# Quadriceps muscle force magnitude and control in the knee scheduled for arthroplasty versus the contralateral knee: A cross-sectional study in patients with end-stage osteoarthritis

## TL;DR

This study found that knee osteoarthritis causes differences in leg strength and muscle control between the affected and healthy knees, but these differences don't always affect daily activities.

## Contribution

The study identifies asymmetries in quadriceps force complexity and strength in knee osteoarthritis patients, linking lateral symmetry in strength to functional performance.

## Key findings

- The affected knee showed significantly lower strength and higher force complexity compared to the contralateral knee.
- Lateral symmetry in strength was positively associated with sitting-to-standing and 30-s sit-to-stand performance.
- Force complexity was not correlated with functional performance measures.

## Abstract

Knee osteoarthritis (KOA) is a leading cause of musculoskeletal disability. Beyond the well-established impairment of reduced strength, deficits in force control (steadiness and complexity) may also influence functional performance. This cross-sectional study investigated quadriceps strength, force steadiness and complexity in patients with KOA and their associations with functional performance.

A total of 48 patients scheduled for unilateral knee arthroplasty performed maximal voluntary isometric contraction in both limbs. A 2-s window from the trial containing the peak torque was used to compute quadriceps strength (average torque, AT), force steadiness (coefficient of variation, CV), and force complexity (sample entropy, SE; detrended fluctuation analysis alpha exponent). Functional performance was assessed via sitting-to-standing, single-leg stance, Timed Up and Go, and 30-s sit-to-stand tests. Comparisons between involved and contralateral limbs used analysis of variance (ANOVA) models, accounting for prior surgery in contralateral knees. Linear regression analyzed associations between functional performance and the lateral symmetry index (LSI) of AT and SE.

Results showed significant differences between limbs for AT (P < 0.001, η2 = 0.074) and SE (P = 0.041, η2 = 0.046), with the involved knee exhibiting lower strength and higher complexity. Regression revealed a positive association between sitting-to-standing and 30-s sit-to-stand performance and LSI–AT (βs are equal to −0.337 and 0.336, respectively; P < 0.027), but no other links were found.

KOA is associated with between-limb asymmetries in quadriceps strength and force complexity, with the involved knee exhibiting deleterious alterations. Nonetheless, force complexity was not correlated with functional performance.