Introduction
This topic covers tendomyosis of the lower arm, a chronic overuse disorder of the poorly vascularised muscle-tendon transition zone of the forearm extensor muscles. It is closely related to lateral epicondylitis (topic 25) and is important in occupational medicine because repetitive hand and wrist work is a common cause.
Definition and aetiology
Tendomyosis is a degenerative-inflammatory condition of the myotendinous junction of the extensor muscles of the hand and fingers. The junction has relatively poor blood supply, so it heals slowly after strain. The main causes are:
- Overloading or incorrect loading during work or sport, such as repetitive gripping, forceful wrist extension, and frequent forearm rotation
- Faulty movement and posture habits, for example awkward working posture, poor tool design, or poor technique
- Age-related degeneration, which reduces tendon vascularity and repair capacity, mainly in middle and later life
Pathogenesis
Repeated microtrauma at the muscle-tendon junction exceeds the local capacity for repair. Irritation of the tendon leads to local inflammation and then to degenerative change, with disorganised collagen and damage at the junction. Pain and reflex protection of the muscle then limit flexion and extension of the hand and fingers. With ageing, the tendon loses elasticity and becomes stiff, so it tolerates load less well and the cycle of injury and poor healing continues.