The Association of Lower Extremity Strength with Step Ascent and Descent Performance in Men with Knee Osteoarthritis

Background: Knee osteoarthritis (OA) is a chronic disease characterized by articular cartilage damage, pain, and muscle weakness. Ambulating stairs is a leading source of pain in people with OA, and disease progression may be marked by asymmetrical gait abnormalities. The primary objective of this study was to determine the relationship between knee peak torque and Step-Up-and-Over (SUO) test performance in individuals with knee OA. The secondary objective was to assess asymmetries in the study participants based on knee peak torque and OA severity. Methods: Twenty-one male Veterans with knee OA (age = 59.8 yrs. ±4.5) from the Washington DC VA Medical Center enrolled in the study. The severity of knee OA was determined by a radiologist using the Kellgren–Lawrence (K-L) grading system during the assessment of participant x-rays. Functional performance was assessed via the SUO test, which involves ascending/descending an 8-inch box on a force plate. The SUO test outcomes included movement time and force-time parameters representing step-up force (concentric muscle control), step-down force (eccentric muscle control), and force-time curve smoothness (lower-limb motor coordination). Peak torque of the knee extensors and flexors were measured using isokinetic dynamometry (180º/s). Correlation analysis was used to determine the association between strength and SUO test outcomes. Paired t-tests were used to assess bilateral differences in peak torque and the K-L grades. Results: The mean within-participant difference in the K-L score was 0.7 ±0.6. Normalized knee peak torque was not significantly greater in the less involved leg (mean = .32 ±.14) compared to the more involved leg (mean = .27 ±.11; p \u3e .05), but was greater in the dominant leg (mean = .34 ±.13) versus the nondominant leg (mean = .25 ±.11; p = .001). Movement time during the SUO test was associated with knee extensor strength (r = -.41, p = 0.009), but not flexor strength (r = -.30, p = .056). Movement time was the only parameter measured during the SUO test that was associated with peak torque. Conclusions: Preliminary findings suggest that strength and OA severity asymmetries were minimal within the sample. Gross measures of knee extensor strength are associated with the movement time of the step ascent/descent task. However, the SUO force-time parameters may be associated with motor coordination rather than peak torque generation. Future work is needed to determine whether motor coordination improves independently of changes in knee strength over the course of OA treatment