Structural severity, phase angle, and quadriceps strength among patients with knee osteoarthritis: the SPSS-OK study

The associations between severity of knee osteoarthritis (KOA) and phase angle (PhA) and between PhA and quadriceps strength in patients with KOA are unclear. This study examined (1) whether the structural severity of KOA affects PhA and (2) whether PhA affects quadriceps strength in patients with KOA.

Data of 1093 patients with KOA, obtained from Screening for People Suffering Sarcopenia in the Orthopedic cohort of Kobe study, were analyzed. PhA was determined by bioimpedance. Quadriceps strength was measured using a handheld dynamometer. Structural severity of KOA was determined using Kellgren-Lawrence radiographic grading scale. A series of general linear models were fitted to estimate the magnitude of differences in PhA by differences in KOA severity and quadriceps strength by differences in PhA.

The mean age of the patients was 72.8 years, and 78% were women. Increasing KOA severity was associated with decreasing PhA, especially in men. In women, only grade 4 KOA was associated with a decrease in PhA (P for interaction = 0.048). PhA per leg was positively associated with quadriceps strength per leg, independent of age, sex, leg muscle mass, pain, and KOA severity (mean difference per 1° increase = 7.54 Nm, 95% confidence interval = 5.51-9.57 Nm). The association between PhA and quadriceps strength differed neither by sex nor by KOA severity (P for interaction = 0.133 and 0.185, respectively).

PhA decreased with increasing KOA severity, and increasing PhA was associated with increasing quadriceps strength. Clinicians should, therefore, evaluate PhA to assess quadriceps strength in patients with KOA. Key Points • PhA gradually decreased with increasing severity of KOA, especially in men. • Increasing PhA was associated with increasing quadriceps strength. • Clinicians should focus on increasing muscle mass and PhA.