Predisposing factors
- trochlear dysplasia
- patella alta
- increased TT–TG distance
- valgus alignment
- rotational malalignment
- generalised ligamentous laxity
- MPFL insufficiency after dislocation
Clinical features
- acute lateral patellar dislocation
- recurrent subluxation or dislocation
- apprehension
- positive J sign
- anterior knee pain
Examination
Assess:
- patellar glide and apprehension
- J sign
- limb alignment
- rotational profile
- generalised laxity
- effusion and osteochondral injury after acute dislocation
Imaging
- AP and lateral knee radiographs
- skyline / Merchant view
- MRI after acute dislocation when osteochondral injury or MPFL injury is suspected
- CT or MRI measurements for rotational anatomy and TT–TG where relevant
Treatment
First-time dislocation
Usually treated non-operatively if there is no large osteochondral fragment or other operative indication.
Recurrent instability
Treatment is individualised to the anatomical abnormality. Procedures may include MPFL reconstruction, tibial tubercle osteotomy or correction of significant bony malalignment.
Diagram
