School of Medicine

Summary : MR imaging reveals significant topographical differences between controls and patients with patellofemoral instability with greater differences at the proximal trochlea and dysplasia of the condyles. Objective: Plain films and CT based imaging were the first to establish measurements that evaluated patellar instability. Limited research has shown MRI's efficacy in evaluating these established measurements. The aim of this study is to identify morphological differences between normal knees and those with patellofemoral instability on MR imaging in order to determine what measurements are significant and the value at which each measurement signifies pathology. Methods : Retrospective review of 81 patients with no history of patellofemoral joint pathology and 40 patients with recurrent patellar instability. Controls had no present symptoms or history of patellofemoral complaints and an exam negative for patellar grind, facet tenderness, and apprehension. Patients with patellar instability had a history of at least 2 frank patellofemoral joint dislocations (PFJD). MRI images were obtained with the knee in non-weight bearing and in full extension. Measurements of patellar tilt, trochlear morphology, and Tibial Tuberosity- Trochlear Groove (TTTG) distance were evaluated on axial slices and patellar height was measured on sagittal images. Trochlear morphology was assessed at the proximal (1st cut) and distal (2nd Cut) trochlea. Results : All measurements of patellar tilt were found to be significantly different between the two groups and reflected an increase in the lateral rotation of the patella in patients with instability. For patellar height, only Insall Salvati (control: 1.08 ± 0.02 PFJD: 1.26 ± 0.03) and Caton Deschamps (control: 1.13 ± 0.02 PFJD: 1.29 ± 0.03) ratios proved to be significantly different. Trochlear morphology had numerous measurements prove to be significantly different proximally and distally. These included classic measurements like sulcus angle (control: 148.