Comparison of Inflammatory Biomarkers in Females with and without Patellofemoral Pain and Associations with Patella Position, Hip and Knee Kinematics, and Pain

Background: /Objectives: Patellofemoral pain (PFP) is believed to be a precursor to knee osteoarthritis (OA). The primary purpose of this study was to compare matrix metalloproteinase-9 (MMP-9) levels in young, adult females with and without PFP. The secondary purpose was to determine associations between MMP-9, patella position, hip and knee kinematics, and pain in females with PFP. Methods: Plasma was analyzed for MMP-9. Patellar position was measured using diagnostic ultrasound as the degree of offset (RAB angle) from the deepest aspect of the femoral trochlear groove to the inferior pole of the patella. A positive RAB angle suggested patella lateralization. Hip and knee kinematics during a single-leg squat were measured using 2-dimensional motion analysis and quantified as the dynamic valgus index (DVI), a combined measure of hip and knee motion. A higher DVI suggests increased valgus loading at the patellofemoral joint. Pain was measured using a 10-cm visual analog scale. Results: Females with PFP had significantly higher levels of MMP-9 than controls (72.7 vs 58.0 ng/mL, p = 0.03). For females with PFP and a more laterally positioned patella (RAB angle > 13˚), a significant positive association existed between MMP-9 and patella lateralization (r = 0.38, p = 0.04) and a significant inverse association with the DVI (r = -0.50, p = 0.007). Conclusions: Females with PFP had higher levels of MMP-9 than controls. The significant association between MMP-9 and patella lateralization provided additional information about the influence of patella position on joint inflammation. The significant, inverse association between MMP-9 levels and the DVI suggested that subjects with higher MMP-9 levels might have altered their movement pattern to avoid knee valgus loading.