Recurrent Patellar Dislocation in the Skeletally Immature
DNB Orthopaedics • October 2024 • Paper IV • 10 Marks
Introduction
Recurrent patellar instability in children and adolescents is usually multifactorial. It results from a combination of osseous malalignment, abnormal trochlear morphology and failure of the medial soft-tissue restraints.
The challenge in the skeletally immature patient is that treatment must restore patellar stability while avoiding injury to the open physes, particularly the distal femoral and proximal tibial growth plates.
Core concept
Recurrent patellar dislocation is rarely due to a single abnormality. Think of it as a combination of trochlea + patella height + tibial tubercle alignment + rotational profile + medial restraint failure.
A. Patho-anatomy
The patella normally tracks within the trochlear groove during knee flexion. In early flexion, before substantial bony engagement occurs, stability depends particularly on medial soft-tissue restraint.
Lateral dislocation usually occurs when the patella is forced laterally, commonly with:
- Valgus force
- Femoral internal rotation
- Tibial external rotation
- Knee near extension or early flexion
1. Medial Patellofemoral Ligament — MPFL
The MPFL is the principal passive restraint to lateral patellar translation in the first approximately 20–30° of knee flexion before the patella is securely engaged within the…