Hamate
Os Hamatum
location_on Distal row of carpal bones, on the ulnar (pinky) side
The hamate is a wedge-shaped carpal bone distinguished by its prominent hook (hamulus) projecting from the palmar surface. The hook is a critical landmark forming the ulnar border of the carpal tunnel and the radial border of Guyon's canal. The hamate articulates distally with the fourth and fifth metacarpals, serving the ring and little finger ray. The hook is vulnerable to fracture in sports involving club or racquet gripping.
Key Anatomical Features
- Hook of hamate (hamulus) projects from the palmar surface toward the palm
- Hook forms the ulnar wall of the carpal tunnel and radial wall of Guyon's canal
- Distal surface has two facets for the fourth and fifth metacarpal bases
- Triangular proximal surface articulates with the lunate
- The hook is palpable 1 cm distal and radial to the pisiform
Muscle Attachments
| Muscle | Attachment | Action |
|---|---|---|
| Flexor digiti minimi brevis | Hook of hamate | Flexes the proximal phalanx of the little finger |
| Opponens digiti minimi | Hook of hamate | Opposes the little finger |
| Flexor retinaculum | Hook of hamate (medial attachment) | Forms the carpal tunnel roof |
| Short muscles of hypothenar eminence | Hook and body of hamate | Provide fine motor control of the little finger |
Joints and Articulations
| Joint | Type | Connects to |
|---|---|---|
| Fourth carpometacarpal joint | Synovial plane | Fourth metacarpal |
| Fifth carpometacarpal joint | Synovial plane (with limited motion) | Fifth metacarpal |
| Triquetrohamate joint | Synovial plane | Triquetrum |
Common Pathologies
Hook of hamate fracture
Classically occurs in golfers, baseball players, and racquet sport athletes from repetitive club/bat impact against the hook. Causes ulnar-sided wrist pain, and may injure the ulnar nerve or rupture flexor tendons.
Ulnar nerve compression at Guyon's canal
The ulnar nerve passes between the pisiform and the hook of the hamate in Guyon's canal and can be compressed by hook fractures, ganglion cysts, or cycling (handlebar palsy).
Flexor tendon rupture
Non-union of a hook of hamate fracture can cause mechanical attrition and rupture of the flexor digitorum profundus tendons to the ring and little fingers.
Clinical Relevance
Hook of hamate fractures are often missed on standard wrist radiographs. A carpal tunnel view or CT scan is needed for diagnosis. The pull test (resisted flexion of the ring and little finger DIP joints) and direct palpation of the hook reproduce pain. Treatment of symptomatic non-union is excision of the hook fragment. Golfers, baseball batters, and cyclists are at highest risk.
Development and Ossification
The hamate body ossifies from a single center appearing between ages 1 and 6 months (the second carpal bone to ossify, after the capitate). The hook may have a separate ossification center that appears around age 12 and fuses shortly after.
Did You Know?
- Hamate means hook-shaped in Latin (hamatus = hooked)
- Hook of hamate fractures are sometimes called the golfer's fracture because the butt end of the club impacts directly against the hook
- The hamate is the second carpal bone to ossify, after the capitate
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