The effect of obesity in self-reported disability, knee pain and isokinetic quadriceps strength in knee osteoarthritis

Abstract

Osteoarthritis (OA) of the knee is one of the most common musculoskeletal conditions resulting in disability. The incidence of knee OA increases with age and will likely increase further as the population becomes more obese and less physically active. Therefore, the objectives of this thesis were 1) to observe whether self-reported disability should be obtained before or after performance-based tests, 2) to assess changes in knee pain and observe whether symptoms of depression predict worsening of knee pain, quality of life (QoL) and increased need for surgery and, 3) to examine changes in quadriceps muscle strength and knee pain after isokinetic muscle testing. In the first study, disability was measured using the WOMAC scores. Results indicated that all WOMAC scores were significantly higher after as compared to before the completion of performance-based tests and a physiologic test (VO2Peak). Obese individuals with knee OA were significantly worse compared to non-obese individuals with knee OA on all WOMAC scores. In the second study, the WOMAC pain subscale and VAS pain were significantly higher after as compared to before the completion of performance-based tests. The VAS ratings captured a significant increase in pain in both groups, but the WOMAC pain subscale only captured a significant change in the obese OA group. Depressive symptoms and BMI explained a significant proportion of variance in knee pain, quality of life and perceived need for surgery. The third study indicated that isokinetic quadriceps muscle strength was significantly different between obese and non-obese individuals with knee OA and compared to a healthy control group at all angular velocities of 60°/s, 90°/s and 120°/s, with the obese OA group demonstrating the lowest peak torque at all angular velocities. However, it was only at 60°/s that the isokinetic peak torque showed a statistically significant difference between the obese and the non-obese groups with knee OA. Likewise, knee pain increased from before to after isokinetic muscle strength testing, but only at the angular velocity of 60°/s. This thesis provides new information regarding the effect of obesity on self-reported disability, knee pain, depressive symptoms and quadriceps muscle strength in knee OA.