Patella Dislocations: Causes & Stabilisation Surgery

What Is a Patella Dislocation?

A patella dislocation occurs when the kneecap (patella) is forcibly displaced out of its groove (the trochlea) on the front of the femur. It almost always dislocates laterally (outwards). First-time dislocation is often caused by a twisting injury, a direct blow to the knee, or simply a sudden change in direction.

Who Is At Risk?

Patella dislocation is most common in adolescents and young adults, particularly females. Predisposing factors include a shallow trochlea (trochlear dysplasia), high-riding patella (patella alta), a laterally positioned tibial tuberosity, and generalised joint laxity.

First-Time Dislocation

The majority of first-time dislocations are managed conservatively: the patella is relocated (reduced) under sedation, the knee is immobilised briefly, and a structured physiotherapy program is commenced focusing on quadriceps and hip strengthening.

However, re-dislocation rates are high, approximately 40–50% after a first dislocation, and even higher in patients with predisposing anatomical risk factors.

Recurrent Dislocation

After two or more dislocations, surgical stabilisation is typically recommended. The medial patellofemoral ligament (MPFL) is the primary restraint to lateral patellar displacement. In virtually all patella dislocations, the MPFL is torn.

MPFL Reconstruction

MPFL reconstruction is the most common surgical procedure for recurrent patella instability. A graft (usually a hamstring tendon) is used to reconstruct the MPFL, anchoring the patella to the medial femoral condyle. It is performed arthroscopically or with a small open incision.

In patients with significant trochlear dysplasia or very high patella alta, additional bony procedures (trochleoplasty, tibial tuberosity transfer) may be required.

Recovery

Following MPFL reconstruction, the knee is braced for approximately 4–6 weeks. Physiotherapy commences early and progresses through strengthening, balance, and sport-specific training. Return to sport is typically at 6–9 months. Results are excellent, with recurrence rates below 5%.

Further Reading

Dr Mooney has written in more detail about this topic on his own site: patellofemoral stabilisation surgery and kneecap instability and recurrent dislocation.