Ankle, Knee, and Hip Contribution to Ambulatory Support Moment and MRI-detected Structural Worsening 2 Years Later in Knee OA

Purpose: During walking, extensor moments generated at the ankle, knee and hip are responsible for vertically supporting the body and advancing the body center of mass forward. Support moment (SM) is the sum of ankle, knee, and hip extensor moments when the limb accepts full body weight during gait (Figure 1). To maintain adequate SM, lower moment at one joint may be compensated by greater moment at the other. Cross-sectional studies have shown that persons with knee OA, compared to healthy controls, have increased ankle and decreased knee contribution to the total SM during walking. It is unclear if the observed joint moment redistribution is beneficial or deleterious to joint health. Because the knee joint does not function in isolation during weight-bearing activities, the role of ankle, knee, and hip mechanics during walking deserves attention. Elucidating patterns of lower limb moment contribution to the total SM that are associated with risk of structural worsening will inform novel interventional strategies that target the whole limb as a functional unit (e.g., movement training to facilitate greater reliance on hip and ankle extensors and less on knee extensors). The objective of this study was to evaluate associations of baseline ankle, knee, and hip moment contributions to the total SM with baseline-to-2-year MRI-based tibiofemoral and patellofemoral tissue damage worsening. Methods: Participants all had knee OA defined by definite osteophyte presence in at least one knee at baseline. Three-dimensional lower limb kinematics and kinetics during ambulation at self-selected pace on a 35 x 4 foot walkway were captured at a rate of 120 Hz, using external passive reflective markers, an 8-camera Digital Real-Time Eagle motion analysis system, and 6 AMTI force plates. Inverse dynamics were used to compute sagittal hip, knee, and ankle moments during stance. Ankle, knee, and hip moment contributions to the total SM were computed as joint moments divided by SM at the time of peak SM, expressed as percentages. Participants underwent 3.0T MRI of both knees at baseline and two years later using double oblique coronal and axial FLASH sequences, coronal T1-weighted spin-echo (SE), and sagittal, coronal and axial fat-suppressed turbo spin echo sequences. Baseline-to-2-year cartilage damage and bone marrow lesion (BML) progression were defined as worsening of WORMS in the tibiofemoral (TF) and patellofemoral (PF) compartments. We used logistic regression models with generalized estimating equations (to account for correlation between 2 limbs of each person) to assess the association of baseline ankle moment percent contribution to SM with cartilage damage and BML worsening 2 years later, unadjusted and then adjusted for baseline age, sex, BMI, gait speed, radiographic disease severity, and pain. Results are reported as odds ratios (ORs) and 95% confidence intervals (CIs). We used similar analytic approaches separately for the knee and hip contributions to SM. Results: The study sample consisted of 391 knees from 204 persons: mean age 64.2 years (SD 10.0); BMI 28.5 kg/m2 (5.7); 156 (76.5%) women. The mean ankle, knee, and hip moment percent contributions to SM were 25.0%, 26.9%, and 48.1%. 25.6% and 33.0% of knees had baseline-to-2-year TF cartilage damage and BML worsening; 13.6% and 21.7% had PF cartilage damage and BML worsening. As shown in Table 1, greater ankle extensor contribution to SM was associated with increased odds of TF cartilage damage worsening (adjusted OR 2.38, 95% CI: 1.02, 5.57) and decreased odds of PF BML worsening (adjusted OR 0.14, 95% CI: 0.03, 0.73). The logistic regression models for greater knee extensor contribution yielded adjusted ORs for TF BML worsening in the protective range, and for PF BML worsening in the deleterious range, but results were not statistically significant (Table 1). There was no significant association between hip contribution to SM and structural worsening. Conclusions: In persons with knee OA, greater baseline ankle extensor moment contribution to the total SM was associated with increased likelihood of baseline-to-2-year TF tissue damage worsening, but decreased likelihood of PF tissue damage worsening. Findings for the knee, while not significant, raise the possibility that greater knee extensor moment contribution may be protective for the TF joint, but deleterious for the PF joint. These findings suggest that movement or therapeutic strategies for preserving PF tissue health (e.g., redistribute moment contribution to SM by increasing ankle and decreasing knee moment) may have a potentially deleterious effect on TF joint health and vice versa. These findings illustrate potential challenges in developing biomechanical interventions beneficial to both TF and PF compartments.View Large Image Figure ViewerDownload Hi-res image Download (PPT)