Assessment of Patellar Lateralization and Its Association with Patellofemoral Osteoarthritis Severity: A Retrospective MRI-Based Study

Background/Objectives: Alteration of the anatomy or congruence of the patellofemoral joint may lead to osteoarthritis. The distance of patellar lateralization in a coronal superimposed MR image (coronal MRI superimposition technique) can be a useful method for evaluating patellar lateralization. Methods: We correlated the presence of patellofemoral osteoarthritis (PFOA) with the tibial tuberosity–trochlear groove (TT-TG) distance and the distance of patellar lateralization. We also evaluated the correlation between the presence of patellar lateralization and the severity of PFOA. This retrospective study included 202 patients (non-severe PFOA, n = 135; severe PFOA, n = 67) who underwent knee magnetic resonance imaging (MRI). PFOA criteria and severity were defined using the International Cartilage Repair Society (ICRS) classification system. All MRI images were independently evaluated by two musculoskeletal radiologists. After dividing the study group into a patellar lateralization group and a control group according to the distance between the patellar long axis and the deepest portion of the trochlear deep notch with a 7 mm threshold, the association between patellar lateralization and PFOA severity was analyzed. Results: Interobserver agreement was excellent for measuring TT-TG distance (ICC = 0.980) and patellar lateralization (ICC = 0.984). The mean distance of patellar lateralization was significantly greater in the severe PFOA group (ICRS grades 2–4) compared to the non-severe group (ICRS grades 0–1) (6.02 mm vs. 4.78 mm; 95% CI of the difference, −2.110 to −0.376; p = 0.005). Also, we found that as the International Cartilage Repair Society (ICRS) grade of the PFOA rose, the proportion of patellar lateralization increased more than normal in each grade (p = 0.009). There were statistically significant differences in the TT-TG distance and patellar lateralization between the non-severe group (Grade 0 and Grade 1) and the severe PFOA group (more than Grade 2) by both interpreters (p = 0.029 and 0.014 for TT-TG distance; p = 0.005 and 0.002 for patellar lateralization). Conclusions: The measurement of patellar lateralization using the coronal MRI superimposition technique on MRI is significantly associated with PFOA and its severity. Thus, the coronal MRI superimposition technique would be a useful method for evaluating the relationship between patellar lateralization and PFOA.