Congenital Dislocation of the Patella

Congenital dislocation of the patella is a rare but important paediatric condition that presents at birth with a fixed lateral position of the patella. It sits at the fixed end of the spectrum covered in paediatric patellar instability, and should not be managed with the adult toolkit described in MPFL injury — most of which requires a closed physis. Unlike habitual dislocation, which is reducible in extension, the congenital form remains dislocated in all positions and is associated with significant flexion contracture, valgus deformity and external tibial torsion. Early recognition and surgical realignment before age two allows trochlear remodelling and prevents lifelong extensor mechanism dysfunction and early osteoarthritis.

Nail-patella syndrome features absent or hypoplastic patellae, nail dysplasia and iliac horns. Trisomy 21 has ligamentous laxity and increased risk of fixed dislocation. Always examine hands, nails and perform karyotype if dysmorphic features present. Syndromic cases may require modified surgical goals.

And look beyond syndromes to limb deficiency. A fixed lateral patella can be one visible component of a postaxial limb deficiency: in the case reported on this page the same child had fibular hemimelia, proximal femoral focal deficiency and a tarsal coalition, with fibular hemimelia in the opposite leg too (PMID 35758357). Examine the fibula, the femoral length and the hindfoot, and image the other leg — the associated deformity may matter more for function than the patella does. The secondary genu valgum and the external tibial torsion are assessed as part of the paediatric rotational profile.

X-rays in infants are limited because the patella is unossified until age 3-5 years. Ultrasound can confirm the cartilaginous patella position lateral to the femur. Do not delay diagnosis waiting for ossification. Clinical examination and attempted reduction are diagnostic.

Q: Why is a tibial tubercle transfer avoided in the skeletally immature knee, and what is used instead? A: The tibial tubercle apophysis is contiguous with the proximal tibial physis; an osteotomy through it risks anterior physeal arrest and genu recurvatum with growth disturbance. Distal realignment in children is therefore performed with soft-tissue transfers - the Roux-Goldthwait hemi-patellar-tendon transfer or a Galeazzi semitendinosus tenodesis - reserving a formal tubercle osteotomy for the adolescent with a closing apophysis.

Q: After a complete lateral release the patella still will not sit in the trochlea without tension - what is the problem and the solution? A: The quadriceps myotendinous unit is intrinsically contracted and short, not just laterally tethered. The solution is to lengthen the extensor mechanism with a V-Y quadricepsplasty (combined with proximal mobilisation of the displaced extensor apparatus), permitting tension-free patellar reduction and knee flexion rather than forcing reduction and producing patella baja or recurrence.

Best prognosis: Surgery before age two, complete lateral release, correction of torsion and valgus, compliant post-operative rehabilitation. Poor prognosis: Delayed presentation after age five, syndromic laxity, incomplete release, persistent external torsion. Key threshold: Age two years - outcomes decline sharply after this window because trochlear remodelling potential is lost.

No dedicated international registry exists for congenital patellar dislocation due to extreme rarity. Evidence is limited to small case series from tertiary paediatric centres. Principles are consistent across guidelines: differentiate fixed from habitual type, release lateral structures extensively, correct alignment early, and monitor for recurrence and arthritis long-term.