| Research into risk factors for knee osteoarthritis (OA) has focused on the tibiofemoral joint despite knowledge that the disease also occurs in the patellofemoral joint (PFJ). Patella alta, or a "high-riding" patella, is measured by the Insall-Salvati ratio (ISR) and has received little attention in the literature as a risk factor for PFJ OA despite its known association with patellar dislocation, patellofemoral malalignment, and decreased PFJ contact area. The overall aim of this dissertation is to investigate the relationship between patella alta and structural features of OA observed on MRI. We hypothesized that knees with high ISRs (patella alta) have more damage to cartilage and underlying bone compared to those with low ISRs. Additionally, we attempted to clarify the complex relationship between PFJ alignment, trochlear morphology, quadriceps strength, patella alta, and PFJ OA. We used lateral radiographs or magnetic resonance images from the Multicenter Osteoarthritis Study to measure the ISR, PFJ alignment (lateral patellar displacement and tilt), and trochlear morphology (lateral trochlear inclination, trochlear angle, and sulcus angle) in 907 knees. Knees came from mostly female subjects (63%) who had a mean body mass index of 30 and mean age of 62. The ISR and lateral trochlear inclination were the best predictors of PFJ malalignment. Knees in the highest ISR quartile had 2.4 to 3.5 fold-increased risk of cartilage damage, bone marrow lesions, and bone attrition compared to those in the lowest ISR quartile. We then investigated if the relationship between the ISR and structural damage was modified by weak quadriceps or abnormal trochlear morphology. We found an absolute increase in the prevalence of structural damage in knees with weak quadriceps and with a high ISR, although there was no significant interaction between these factors. Knees with low lateral trochlear inclination had significantly greater structural damage than knees with high lateral trochlear inclination and those with both high ISR and low lateral trochlear inclination had an even higher risk of damage (p for interaction = 0.06). In summary, these results demonstrate a strong association between patella alta and lateral trochlear inclination with PFJ malalignment and structural features of PFJ OA. |
