The Association Between Medial Compartment Osteoarthritis of the Knee and Foot Posture Characteristics Among Patients Attending Kenyatta National Hospital, Nairobi

Abstract

Background: Foot posture characteristics such as foot posture index (particularly pronated foot posture), medial arch index, navicular height and drop have been postulated to modify the risk of Medial Compartment Osteoarthritits (MCOA) of the knee by altering the mechanical alignment and loading of the knee joint. Furthermore, altered foot posture may cause other musculoskeletal conditions of the lower limb such as postural instability. Focus has therefore been shifted to foot posture in patients with MCOA, to further clarify its association with knee osteoarthritis (KOA), as well as inform non-invasive therapeutic avenues such as foot orthoses and footwear for treatment of MCOA. Study objective: To determine the association between MCOA and foot posture characteristics among patients presenting at Kenyatta National Hospital (KNH). Study design: Case-control study. Study setting: The study was conducted at the orthopaedic clinic (OC) and medical outpatient clinics (MOPC) in the Kenyatta National Hospital (KNH). Study duration: December 2021 to February 2022. Patients and methods: The study population included 80 consenting patients (40 cases and 40 controls) above the age of 18 years visiting the OC (cases) and MOPC (controls) in KNH between December 2021 and February 2022. Cases included patients visiting the OC with a diagnosis of medial compartment osteoarthritis (MCOA), defined on the basis of knee radiograph assessment using the Kellgren Lawrence Classification system (K-L grade). Patients with grade 1 OA and above were defined as cases (with MCOA). Patients visiting MOPC, who were asymptomatic and with a K-L grade of 0 served as the control group (without MCOA). Variables collected included patient age, sex, body mass index, presence of medial xiii compartment osteoarthritis (MCOA), as well as foot posture characteristics (foot posture index, medial arch index, navicular height and navicular drop). Data management and analysis: The collected data were transferred from password-coded data digital collection sheets into analysis software for data cleaning and coding prior to analysis. Data were stored in password-protected computer folders to maintain anonymity of the study subjects. Analysis of the data was carried out using Prism 7 (GraphPad Software, San Diego, CA, USA) and SPSS (IBM Statistics Software Version 25, Armonk, New York, USA). Categorial data were reported as frequencies (%). Continuous data were subjected to normality tests (histogram and Q-Q plots with Kolmogorov-Smirnov test), and reported as mean and standard deviation (SD) since it was normally distributed. Comparison of foot posture characteristics (foot posture index, medial arch index, navicular height and navicular drop) between patients with medial compartment osteoarthritis (MCOA) (cases) and without MCOA (NMCOA/control group) was carried out using the Independent Student’s t-test. Multivariate logistic regression analysis was performed to estimate the effect of foot posture characteristics on MCOA, adjusting for age, sex and body mass index, and to calculate adjusted odds ratios (ORs) with the corresponding 95% Wald CI. Throughout the analysis, a p<0.05 was considered statistically significant at a 95% confidence interval. Results: No significant differences in age (61.7±13.2 vs 58.9±11.1 years, p=0.311), sex composition (males- 45% vs 55%, p= 0.503) or body mass index (BMI) (24.8±3.3 vs 25.3±3.4 Kg/M2, p= 0.528) were observed between the cases and controls. The foot posture index (FPI) was found to be significantly higher in the MCOA group than NMCOA group (3.4±2.2 vs 0.3±2.1, p<0.001). Similarly, patients with MCOA had a significantly higher medial arch index (MAI) (0.32±0.1 vs 0.25±0.1, p<0.001), and navicular drop (ND) (0.79±0.3 vs 0.55±0.2, p<0.001) than NMCOA group. No significant differences in the navicular height (NH) were observed between the two group (4.7±0.4 vs 4.8±0.3, p=0.415). Foot posture index (FPI) (r=0.675, p<0.001), MAI (r=0.576, p<0.001) and ND (r=0.573, p<0.001) positively correlated with Kellgren-Lawrence (K-L) grade of MCOA. In the multivariate adjusted logistic regression model, pronated foot posture (OR= 1.79, 95% CI 1.22-2.65, p=0.003), higher medial arch index (OR= 4.93, 1.27-19.10, p=0.021) were significant predictors of MCOA. Conclusion: Foot posture characteristics such as pronated foot posture are associated with MCOA. We therefore recommend that foot characteristics be routinely assessed in these patients to guide therapeutic interventions.