Muscle characteristics of lower limb in association with physical activity in candidates of total knee arthroplasty with knee osteoarthritis.

BACKGROUND & AIMS: This study aimed to clarify the association between physical activity (PA) and physical functions, including both muscle quantity and quality of ankle plantar flexor muscles in patients with knee osteoarthritis (OA).

METHODS

A retrospective cohort study was conducted with ninety-two patients with knee OA. PA, leg muscle cross-sectional area (CSA), knee strength, passive knee angle, and knee pain of the affected side were assessed. PA was assessed by the 2011 Knee Society scoring system. CSA of the quadriceps and ankle plantar flexor muscles on the affected side was measured using a computed tomography image. Based on muscle attenuation assessed with Hounsfield units (HU), the muscle quality of targeted muscle was divided into 4 groups as follows: fat tissue (-190 to -30 HU), very low-density muscle (-29 to -1 HU), low-density muscle (0 to 34 HU), and normal-density muscle (NDM, 35 to 100 HU). The CSA was obtained for each of the 4 groups. Univariate and multivariate linear regression analyses were performed to determine the factors associated with PA.

RESULTS

The regression analysis revealed that higher PA was independently associated with the NDM CSA of ankle plantar flexor (β = 0.51), higher knee extension strength (β = 0.28), and milder knee pain (β = -0.29) after adjustment with age, sex, height, weight, and body mass index.

CONCLUSION

The present study suggested that NDM CSA of ankle plantar flexor in addition to knee function is one of the factors determining the PA in patients with knee OA.