Incidence is reported as 5.8 per 100,000 but could be as high as 29 per 100,000 in the adolescent population
Patellofemoral Dislocation
Dislocation is usually to the lateral (or outer) side, often tearing the medial patellofemoral ligament (MPFL) on the medial side.
During the dislocation event the joint looks horribly deformed.
Normal Patellar Restraints
The patella is normally restrained in its underlying groove in the femur by -
- the walls of the trochlear groove in the femur
- its containment within the patellar tendon, which is attached below to the tibia and above it expands into the quadriceps muscle
- the medial (MPFL) and lateral patellofemoral ligaments tethering the sides of the patella to the femur
The medial patellofemoral ligament (MPFL) is the primary static restraint to lateral patellar instability during the first 20 degrees of knee flexion.
A dislocation event of the M{FL may tear the ligament, rendering the patient more liable to repeat events.
Predisposing Anatomy for patellar dislocation
The following may predispose to subluxation or dislocation of the patella -
- a previous dislocation event
- patella alta
- patellar dysplasia
- patellar tilt
Reduction of patellofemoral dislocation
The dislocation may reduce spontaneously at the time, or it may need to be reduced under sedation or anaesthesia.
Relevant links on KNEEguru
A-Z Keywords
Medial patello-femoral ligament
Primer - 2019 - All about dislocation of the patella
Journal Interpretation- 2023 - Framing Patellar Instability: From Diagnosis to the Treatment of the First Episode
Contributions by experts -
- Dr Lars Blønd - 2017 - Patellar instability - a Continuum