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It is important to suspect and recognise carpal injuries as they are difficult to diagnose and can cause permanent disability if untreated.
The usual mechanism of injury causing a carpal fracture is either a fall on to the outstretched hand, or direct trauma to the wrist area. Higher-impact injuries from falls or severe road traffic accidents can lead to dislocations of the carpal bones.
- There are eight carpal bones in the region of the wrist, arranged in two rows.
- The proximal row includes the scaphoid, lunate, triquetrum and pisiform. These bones are closely approximated to the distal radius, with the scaphoid located most radially.
- The distal row includes the hamate, capitate, trapezoid and trapezium. This row is closely approximated to the metacarpal bones. The trapezium is located most radially.
- The scaphoid links the two rows of carpals.
- The lunate acts as a central anchor for the carpal bones.
- The carpal bones are bound to each other by short intercarpal ligaments; for example, the scapholunate and the triquetrolunate.
- The distal radius articulates with the bones of the proximal carpal row (except the pisiform and triquetrum) at the radiocarpal joint. The radiocarpal and intercarpal ligaments support this joint.
- The proximal carpal row articulates with the distal row at the carpocarpal joints. The intercarpal ligaments support these joints.
- The distal carpal row articulates with the proximal end of the metacarpal bones at the carpometacarpal joints.
- Fractures involving the carpal bones account for 18% of hand fractures.
- 70% of carpal fractures involve the scaphoid; the second most common is a fracture of the triquetrum.
- Other carpal bones are much less commonly fractured. Capitate fractures are especially rare because the capitate bone sits in a protected position.
- Where carpal fracture is suspected, X-rays in the anteroposterior (AP), lateral and oblique views are needed. Bone scans and CT scans are sometimes helpful if the fracture is not obvious on plain X-ray.
This is discussed in the separate article Wrist Fractures.
The triquetrum lies just distal to the ulnar styloid in the proximal carpal row. It lies under the pisiform bone so is difficult to palpate. To allow palpation, the hand must be radially deviated, exposing the triquetrum from beneath the ulnar styloid. Fractures can either be of a peripheral chip or through the body.
- Usual mechanism of injury: direct blow to the dorsum of the hand or a fall resulting in extreme dorsiflexion of the wrist.
- Diagnosis: if there is a fracture, point tenderness is usually found. X-ray confirms diagnosis.
- Management: uncomplicated fractures can usually be treated with immobilisation in a cast and physiotherapy after cast removal. Displaced fractures through the body require closed reduction and pinning or open reduction and internal fixation.
The lunate articulates proximally with the radius and distally with the capitate. It is palpable just distal to the radial tubercle.
- Usual mechanism of injury: either a direct blow to the wrist, or following chronic recurrent trauma. The recurrent trauma is thought to cause microfractures and lead to avascular necrosis of the lunate (Kienböck's disease). There is eventual collapse of the lunate and associated arthritis. There is a separate article on Kienböck's disease.
- Diagnosis: local tenderness to palpation is usual following an acute fracture. Suspect Kienböck's disease in someone who complains of central dorsal wrist pain, reduced grip strength and reduced wrist movement.
- Management: immobilisation, stress reduction, revascularisation and lunate replacement are management options, depending on the severity and pattern of fracture.
The hook or the body of the hamate bone may be fractured.
- Usual mechanism of injury: may be caused by a fall on to the outstretched hand. Often occurs when the patient falls while holding an object and the object lands between the ground and the ulnar side of the palm. Can follow direct trauma to the hypothenar eminence; for example, while gripping the handle of a racquet, bat or golf club, with an abnormal swing causing the handle to impact against the bone.
- Diagnosis: pain is usually felt on the ulnar aspect of the palm or dorsoulnar aspect of the wrist, and is worsened by gripping. Grip strength may be reduced. Test the ulnar nerve as this is closely associated. Carpal tunnel X-ray view may be needed to detect hook fractures. CT scanning is also helpful.
- Management: non-displaced fractures are treated conservatively by cast immobilisation for six weeks. Displaced fractures usually require open reduction and internal fixation.
- Complications: there can be avascular changes after hook fractures which can lead to necrosis and nonunion of the hamate hook. Excision of the hook may eventually be needed for pain control.
This is the third most common carpal fracture.
- Usual mechanism of injury: direct blow to the dorsum of the hand or a fall on to a radially deviated closed fist.
- Diagnosis: point tenderness over the trapezium. The patient complains of a weak and painful pinch grip. Carpal tunnel X-ray views may be needed.
- Management: treated conservatively if non-displaced. A thumb spica cast is usually used. Displaced fractures are usually treated surgically.
Other carpal bone fractures
Other carpal bones are very rarely fractured. Fracture can occur with a powerful direct force, and multiple fractures are possible. Undisplaced fractures are usually treated conservatively. Surgery is often required for displaced fractures.
- These are uncommon injuries. They can be associated with a carpal fracture. Fracture dislocations are twice as common as pure ligamentous dislocations. Isolated carpal dislocations are rare.
- The most common carpal dislocations are the lunate, the lunate with a scaphoid fracture, and perilunate dislocation. Perilunate dislocations result from dislocation of the distal carpal row. Scaphoid fractures often accompany perilunate dislocation.
- Carpal dislocations can lead to chronic pain and wrist instability. They are difficult to diagnose and are often missed.
Usual mechanism of injury
- A high-impact fall on to an outstretched hand with hand rotation/wrist deviation.
- Patient may just have diffuse wrist pain and diffuse tenderness to palpation. There may be associated swelling.
- Vascular and neurological integrity of the hand should be checked and documented.
- AP X-ray view: when looking at the AP view to diagnose carpal dislocations, one approach is to imagine three arcs:
- The first arc is formed by connecting the proximal articular margins of the proximal carpal row (the scaphoid, lunate and triquetrum).
- The second arc is formed by connecting the distal articular margins of the same proximal carpal row.
- The third arc is formed by joining the proximal articular margins of the capitate and hamate.
- Any disruption of these parallel lines indicates subluxation or dislocation of the carpal bones.
- Lateral X-ray view: there is normally a column seen with the radius below, then the lunate sitting in the radius cup and the capitate sitting in the lunate cup. If this column alignment is lost, it can mean a lunate or perilunate dislocation.
- The wrist should be rapidly immobilised with a cast, even if no injury is obvious on X-ray. Splinting should be to the fingertips.
- Where carpal dislocation has occurred, or is suspected, urgent referral for orthopaedic opinion is necessary. Adequate analgesia should be given.
- Minor dislocations may be treated by closed reduction; more complex injuries usually require open reduction and internal fixation.
- Chronic wrist pain/instability.
Further reading & references
- Hoynak BC; Fractures, Wrist, eMedicine, Jun 2010
- Kouris GJ; Carpal Fractures, eMedicine, Mar 2008
- Capitate, Wheeless' Textbook of Orthopaedics
- Triquetrium, Wheeless' Textbook of Orthopaedics
- Lunate, Wheeless' Textbook of Orthopaedics
- Hamate, Wheeless' Textbook of Orthopaedics
- Morhart M; Hand, Fractures and Dislocations: Wrist, eMedicine, Oct 2008
- Beeson MS; Dislocations, Wrist, eMedicine, Oct 2008
- Hodgkinson DW, Kurdy N, Nicholson DA, et al; ABC of emergency radiology. The wrist. BMJ. 1994 Feb 12;308(6926):464-8.
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|Original Author: Dr Michelle Wright||Current Version: Dr Hayley Willacy|
|Last Checked: 17/09/2010||Document ID: 1917 Version: 21||© EMIS|