proximally through a small distal incision in the plane beneath the vastus lateralis muscle. Reduction of the fracture is achieved as the plate is secured to the femur with the use of screws placed percutaneously proximal and distal to the fracture site. Locking plates should be used in distal fractures in which the amount of space for placement of the screws is limited.
No immobilization is used postoperatively, and the patients are encouraged to begin immediate motion of the knee, as tolerated. Toe-touch weight-bearing is maintained until early callus is seen. The plate may be removed 6 to 8 months after the injury. The minimal soft tissue dissection used in this technique is believed to lead to more rapid fracture healing and a faster return of function than that from traditional open reduction and plate fixation.
Outcome
In the absence of neurovascular complications, the outcome of fractures of the distal femoral metaphysis is excellent. Fractures in this region heal rapidly, and early return to full activities is the rule.
Complications
Malunion is a potential complication after the treatment of a distal femoral metaphyseal fracture. Flexion and extension types of malunion have a good capacity to remodel, depending on the age of the patient. Malunion in the coronal plane has limited remodeling potential. Significant residual varus or valgus deformity may be addressed by guided growth or osteotomy.
Avoiding malunion requires that some anatomic relations be kept in mind. The anatomic axis of the shaft of the femur is different from the mechanical (weight-bearing) axis. The mechanical axis passes through the head of the femur and the middle of the knee joint and generally subtends an angle of 3° from the vertical. The anatomic axis has an average valgus angulation of 6° relative to the vertical axis. The knee joint line is normally parallel to the ground, and the anatomic femoral axis subtends an 81° lateral distal femoral angle relative to the knee joint. For each patient, it is important to confirm this angle by comparing it to the opposite femur because individual variations do occur. Complications that are unique to a particular treatment method are discussed under the appropriate heading.
Fractures of the Distal Femoral Physis
Fractures of the distal femoral physis account for 1.4% to 5.5% of all physeal injuries and slightly more than 1% of all fractures occurring in children.
Pertinent Anatomy
The epiphyseal ossification center of the distal part of the femur is usually present in a full-term newborn infant. With subsequent growth, this ossification center rapidly expands to fill both condylar regions. The distal femoral physis is the largest and most rapidly growing physis in the body. It contributes almost 70% of the length of the femur and 40% of the length of the entire leg and averages approximately 1 cm of growth each year until maturity. Closure of this growth plate usually occurs between 14 and 16 years of age in girls and between 16 and 18 years in boys. Any injury that partially or completely disrupts growth of the distal end of the femur may lead to significant angular deformity or shortening of the extremity. The younger the patient is at the time of such injury, the greater the potential for these sequelae.
The distal epiphysis includes the entire articular surface of the lower end of the femur and serves as the origin for part of the gastrocnemius muscle. Both the medial and lateral collateral ligaments originate from the distal femoral epiphysis. When a varus or valgus force is exerted on the knee, these ligaments most commonly remain uninjured because the force is transmitted to the distal femoral epiphysis and often leads to a physeal fracture.
The configuration of the distal femoral physis is unique and has been well described by Roberts. The distal surface of the metaphysis consists of four gentle mounds, one in each quadrant of the cross section. These mounds fit into four shallow depressions on the proximal surface of the epiphysis. This complex anatomy has been demonstrated with the use of three-dimensional MRI modeling. Although this undulating contour probably provides resistance to shear and torsional forces, it may also predispose regions of the epiphysis to grind against the metaphyseal projections when a separation occurs, which causes damage to the germinal layer and vascularity of the growth plate. These factors may help explain why a growth disturbance after distal femoral physeal injury is so common.
The relevant vascular anatomy has been outlined in the preceding section.
Mechanism of Injury
Most of these fractures are sustained in automobile–pedestrian accidents or sports activities. Riseborough and colleagues observed that fractures in the juvenile group—ages 2 to 11 years—were invariably caused by severe trauma, such as being struck by an automobile, whereas fractures in the adolescent age group were caused by less severe trauma, most often sports-related.
Because the growth plate provides less resistance to traumatic forces than the attached ligaments do, varus or valgus stress applied to an immature knee is more apt to lead to physeal separation than to a collateral ligament injury. If hyperextension of the knee occurs, the epiphysis may be displaced anteriorly. This mechanism of injury is similar to the mechanism causing knee dislocation in adults. It is important to recognize this pattern of injury because of the potential for associated neurovascular injury. Posterior displacement of the epiphysis is relatively uncommon and is caused by a blow to the anterior aspect of a flexed knee.
As noted in the preceding section, children who are seen with injuries to the distal femur who are younger than 4 years, especially those younger than 1 year, should be considered for possible child abuse. The lack of a reasonable explanation for the injury, an unreasonable delay in seeking medical care, or the presence of additional injuries should raise the level of suspicion of abuse. A corner fracture, or bucket-handle lesion, at the level of the distal metaphysis makes child abuse a strong possibility.
Distal femoral physeal separations can also occur from birth injuries. These injuries are rare and have been associated with breech presentation, macrosomia, and difficult delivery. Although the clinical appearance of these injuries may be confused with septic arthritis of the knee, close evaluation of the radiographs will usually reveal the diagnosis.
Evaluation
Examination
A careful description of the accident should be elicited. It is particularly important to determine the direction of the force that produced the injury.
A patient with a distal femoral physeal fracture may be seen with pain, effusion of the knee joint, local soft tissue swelling, and tenderness over the physis. These symptoms will vary depending on the displacement of the fracture. In displaced injuries, the patient is unable to bear weight on the injured limb. In addition, in displaced injuries, deformity may be evident, and soft or muffled crepitus can often be felt because of the grinding between the cartilaginous fracture surfaces. Absence of crepitus may suggest the interposition of soft tissue or periosteum in the fracture site. Most often, the displacement results in a varus or valgus deformity. In these cases, the metaphyseal fragment becomes prominent medially or laterally and may be palpable. In an anteriorly displaced, or hyperextension, injury, the patella is prominent, and dimpling of the anterior skin is often evident. With posterior displacement of the epiphysis, the distal metaphyseal fragment becomes prominent just above the patella.
Imaging
AP and lateral radiographs should be obtained. Oblique radiographs may be helpful in revealing fractures that are minimally displaced ( Fig. 15-4 ). Lippert and colleagues observed that plain radiographs underestimated the displacement of Salter–Harris type III fractures and urged that magnetic resonance imaging (MRI) or computed tomographic (CT) scans be obtained to properly evaluate these injuries. These imaging modalities are also useful in detecting the presence of a coronal shear injury. Type III fractures may be associated with injury to the cruciate ligaments. Accordingly, MRI may provide useful information in these patients.
If plain radiographs show no fracture and knee instability has been noted on clinical examination, gentle stress radiographs have been used in the past to distinguish between a physeal fracture and a ligamentous injury. If this study is done, adequate analgesia is helpful for alleviating muscle spasm and protecting the physis from further damage during the examination. Care should be taken to avoid excessive force that could convert a nondisplaced physeal injury to a displaced physeal separation. The usefulness of stress radiographs has been called into question by Stanitski. He points out that because collateral ligament injuries are no longer surgically repaired, early differentiation between a nondisplaced physeal fracture and a collateral ligament tear is usually unnecessary. In addition, he notes that stress radiographs may potentially cause further damage to an already injured physis. Instead, he suggests that immobilizing the extremity and obtaining a follow-up radiograph in 10 to 14 days will document the presence of a healing physeal fracture.
On occasion, MRI or CT may help identify fracture lines in suspected nondisplaced injuries. ∗
∗
As noted earlier, these studies may be especially useful in evaluating Salter–Harris type III and IV injuries.Classification
The most commonly used classification system for distal femoral epiphyseal fractures is that of Salter and Harris ( Fig. 15-5 ). Type I fractures are characterized by complete separation through the physis without any involvement of the adjacent metaphysis or epiphysis. In type II fractures, which are the most common, the fracture line traverses the physis before exiting obliquely across one corner of the metaphysic, which results in a roughly triangular-shaped Thurston–Holland metaphyseal fragment. Displacement is usually toward the side of the metaphyseal fragment. The periosteum is generally intact on the side of the metaphyseal fragment and may aid in maintaining reduction of the fracture. Interposed soft tissue that may impede reduction is most likely to be found on the side opposite the metaphyseal fragment. A type III injury consists of a fracture through the physis that exits through the epiphysis into the joint. A type IV injury describes a vertical, intraarticular fracture that traverses the metaphysis, physis, and epiphysis. Type V fractures are crush injuries to the physeal cartilage. These rare injuries are usually diagnosed in retrospect.
Coronal fractures of the femoral condyles—so-called Hoffa fractures—have been described in children. Depending on the location of the fracture line, these injuries may fall into the type III Salter–Harris classification, or they may be entirely intraepiphyseal ( Fig. 15-6 ).
Emergent Treatment
A careful neurovascular examination is warranted in these injuries, especially in hyperextension injuries. The presence and strength of the pedal pulses and the function of the common peroneal and posterior tibial nerves should be documented. An assessment of the ABI may be useful in adolescents. If the clinical findings of acute ischemia are present—extremity pallor, coolness, cyanosis, or delayed capillary refilling—reduction of the fracture should be attempted as soon as possible. If these findings persist after the reduction attempt, immediate vascular exploration is indicated. In the absence of an obviously ischemic limb, patients with an abnormal pulse or patients who recover pulses and perfusion after reduction of the fracture should be carefully monitored for signs of late ischemia or compartment syndrome and may warrant arteriography or other vascular imaging. As described for fractures of the distal femoral metaphysis, ongoing evaluation of the lower extremity is important during the first few days after the fracture so that a developing compartment syndrome or intimal tear with thrombosis can be detected promptly.
After examination and any emergent treatment that is warranted, the patient should have the injured extremity elevated and splinted in a position of comfort, and ice should be applied to control swelling.
Nonoperative Treatment
Nonoperative treatment may be appropriate in nondisplaced Salter–Harris I and II injuries. The duration of immobilization varies with the age of the patient. Short, obese children or patients who may be unreliable are probably better treated with a hip spica cast. These patients should be observed closely and have follow-up radiographs taken 5 to 7 days after the injury so that any displacement can be promptly addressed.
Although nondisplaced type III and IV injuries may be treated by cast immobilization and careful follow-up, it may be preferable to treat these injuries with percutaneous placement of pins or screws, followed by cast immobilization to prevent the risk of development of incongruity at either the growth plate or articular surface. Wall and May have recently urged that nondisplaced type III and IV fractures undergo operative fixation. They found that imaging studies may underestimate the amount of displacement at the articular surface and recommend making a 3-cm long medial or lateral parapatellar incision to allow direct palpation of the joint surface during reduction and fixation.
Surgical Treatment
Surgical treatment is indicated for displaced fractures of the distal femoral physis to control the alignment of the fracture during the healing process. Treatment options for this injury include closed reduction and percutaneous pin fixation followed by application of a long leg cast and open reduction and internal fixation.
Closed Reduction and Percutaneous Fixation
Closed reduction and percutaneous fixation is recommended for displaced type I and II fractures and for nondisplaced type III and IV fractures. Displaced fractures are reduced under general anesthesia.
The technique of reduction will vary depending on the displacement of the fracture. In general, the assistant secures the proximal thigh while the surgeon applies longitudinal traction. It is important to emphasize that traction during the reduction maneuver avoids further damage to the physis. As traction is continued, the surgeon accentuates the angulation slightly, before applying a gentle force over the distal fragment in the appropriate direction to achieve reduction. In instances in which the distal fragment is displaced anteriorly, the reduction maneuver may be performed with the patient placed in either the supine or prone position.
Internal fixation makes subsequent displacement less likely, allows the use of a long leg cast with a greater margin of safety, and avoids having to place the knee in an extreme position of flexion or extension to maintain the reduction. After the fracture is reduced under image intensifier control, smooth transphyseal pins are inserted in a crossed fashion for type I injuries and type II injuries with small metaphyseal fragments ( Fig. 15-7 ). For enhanced stability, the pins should cross above the physis and engage the metaphyseal cortex. The pins are bent to avoid migration. They may be bent and cut off beneath the skin or left out percutaneously. Type II fractures with an adequately sized metaphyseal fragment on both AP and lateral views are best stabilized with cannulated screws across the metaphyseal portion of the fracture ( Fig. 15-8 ). For type III fractures, smooth pins or cannulated screws are placed into the epiphysis so that they do not cross the adjacent growth plate. Type IV fractures are stabilized with smooth pins or screws across the metaphyseal fracture site and, if required for stability, across the epiphyseal fracture site ( Fig. 15-9 ).
After fixation is achieved, movement of the knee through a full range of motion under fluoroscopy confirms the stability of the reduction. A long leg cast is applied with the knee immobilized in 20° to 30° of flexion. If the pins were left out percutaneously it is best to remove them at 4 weeks so that the risk of infection is reduced. After 6 weeks, healing is usually sufficient to allow the cast to be discontinued and begin rehabilitation of the knee.
Open Reduction and Internal Fixation
Open reduction is indicated for all type I and II fractures that cannot be accurately reduced by closed methods or if an arterial injury has occurred at the time of fracture. If the epiphysis is displaced laterally, a medial approach provides visualization of any obstacles to reduction and avoids disruption of the intact lateral periosteal hinge. If the epiphysis is displaced medially, a lateral approach is used. A posterior approach is necessary if arterial exploration is indicated. Once the fracture is reduced, fixation is achieved as described earlier.
Open reduction with internal fixation is also needed for all displaced type III and type IV fractures to restore congruity of the articular surface and align the physis. Because type III and type IV fractures are intraarticular, a more extensive approach is needed to visualize both the articular surface and the physis or metaphysis.
Type III fractures are approached through an anteromedial or anterolateral arthrotomy, depending on the location of the vertical component of the fracture through the epiphysis. After the knee joint is opened, thorough irrigation eliminates the hemarthrosis and clot from the fracture surfaces. Once accurate reduction is achieved, the fracture is stabilized with cancellous screws placed transversely across the fracture site under image intensifier control. In younger patients, the screws should be placed so that they avoid crossing the physis. It is preferable that the threaded portion of the screw does not span the fracture site so that better compression is achieved (see Fig. 15-4 ).
For type IV fractures, the approach is made on the side of the metaphyseal portion attached to the physis. Both the joint and the metaphyseal portion of the femur are exposed. Once accurate reduction is achieved, the fracture is stabilized with one or two cancellous screws placed across the metaphysis. An epiphyseal screw is needed only if adequate stability of the fracture cannot be achieved by fixation of the metaphyseal fragment alone. Postoperatively, a long leg cast is applied. The cast is removed at 6 weeks and rehabilitation of the knee is begun. Because these are intraarticular fractures, weight-bearing should be avoided until radiographs confirm that the fracture is fully healed.
Open reduction and internal fixation are indicated for coronal shear fractures. The fracture is exposed through a medial or lateral approach, depending on which condyle is affected. After anatomic reduction, interfragmentary lag screws are placed through the articular cartilage of the epiphysis without contacting the physis. Postoperatively, a long leg cast or brace is used. If secure fixation is achieved, early range of motion of the knee may be encouraged. As with type III and type IV fractures, weight-bearing should be avoided until radiographs confirm that the fracture is fully healed.
Outcome
The outcome of fractures of the distal femoral physis is generally good. The patient should continue to be followed up after healing to allow complications, such as the development of a growth disturbance or an accompanying ligamentous injury, that may have escaped detection at the time of the original injury to be detected.
Complications
Late Displacement
A displaced fracture may be present in a child who is seen several days after the injury. In addition, loss of initial reduction may occur in fractures treated by closed reduction and cast immobilization. Although sound clinical evidence is lacking, the consensus of most authorities is that type I and type II fractures should not undergo manipulative reduction after 7 to 10 days for fear of causing further damage to the growth plate. It is probably better to accept malunion after this period of time and allow the fracture to heal and remodel before consideration is given to further intervention rather than to perform a late open reduction. Depending on patient age and outcome, residual deformity can be addressed with an osteotomy or guided growth.
Type III and type IV fractures with late displacement should undergo open reduction and internal fixation as soon as possible to restore the congruity of the joint surface.
Neurovascular Injury
The incidence of compartment syndrome after a distal femoral physeal fracture has been estimated to be around 1%. Eid and Hafez reported two patients who developed Volkmann ischemic contracture in their series of 151 fractures of the distal femoral physis. Although the reported incidence of this complication is low, the consequences are often devastating. The importance of early recognition and prompt intervention in children who demonstrate the signs and symptoms of compartment syndrome cannot be overemphasized. In that same clinical series, peroneal nerve palsy was observed in 7.3% of patients. Because all cases resolved within 3 months, the authors did not believe that routine surgical exploration was necessary. However, in cases in which the neurologic deficit persists beyond 3 months, electromyographic testing may be indicated, and further intervention based on the findings may be warranted.
Ligament and Meniscal Injury
A number of authors have shown that distal femoral physeal fractures and ligamentous injuries can be present simultaneously. ∗
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Most often, the ligamentous injuries are not appreciated at the time the physeal injuries are treated. In these instances, laxity of the knee joint is discovered after the fracture has healed. Anterior laxity has been reported most frequently, followed by lateral and medial laxity. These reports emphasize the need to continue to follow up and evaluate these children after their fractures have healed.Growth Disturbance
Although the prognosis for a fracture of the distal femoral physis is generally good, problems with shortening and angular deformity are more common than one might expect according to the Salter–Harris classification. †
† ,
A metaanalysis by Basener and colleagues reviewed 564 fractures involving the distal femoral physis. Overall, 52% of the fractures developed a growth disturbance. This complication occurred in 36% of type I fractures, 58% of type II fractures, 49% of type III fractures, and 64% of type IV fractures.The poorer than expected prognosis after distal femoral physeal injuries may be attributable to the greater force needed to cause physeal separation at this site, especially in younger patients, whose thicker periosteal and perichondrial sheaths provide greater stability.
Growth problems are more likely to occur after fractures that are initially displaced and in fractures in younger patients. Riseborough and colleagues observed that fractures of the distal femoral epiphysis in juvenile patients 2 to 11 years of age were caused by more severe trauma and were more likely to result in growth problems than similar fractures in adolescents.
Careful clinical evaluation is recommended at 6-month intervals after the injury to assess lower extremity alignment and leg length. Comparative radiographs should be taken of both lower extremities. Partial inhibition of growth, or growth deceleration, can occur after distal femoral physeal injuries. Isolated instances of growth stimulation after these fractures have also been reported. Therefore it is probably wise to monitor these patients to skeletal maturity, even if radiographs show an open physis. Garrett and colleagues used the configuration of the Harris growth arrest line to detect a growth disturbance early after fracture treatment. If these lines were seen to extend across the entire metaphysis in both planes and remained parallel to it, a growth arrest was unlikely to occur.
Leg-length inequalities estimated to be less than 2 cm at skeletal maturity require no treatment other than a shoe-lift, if deemed necessary. If the estimated discrepancy at maturity is between 2 and 5 cm, an appropriately timed epiphysiodesis of the contralateral extremity may be indicated. For inequalities estimated at maturity to be more than 5 cm, leg lengthening should be considered.
Angular deformities may be due to either malunion or a partial growth disturbance. Significant angular deformity caused by malunion may be managed by osteotomy or, when appropriate, by hemiepiphysiodesis. Treatment options for a progressive angular deformity caused by a partial growth disturbance include osseous bridge resection, osteotomy, or epiphysiodesis of the remaining portion of the physis. Osseous bridge resection may be considered for lesions involving less than 50% of the physis in children who have at least 2 years of growth remaining. Results are best if the bar is located peripherally. The surgical incision is made either laterally or medially, depending on the location of the bar to be resected. The area of resection is determined preoperatively by the appearance of the bar on tomograms. A high-speed bur is used to excise the osseous bridge until normal physeal cartilage can be seen circumferentially within the defect. The defect is then packed with either autogenous fat (from the buttock region) or methyl methacrylate (Cranioplast) to prevent re-formation of the osseous bridge. Small metal markers are placed in the metaphysis and the epiphysis to allow resumption of physeal growth to be evaluated on radiographs. If varus or valgus deformity of the distal end of the femur is greater than 20° at the time of bridge resection, a distal femoral osteotomy should also be performed to realign the knee joint.
An osteotomy with epiphysiodesis of the remaining portion of the physis may be necessary when the bridge is too large to excise or in children who are approaching skeletal maturity.
Nonunion
Nonunion has been reported after coronal shear fractures involving the femoral epiphysis. These cases emphasize the importance of early diagnosis and treatment of these uncommon injuries by open reduction and internal fixation.
Osteochondral Fractures
An osteochondral fracture of the knee is most commonly seen in adolescent patients and is often associated with a dislocation of the patella. These fractures are seen in 25% to 75% of acute patellar fractures in children and adolescents.
Pertinent Anatomy
The etiology of these fractures is likely related to the unique structure of the cartilage–bone interface in the developing knee. Rosenberg suggested that because adolescents have little calcified cartilage, forces tangential to the articular surface of the knee are transmitted to the subchondral region and produce a fracture that is in the horizontal plane and mostly within bone. The same forces applied to the knee in an adult often result in a chondral tear at the “tide mark” between the calcified and uncalcified zones of the articular cartilage, with sparing of subchondral bone. In a histopathologic study, Flachsmann and colleagues concluded that adolescents were particularly susceptible to osteochondral fracture because of structural changes in the important anchoring region of the osteochondral junction that occur during maturation. They noted that, in immature tissue, fingers of compliant cartilage penetrate deep into the subchondral bone to provide a strong anchor. In mature tissue, the cartilage is secured to the subchondral bone by a well-defined layer of calcified cartilage. The irregular lower surface of the calcified layer, called the cement line, provides a large area of contact to secure the cartilage to the subchondral bone. In the adolescent, as the tissue matures, the interdigitating fingers of subchondral bone are replaced by a calcified matrix before the layer of calcified cartilage is fully developed. This makes the adolescent more susceptible to failure in the osteochondral region.
Mechanism of Injury
Osteochondral fractures of the knee are most often due to either a direct blow on a flexed knee or, more commonly, shearing forces associated with acute dislocation of the patella. These injuries most commonly occur in adolescents. When associated with patellar dislocation, these fractures occur when the dislocated patella slides back tangentially over the surface of the lateral femoral condyle. The fracture may occur during either the dislocation or relocation phase. Rorabeck and Bobechko estimated that osteochondral fractures occur in approximately 5% of all acute patellar dislocations occurring in children. Nietosvaara and colleagues found associated osteochondral fractures, either capsular avulsions or intraarticular loose bodies, in 28 of 72 children (39%) after an acute patellar dislocation. Stanitski and Paletta reported arthroscopically documented articular injuries in 34 of 48 older children and adolescents (71%) after acute patellar dislocation. More recently, Seeley and colleagues noted 46 osteochondral injuries in 122 children (38%) who had acute patellar dislocation.
Evaluation
Examination
Most patients with an osteochondral fracture give a history of a twisting injury on a flexed knee. Usually, a painful “snap” is heard or felt. The child may report a sensation of “giving way” or that the knee “went out of joint.” Hemarthrosis occurs rapidly, and the patient may experience pain on attempts to bear weight.
A child with an osteochondral fracture is seen with a painful, swollen joint. The child may hold the knee in 10° to 15° of flexion, and any attempt to flex or extend the knee is resisted. Tenderness may be elicited over the injured portion of the articular surface. The patient may also exhibit tenderness over the medial patellar retinaculum and a positive apprehension sign. One should ascertain the presence of hypermobility in other joints because adolescents without generalized joint laxity have a twofold increased frequency of articular lesions after acute patellar dislocation.
Imaging
Radiographic evaluation should include AP and lateral views of the knee, as well as tunnel and patellar skyline views. Osteochondral fractures may be difficult to see on plain radiographs, especially if the ossified portion of the fragment is small. ∗
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If radiographs fail to reveal a fracture, particularly if the history suggests acute patellar dislocation, the knee joint can be aspirated under sterile conditions to confirm the presence of hemarthrosis. The presence of fat globules within a bloody aspirate is presumptive evidence of an osteochondral fracture somewhere in the knee.
Although arthrography or CT 74 has historical value as aids in diagnosis of these injuries, MRI is probably now the gold standard for visualizing the size and location of osteochondral fragments. Seeley and colleagues reported that, in 21 of 46 children (44%), MRI confirmed an osteochondral injury that was not seen on plain radiographs.
In cases of traumatic knee hemarthrosis where MRI does not show any abnormalities, diagnostic arthroscopy may be considered. †
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Matelic and colleagues found that preoperative radiographs failed to identify an osteochondral fracture in 5 of 14 patients (36%) who were found to have these fractures during arthroscopy. Stanitski and Paletta reported that 20 of 28 osteochondral loose bodies (71%) confirmed by arthroscopic examination could not be identified on a complete four-view radiographic series.Classification
Rorabeck and Bobechko described three patterns of osteochondral fracture that are seen in children after acute patellar dislocations: inferomedial fracture of the patella, fracture of the lateral femoral condyle, and a combination of the two ( Fig. 15-10 ). Fractures involving the medial femoral condyle are less common and are usually caused by a direct blow to the knee.
Emergent Treatment
After examination, the patient with an osteochondral fracture should have the injured extremity elevated and splinted in a position of comfort, and ice should be applied to control swelling. If a tense hemarthosis is present, it may be aspirated to relieve pain. Distally, the circulation, sensation, and motor function of the limb should be monitored pending definitive treatment.
Nonoperative Treatment
It may be elected to manage patients having small fragment conservatively and reserve arthroscopy for persistent mechanical symptoms or effusion. These patients may be managed by a short period in a knee immobilizer. Once the swelling has subsided, rehabilitation of the knee can be initiated.
Surgical Treatment
Most authorities recommend early operative management of acute osteochondral fractures of the knee. ∗
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Whether the fragment is excised or reattached depends on the size and origin of the fragment. However, authors do not agree on the size of the fragment that mandates reattachment. In general, if the fragment is small and from a non–weight-bearing surface, it may be removed arthroscopically. Larger fragments from weight-bearing areas should be replaced.Osteochondral fractures can be reattached with the use of several fixation techniques. Reattachment can be performed by either arthrotomy or arthroscopy. Bone pegs, Smillie nails, countersunk Arbeitsgemeinschaft für Osteosynthesefragen (AO) minifragment screws ( Fig. 15-11 ), Herbert screws, small threaded Steinmann pins inserted in a retrograde fashion, fibrin sealant or other adhesives, and bioabsorbable pegs ( Fig. 15-12 ) have all been used with similar results. Significant aseptic synovitis of the foreign body type has been reported in some patients treated with intraarticular biodegradable internal fixation.
Postoperative regimens vary depending on the degree of stability achieved at the time of surgery. If adequate stability of the fracture is achieved, a postoperative brace can be applied, and early range of motion of the joint and quadriceps muscle-strengthening exercises can be initiated. Full weight-bearing is not allowed until radiographs show that the fracture has healed.
When an acute patellar dislocation requires excision or reattachment of an osteochondral fragment, several authors have recommended additional procedures to realign the extensor apparatus of the knee to prevent redislocation, especially when factors associated with patellofemoral malalignment are present. ∗
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These procedures generally involve repair of the medial retinaculum and medial patellofemoral ligament.Outcome
Although the outcome after fixation or arthroscopic removal of osteochondral fractures of the knee is generally good, there is no evidence stronger than retrospective case series to guide treatment of osteochondral fractures of the knee in children. Several studies have described satisfactory short- and intermediate-term outcome of fixation of osteochondral fractures in children and adolescents. One study suggested that patients with fractures involving the weight-bearing lateral condyle may have a poorer outcome. Further research is needed to determine whether surgical repair of these injuries will prevent the development of osteoarthritis in the long term.
Complications
Complications of surgical treatment include stiffness from adhesions, quadriceps atrophy, and loss of knee motion. Kramer and Pace observed that partially threaded cannulated screws may leave an indentation on the articular surface and, if not countersunk, may abrade the tibial surface, requiring later removal. They also noted that headless screws, while they can be buried below the articular cartilage surface and provide compression, may back out over time and require removal.
Fractures of the Patella
The patella is the largest sesamoid bone in the body. It lies within the tendon of the quadriceps and functions to make the quadriceps a more efficient extensor of the knee. In general, patellar fractures in children are uncommon, representing about 1% of all pediatric fractures. Most fractures of the body of the patella are seen in adolescents, whereas sleeve-type avulsion fractures are seen more commonly in children.
Pertinent Anatomy
The patella begins to ossify between 3 and 5 years of age. Ossification often begins as multiple foci that gradually coalesce. As the patellar ossification center expands, the peripheral margins may appear irregular and may be associated with accessory ossification centers. Incomplete coalescence of a superolaterally located accessory center of ossification results in a bipartite patella, which may be confused with a fracture. When present, a bipartite patella is usually evident by 12 years of age and may persist into adult years. Ossification of the patella is generally complete by late adolescence.
Mechanism of Injury
Transverse or comminuted fractures of the main body of the patella rarely occur in children because the patella is largely cartilaginous and has greater mobility than in adults. Most of these injuries occur in adolescence when ossification is nearly complete. As in adults, fractures of the patella in children may result from either direct or indirect forces. An avulsion fracture of the inferior or superior pole of the patella, the so-called sleeve fracture, is an indirect injury caused by powerful contraction of the quadriceps muscle applied to a flexed knee. These fractures usually occur in individuals involved in explosive acceleration activities, such as jumping.
Fractures of the patella have also been attributed to repetitive stress. Hensal and colleagues reported bilateral simultaneous fractures of the patella that resulted from indirect trauma in a 17-year-old boy. At surgery, sclerosis of the fracture edges was thought to be indicative of underlying areas of stress reaction. Iwaya and Takatori described lateral longitudinal fractures of the patella occurring in three children ages 10 to 12 years. The authors attributed these to repetitive activities. Ogden and colleagues suggested that instances of painful bipartite patella may be due to a chronic stress fracture.
Evaluation
Examination
A patient with a fracture of the main body of the patella usually has local tenderness and soft tissue swelling. Hemarthrosis of the knee joint is often present. Active extension of the knee is difficult, especially against resistance. However, the child might be able to lift the leg by internally rotating the affected limb using tension of the fascia lata if the disruption is minimal. A palpable gap at either the upper or the lower end of the patella indicates the presence of a sleeve fracture. A high-riding patella (patella alta) suggests that the extensor mechanism has been disrupted.
With marginal fractures, local tenderness and swelling over the affected region of the patella may be the only findings present. In these injuries, straight leg raising may often be possible. The presence of an avulsion fracture of the medial margin suggests the diagnosis of acute patellar dislocation that may have reduced spontaneously. With an associated dislocation, other findings such as medial retinacular tenderness and a positive apprehension sign may also be present.
Imaging
AP and lateral radiographs are needed to evaluate fractures of the main body of the patella. Transverse fractures are best visualized on the lateral view. A lateral radiograph taken with the knee in 30° of flexion may better define the soft tissue stability and true extent of displacement that is present.
Small flecks of bone adjacent to the superior or inferior pole in a patient who has sustained an acute injury may indicate the presence of a sleeve fracture. Lateral radiographs of both the injured and unaffected knee in 30° of flexion may be helpful for confirming the presence of patella alta on the injured side when a sleeve fracture is suspected. MRI or ultrasound may be helpful for detecting a sleeve fracture when the diagnosis is not clear from the clinical and plain radiographic findings. Marginal fractures that are oriented longitudinally may be best seen on a skyline view of the patella.
Classification
Fractures of the patella in children are generally classified according to the location, pattern, and degree of displacement. One fracture unique to children is the so-called sleeve fracture that traditionally was described as occurring through the cartilage on the inferior pole of the patella ( Fig. 15-13 ). This fracture is most commonly seen in children 8 to 12 years of age. With this injury, a large sleeve of cartilage is pulled off the main body of the patella along with a small piece of bone from the distal pole. Grogan and colleagues observed that avulsion fractures may involve any region of the periphery of the patella. They described four patterns of injury: superior, inferior, medial (which often accompanies an acute dislocation of the patella), and lateral (which they attributed to chronic stress caused by repetitive pulling from the vastus lateralis muscle). Other authors have further described the occurrence and treatment of the less common superior sleeve fracture.
Emergent Treatment
After examination, the patient with a patellar fracture should have the injured extremity elevated and splinted in a position of comfort, and ice should be applied to control swelling. If a tense hemarthrosis is present, it may be aspirated to relieve pain. Distally, the circulation, sensation, and motor function of the limb should be monitored pending definitive treatment.
Nonoperative Treatment
Closed treatment in a cylinder cast or knee immobilizer with the knee in full extension is recommended for nondisplaced transverse fractures and small marginal fractures, particularly if active extension of the knee is present. The patient may be permitted to bear weight as tolerated with crutches. The immobilization can be removed in 4 to 6 weeks when healing is complete, and gradual range of motion exercises can be initiated.
Surgical Treatment
The treatment guidelines for transverse patellar fractures in children are generally the same as those for adults. Operative treatment is necessary for transverse fractures that show more than 3 mm of diastasis or step-off at the articular surface. Fixation may best be achieved with the use of the modified tension band technique with a wire loop around two longitudinally placed K-wires ( Fig. 15-14 ). The use of an absorbable suture, as an alternative to the more traditional stainless steel wire, has recently been described. The use of an absorbable suture may facilitate later removal of the implant by limiting the amount of soft tissue dissection needed. Other fixation options include a circumferential wire loop, interfragmentary screws, or cannulated screws in combination with a tension band wire. The retinaculum should be repaired at the time of osseous fixation.
Similarly, sleeve fractures must be accurately reduced and stabilized with the use of suture fixation ( Fig. 15-15 ) or the modified tension band technique if the size of the osseous fragment is sufficient ( Fig. 15-16 ).
Comminuted fractures of the distal pole are best managed by partial patellectomy. Total patellectomy is reserved for injuries in which the comminution is widespread.
Outcome
Although the outcome after treatment of a fracture of the patella is generally good, no evidence stronger than retrospective case series exists to guide treatment of these injuries in children. Reported results are poorer after fractures that show greater displacement and comminution. The long-term outcome may also be influenced by accompanying cartilage damage. Further research is needed to determine whether surgical repair of these injuries will provide satisfactory function and prevent the development of osteoarthritis in the long term.
Complications
Complications that may occur after displaced fractures that are not adequately reduced include patella alta, extensor lag, and quadriceps atrophy.
Tibial Eminence Fracture
The anterior tibial eminence, or anterior tibial spine, is the distal site of attachment of the anterior cruciate ligament. These fractures are seen most commonly in children between 8 and 14 years of age.
Pertinent Anatomy
Before complete ossification of the proximal end of the tibia, the surface of the anterior tibial spine is cartilaginous. The anterior cruciate ligament arises from the medial side of the lateral femoral condyle and attaches distally in the anterior intercondylar region of the tibia. The anterior horn of the lateral meniscus is attached in close proximity. The femoral attachment of the posterior cruciate ligament is to the lateral surface of the medial femoral condyle. Distally, this ligament attaches to the posterior intercondylar area of the proximal tibia.
Mechanism of Injury
When excessive tensile stress is applied to the anterior cruciate ligament, the incompletely ossified tibial spine offers less resistance than the ligament, and the tensile stress thus leads to failure through the cancellous bone beneath the tibial spine.
Tibial spine fractures are most likely to be caused by hyperextension or valgus and external rotation of the knee. Traumatic forces that would normally rupture the anterior cruciate ligament in an adult will lead to a tibial spine fracture in a child. The injury almost always involves the anterior spine. Fractures of the posterior tibial spine are extremely rare in children and are more likely to occur in skeletally mature individuals ( Fig. 15-17 ).
