Summary

Reduced knee extensor muscle strength may affect the ability of patients with knee osteoarthritis to walk, characterised by sustained bi-articular muscle activity at hip and knee joints, which may provide joint stability during walking.

Abstract

Introduction

Reduced hip abductor and knee extensor strength are characteristic of patients with knee osteoarthritis (KOA). The knee extensor strength required for stable walking is generally considered to be at least 0.45 times the weight-bearing index (WBI).
The major limitation of previous studies on muscle activity during walking has been the use of surface electromyography to assess surface muscles selectively. Therefore, we focused on 18F-fluorodeoxyglucose (FDG) positron emission tomography (PET), which evaluates muscle activity by injecting FDG into the body and observing muscle glucose metabolism. This technique can capture whole-body skeletal muscle metabolism after walking in patients with KOA. This study aimed to determine, using FDG-PET, whether knee extensor muscle strength affects whole-body muscle metabolism after walking in patients with KOA. The hypothesis was that KOA patients with reduced knee extensor strength would have an overall reduced muscle metabolism assessed after walking.

Methods

The study was conducted on 22 participants with Kellgren-Lawrence grade 2 KOA (11 males and 11 females) from January 2022 to April 2023. The physical evaluation included knee joint pain, isometric hip abductor and knee extensor strength, and muscle glucose metabolism of lower extremity muscles assessed by PET-computed tomography (CT) after walking. Knee pain was assessed with a visual analog scale (VAS), and isometric knee extensor strength was assessed with a hand-held dynamometer. For the evaluation of muscle metabolism after walking, the participants performed a 10-minute treadmill walk at 3.5 km/h, followed by an intravenous injection of 37 MBp FDG and another 10 minutes of treadmill walking. PET-CT imaging was then performed after 50 minutes of rest. Comparisons between the two groups were made based on a WBI of 0.45, which is required for adaptation to walking, and were divided into Group A (n=7, males: 5, females: 2) with a WBI of 0.45 or greater and Group B (n=15, males: 6 females: 9) with a WBI of less than 0.45.

Results

The VAS used to assess pain did not show statistically significant differences but tended to be higher in Group B (p=0.06, Effect size=1.10). Hip abductor strength of WBI on the involved limb was not statistically significantly different (p=0.08, Effect size=0.91), but knee extensor strength of WBI was considerably higher in Group A (p<0.01, Effect size=2.58). Effect sizes were large for hip abductor and knee extensor strength.
Finally, there were no statistically significant differences in muscle metabolism, but Group B tended to have higher muscle metabolism in the bi-articular muscles, mainly the tensor facia latae, gracilis, semitendinosus, and semimembranosus muscles, with medium to large effect size.

Conclusion

Reduced knee extensor strength may affect the ability of participants with KOA to walk. A characteristic of this is that sustained bi-articular muscle activity at the hip and knee joints may provide joint stability during gait.