Congenital patellar dislocation is intrauterine in onset and the dislocation is associated with significant deformities (flexion, external rotation, and valgus of knee) at birth. It is to be differentiated from other forms of patellar dislocation that would manifest after walking age and are not associated with significant deformities at birth.
Habitual patellar dislocation is defined as patellar dislocation and relocation with each cycle of knee flexion and extension. The patella can dislocate either in extension and relocate in flexion (habitual dislocation in extension) or it can dislocate in flexion and relocate in extension (habitual dislocation in flexion).
Other names used for habitual patellar dislocation are obligatory dislocation or involuntary dislocation of patella. In a way, habitual dislocation is a misnomer as it attributes the reason for dislocation to patient’s habit, behavior, or will. Habitual dislocation is involuntary and not in patient’s control.
Habitual dislocation in extension (sometimes reported as an exaggerated J sign) has less severe dysplasia associated with it compared to habitual dislocation in flexion. As the knee is extended from a flexed position, if the patella jumps out (dislocates) with the knee in greater than 30° of knee flexion, then it is true habitual dislocation in extension. This is different when compared to J sign, where the patella lateralizes or slides out of trochlea between 0° and 30° of knee motion. Habitual dislocation in extension does not routinely require quadricepsplasty.
Habitual dislocation in flexion, on the other hand, has significant associated dysplasias and would most likely require quadricepsplasty for correction.
Permanent dislocation of patella could be developmental in nature or could be associated with syndromes (Figure 30.1). Different types of patellar instability patterns are discussed in Chapter 3.
The pathoanatomy of habitual/permanent dislocation of patella is external rotation of the quadriceps mechanism, such that the quadriceps tendon, patella, and patellar tendon are positioned on the lateral aspect of the knee. Besides external rotation and lateral positioning, there is relative shortening of the quadriceps mechanism.
Figure 30.1 Permanent lateral patellar dislocation (arrows) in a young girl with Joubert syndrome (cerebellar malformation).
As the quadriceps mechanism is relatively short, if the patella is passively and forcibly positioned over the trochlea, knee flexion would be significantly decreased. The only way to further flex the knee would be to allow the patella to dislocate laterally.
Initially, the dislocation may be passively reducible, but with growth, it would become permanent irreducible dislocation (Figure 30.2).
It could be unilateral or bilateral.
It could be associated with other deformities, such as clubfeet, limb length discrepancy, or developmental dislocation of hip. Patellar dislocation may be part of a syndrome.
To address such complex instability patterns, an isolated medial patellofemoral ligament (MPFL) reconstruction would not be sufficient or successful.
Because the pathology of habitual/permanent dislocation is related to altered positioning and length of quadriceps mechanism, its correction would require reorientation, with or without lengthening the quadriceps tendon. The procedure of reorientation or lengthening of the quadriceps tendon is termed quadricepsplasty.
There are various types of quadricepsplasty. Chapter 13 provides an overview of different types of quadricepsplasty.
Quadricepsplasty could be broadly categorized as techniques that address the distal quadriceps mechanism or those that address the entire (proximal and distal) quadriceps mechanism.
Chapter 31 provides details on quadriceps lengthening procedure.
Quadricepsplasty has to be differentiated from proximal realignment/capsular procedures (vastus medialis obliqus [VMO] plasty, VMO imbrication, VMO advancement, medial plication). Quadricepsplasty is a more extensive procedure.
Our 4-in-1 quadricepsplasty technique is a combination of lateral retinacular lengthening (with extended lateral releases), modified Insall’s proximal “tube” realignment, Roux-Goldthwait procedure, and quadriceps slide/lengthening.1,2 Figures 30.3 and 30.4 show schematic representations of key steps for this procedure.
When treating pediatric patients, especially children, it is important to familiarize with various patterns of patellar instability that can exist in this younger population.
The authors have reported different types of instability patterns, especially in pediatric patients, to help decide which patients would do well with MPFL reconstruction and which patients need quadricepsplasty.
Patients with type III (dislocatable) and type IV (dislocated) patella frequently need quadricepsplasty. They may or may not need MPFL reconstruction.
Table 30.1 lists indications and contraindications for quadricepsplasty.
Parents bring their child due to increasing knee deformity (genu valgum), frequent falls, or abnormal gait.
Parents complain of their child’s altered gait and limp that has progressively worsened with growth.
Parents may have noticed dislocated patella or may not be aware of it.
Older children typically complain of pain, giving-way episodes, frequent falls, and antalgic gait. In younger patients, pain is usually not present.
History of treatment for clubfeet, developmental dysplasia of hip, developmental delays, or any syndromic association
Family history of, for example, nail-patella syndrome
Physical examination should include complete examination of the child, including spine, hips, knees, ankle, and feet.
Limb length discrepancy and limb deformity in supine and standing position should be evaluated. In the presence of genu valgum, it should be checked if it is passively correctible.
TABLE 30.1 Indications and Contraindications of Quadricepsplasty
Habitual dislocation of patella in flexion
Permanent dislocation of the patella
Developmental dislocation of the patella
Congenital dislocation of the patella
Habitual dislocation of the patella in extension may or may not require quadricepsplasty
Traumatic patellar dislocation does not require quadricepsplasty
Patients with certain syndromes, neuromuscular disorders, and nonambulators (relative contraindications)
Anesthesia risks or too ill for surgical treatment
Gait should be evaluated for asymmetry, limp, antalgia, and compensation.
The knee examination should be compared with the contralateral knee and should include assessment for tenderness, range of motion, patellar position and reducibility, and patellofemoral tracking. If patella is reducible, it is held reduced over the trochlea and knee flexion is performed. If the knee could be flexed up to 90° with patella reduced, quadriceps lengthening would not be necessary.
Patellar dislocation may be missed with the knee in extension, but would be apparent with knee flexion.
Joint hypermobility is common in children. Beighton scores are calculated but the threshold for score to be classified as “lax” has varied in the literature.3,4
Knee examination is usually painless, but if the child exhibits pain or cries during knee evaluation, chondral lesions should be considered.
The tightness of the lateral retinaculum should also be assessed by evaluation of medial patellar translation and the degree to which the patella can be everted.
The knee range of motion and patellar tracking should be checked with the hip in extension and then with the hip flexed to 90°. The contribution of the rectus femoris to the instability can be appreciated when the patellofemoral tracking would appear to be normal with the hips flexed but the patella would dislocate with the hips extended.
Plain radiographs of the knee to include an AP, true lateral view of the knee in 20° to 30° of flexion, and an axial view
Patellar ossification starts between 3 and 5 years age. The lateral and axial view may not show the patella in the very young patient.
Full-length lower-extremity films are useful for assessment of overall alignment and should be obtained in skeletally immature patients and those patients in whom significant varus or valgus is suspected on the basis of physical examination. The lateral distal femoral and medial proximal tibial angles should be calculated to identify the source of deformity. Frequently, the source of genu valgum is tethering of lateral tissues, and the valgus would correct once adequate lateral releases and quadricepsplasty are performed and once the patella is relocated.
MRI is useful to visualize the dislocated patella, assess articular cartilage surfaces, assess trochlear anatomy, and allow for measurement of the tibial tubercle-trochlear groove (TT-TG) distance. In younger patients (typically less than 8 years of age), conscious sedation may be required to obtain MRI.
Ultrasound can provide useful information about patellar position and patellofemoral geometry, though its interpretation may be difficult for those not used to it, and it is technique/user dependent.
Syndromes with joint hypermobility, such as Down syndrome
Other syndromes: Kabuki syndrome, Rubinstein-Taybi syndrome, nail-patella syndrome, patellar aplasia
Neuromuscular disorders, including cerebral palsy
Spectrum of lower-extremity malformation, including proximal femoral focal deficiency, lateral femoral condyle hypoplasia, cruciate ligament deficiency, fibular hemimelia, ball-and-socket ankle joint, tarsal coalition, and/or missing lateral rays
Habitual dislocation in flexion and permanent dislocation would typically require operative treatment because functional deficits are likely to continue and may worsen with growth. The role of nonoperative management in these patients is limited to those too ill for surgical treatment or with other contraindications to surgery.
While the 4-in-1 quadricepsplasty technique is successful in restoring patellar stability and function in most, all anatomic risk factors associated with instability should be evaluated.
Once the patella is repositioned on the trochlea, only then would the increased lateral vector of patellar tendon be apparent. If the tibial tubercle apophysis and proximal tibial physis are open, a tibial tubercle osteotomy and transfer are contraindicated. Either hemi-transfer of patellar tendon (Roux-Goldthwait
procedure) or complete detachment and transfer of the entire patellar tendon could be performed.5
Lateral retinacular release could be performed instead of lateral retinacular lengthening. However, a lateral release would leave a large void (and an open joint) on the lateral side in the area where the patella was positioned before reduction. Lateral lengthening would help to cover this void (Figure 30.3).
MPFL reconstruction could be added, if needed, after quadricepsplasty, though it is typically not required.
Trochleoplasty could be performed at the time of quadricepsplasty, though author has not felt the need for it till now. The younger the patient, the higher is the chance that patellar stabilization would help in trochlear remodeling. Trochlear remodeling is minimal after age 10 – 11 years.
In children with dislocated patella, the apparent valgus is usually due to lateral tethers and position of the patella and not due to underlying femoral or tibial deformities. The extended lateral releases, quadricepsplasty, and repositioning of the patella would frequently correct these knee deformities, including genu valgum.
C-arm, implants, or autografts/allografts are not required during the 4-in-1 procedure. If additional procedures are planned, they may be then required.
There are several techniques of quadricepsplasty, each with pros and cons. There are no comparative studies suggesting superiority of one technique over the other.
The technique described in this chapter is based on Insall’s proximal “tube” realignment technique.1 The original technique was described for adults and involved subperiosteal elevated of a medial flap from patella, extending to the quadriceps and patellar tendon. The results of this technique, in isolation, are not very favorable.
The original technique of “tube” realignment has been modified to include medial parapatellar arthrotomy (not medial subperiosteal flap) and extended lateral releases. Also, other procedures are concomitantly performed, including lateral retinacular lengthening, Roux-Goldthwait procedure, and quadriceps slide/lengthening (if required).
The patient is placed in a supine position on the operating table.
A tourniquet is applied over the proximal thigh. It could be deflated to assess patellar tracking during or after quadricepsplasty, as needed.
A small bump is placed under the operative hip.
General anesthesia with adequate muscle relaxation is used.
Medial and lateral excursion of the patella and tightness of the lateral retinaculum are assessed. It is checked if the patella is reducible or not. If reducible, the degrees of knee flexion that could be achieved with the patella reduced is noted. This would give an idea about the need for quadriceps lengthening.
The tourniquet is inflated to 225 mm Hg.
A diagnostic knee arthroscopy is then performed using standard portals. Arthroscopy from superolateral portal can help in assessment of patellar position and patellofemoral tracking. Any associated intra-articular pathology is addressed.
Diagnostic arthroscopy is optional and could be avoided.
The knee is flexed and an anterior midline longitudinal incision is planned. The incision would measure around 12 and 15 cm, depending on the size of the knee. The dislocated patella should be ignored while planning the incision. The center of the distal femur should be marked after palpating the outer aspect of medial and the lateral femoral condyles. The tibial tubercle is marked, and the incision is planned medial to the tibial tubercle. Due to genu valgum the incision may appear to be oblique, but after correction, it would be straighter (Figure 30.5).
The anterior incision is made, and dissection is carried down through the subcutaneous tissue until the patella is visible. Subcutaneous planes are created all around the patella so that the quadriceps tendon, VMO, vastus lateralis tendon, medial and lateral retinaculum, iliotibial band, patellar tendon, and tibial tubercle are visualized. There may be some adhesions or fibrous connections between the lateral aspect of
the patella and subcutaneous tissues, and these are released.