Congenital Dislocation of Patella
- The patella is dislocated laterally from the trochlear groove at birth
- Etiology is failure or improper fetal myotome development
- May present later with quadriceps weakness and functional deficits
- Ultrasound may be more useful than radiographs in a younger child due to incomplete patellar and epiphyseal ossification
- Surgical goals are to reduce the patella within the trochlear groove and to medialize and possibly lengthen the anterior thigh structures
- Recurrence and extensor lag may be noted post-operatively
Description:Congenital dislocation of the patella is a rare condition present at birth. The knee characteristically has a laterally dislocated patella with a flexion contracture and valgus deformity. Surgical correction is generally the recommended treatment.
Epidemiology:Congenital dislocation of the patella is rare, and prevalence is not known. Although some studies have grouped it within a spectrum of conditions that include acquired irreducible dislocation before age 10 years (Gordon, 1999) and patellar instability, most agree that it is a separate entity. (Ghanem 2000; Stanisavljevic, 1976; Conn, 1925; Mumford, 1947; Wada, 2008) Congenital patellar dislocation may be associated with a variety of conditions, including diastrophic dysplasia, arthrogryposis, Down syndrome, Rubinstein-Taybi syndrome, nail-patella syndrome, Larsen syndrome, and Ellis-van Creveld syndrome.
Clinical Findings:Clinical findings can be subtle at birth owing to the size and character of the structures being examined. Careful exam will reveal a newborn knee with:
- hypoplastic patella dislocated laterally, resting adjacent to the lateral femoral condyle
- empty trochlear groove
- knee flexion contracture, or the inability to achieve full active extension
- tibia in valgus with external rotation, depending on the severity of deformity
The quadriceps contracts voluntarily and the knee may achieve full active extension. If the flexion deformity is greater than 90 degrees, the lateralized extensor mechanism will act as a flexor. (Ghanem, 2000) Commonly, hip and foot deformities such as club foot or vertical talus coexist. (Ghanem, 2000; Bistolfi, 2012) Older children with more subtle presentation are noted to have delayed ambulation, weak quadriceps, and anterior knee pain. (Gordon, 1999; Ghanem, 2000; Conn, 1925)
Imaging Studies:The diagnosis may be missed early because the dislocated patella will not be seen on plain radiographs until the patella ossifies at around 3 years of age. In school age children, it is readily diagnosed by radiographs with an axial x-ray of the knee, but prior to that ultrasound is a better imaging study. (Wada, 2008; Walker, 1991) Ultrasound and the clinical findings of a palpable laterally displaced patella, flexion contracture, and inability to reduce the patella into the trochlear groove provide the basis of diagnosis, rendering advanced imaging unnecessary. (Ghanem, 2000)
Treatment:The mainstay of treatment is corrective surgery. With the reported age at diagnosis ranging from 4 days to 15 years, the preferred timing of surgery has not been agreed upon. (Gordon, 1999; Ghanem, 2000; Wada, 2008) Serial casting may correct the flexion deformity but will not reduce the patella. (Wada, 2008)
Several different surgical techniques are described, (Gordon, 1999; Ghanem 2000; Stanisavljevic, 1976; Conn, 1925; Wada, 2008) but all follow the same principles:
- extensive lateral release to allow centralization of the patella and quadriceps
- iliotibial band release
- lateral capsulotomy
- biceps femoris lengthening is performed if there is valgus subluxation of the tibia
- posterior capsule release may be considered if there is a significant knee flexion contracture
- V-Y quadricepsplasty, z-lengthening, or femoral shortening may be necessary if the extensor mechanism is shortened and cannot be centralized
- imbrication of the redundant medial capsule to stabilize the patella
A medial patellofemoral ligament reconstruction may be considered to supplement the medial imbrication. If the patellar tendon insertion is excessively lateral, a distal realignment may be performed with a Roux-Goldthwait transfer or with complete medialization of the patellar tendon. (Langenskiold, 1992)
Complications:Reported post-operative complications include persistent medial or lateral patellofemoral dislocation, persistent extensor lag, stiffness, and peroneal nerve palsy.
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- Gordon JE, Schoencker PL. Surgical treatment of congenital dislocation of the patella. J Pediatr Orthop. 1999; 19(2): 260-4.
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Top Contributors:Jennifer Bauer MD
Jeff Martus MD