Scaphoid

one of the bones in the proximal row of carpal bones. Also, see scaphoid.

2. Pathology

This bone may be involved in various pathologic conditions affecting the wrist.

In rheumatoid arthritis, erosions may develop as a consequence of synovial inflammation, especially at the site of the "bare area" devoid of cartilage.

Osteonecrosis frequently affects the proximal pole of the scaphoid bone after trauma to this region; the distal pole is less likely to undergo necrosis (Fig.1). Sometimes this condition is not apparent on radiographs until 4 8 weeks after injury. Delayed fracture union or nonunion, collapse of the necrotic segment, and secondary degenerative joint disease may complicate this process. Diagnosis may be facilitated by MR imaging or scintigraphy. A spontaneous ostenecrosis of the scaphoid, or Preisers disease, has also been reported. The radiographic findings resemble those of Kienbocks disease.

Among the carpal abnormalities caused by physical injury or developmental defects are instability, fractures and dislocations.

Lateral instability usually occurs between the scaphoid and the lunate bones. Another pattern of instability results from disruption of ligaments (e.g. the scapholunate interosseous ligament) between the scaphoid and lunate; when the distance between the scaphoid and lunate bones is increased to more than 4 mm, scapholunate dissociation with rotary subluxation of the scaphoid is said to occur. Scapholunate dissociation leads to an abnormality termed dorsal intercalary segmental carpal instability DISI . Most patterns of carpal instability can be diagnosed on plain radiographs, but arthrography and MR imaging also provide diagnostic information.

Trauma to the wrist may involve greater arc or lesser arc injuries to the carpal bones. In lesser arc injuries, usually only stage I (scapholunate dissociation) involves the scaphoid bone. Greater arc injuries represent fracture dislocations through the scaphoid and other bones of the carpus. Carpal fractures most frequently involve the scaphoid bone; various sites may be affected (proximal pole, waist, distal part of the body, tuberosity). Often these fractures are associated with delayed union, nonunion or osteonecrosis.

DR/RB