Wrist and hand

CLASSIFICATION The injuries to be described may be classified by anatomical site as follows: Injuries of the carpus [1] Fracture of the scaphoid bone [2] Fractures of other carpal bones [3]Dislocations of the lunate or other carpal bones injuries of the metacarpal bones and phalanges [4]Fracture of the base of the first metacarpal [5] Other fractures of the metacarpal bones [6] Fractures of the phalanges [7]Dislocations of the metacarpo- phalangeal and interphalangeal joints Strains of the interphalangeal joints

INJURIES OF THE CARPUS FRACTURE OF THE SCAPHOID BONE Fracture of the scaphoid bone is common in young adults. It is not common in children or in patients of beyond middle age. The usual cause is a fall onto the outstretched hand. The fracture nearly always occurs transversely through the middle, or waist, of the scaphoid; so the proximal and distal fragments are of about equal size (Fig. 13.1). Rarely, the fracture is through the proximal pole. Usually there is no displacement of the fragments, which lie in close apposition. If displacement does occur and is allowed to persist, it leads to a 'step' between the fragments and favors the development of degenerative arthritis. Fractures of the distal pole through the tuberosity are rare in comparison with those of the waist of the bone, but are relatively more common in adolescent boys. They are not a clinical problem since they unite readily with minimal splintage and without long-term complications.

Diagnosis fractures of the scaphoid bone are often overlooked, either through failure to have the wrist radiographed or through failure to detect the fracture in the radiographs. In many cases the pain from the injury is slight and the patient can continue to use the hand. Thus the patient may regard the injury as a sprain and may not even consult a doctor. In other cases the doctor may be at fault because, finding little in the nature of clinical signs, the patient is not sent for radiography.

Treatment The standard method of treatment in uncomplicated cases is to immobilize the wrist by plaster cast. The plaster generally used for a scaphoid fracture is slightly more extensive than that used for a fracture of the lower end of the radius. It should extend down the thumb to the level of the interphalangeal joint, and it must be moulded firmly round the first metacarpal bone (Fig. 13.4). The palm is left free beyond the proximal skin crease to allow a full range of movement at the metacarpo-phalangeal joints of the fingers, and the thumb should be free to move at the interphalangeal joint. In the unusual cases in which some displacement of the fragments has occurred, there is a place for operative reduction and fixation by a special compression screw.

Fig MRI scan of undisplaced scaphoid fracture (arrow).

Complications Fractures of the scaphoid bone, even when undisplaced, are potentially troublesome and the incidence of complications is high. The most important complications are: 1-Delayed union 2-Non-union 3-Avascular necrosis 4-Osteoarthritis.

Fig A case in which delayed union of a scaphoid fracture was treated by fixation by a Herbert compression screw.

Fig Established non-union of a fracture of the scaphoid bone. Note the well-defined fracture line and the sclerotic bone margins, suggesting a false joint between the fragments. Fig Avascular necrosis of the proximal half of a fractured scaphoid bone. The dead fragment has not shared in the disuse osteoporosis that has affected the other bones.

Mallet finger (Baseball finger) Sudden passive flexion of the distal interphalangeal joint (as by a ball striking the tip of the finger) may rupture the extensor tendon at the point of its insertion into the base of the distal phalanx. Sometimes a fragment of bone is avulsed from the phalanx. Clinically, the distal interphalangeal joint rests in moderate flexion and cannot be actively extended. In the early stages there is tenderness over the site of avulsion. Treatment Tendon avulsion, with or without a small bone fragment, is treated by uninterrupted splintage in the fully straight position for 6 weeks. Immobilization is confined to the distal interphalangeal joints, the proximal joint being left free. Healing may occur with a small residual extensor lag, but this is functionally acceptable.

If a larger fragment of bone has been avulsed the displacement may be reduced at operation and the fragment held in position by a Kirschner wire passed through the distal phalanx and the reduced fragment, and across the joint to hold it fully extended.