The median nerve may be cut cleanly across at the wrist or palm by sharp objects or by falls through windows.

The ulnar nerve can also be damaged in this way but it lies deeper than the median nerve and is protected by the tendon of flexor carpi ulnaris.

The palmar digital nerves are very vulnerable and are cut if the patient grips a blade or a sharp object. The digital artery is usually damaged at the same time. Because the volar digital nerve supplies the pulp of the finger, injuries to it can seriously impair function.

Contaminated or untidy nerve lesions are not suitable for immediate repair.

The flexor tendons run part of their course through synovial and fibrous sheaths. The fibrous sheaths, which are lined with synovium, run from the distal interphalangeal (d.i.p.) joints to the distal palmar skin crease and prevent the tendon ‘bowstringing’ when the finger is flexed.

The synovial sheaths of the thumb and little fingers extend proximally through the carpal tunnel. The three central digits (index, middle and ring) have a separate flexor sheath in the fingers. There is also a sheath in the palm which extends proximal to the wrist (Fig. 13.2).

Because of these complexities, flexor tendon injuries should be treated only by experienced surgeons.

Injuries distal to the d.i.p. joint lie outside the sheath.

Management of flexor injuries in the fingers depends on the tendons involved and the site of injury (Fig. 13.3). The first step is to decide which tendon has been damaged.

Profundus and superficialis action can be distinguished by asking the patient to flex the distal phalanx with the middle phalanx held still (see Fig. 2.26). Only flexor profundus will do this because superficialis does not extend beyond the middle phalanx (Fig. 13.4).

To assess superficialis, hold all the fingers down except the one that is to be tested and ask the patient to flex that finger. If the finger flexes at the proximal interphalangeal (p.i.p.) joint, superficialis is intact. Test this on your own hand.

Division of the flexor tendons in the palm is less serious than division in the fingers because the repair can be done outside the fibrous or synovial sheaths.

Eleven flexor tendons (flexor digitorum superficialis (4), flexor digitorum profundus (4), flexor pollicis longus, flexor carpi ulnaris and flexor carpi radialis) cross the volar aspect of the wrist (Fig. 13.5). If all these are divided, there will be 22 cut tendon ends. If the median nerve is divided as well, there will be 24 structures, which must be carefully identified, and if each pair is joined there will be 12 suture lines very close together. However carefully repaired, the tendons and nerves may stick together and form a solid mass which restricts movement at the wrist.

Injuries in the forearm lie outside any sheath and can be accurately repaired more easily than elsewhere.

If the wound is untidy and dirty it must be debrided and all dead tissue removed. If the wound is untidy but clean it is sometimes better to excise the tendon and replace it with a Silastic rod, which can itself be replaced with a graft when the wound has healed.

If the wound is contaminated, a clean and well- healed wound must be obtained before definitive treatment is undertaken.

The hand should be mobilized actively and passively as soon as pain and swelling permit.

Because the extensor tendons only have a synovial sheath where they cross the wrist, the problems encountered in repairing flexor tendons in the fingers do not arise. The tendons are easily identified, repair is straightforward and the fingers can be mobilized after 3 or 4 weeks.

If the tendons are divided on the dorsum of the hand they cannot contract for more than a few millimetres because they are restricted by linking fibrous bands. Even without repair some extensor function will eventually return (Fig. 13.6).

Violent flexion injuries to, or lacerations across the back of, the d.i.p. joint can avulse or divide the insertion of the extensor digitorum longus at the base of the distal phalanx (Fig. 13.7 and Fig. 13.8).

Untreated, the lesion causes the distal phalanx to droop and leaves a ‘mallet’ finger deformity. The condition is inconvenient but function improves without treatment and it is exceptional for the patient to be seriously troubled by the injury 12 months later.

The central slip of the extensor expansion can be detached from its insertion at the base of the middle phalanx by a cut or by violent muscle contraction. This allows the two lateral slips to fall sideways and the p.i.p. joint to protrude between the two, which produces a characteristic deformity and may impair function (Fig. 13.9).

Damage to the radial or ulnar arteries at the wrist causes severe arterial bleeding, which can be controlled by firm pressure and elevation.

The deep palmar arch can be cut by penetrating injuries and causes serious bleeding.

Fingers can be crushed so hard that the skin bursts. These injuries must be treated by elevation of the arm and hand and the wounds must never be sutured. Although it is technically possible to close the wounds soon after injury, the sutures prevent the soft tissues from swelling and a stiff or dead digit will follow.

If the hand is caught in machinery, the skin of the hand and fingers can be peeled off like a glove (Fig. 13.10). This is a serious lesion and cannot be treated by rolling the skin back into place. The lesion can be caused by a ring.

Accidental contact with a grindstone removes skin, subcutaneous tissue and bone (Fig. 13.11). The wound is contaminated and the loss of tissue can be irreparable.

Although rare, the injuries caused by high pressure injection devices such as high pressure water nozzles, paint sprays and grease guns can cause serious problems. These implements can force grease or water through the skin and into the subcutaneous tissues without any opening in the skin itself. The irritation in the soft tissues can lead to tissue necrosis and the integrity of the skin is misleading.

Skin incisions or lacerations that cross skin creases on the flexor aspect of joints may shorten when they heal and form a tight fibrous contracture that holds the joint flexed. While there is no choice in the position of a laceration, incisions used to repair tendons and nerves must not cross skin creases transversely.

Genuine human bites are uncommon away from the rugby field but knuckles are often injured against teeth – a ‘fight bite’. Injuries caused in this way often fail to heal and become badly infected with a cocktail of exotic organisms.

The scaphoid has a small bony tubercle which can be avulsed. Fracture of the tubercle of the scaphoid is benign but unfortunately far less common than a fracture through the waist.

Violent hyperextension of the wrist can separate a flake of bone from the triquetral.

Injuries to the carpus cause serious problems and they are frequently missed in the accident department, which makes the consequences even more serious. Like scaphoid fractures, they have a deservedly treacherous reputation.

Many types of instability occur but the commonest are: (1) perilunate dislocation, (2) trans-scaphoid perilunate dislocation and (3) other types of carpal instability.

The fifth metacarpal is broken more often than the others. There are three types of fracture: (1) fractures of the neck, (2) oblique fractures, and (3) transverse comminuted fractures.

The metacarpophalangeal joints can be dislocated by hyperextension and rotational strains. The injury is uncommon.

Treatment. Radiologically, these dislocations look deceptively easy to reduce but the metacarpal head sometimes ‘buttonholes’ through the volar tissues and becomes irreducible. Open reduction is then required.

The phalanges are fractured most often by twisting or angular forces (Fig. 13.20). Angulation is easily corrected but rotational deformities from spiral fractures are more difficult.

The bone usually unites soundly, the most urgent problem being the preservation of normal movement between tendon and bone.

Treatment. The simplest and most effective treatment for stable phalangeal fractures is to hold the damaged finger against its neighbour and encourage flexion, which is impossible if there is a rotational deformity (Fig. 13.21).

The fingers should be held lightly together with elastic strapping to allow room for the swelling that is bound to follow a fracture, and a small layer of felt or other absorbable material placed between the two fingers to absorb sweat and avoid skin irritation.

Unstable fractures sometimes need internal fixation (Fig. 13.22).

Amputation of the fingertip is a regrettably common industrial accident, although guards on machines in sawmills and sheet metal works have reduced the incidence considerably.

The aim of treatment should be a mobile finger with innervated skin and a useful tip. If the fingertip lacks sensibility or, worse, is exquisitely tender, it will not be used and it is far better to take more off the finger if this will leave a better stump. For this reason, it is not always helpful to reattach amputated fingers, however cleanly they may have been amputated.

Many amputations are clean transverse cuts made with a clean blade. Others are contaminated crushing injuries.

Traumatic amputation of the thumb is a serious and disabling injury – worse than losing several fingers. If you do not believe this, tuck your thumb into the palm and see how much you can do with just the fingers.

The hand depends for its function upon the movement of its constituent parts over each other. Most fracture management is centred upon encouraging bones to unite soundly in the correct position, even if this means immobilizing soft tissues, but the aim in treating fractures of the hand is to keep the soft tissues moving while the fracture is uniting.

Each finger has seven tendons (extensor digitorum, two interossei and one lumbrical, two slips of flexor digitorum superficialis and one flexor digitorum longus). If any of these tendons stick to bone or to another tendon, movement of the finger will be restricted.

The power grip is used for holding hammers, tennis racquets and golf clubs. A full range of flexion of the fingers is essential. The little, ring and middle fingers are more important than the thumb and index, which are used primarily for precision work.

In right-handed patients, the power grip in the left hand may be more important than the right because it is the left hand that holds the objects being worked upon by the right hand.

The curled fingers can be used as a hook for carrying baskets and swinging from branches. This is one of the few functions still possible if the metacarpophalangeal joints become stiff in extension.