Scaphoid fracture is the most common type of bone fracture in the carpus (ie, wrist). Frequently, however, the diagnosis of this scaphoid injury is delayed; a delay in the diagnosis and treatment of a scaphoid fracture may alter the prognosis for union, increase the risk of avascular necrosis, and dramatically increase the long-term likelihood of arthritis.
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The carpus contains 8 small bones, which are arranged in 2 rows, proximal and distal. The proximal bones, from the radial to the medial side, are the scaphoid, lunate, triquetrum, and pisiform. Only the scaphoid and lunate articulate with the radius; thus, these 2 bones transmit the entire force of a fall on the hand to the forearm. The distal bones are, starting from the radial side, the trapezium, trapezoid, capitate, and hamate.
Anatomically, the scaphoid may be divided into proximal, middle (termed the waist), and distal thirds. Most of the blood supply to the scaphoid enters distally. The proximal part of the scaphoid has no blood vessels entering it, depending instead on vessels that pierce the midportion. Fractures of the proximal third of the scaphoid account for 20% of scaphoid fractures, those of the middle portion account for 60%, and fractures of the distal part make up the remaining 20%. Diminished blood flow to the proximal pole is noted in about one third of fractures at the waist level. This reduced blood supply may result in avascular necrosis of the proximal pole of the scaphoid. Almost 100% of proximal pole fractures result in aseptic necrosis. Displaced scaphoid fractures have a nonunion rate of 55-90%.
Fall onto outstretched hand
The usual mechanism of injury is a fall onto the outstretched hand (FOOSH) that results in forceful dorsiflexion and impaction of the scaphoid against the dorsal rim of the radius. This mechanism explains why snuffbox tenderness is so common, even in the absence of a scaphoid fracture. Conventional medical wisdom dictates that snuffbox tenderness should be equated with a scaphoid fracture unless radiographs prove otherwise. If initial radiographs do not show fracture, follow-up radiographs should be obtained in 7-14 days, because the fracture line may be more visible after some resorption.
Scaphoid fracture has been reported in people aged 10-70 years, although it is most common in young adult men following a fall, athletic injury, or motor vehicle accident.
The scaphoid has no ligamentous or tendinous attachments, but joint compressive forces, trapezial-scaphoid shear stress, and capitolunate rotation moments exert control on the scaphoid. Therefore, scaphoid fractures have a high incidence of nonunion (8-10%), frequent malunion, and late sequelae of carpal instability and posttraumatic arthritis.
A higher incidence of aseptic necrosis and nonunion is noted with fractures of the proximal pole of the scaphoid, because no blood vessels enter it.
A scaphoid fracture can present as a nondisplaced, stable fracture or as a displaced, unstable fracture. Displaced fractures frequently are associated with ligamentous tears in the wrist and require thorough evaluation and follow-up.
No known correlation exists between race and scaphoid fracture.
Scaphoid injuries are more common in men than in women.
Scaphoid fracture is uncommon in children because the physis of the distal radius usually fails first, resulting in Salter type I or II fractures of the distal radius. Similarly, in elderly patients, the distal radial metaphysis usually fails before the scaphoid can fracture.
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