The Effect of Thumb Immobilization on Fractures of the Hook of the Hamate: A Cadaver Study

Abstract

Background: Fractures of the hook of the hamate are rare. Nonoperative management has historically been immobilization in a short arm cast (SAC) without thumb immobilization with a high reported incidence of nonunion. The high prevalence of nonunion following nonoperative treatment may be secondary to motion at the fracture site. The transverse carpal ligament's attachment to the hook of the hamate results in movement at the fracture site during thumb motion. Methods: A cadaveric study using 8 fresh frozen cadaver arms amputated at the mid-humeral level was performed. Computed tomography (CT) imaging was used to assess the bony anatomy and assure no preexisting fractures were present. Osteotomy of the hook of the hamate was performed through a skin incision proximal to the hook of the hamate and the transverse carpal ligament. Each arm was then mounted in a jig designed to hold and stabilize the arm and hand in supination. CT scans were performed without cast immobilization with the thumb in extension and abduction, with SAC without thumb carpometacarpal joint immobilization, and SAC with thumb carpometacarpal joint immobilization. Results: Motion of the fractured hook of the hamate was found to occur in all noncasted specimens, greatest with base fractures. SAC without thumb immobilization had little to no effect in eliminating fracture motion. SAC including the thumb reduced fracture motion in all specimens. Conclusions: Previous poor experience with nonoperative management of fractures of the hook of the hamate may be partially due to inability to adequately immobilize the fracture fragment. Fracture motion of the hamate hook occurs during thumb movement, likely from traction on the fracture fragment by the transverse carpal ligament.

Keywords: hamate fracture; hook of hamate; thumb immobilization; thumb spica cast; transverse carpal ligament.

Figure 1.

An elastic band is wrapped securely around the distal phalanx of the thumb passively holding the thumb in the desired position.

Figure 2.

The third phase scans were done with the hand and forearm immobilized in a short arm plaster cast leaving the carpometacarpal, metacarpophalangeal, and interphalangeal joints of the thumb free.

Figure 3.

(a) Computed tomography scan immediately after osteotomy. (b) Thumb extension in short arm cast with thumb free allows displacement of the fracture fragment.

Figure 4.

Computed tomography scan (a) with thumb in neutral and (b) with thumb extended and abducted shows motion of the fracture fragment. (c) Carpometacarpal joint immobilization with the thumb pulled into abduction and extension.