Introduction
Background
Although hamate fractures are increasing in incidence secondary to the popularity of sports activities involving racquets, bats, and clubs, these injuries remain relatively rare. Estimates suggest hamate fractures constitute 2% of all carpal fractures. The hamate bone is a roughly triangular-shaped bone composed of both a body and a hook (see Images 1-2). Hamate fractures are thus classified as type I fractures involving the hook and type II fractures involving the body. Type I fractures are more common than type II fractures.1,2
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Frequency
United States
Hamate fractures account for 2% of all carpal fractures. Of the 2%, one third are hamate hook fractures due to repetitive swinging by golfers.
Functional Anatomy
The hamate is a triangular bone located in the distal carpal row farthest to the ulnar side (see Images 1-2). The hamate is bordered proximally by the pisiform and the lunate in the proximal carpal row, radially by the capitate, and distally by the bases of the fourth and fifth metacarpals.
A roughly circular projection or hook on the volar surface of the hamate is the inferolateral border of the Guyon canal. The roof (superficial) of the canal is formed by the palmar carpal ligament, and the floor (deep) is formed by the flexor retinaculum. The canal carries the ulnar artery and nerve, and, for this reason, hook fractures should suggest a high probability of ulnar artery and nerve damage.3 In addition, the hamate hook has a dual blood supply, with vessels entering from both the ulnar tip and radial base. These vessels often have a poor anastomosis, which clinically can result in nonunion due to insufficient blood supply.
Sport-Specific Biomechanics
Type I fractures involving the hook of the hamate are the most common and can occur via several different mechanisms.1,2,4,5,6,7 First, repeated microtrauma to the hook during sports involving swinging clubs, bats, or racquets can result in a hook stress fracture. These usually occur in the nondominant hand and account for approximately one third of hamate fractures. Second, direct trauma can be applied during sports when the butt of the club rests on the hamate and the force of the swing is then transmitted directly to the bone. In addition, indirect trauma can be applied to the hook through its muscular and ligamentous attachments. This can occur either when falling on a hyperextended wrist or during power grips.
Type II fractures involving the body of the hamate are less common than type I fractures and always require direct force.4 Most commonly, these fractures occur with a punch-press injury or dorsopalmar compression of the wrist between heavy weights.
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Clinical
History
Hamate hook fractures are usually seen in individuals who participate in sports involving a racquet, bat, or club or in individuals who have a history of falling on an outstretched hand.,2,4,5,6,7 Because most patients with this injury seek medical advice only after persistent symptoms, they often present weeks to months after the initial injury. Most report palmar pain aggravated by grasp, pain with dorsoulnar deviation, and pain with flexion of the fourth and fifth digits.
In the case of a hamate body fracture or direct trauma, persons may present immediately. Fractures involving the body of the hamate are typically associated with high-energy, direct-force trauma or crushing injuries. External evidence of these forces is evident in these individuals.
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Related Medscape topics:
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Physical
Physical examination findings are usually nonspecific and may even be absent. If symptoms are present, physical examination typically reveals discrete point tenderness with palpation over the hook of the hamate, diminished grip strength, and, secondary to the proximity of hamate fractures to the ulnar nerve, paresthesia may be present in the fourth and fifth fingers.
Resisted distal interphalangeal flexion of the fourth and fifth fingers with the wrist in ulnar deviation causes pain over the fractured hook, whereas testing in radial deviation does not. In the case of more severe injury, brief examination for neurologic and vascular competency, accompanied by basic radiographs, are all that is appropriate in an emergency department setting. More detailed exploration and radiographic studies should be performed later, while the patient is under anesthesia.
Causes
Hamate fractures are generally associated with sports activities that use a racquet, bat, or club. For a more complete discussion of the causes and mechanisms of hamate fractures, see Sport-Specific Biomechanics.
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References
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Further Reading
Keywords
fracture of the hook, hook fracture, fracture of the hamate, hook of hamate fracture, fracture of the hook of hamate, wrist fracture, wrist trauma, hamate trauma, broken wrist, wrist injury
