The scaphoid is an oblong bone that has the unique role of linking and stabilizing the two rows of carpal bones. This, unfortunately, increases its propensity to injury, making it the most common carpal fracture. The injuries usually result from a fall on an outstretched dorsiflexed hand or by an axial load directed along the thumb's metacarpal. There is pain along the radial side of the wrist and localized tenderness in the anatomical snuffbox. Examining the wrist in ulnar deviation exposes more of the scaphoid to direct palpation in the anatomical snuffbox. Eliciting pain in this area, when the patient resists supination or pronation of their hand, or pain with axial pressure directed along the thumb's metacarpal is also suggestive of injury.
Standard and scaphoid views should be carefully examined for any cortical disruption (see Fig, 2.6.2.-8). The scaphoid view profiles the bone lengthwise and may assist in detecting subtle fractures. Distortion of a soft tissue fat stripe that lies adjacent to the radial side of the scaphoid is also suggestive of injury. Two-thirds of the fractures occur at the waist or middle third of the bone, 16 to 28 percent in the proximal third, and 10 percent in the distal third. A scaphoid fracture may also have an associated injury in 12 percent of cases involving either the radius, neighboring carpals, a carpal instability pattern, or dislocation.
A scaphoid fracture can develop avascular necrosis of the proximal fracture segment that can lead to disabling arthritis. There are several reasons that this occurs. The vascular supply to the scaphoid enters the distal portion of the bone through small branches off the radial artery and the palmar and superficial arteries. A fracture could therefore disrupt the blood supply to the proximal segment. In general, the more proximal, oblique, or displaced the fracture, the greater the risk of developing avascular necrosis. A scaphoid fracture is considered unstable if there is even as little as 1 mm of displacement, rotation, angulation, shortening, or if a carpal instability pattern is present. Two thirds of the scaphoid's surface is also articular. This only adds to the scaphoid's problems, because articular fractures are more difficult to heal.
Because 10 percent of initial radiographs fail to detect a fracture, it is imperative that initial treatment also be directed by clinical suspicion until follow up studies can exclude the diagnosis. Nondisplaced fractures and those that are only clinically suspected can be treated in a short-arm thumb spica splint or cast. Displaced or unstable fractures should be placed in a long-arm thumb spica splint or cast, and should be seen promptly by the orthopedic surgeon for definitive treatment. The main complications are avascular necrosis, delayed union, nonunion, malunion, and subsequent early degenerative arthritis.
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