Capitate fractures are most often high-energy injuries. Nearly 80% of patients with capitate fractures will have an associated fracture of the wrist and hand, with most these cases being transscaphoid, transcapitate perilunate dislocations. The capitate is the recipient of numerous intrinsic and extrinsic ligaments of the wrist, predominantly on the volar aspect. The proximal pole is dependent on a retrograde blood supply which can lead to an increased risk of delayed union and nonunion.
Physical examination of a capitate fracture, given the high likelihood of surrounding osseous and soft-tissue injury, will demonstrate diffuse swelling and ecchymosis of the midhand. The bone can be palpated dorsally by first palpating the crucifixion fossa (scapholunate junction) and moving distally in-line with the third ray until the hard, flat surface of the dorsal capitate is palpated. Flexion of the wrist will assist with palpation. Standard hand radiographs (PA, lateral, and oblique) are generally sufficient to diagnose a capitate fracture. PA radiographs with radial and ulnar deviation may assist with identifying minimally displaced fractures. In cases where there is concern for occult fractures, both MRI and CT have been used with acceptable sensitivity for diagnosis.[26,27]
There are three main fracture patterns that can occur with capitate fractures: body, tip avulsion, and shear depression (Table 1). The most common is a transverse fracture at the waist which often occurs in conjuncture with a scaphoid waist fracture and subsequent perilunate dislocation, formally called scaphocapitate syndrome. This injury occurs during forced extension of the wrist, with the dorsal aspects of both the scaphoid waist and the capitate waist impinging on the dorsal ridge of the distal radius (Figure 8). As the wrist returns to neutral position, one of three things can occur: (1) the proximal pole fragment can rotate 180°, (2) the capitate fracture can reduce without malrotation, or (3) the carpus can remain dislocated. Nondisplaced neck fractures can be managed nonsurgically with short arm casting 6 to 8 weeks, given an expected increased duration of healing. Displacement of the neck may disrupt blood supply to the proximal pole and should therefore be managed with open reduction and internal fixation via headless compression screws. Nondisplaced coronal and sagittal avulsion fractures can be managed with 4 to 6 weeks of short arm cast immobilization. Displaced fractures should undergo fracture fixation or fragment excision with ligamentous repair. The dorsal approach through the interval of the third and fourth extensor compartments provides access to the capitate—the surgeon should attempt to minimize dissection off the dorsal distal capitate because this is the blood supply for the proximal pole in most cases. If the proximal pole is inverted, the wrist can be flexed to expose the proximal pole and allow for reduction. Bone loss secondary to impaction can be augmented with allograft versus autograft.
Illustration depicting the mechanism for capitate waist fractures. With the wrist in hyperextension, the force of the distal radius ridge (blue down arrow) causes a compressive force on the dorsal capitate, whereas the surrounding ligamentous and osseous connections produce a distracting force on the volar cortex (blue arrows).
Capitate fractures are notorious for developing nonunion and proximal pole osteonecrosis, attributable to the retrograde blood supply. This dogma is based on early case series and reports that demonstrated a high prevalence of these complications. The largest early study was by Rand et al, published in 1982 on a series of 13 patients, four of whom developed nonunion. More recently, a large review of 53 patients with capitate fractures revealed the actual incidence of nonunion and osteonecrosis may be much less than initially thought, and midcarpal arthrosis may be a more common complication. This however could be related to the improvement in surgical techniques and early intervention.
J Am Acad Orthop Surg. 2020;28(15):e651-e661. © 2020 American Academy of Orthopaedic Surgeons