Other carpal fractures

After the scaphoid, the triquetrum is the most commonly broken carpal bone, usually as a small dorsal chip. Fractures of the hook of the hamate, the trapezium, the capitate and the lunate are uncommon and easy to miss on plain films; capitate and lunate fractures in particular may be part of a greater-arc (perilunate) injury, so look for a ligament injury around them.

Mechanism

Triquetrum: fall on the extended, ulnarly deviated wrist (impaction of the ulnar styloid or avulsion of the dorsal ligaments). Hook of hamate: a bat, club or racket handle pressing on the hypothenar eminence. Trapezium: axial load through the thumb. Capitate and scaphocapitate: forced hyperextension, high energy. Lunate: hyperextension and axial load; also seen in Kienböck disease.

Clinical findings

• Point tenderness: dorsal triquetrum just distal to the ulnar styloid; hook of hamate about 2 cm distal and radial to the pisiform in the palm; trapezium at the base of the thenar eminence.
• Hook of hamate: pain on gripping, weakness, ulnar nerve paraesthesia (Guyon canal) and, later, rupture of the little-finger flexor tendons.
• Always examine for a perilunate injury and the median and ulnar nerves.

Imaging

• PA, lateral and 45° oblique views of the wrist.
• Carpal tunnel view (hook of hamate), Robert view (trapezium), lateral (dorsal triquetral flake).
• CT whenever a carpal fracture is suspected but not seen, and to look for a greater-arc injury; MRI for occult fractures.

• PA, lateral and oblique views of the wrist. A dorsal triquetral chip is often visible only on the lateral (a flake behind the proximal carpal row).
• Carpal tunnel view for the hook of hamate; Robert or Bett view and CT for the trapezium.
• CT is the test of choice when a carpal fracture is suspected but not seen; MRI for occult fractures and bone vitality.

Classification

71

Lunate

72

Scaphoid (see the scaphoid entry)

73

Capitate

74

Hamate: body and hook (hamulus)

75

Trapezium: body and ridge

76

Other carpal bones: 76.1 pisiform, 76.2 triquetrum, 76.3 trapezoid

Types shown in 3D

Triquetrum, dorsal chip (76.2A)

The commonest triquetral fracture: a flake from the dorsal cortex (ligament avulsion or impaction by the ulnar styloid), seen best on the lateral view. Splint for 3–4 weeks.

Hook of hamate (74.x)

The hook breaks at its base from a direct blow by a handle (golf, baseball, racket sports). Missed on standard views: carpal tunnel view or CT. Excision of the fragment for a symptomatic non-union.

Trapezium body (75.x)

A vertical split of the trapezium carries the thumb metacarpal radially and proximally with it, like a Bennett fracture of the carpus. Displaced fractures are fixed with screws.

Scaphocapitate (73.x + 72)

A greater-arc injury: the scaphoid waist and the capitate neck break, and the proximal capitate fragment can rotate up to 180° so its joint surface faces distally. High risk of avascular necrosis: open reduction and screws.

Lunate, volar pole (71.x)

Rare; the volar pole is the commonest pattern (Teisen). Look for an associated perilunate injury and, in a sclerotic lunate, for Kienböck disease. Large displaced fragments are fixed.

Treatment

Non-operative

Dorsal triquetral chips, undisplaced body fractures and most trapezial ridge fractures: wrist splint or short cast for 3–6 weeks.

Operative

Displaced trapezium body fractures (joint with the thumb): screw fixation. Hook of hamate non-union or symptomatic fractures: excision of the hook (quick return to sport) or fixation. Displaced capitate and scaphocapitate fractures: open reduction and headless screws, since the proximal capitate pole is at risk of avascular necrosis. Lunate fractures: screw or K-wire fixation of large displaced fragments. Fix associated ligament injuries.

Aftercare

Splint or cast until tenderness settles; CT to confirm union for the capitate, lunate and hamate.

Complications

• Missed fracture or associated perilunate injury
• Non-union (hook of hamate, capitate)
• Avascular necrosis (proximal capitate, lunate)
• Ulnar nerve irritation and flexor tendon rupture (hook of hamate)
• Post-traumatic arthritis (trapezium)