Prevalence of cartilage lesions and early osteoarthritis in patients with patellar dislocation.

Objectives: Assessment of cartilage lesions and osteoarthritis (OA) of the patellofemoral joint in patients following lateral patellar dislocation using magnetic resonance imaging (MRI).

Methods: MR images of 129 knees (mean age 26 years, range 11-56) grouped as acute (A), recurrent (B), and chronic (C) dislocators were analysed regarding the prevalence and severity of patellofemoral cartilage lesions. Grades of OA were assessed using modified WORMS.

Results: In groups A, B, and C the prevalence of cartilage lesions was 71%, 82%, and 97%, respectively. Most lesions were located on the central patella in groups A and B (central 69% and 78%; medial 56% and 47%; lateral 31% and 42%), whereas group C revealed all regions affected (73%, 61%, and 67%). Of group A, 14% had mild OA and 64% of group B. Group C showed mild OA in 62% and moderate OA in 18%. Cartilage defect size and prevalence of OA was correlated with number of dislocations (r = 0.41 and r = 0.59; P < 0.001).

Conclusions: Cartilage lesions and early OA are common after patellar dislocation and appear to increase with the frequency of dislocation. Both conditions should be considered when interpreting MRI in such patients, because of implications for treatment.

Key Points: • Cartilage lesions are very common after patellar dislocation. • The severity of cartilage lesions increases with number of dislocations. • Osteoarthritis is common after recurrent patellar dislocation, even in young patients. • Detecting cartilage lesions is important after patellar dislocation.