Contraction-Evoked Pain and Its Association with Strength and Function in Knee Osteoarthritis

Knee strength deficits have been associated with pain and impaired physical function in individuals with knee osteoarthritis (KOA). Isometric maximal voluntary contraction (MVC) testing using a dynamometer is considered as the gold standard for assessing quadriceps and hamstring strength. However, it remains unclear how pain is experienced during knee strength testing and how it relates to functional performance and strength outcomes in individuals with KOA. PURPOSE: To determine the presence of knee pain during knee extension and flexion of MVC in individuals with KOA, and to assess its relationship with physical performance. METHODS: Fourteen individuals with KOA (58.1 ± 11.5 years) were included. To assess strength, participants performed isometric MVCs for knee extension and flexion on an isokinetic dynamometer. Peak torque (N·m) was recorded for both knee extension and flexion. Pain intensity was evaluated using a numeric rating scale (0-10) before (pre) and during MVC testing. Participants also completed five functional tests: timed up & go (sec), 5-time-sit-to-stand (sec), 40-meter fast-paced walk (sec), stair climb (sec), and 30-second sit-to-stand (rep). Paired t-tests were used to assess differences in pain levels before and during the tests. Pearson correlation coefficients (r) were calculated to examine the relationships between pain during MVCs and (1) functional measures and (2) strength outcomes. Statistical significance was set at p < 0.05. RESULTS: Higher levels of knee pain were reported during knee extension (pre-test 1.8 ± 2.0 vs. during 3.4 ± 2.5, p = 0.003) and knee flexion (pre-test 1.9 ± 1.7 vs. during 2.7 ± 2.3, p = 0.05) MVCs as compared to pre-test levels. Pain evoked during knee extension and flexion MVCs was significantly correlated with the 40-meter fast-paced walk (extension: r = 0.61, p = 0.019; flexion: r = 0.78, p = 0.001) and stair climbing (extension: r = 0.60, p = 0.001; flexion: r = 0.73, p = 0.003). However, the pain was not correlated with peak strength outputs or the other functional measures (p > 0.05). CONCLUSION: Increased knee pain observed during both knee extension and flexion MVCs was not associated with peak strength outputs, but did correlate with walking and stair-climbing abilities, indicating that greater pain corresponded to greater functional limitations in individuals with KOA.