Define Fracture of the Shaft of the Humerus & Radial Nerve Palsy. Describe its clinical features and management.

The radial nerve winds around the spiral groove of the humeral shaft, so a mid-shaft fracture may cause a radial-nerve palsy (wrist drop). Most palsies are neurapraxia and recover spontaneously, so a palsy present before reduction is observed; a palsy that appears after manipulation, or accompanies an open fracture, is explored. Most humeral shaft fractures unite with a functional brace.

The Fracture and its Special Relationship

The shaft of the humerus is a common site of fracture, from a fall, a direct blow or (in the elderly) a low-energy injury through osteoporotic or metastatic bone. Its clinical importance rests on one anatomical fact: the radial nerve winds around the back of the humerus in the spiral (radial) groove, in close contact with the bone at the junction of the middle and lower thirds. Hence a fracture at this level may injure the radial nerve, producing a wrist drop. The Holstein–Lewis fracture — a spiral fracture of the distal third — is particularly associated with radial-nerve entrapment.

Clinical Features

There is pain, swelling, abnormal mobility and shortening of the arm, with crepitus. The essential additional step is to examine the radial nerve: a palsy produces inability to extend the wrist, the fingers at the metacarpophalangeal joints, and the thumb (wrist drop), with sensory loss over the dorsal aspect of the first web space. Grip is weak because the wrist cannot be stabilised in extension. The distal circulation is also checked.

Management of the Fracture

The humeral shaft has an excellent capacity to heal and tolerates a surprising degree of angulation without functional loss, so most fractures are treated conservatively. The limb is supported initially in a U-slab or a hanging cast, and after a week or two converted to a functional (Sarmiento) brace, which controls the fracture while allowing shoulder and elbow movement — union is expected in 8–12 weeks. Operative fixation (compression plating or intramedullary nailing) is indicated for: open fractures, polytrauma, segmental fractures, a 'floating elbow' (with a forearm fracture), bilateral fractures, pathological fractures, vascular injury, and established non-union.

Management of the Radial-nerve Palsy — the Crucial Rule

Most radial-nerve palsies associated with a humeral shaft fracture are a neurapraxia (a stretch injury) that recovers spontaneously over 3–4 months. Management therefore depends on when the palsy is noticed: a palsy present at the time of injury (before reduction) is observed — the wrist and fingers are supported with a cock-up splint to prevent stiffness, and recovery is awaited (if there is no clinical or electrophysiological recovery by about 3–4 months, exploration is considered). A palsy that appears after manipulation or is associated with an open fracture should be explored, because the nerve may have become trapped in the fracture or been lacerated.

• The radial nerve lies in the spiral groove against the bone at the mid/lower-third junction, so a shaft fracture there may cause a radial-nerve palsy (wrist drop). The Holstein–Lewis (distal spiral) fracture is classically associated.
• Radial-nerve palsy = loss of wrist, finger (MCP) and thumb extension + sensory loss over the dorsal first web space; grip is weak because the wrist cannot be stabilised.
• Most humeral shaft fractures unite with conservative treatment: U-slab/hanging cast → functional (Sarmiento) brace.
• Surgery (plating/nailing) for: open, polytrauma, segmental, floating elbow, bilateral, pathological, vascular injury or non-union.
• Radial-nerve palsy present before reduction → observe (usually neurapraxia; splint and wait 3–4 months). Palsy appearing after manipulation, or with an open fracture → explore.