Inverted Rearfoot posture in subjects with coexisting patellofemoral osteoarthritis in medial knee osteoarthritis: an exploratory study

BACKGROUND: While abnormal rearfoot posture and its relationship to patellofemoral (PF) pain has been thoroughly discussed in the literature, its relationship to patellofemoral osteoarthritis (PFOA) has not been determined. This study aimed to examine whether rearfoot posture is associated with a higher prevalence of radiographic PFOA in a compartment-specific manner in patients with medial tibiofemoral osteoarthritis (TFOA). METHODS: Participants from orthopedic clinics (n = 68, age 56–90 years, 75.0% female), diagnosed with radiographic medial TFOA (Kellgren/Lawrence [K/L] grade ≥ 2) were included in this study. The presence of PFOA and static rearfoot posture were evaluated using a radiographic skyline view and a footprint automatic measurement apparatus, respectively. The relationship between rearfoot posture and PFOA was examined using analysis of covariance and propensity score-adjusted logistic regression analysis. RESULTS: On average, patients with coexisting PFOA and medial TFOA (n = 39) had an inverted calcaneus 3.1° greater than those with isolated medial TFOA (n = 29). Increased calcaneus inverted angle was significantly associated with a higher probability of the presence of medial PFOA (odds ratio: 1.180, 95% confidence interval: [1.005, 1.439]; p = 0.043). Calcaneus inverted angle was not associated with higher odds of lateral PFOA presence based on the adjusted values. CONCLUSIONS: The presence of an inverted rearfoot was associated with PFOA. Although these findings do not clearly indicate a biomechanical link between rearfoot posture and PFOA, this study shed light on the potential relationship between altered rearfoot posture and PFOA, as can be seen between rearfoot abnormality and PF pain.