Hook of Hamate Fractures

Katherine M. Dederer

Reid W. Draeger

INTRODUCTION

Incidence and epidemiology
- Hook of hamate fractures are estimated at 2% of all carpal fractures¹
- Likely underreported due to chronic or low-level symptoms in patients who never present to a hand surgeon or in whom standard radiographs fail to reveal the fracture²
- Most common in athletes involved in racquet or striking sports such as those playing baseball, hockey, golf, and tennis from direct transfer of force during contact or shearing forces associated with ulnar deviation of the wrist during swing³
- Commonly presents in a delayed fashion 5 to 10 months postinjury⁴,⁵
Mechanism
- Typically involves the nondominant hand in golfers and baseball players and the dominant hand in racquet sport athletes
- May be caused by a sudden direct blow such as striking the ground with a golf club, or an injury from repetitive trauma such as batting⁶
- Also seen in laborers, construction workers, and others subject to repetitive mechanical trauma to the ulnar hand

ANATOMY

Located in the ulnar palm radial to the pisiform and ulnar to the transverse carpal ligament
Ulnar artery is typically found radial or volar to the hook, while the sensory and motor branches of the ulnar nerve may be found ulnar or volar to the hook and are vulnerable to injury during surgery (Figure 16.1).⁷
Attachments
- The hamate hook is the site of origin for the flexor digiti minimi muscle, opponens digiti minimi muscle, hypothenar muscles, pisohamate ligaments, and abuts the distal ulnar extent of the transverse carpal ligament.⁸
  - Hook of the hamate is prominent just radial and distal to the pisiform; total dorsal-volar size averages 26 mm from dorsal cortex to tip of hook.⁹
  - Three anatomic variations from the normal anatomy of the hamate hook: bipartite, hypoplastic, and hook aplastic (Figure 16.2)¹⁰
  - Fractures may occur at the base, waist, or tip of the hook, although base fractures are most common (Figure 16.3).¹¹
  - Blood supply
    - Most of the hook is fed via a basal nutrient artery, which originates from the ulnar artery at the level of Guyon’s canal.
    - 71% of patients have a nutrient artery to the tip of the hook, creating a watershed area at the waist of the hook (Figure 16.4).¹²
    - Risk for nonunion and avascular necrosis with waist or tip fractures
Biomechanics
- Hook acts as a fulcrum for flexor tendons to the ring and small fingers, increasing grip power.

FIGURE 16.1 Cross-sectional anatomy of the volar ulnar wrist. A, ulnar nerve and artery are volar to the hook of the hamate (bottom, labeled H), B, enlargement showing the ulnar nerve (N) and artery (A) volar and radial to the hook of the hamate, respectively. T, thenar musculature; R, flexor retinaculum. Reprinted from Cobb TK, Carmichael SW, Cooney WP. Guyon’s canal revisited: an anatomic study of the carpal ulnar neurovascular space. J Hand Surg. 1996;21:861-869. Copyright © 1996, with permission from Elsevier.

FIGURE 16.2 Types of hamate hooks. A, Bipartite hook (arrow), B, Hypoplastic hook (arrow), C, Aplastic hook (arrow). Reprinted from Chow JC, Weiss MA, Gu Y. Anatomic variations of the hook of hamate and the relationship to carpal tunnel syndrome. J Hand Surg Am. 2005;30(6):1242-1247. Copyright © 2005 American Society for Surgery of the Hand. With permission.

FIGURE 16.3 Of 62 identified hook of hamate fractures, 47 were located in the proximal one-third of the hook. Reprinted with permission from Stark HH, Chao EK, Zemel NP, et al. Fracture of the hook of the hamate. J Bone Joint Surg Am. 1989;71(8):1202-1207.

FIGURE 16.4 Presence of various nutrient arteries to the hook of the hamate. RH, radial hook; UH, ulnar hook; RB, radial base; UPB, ulnar palmar branch. Reprinted from Failla J. Hook of hamate vascularity: vulnerability to osteonecrosis and nonunion. J Hand Surg Am. 1993;18(6):1075-1079. Copyright © 1993 Elsevier Inc. With permission.

PRESENTING SIGNS AND SYMPTOMS