Summary

Patellar OCDs, which are much more rare, present at more advanced and unstable stages, compared to the ‘classic’ medial femoral condyle OCD, and are much more likely to undergo primary surgical treatment.

Abstract

Introduction

Recently, a large multi-center epidemiologic report described the variability in presentations of knee osteochondritis dissecans (OCD). While the medial femoral condyle (MFC) is the most common site of presentation, patella lesions are quite rare, but pose unique challenges to the treating provider, which warrants enhanced investigation efforts.

Purpose

To study the presenting demographic, clinical, and radiologic differences in patellar OCD lesions, when compared to MFC OCD lesions.

Methods

A query of baseline characteristics from a multi-center prospective cohort of osteochondritis dissecans of the knee was performed. Inclusion criteria for the prospective cohort included any knee OCD at any stage of treatment presenting to a participating surgeon. Exclusion criteria included lesions not clearly meeting diagnostic criteria for osteochondritis dissecans (e.g. chondral lesions without subchondral bone involvement). Demographic data, physical exam findings, radiographic, and MRI features were analyzed. A comparison between patella OCD (pOCD) and medial femoral condyle OCD (mfcOCD) was performed using ANOVA and t-test for continuous variable and a Chi-squared for categorical variables with a p value set to 0.05.

Results

A total of 940 lesions in either cohort (mean age 13.1 years, range 5.4 – 17.9 and 31.5% females) were identified in the prospective cohort. pOCD presented at an older mean age than mfcOCD (14.3 vs. 13.11 years-old, p<0.001). pOCD patients were more likely to present having undergone a previous surgery (17.6% vs. 7.7%, p=0.005) and with an effusion on physical exam (50.8% vs. 14.4%, p<0.001). pOCD presented with more advanced and unstable MRI features than mfcOCD (displacement: 64.7% vs. 20.5%, p<0.001; articular breach: 88.0% vs. 18.6%, p<0.001; extensive edema: 62.9% vs. 32%, p>0.001). More pOCD underwent initial operative management than mfcOCD (75.0% vs. 53.5%, p<0.001). Of those that underwent surgery, arthroscopic assessment showed significantly higher rates of mobile pOCD than mfcOCD (95% vs. 41.7%, p<0.001). Of the mobile lesions, pOCD were more likely to be a trap door or crater, while mfcOCD had equal distribution of mobile lesion types.

Conclusion

Patellar OCDs, which are much more rare, present at more advanced and unstable stages, compared to the ‘classic’ medial femoral condyle OCD, and are much more likely to undergo primary surgical treatment. These findings may suggest a different pathophysiology or etiologic pathways for patellar OCD, clearly warranting greater investigation efforts for these ‘bad actors’, which face grave risks for the long-term joint health of affected adolescents.