Summary

Nearly one-in-four patients with a patellar instability event may have an osteochondral fracture, and the risk of future osteochondral fracture without surgical stabilization is just less than 20%.

Abstract

Background

Radiologic risk factors for osteochondral fractures associated with patellar instability events are rarely studied, particularly in patients with recurrent instability. Presence of an osteochondral fracture increases injury severity and often necessitates surgical stabilization. We hypothesize that specific radiologic characteristics will relate to increased prevalence of osteochondral fractures associated with patellar instability.

Methods

Patient data (N=730) in a prospective multi-center study were reviewed for radiologic findings. Trochlear Crossing Sign and Caton-Deschamps Index were measured on radiographs while tibial tubercle-trochlear groove (TT-TG) distance, patellar tilt, trochlear depth, trochlear bump, sulcus angle, and patellar subluxation were measured on magnetic resonance imaging. Potential radiologic risk factors were classified as At-Risk or Not At-Risk based on pathologic thresholds for general patellar instability. Patients were grouped according to presence or absence of an osteochondral fracture and analyzed with Mann-Whitney tests, Chi-Square tests, and multivariate regression modeling with a 95% confidence interval.

Results

In the total cohort (17.0 +/- 4.4 years; 57.3% female), 170/730 (23.3%) patients had an osteochondral fracture, while 76/413 (18.4%) of those with recurrent instability had an osteochondral fracture. High Caton-Deschamps Index (>1.2) was found to be protective of an osteochondral fracture with an odds ratio of 0.43, while high TT-TG distance (>=13mm) was found to be a risk factor for an osteochondral fracture with 2.17 times increased odds. Though first-time dislocations increased odds of an osteochondral fracture by 4.72 times, those with recurrent instability were found to have a similar predictive relationship of Caton-Deschamps Index and TT-TG with osteochondral fracture incidence. In Chi-Square analyses, lower Caton-Deschamps Index, shallower Trochlear Depth, smaller Trochlear Bump, and presence of Patellar Subluxation were more common in patients with osteochondral fractures. Lower Caton-Deschamps Index, positive Trochlear Crossing Sign, and shallower Trochlear Depth were more common among those with osteochondral fractures in a subset of patients with recurrent instability.

Conclusion

Nearly one-in-four patients with a patellar instability event may have an osteochondral fracture, and the risk of future osteochondral fracture without surgical stabilization is just less than 20%. Patella alta was found to be protective of osteochondral fractures in patients with first-time and recurrent instability while a lateralized tibial tubercle was found to be a risk factor. These radiologic characteristics should guide healthcare professionals on the risk of future osteochondral fracture during treatment planning after a patellar instability event.