Patellofemoral Friction Syndrome

Abstract

OBJECTIVE To investigate whether patellofemoral T2 cartilage changes are associated with lateral patellofemoral friction syndrome (PFS), as indicated by edema-like signal within the superolateral infrapatellar (Hoffa) fat pad. METHODS In this IRB-approved retrospective study of 510 consecutive patients, 49 patients with 50 knee MR imaging exams demonstrating normal or low-grade patellofemoral cartilage abnormalities (WORMS score ≤2) were included. 22 exams with PFS (cases) were compared with an age- and gender-matched cohort of 28 exams without PFS (controls). 3T MR imaging was performed with multi-echo, spin echo T2 mapping. Two readers measured in consensus malalignment parameters, including patellar height index, tibial tuberosity to trochlear groove distance (TT-TG), and sulcus angle. Bulk T2 cartilage values in the lateral and medial patellofemoral compartment, central weight-bearing medial and lateral femoral condyles were measured independently. Interobserver agreement was quantified using concordance correlation coefficients (CCC). Demographics, anatomic measurements, WORMS scores, and cartilage T2 values were compared between cases and controls using Fisher’s exact test, Wilcoxon rank-sum, and mixed effects models. RESULTS Cases demonstrated higher patellar height index (p=0.002) and TT-TG (p=0.02). Interobserver agreement for T2 values was good overall (CCC range: 0.65–0.93). Cases demonstrated higher medial facet patellar bulk T2 (38.1±7.5 ms) versus controls (33.6±7.3 ms) (p=0.02); otherwise there were no significant differences in regional T2 values. CONCLUSION T2 mapping in patients with PFS demonstrates increased cartilage T2 in the medial patellar facet, possibly reflecting collagen alteration from early chondromalacia (softening) or increased water content related to altered contact pressures.