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Hand & fingers


The standard radiographs

Depends on site of injury:

  • ▪

    Injury to a metacarpal or several phalanges: PA of hand and oblique of entire hand and wrist .

  • ▪

    Injury to the thumb or to a single digit: PA and lateral of the digit .

Regularly overlooked injuries

  • ▪

    Dislocations at 4th & 5th CMC joints.

  • ▪

    Fractures at base of 4th or 5th MCs.

  • ▪

    Fracture of the hamate.

Abbreviations

  • CMC, carpometacarpal;

  • IPJ, interphalangeal joint;

  • MC, metacarpal;

  • MCPJ, metacarpophalangeal joint;

  • PA, posterior-anterior (view).

Normal anatomy

Knowledge of the anatomical attachments of (a few) tendons and ligaments is essential. A seemingly trivial fragment of bone on the radiograph may indicate that a particular tendon or ligament is no longer anchored to the bone. Failure to recognise the functional implication can lead to inappropriate management.

PA view of hand and wrist.

The collateral ligaments arise from the lateral and medial margins of each metacarpal and each phalanx. They extend across the joint and insert into the same margin at the base of the adjacent phalanx.

Oblique view of hand and wrist.

The extensor tendons insert into the dorsal surface at the base of each phalanx.

The volar plate is a fibrous thickening of the joint capsule on the palmar aspect of each joint. It is attached to the bases of the adjacent phalanges.

The thumb

Thumb. The tendon of the abductor pollicis longus is inserted into the radial aspect of the intra-articular portion of the base of the first metacarpal. This is the important anatomical feature in a Bennett's fracture dislocation.

Thumb.

The stability of the carpometacarpal (CMC) joint of the thumb depends on fairly lax but very tough capsular ligaments . The deep ulnar ligament is the thickened part of the capsule on the palmar aspect of the 1st CMC joint. This strong ligament extends from the first metacarpal to the trapezium. The capsular ligaments and the shape of the first CMC joint (ie the trapezium–metacarpal joint) enables the thumb to adopt an extraordinary degree of mobility including the crucial ability of opposition.

1st CMC joint = basal joint of the thumb.

The carpometacarpal (CMC) joints

The 2nd and 3rd metacarpals are attached to the distal row of the carpal bones by thick, strong, ligaments.

The 4th and 5th metacarpals have fewer ligaments anchoring them . These two CMC joints are consequently: (a) very mobile, and (b) vulnerable to injury.

On the PA view of the hand:

  • ▪

    The articular cortex at the base of each metacarpal parallels the articular surface of the adjacent carpal bone.

  • ▪

    The CMC joint spaces are clearly seen; they are equal (approximately1–2 mm) in width.

  • ▪

    The 2nd to 5th CMC joints are visualised as a zigzag tram line (see opposite).

The normal CMC joints

On the PA radiograph, the joint surfaces of the 2nd through to the 5th metacarpal and their adjacent carpal bones articulate, and their articular surfaces parallel one another. These joints are thus seen as a zigzag tram line , shown as a thick dark line on this drawing.

The zigzag line is analogous to “seeing the light of day” through each of the CMC joints.

Useful rule:

On a normal PA view of the hand there will always—yes, always—be “the light of day” seen between the bases of the 4th and 5th metacarpals and the hamate bone.

A stylised drawing of the important alignment between the bases of the hamate and the 4th and 5th CMC joints. Understanding the radiographic appearance of these two joints on the PA view is important. In some people the normal joints look like (a); in others the normal joints look more like (b).

See also pp. 167–168.

Analysis: the checklist

Adopt a three-step approach:

  • 1.

    Target the precise clinical site of injury.

  • 2.

    Search for fractures and for any evidence of subluxation/dislocation.

  • 3.

    Review the relevant muscle and ligamentous attachments because a small fracture may indicate a big loss of function.

Hand, PA view.

Check for fractures, dislocations, and subluxations; check whether the 4th and 5th carpometacarpal (CMC) joints show “the light of day” (p. 157); check the basal joint of the thumb; if there is a fracture of the 1st metacarpal determine whether it is intra-articular (Bennett's fracture) or extra-articular. This is a normal PA view.

Hand, oblique view.

Check for fractures, dislocations and subluxations. This, the routine second view, will invariably clarify/categorise any abnormality that is suspected on the PA radiograph. This is a normal oblique view.

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