Sarcopenic obesity and pain sensitivity, central sensitization-related symptoms, and physical function among patients undergoing total knee arthroplasty: A cross-sectional study

Sarcopenic obesity is associated with poor physical function in patients with knee osteoarthritis (OA). However, its association with pain sensitivity and central sensitization-related symptoms remains unclear.

To investigate pain-related characteristics and physical function associated with sarcopenic obesity in patients with end-stage knee OA undergoing total knee arthroplasty (TKA).

This cross-sectional study included patients undergoing TKA. Patients were categorized into four body composition phenotypes based on the Japanese Working Group on Sarcopenic Obesity criteria: no obesity/sarcopenia, obesity, sarcopenia, and sarcopenic obesity. The primary outcomes were pain intensity, pain sensitivity, and central sensitization-related symptoms, assessed using pain intensity at rest and during movement, pressure pain thresholds (PPTs) at the affected knee and forearm, and the Central Sensitization Inventory-9 (CSI-9). The secondary outcomes were physical function and disability, assessed using quadriceps strength, Timed Up and Go (TUG), and Oxford Knee Score (OKS). Analyses of covariance were adjusted for age, sex, Kellgren-Lawrence grade, C-reactive protein, Geriatric Nutritional Risk Index, and Life-Space Assessment. Exploratory pairwise comparisons were performed between the sarcopenic obesity group and the other groups.

Among 636 patients, 55 had sarcopenic obesity. Compared with the no obesity/sarcopenia and obesity groups, the sarcopenic obesity group had higher CSI-9 scores (adjusted mean differences, 3.89 [95% CI, 0.96 to 6.82] and 3.47 [0.58 to 6.37], respectively) and lower affected-knee PPTs (-0.64 [-1.15 to -0.13] and -0.52 [-0.88 to -0.16] kgf/cm², respectively). Corresponding differences versus the sarcopenia group were 1.28 (-2.32 to 4.88) for CSI-9 and -0.33 kgf/cm² (-1.17 to 0.52) for PPT. Compared with the no obesity/sarcopenia group, the sarcopenic obesity group also had lower quadriceps strength (-0.06 kgf/kg [-0.11 to -0.01]) and slower TUG performance (2.14 s [0.22 to 4.06]).

Differences in pain-related characteristics and physical function were observed across body composition phenotypes. Exploratory comparisons showed higher CSI-9 scores and lower affected-knee PPTs in patients with sarcopenic obesity than in those with no obesity/sarcopenia and obesity. However, the mechanisms underlying these differences remain unclear because neuropathic-like pain was not assessed. Further studies incorporating neuropathic-like pain assessment are needed to clarify associations between body composition phenotypes and pain-related characteristics.