Congenital Dislocation of Patella

Key Points:

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:
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:
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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References:

  1. Bistolfi A, et al. Adult congenital permament bilateral dislocation of the patella with full knee function: case report and literature review. Case Rep Med. 2012; 182795.
  2. Conn HR. A new method of operative reduction for congenital luxation of the patella. J Bone Joint Surg Am. 1925; 7(2): 370-383.
  3. Gordon JE, Schoencker PL. Surgical treatment of congenital dislocation of the patella. J Pediatr Orthop. 1999; 19(2): 260-4.  
  4. Ghanem I, Wattincourt L, Seringe R. Congenital dislocation of the patella.  Part I: pathology anatomy. J Pediatr Orthop. 2000; 20(6): 812-6.
  5. Ghanem I, Wattincourt L, Seringe R. Congenital dislocation of the patella.  Part II: orthopaedic management. J Pediatr Orthop. 2000; 20(6): 817-22.
  6. Gupta P, Jindal R, Gupta R. Congenital dislocation of the patella with ipsilateral hip flexion-abduction deformity: a case report. J Pediatr Orthop B. 2008; 17(4): 199-201.  
  7. Langenskiold A, Risila V. Congenital dislocation of the patella and its operative treatment. J Pediatr Orthop. 1992; 12(3): 315-323.
  8. Mumford EB. Congenital dislocation of the patella: Case report with history of four generations.  J Bone Joint Surg Am. 1947; (4): 1083-1086.
  9. Stanisavljevic S, Zemenick G, Miller D. Congenital, irreducible, permanent lateral dislocation of the patella. Clin Orthop Relat Res. 1976; 116:190-9.  
  10. Wada A, et al. Congenital dislocation of the patella. J Child Orthop. 2008; 2(2):119-23.  
  11. Walker J, Rang M, Daneman A. Ultrasonography of the unossified patella in young children. J Pediatr Orthop. 1991; 11(1):100-2.
    

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