The Role of Skeletal Muscle in the Incidence and Progression of Knee Osteoarthritis

Abstract

Skeletal muscle quality may play a role in skeletal muscle health affecting its response to muscle strengthening exercises and susceptibility to osteoarthritis (OA). Chapter One of this thesis provides an introduction to the role of skeletal muscle in the incidence, progression and exercise management of knee OA. Chapter Two examines skeletal muscle quality (muscle attenuation and lean muscle volume), knee extensor strength and percentage whole-body fat as mediators in the symptomatic and functional improvements achieved in a diet and exercise (D+E) compared to D (diet) or E (exercise) interventions. Null mediation results were found for skeletal muscle quality and knee extensor strength. However, a reduction in the percentage of whole- body fat significantly partially mediated pain, function, 6-minute walk test and gait speed improvements achieved in the D+E compared to E groups. Chapter Three presents the relationship between a change in lower extremity lean mass (LM) and fat mass (FM) with radiographic knee OA (RKOA) incidence in women longitudinally and concurrently. A 2-year change in LM or FM measures did not predict subsequent RKOA incidence. A 5-year increase of LM percentage was associated with a 10% reduced odds of RKOA incidence (OR 0.90, 95% CI 0.82-0.98, P=0.016]. A 0.25 unit increase in LM:FM ratio over 5 years was associated with a 31% reduced odds of RKOA incidence [OR 0.69, 95% CI 0.49-0.97, P=0.032]. Thigh muscle quality and knee extensor strength did not mediate symptomatic and functional improvements, however, a reduction in percentage whole-body fat partially mediated symptomatic and functional improvements achieved in a D+E compared to E groups. Lower extremity LM and FM changes were significantly associated with RKOA incidence concurrently, but did not precede RKOA incidence longitudinally. Further understanding of skeletal muscle properties would enable a higher treatment effect size to be achieved from rehabilitation programmes in knee OA.