33. Mononeuropathy in entrapment compression syndromes of the carpal, cubital and Guyon’s cannal - etiology, pathogenesis, clinical manifestations, diagnosis, differential diagnosis, treatment, medical expertise.

Introduction

This topic covers entrapment (compression) mononeuropathies of three work-related upper-limb nerve sites: the median nerve in the carpal tunnel, the ulnar nerve in the cubital tunnel at the elbow, and the ulnar nerve in Guyon's canal at the wrist. For each, be able to describe the anatomy, the occupational causes, the clinical picture, the confirmatory tests and the treatment, and to explain how such cases are assessed for work capacity.

General principles of nerve entrapment

A peripheral nerve passing through a fibrous or fibro-osseous tunnel is vulnerable when the tunnel's volume falls or its contents swell. Repetitive, forceful or prolonged movements and sustained static postures cause tendon or paratendon swelling, microtrauma and local ischaemia of the nerve. Early changes are conduction slowing and focal demyelination; later changes are axonal loss and fibrosis.

• Pathogenesis: tendon or paratendon swelling, epineurial microtrauma, venous congestion and ischaemia, then demyelination and axonal change.
• Occupational risk factors: repetitive flexion and extension, forceful gripping, hand-arm vibration, sustained wrist or elbow flexion, direct pressure on the palm or elbow, and cold exposure.
• Personal predisposition: diabetes, hypothyroidism, pregnancy, obesity, rheumatoid arthritis, previous fracture, and female sex (especially for carpal tunnel syndrome).
• Key principle: early cases are reversible once the exposure is removed; long-standing cases leave permanent motor and sensory deficit.