The scaphoid has a complex three-dimensional geometry that has been likened to a “twisted peanut.” It can be divided into three regions: proximal pole, waist, and distal pole.

The scaphoid functions as the primary link between the forearm and the distal carpal row and therefore plays a critical role in maintaining normal carpal kinematics.

Articulating with the scaphoid fossa of the radius, the lunate, capitate, trapezium, and trapezoid, more than 70% of the scaphoid is covered with articular cartilage.

Gelberman and Menon⁸ have described the vascular supply of the scaphoid. The main arterial supply is from the radial artery; it enters the scaphoid via two main branches:

The proximal pole is at increased risk for AVN secondary to disruption of its tenuous retrograde blood supply after a fracture of the scaphoid waist or proximal pole.

Due to its tenuous vascular supply, the scaphoid heals almost entirely by primary bone healing, resulting in minimal callus formation.

The size and shape of the scaphoid, in combination with its precarious blood supply, demands attention to detail and accurate implantation of fixation devices during fracture fixation. Scaphoid dimensions vary between genders; the male scaphoid is usually longer and wider than the females. In addition, the diameter of most commercially available standard screws are larger than the proximal pole of the female scaphoid.¹¹

Scaphoid fractures are most commonly seen in young, active males.¹⁵

With the wrist dorsiflexed greater than 95 degrees, in combination with 10 degrees or more of radial deviation, the distal radius abuts the scaphoid and precipitates a fracture.¹⁵

The scaphoid can also be fractured with forced palmar flexion of the wrist²⁰ or axial loading of the flexed wrist.¹²

Most of these fractures occur at the waist region, although 10% to 20% occur in the proximal pole.

Proximal pole fractures are associated with an increased risk of nonunion, delayed union, and AVN.

In children, scaphoid fractures are less common and are most frequently seen in the distal pole.

An untreated or inadequately treated scaphoid fracture has a higher likelihood of nonunion. The overall incidence of nonunion is estimated at 5% to 10%, but the risk is significantly increased with nonoperative treatment of a displaced waist or proximal pole fracture.

The natural history of scaphoid nonunions is controversial, but they are believed to result in a predictable pattern of progressive radiocarpal and midcarpal arthritis.^{8, 9, 14, 17, 18, 21, 25}

In an established scaphoid nonunion, the distal portion of the scaphoid may flex, producing a “humpback” deformity of the scaphoid. The loss of scaphoid integrity can result in carpal instability and abnormal carpal kinematics, most frequently manifesting as a dorsal intercalated segment instability (DISI) pattern.

Factors associated with the development of a scaphoid fracture nonunion include the following¹⁷:

Scaphoid fractures classically occur in the active, young adult population. Patients present with radial-sided wrist pain.

Classic physical examination findings include the following:

Scaphoid fractures can be part of a greater arc injury.

The following plain radiographs should routinely be ordered in the patient with a suspected scaphoid fracture: posteroanterior (PA), oblique, lateral, and dedicated scaphoid views.

The following criteria define a displaced or unstable fracture as noted on plain radiographs^{2, 9, 17}:

Computed tomography (CT) with reconstruction images in multiple planes is used to identify an acute fracture not detected on plain radiographs and to determine the amount of displacement and comminution (FIG 1B,C).

Magnetic resonance imaging (MRI) may be indicated in the evaluation of a suspected scaphoid fracture not detected on plain radiographs (FIG 1D,E). MRI is highly sensitive, with
a specificity approaching 100% when performed within 48 hours of injury.¹⁶

A technetium bone scan has been shown to be up to 100% sensitive in identifying an occult fracture.²⁷ Unfortunately, it is also associated with a low specificity and often will not be positive immediately after the fracture.

Nonoperative management is indicated for a nondisplaced, stable scaphoid waist or distal pole fracture.

The appropriate type and duration of cast immobilization remain controversial and none has proven to be superior. Our preference is a short-arm thumb spica cast until the clinical examination and radiologic studies (usually a CT scan) confirm fracture union. If there are concerns for patient compliance, we prefer an initial period (4 to 6 weeks) of long-arm thumb spica cast immobilization.