Adverse changes in tendon–muscle physiology and physical function caused by an isolated acute rheumatoid knee effusion: A case study

Abstract

Introduction Patients with rheumatoid arthritis (RA) have reduced muscle mass, probably due to the catabolic effects of systemic inflammation and disuse (1). This loss leads to reduced strength and physical function (1,2). In addition, the presence of effusion in the knee joint results in reflex inhibition of the quadriceps as demonstrated by reduced electromyogram (EMG) activity and diminished strength (3,4). The wider characteristics of the tendon–muscle complex have not been investigated in acute RA or in joint effusions of other etiologies. In exercise science, electrophysiologic methods are used to investigate tendon– muscle properties in healthy populations. These include assessments of muscle-specific force (force/cross-sectional area), architecture (fiber fascicle length and pennation angle), voluntary activation capacity, contractile properties, and tendon stiffness. Application of these techniques in aging and disuse has demonstrated adverse changes in tendon and muscle properties that result in impaired function but respond well to exercise training (5,6). We have previously applied these methods in patients with well-controlled RA and found that tendon stiffness was reduced (Matschke V et al: unpublished observations), while muscle quality (specific force, voluntary activation capacity, contractile properties) was unaffected (7,8). To our knowledge, these electrophysiologic methods have not been applied in acute RA, probably due to difficulties arising from confounding factors such as pain, fatigue, and the acute effects of inflammation in other joints.