Case History
This 40 year old male patient fell on an outstretched hand while working in a factory years ago.
Fracture of the left scaphoid (navicular)
The margins of the fracture demonstrate a very sclerotic surface. This is indicative of nonunion from a previous fracture. The scaphoid is the most common fractured carpal bone. The usual age of occurrence is between 15 and 40 years. Scaphoid fractures are very rare in children. The mechanism of injury is complex, but it essentially consists of various degrees of hyperextension and radial flexion such as falling on an outstretched hand (FOOSH). These fractures are frequently overlooked and exhibit a significant incidence of complications. The scaphoid is the most common site for occult fracture in the entire human skeleton.
The scaphoid is divided into three regions; 1) the distal pole; 2) the waist; 3) the proximal pole. Approximately 70% of the fractures involve the waist, 20% the proximal pole and 10% the distal pole. Ulnar deviation projections of the hand may help in laying out the actual waist of the scaphoid. If no fracture is seen initially yet the clinical picture is suspicious then precautionary immobilization should be applied and the wrist re-x-rayed in 7 to 10 days. A fracture, if present, will be visible by 20 days post-injury.
A useful soft tissue sign of a subtle scaphoid fracture can be found in alterations to the adjacent scaphoid fat stripe. The normal fat stripe (“navicular stripe”) is a linear collection of fat between the radial collateral ligament and the tendon sheaths of the extensor pollicus brevis and the abductor pollicus longus. In almost 90% of the fractures involving the radial compartment of the wrist the fat stripe will be displaced laterally or totally obliterated. Healing occurs without periosteal callus, the fracture line just gradually disappearing.
Complications: Avascular necrosis, nonunion, carpal instability, and radiocarpal degeneration
Avascular necrosis is encountered in 15% of scaphoid fractures. The scaphoid is anatomically predisposed to avascular necrosis following fracture due to the pattern of the nutrient blood supply. The scaphoid receives a dual blood supply. A small artery enters and perfuses the distal pole and tuberosity. A larger vessel, with an entry site that may be proximal or distal to the scaphoid waist, is responsible for perfusing the remaining areas of the bone. In the development of complicating avascular necrosis, the position of the fracture relative to the principal artery is the most crucial factor. If the fracture is distal to the major vessel, then avascular necrosis is unlikely, if proximal then the probability for avascular necrosis increases significantly. In general, the more proximal this fracture line the greater the probability for avascular necrosis.
Radiological signs of avascular necrosis include increased density and fragmentation. The fracture line will appear wider and is often cystic in appearance. All of the signs will take a variable time after the fracture incident to appear, ranging from months to years. Nonunion occurs in approximately 30% of fractures involving the waist of the scaphoid.