Ankle Joint Laxity Is Decreased In Patients With Moderate Knee Osteoarthritis

Abstract

Changes in knee joint alignment associated with progressive knee osteoarthritis (OA) results in altered joint mechanics during walking gait, as well as deficits in other measures of functional activity. It is believed that changes in ankle joint motion may also contribute to the gait and functional activity deficits observed. PURPOSE: To evaluate the ankle joint mechanical stability in patients with knee OA. METHODS: Fifteen subjects with knee OA (5 males and 10 females, age=60.3 ± 10.2yr., mass= 93.9±18.3kg, ht= 167.23 ± 9.5cm) were matched by gender, age, and weight to 15 healthy controls (5 males and 10 females, age=59.6 ± 12.6yr., mass=83.5 ± 19.2kg, ht=169.7 ± 12.6cm). Standardized radiographs of all knees for each subject were performed to determine study eligibility as well as to quantify knee OA severity using a standardized scoring system. Mechanical ankle joint stability was assessed in all subjects with an instrumented arthrometer. The arthrometer measured ankle-subtalar joint motion for anterior/posterior displacement (mm) during loading at 125 N and inversion/eversion rotation (degrees of ROM) during loading at 4000 N·mm. Separate 2 × 2 (group x side) mixed model ANOVAs were performed for all dependent measures. RESULTS: There were significant group x side interactions for: anterior and posterior displacement (P <.05). The subjects with knee OA had significantly less anterior (7.4 +.51mm) and posterior (2.2 +.31mm) ankle displacement compared to values observed in the healthy group (anterior 10.5 +.51mm, posterior 4.2 +.31mm), as well as compared to their unaffected extremity (anterior 9.5 +.48mm, posterior 2.6 +.25mm). There were significant main effects for group on inversion rotation and eversion rotation (P <.05). The knee OA group had significantly less inversion (25.4° + 1.6) and eversion (13.1° + 1.1) rotation compared to the healthy group (31.1° + 1.6, 20.2° +1.3). CONCLUSION: Knee OA subjects demonstrated significant decreases in anterior and posterior displacement as well as inversion and eversion rotation compared to healthy controls. These impairments may be the result of alterations in ankle joint alignment secondary to structural changes at the knee. Deviations in ankle joint mechanics must also be considered when addressing functional deficits in patients with knee OA.