Repetitive Strain Injury

Repetitive strain injury is a non-diagnostic umbrella term for pain and dysfunction of muscles, tendons, nerves and joints, usually in the upper limb and neck, related to repetitive tasks, forceful exertion or sustained postures. It covers specific conditions and a non-specific diffuse pain syndrome.

Specific forms. Lateral and medial epicondylitis, De Quervain tenosynovitis, trigger finger, intersection syndrome, flexor and extensor tendinopathy, carpal tunnel syndrome and cubital tunnel syndrome.

Non-specific form. Diffuse arm, forearm and shoulder pain without a defined lesion, often with tenderness and weakness.

Epidemiology. One of the commonest causes of work related morbidity in computer, assembly line, meat processing, cleaning, sewing and musical occupations. It is more frequent in women and in people aged 30 to 60.

Risk factors. High repetition, force, awkward posture, vibration, low recovery time, psychosocial stress, and individual factors such as diabetes, obesity, hypothyroidism, rheumatoid disease and pregnancy.

Pathophysiology.

Repeated loading exceeds tissue repair, producing tendon degeneration (tendinosis) with disordered collagen and neovascularisation rather than classic inflammation. Nerve compression arises from swelling in confined spaces.

In chronic non-specific pain, central sensitisation, muscle overload and psychosocial factors contribute.

• Pain on use of the affected part, stiffness, weakness and loss of dexterity.
• Localised swelling and tenderness over a tendon in specific forms.
• Paraesthesia and night waking with nerve compression.

Red flags.

• Constant or severe night pain, fever, weight loss or a hot swollen joint.
• Progressive weakness, muscle wasting or sensory loss.
• Neck pain with myelopathic features, or a history of cancer.

• Task history: duration, repetition, force, posture, breaks, equipment and recent change in workload.
• Specific tests: Finkelstein, Cozen and Mills tests, Phalen and Tinel signs, and carpal compression test.
• Ultrasound for tendon pathology and effusion.
• Nerve conduction studies for suspected nerve entrapment or when the picture is atypical.
• Blood tests (ESR, CRP, TSH, glucose, rheumatoid factor) when systemic disease is suspected.
• Workplace ergonomic assessment.

Differential diagnosis. Inflammatory arthritis, osteoarthritis, cervical radiculopathy, thoracic outlet syndrome, fibromyalgia, diabetic and other neuropathies, hypothyroidism, gout and ulnar neuropathy.

• Modify tasks: ergonomic adjustment, workload and rate reduction, task rotation, scheduled micro-breaks, and tool and posture changes.
• Short term splinting for specific lesions, with physiotherapy including eccentric loading and graded return to activity.
• Paracetamol 1 g orally every 6 hours as needed, maximum 4 g in 24 hours (3 g if under 50 kg, chronic alcohol excess or liver disease), for the shortest period that controls pain. Monitor liver function with prolonged use. Reduce dose in hepatic impairment; extend dosing interval when eGFR is under 30.
• Diclofenac 1% gel applied topically, 2 g to the affected upper limb joint four times daily, for up to 3 weeks. Maximum 8 g daily to any one upper limb joint and 32 g daily in total. Monitor skin reaction and renal function with prolonged use. Avoid on broken skin, in aspirin sensitive asthma and in the third trimester; avoid when eGFR is under 30.
• Specific tendon or nerve lesions failing 6 weeks of conservative care: methylprednisolone acetate 20 to 40 mg with local anaesthetic injected locally, once, repeated once after 6 weeks if benefit was partial. Maximum 2 injections in the same site. Monitor for tendon rupture, skin atrophy, depigmentation and transient hyperglycaemia in diabetes. Avoid injection into infected areas; use caution with anticoagulation.
• Carpal tunnel decompression for persistent entrapment with sensory loss or weakness.
• Early return to modified work is better than prolonged rest.

Monitoring. Review at 4 to 6 weeks, then every 3 months; escalate if no improvement after 3 months.

Referral and escalation. Occupational physician for workplace adjustment; orthopaedic or hand surgery for surgical lesions; rheumatology for inflammatory features; notification and compensation where required.

Special groups. Pregnancy: carpal tunnel syndrome often settles after delivery; use splinting first. Diabetes: expect transient glucose rise after corticosteroid injection.