Foot posture assessment in people with primary medial compartment knee osteoarthritis

Abstract

BACKGROUND: Foot postures are integral to the biomechanical alignment and the dynamic function of the lower extremity. This study compared foot postures in people with primary medial compartment osteoarthritis (OA) and age-, gender-, and body mass index (BMI)-matched controls using various foot measures. Grade-wise variations were also assessed. AIM: The aim of the study was to assess the foot postures in people with primary medial compartment knee OA. METHODS: This was an observational, analytical study and the subjects were recruited by convenient sampling from tertiary hospitals in Pune. The target population were primary knee OA who were clinically and radiologically diagnosed for their severity based on the Kellgren–Lawrence grading, a severity classification based on radiographic evidence. The Centre of Rheumatic Diseases version of Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and the Foot Function Index (FFI) which are both self-report questionnaires were duly filled by the knee OA subjects for the pain and dysfunction of the knee and foot, respectively. The control group consisted of age-, gender-, and BMI-matched asymptomatic healthy subjects. Foot postures of all subjects namely, the OA (n=48) and controls (n = 33) were assessed using the foot posture index (FPI), arch index, and navicular drop test. The FPI as well as the navicular drop test categorized the subjects into 3 groups: pronated, neutral, and supinated. The arch index was calculated from the inked imprint of the foot of the affected limb where higher values indicated dropped arch. STATISTICAL ANALYSIS AND RESULTS: Independent samples Mann–Whitney U-test and unpaired t-test were used to investigate the differences between the two groups in the foot characteristics. The Spearman's rho was used to analyze the correlation of FPI with the grades of OA and of WOMAC with the FFI within the OA group. The study included 48 medial knee OA subjects (48 knees and the corresponding foot) and 33 age-, gender-, and BMI-matched healthy controls. The percentages of foot postures (neutral, pronated and highly pronated) of both groups were 71%, 25% and 4% respectively in the OA group and 92%, 2% and 6% respectively in the control group. Comparative study of foot postures between the two groups showed more pronated feet in the OA group (P < 0.001). Correlation of the FPI scores with the grades of OA showed no association (β = −0.005; P = 0.97) and between WOMAC and the FFI in the knee OA group showed weak association. (β = 0.0349; P < 0.05). CONCLUSION: The foot postures were altered in the knee OA group as compared to healthy controls, with the OA group showing more pronated foot type.