Hand & fingers
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 ligaments1. 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 them2. 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 line3 (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 line3, 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.
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.
Injury to the basal joint of the thumb.
An intra-articular fracture of the base of the 1st metacarpal.
Single digit injury.
Check for fracture and dislocation/subluxation. These two patients have sustained a volar plate injury (ie a fragment is detached from the capsular region of the palmar aspect of an interphalangeal joint).
The common injuries
Fractures of the phalanges or metacarpals
Most fractures involving the mid-shaft of a phalanx or metacarpal are stable and pose few clinical problems. Phalangeal fractures are frequently managed by strapping to an adjacent digit (ie garter strapping or buddy strapping).
There are some “problem fractures”, for which careful orthopaedic assessment is essential. The most common of these are shown on the next four pages.
Avulsion of a small fragment at the base of a phalanx.
The ligament or tendon most likely to be compromised is indicated by the position of the fragment:
Mallet finger.
A flexion deformity (known as a mallet or baseball finger) of the distal phalanx.
An isolated flexion deformity is almost impossible without either a rupture of the extensor tendon or an avulsion fracture.
A deformity necessitates very careful clinical examination because a fracture is present in only 25% of mallet fingers.
Volar plate fracture.
Caused by forced extension of a finger.
The detached fragment will be visualised on the oblique view—not on the PA view.
These fractures are nearly always displaced and thus unstable.
Spiral fracture of the shaft of a phalanx or metacarpal.
These fractures are often unstable and significant shortening may occur. The fracture frequently requires open reduction and internal fixation4.
Fracture involving a joint surface.
If there is displacement and/or comminution then surgical repair can be challenging because the fragments are invariably very small5.
Boxer's fracture. These two patients have sustained a fracture through the neck of a metacarpal (left, 4th metacarpal; right, 5th metacarpal).
Uncommon but important injuries
Fractures and dislocations involving the thumb
The basal joint (ie the carpometacarpal or CMC joint) of the thumb is remarkable. It is multifunctional. It can adduct, abduct, oppose and circumduct (see p. 155). If the multifunctional ability of this joint is to be maintained then any injury close to this joint needs to be recognised, characterized, and treated early1,6.
Distinguishing between an intra-articular and an extra-articular fracture at the base of the thumb is crucial. The distinction determines the appropriate treatment.
Base of thumb: extra-articular fracture
The fracture line is distal to the joint capsule. Consequently it is distal to both the deep ulnar ligament and to the insertion of the tendon of abductor pollicis longus and there is no involvement of the CMC joint and no risk of dislocation.
This is important because almost all extra-articular fractures at the base of the thumb are treated simply by closed reduction.
Base of thumb fracture.
The fracture line is distal to the insertion of the tendon of the abductor pollicis longus muscle. The CMC joint is not involved.
No risk of dislocation.
Extra articular fracture, base of 1st metacarpal.
The articular surface is not involved. The proximal fragment remains in a stable position.
Bennett's fracture.
A fracture involving the base of the 1st metacarpal. Crucially, the joint surface is involved.
The larger metacarpal fragment is pulled dorsally and radially by the abductor pollicis longus muscle.
This injury is more properly termed a Bennett's fracture–dislocation. It is unstable.
Early orthopaedic treatment (often open reduction) is essential because retention of the multiple movements at this special CMC joint are so important4,6.
Rolando's fracture.
A comminuted intra-articular fracture of the base of the 1st metacarpal. The comminuted fragments often adopt a Y, V or T configuration. It is highly unstable.
This fracture can be difficult to treat because of the comminution and displacement of the articular fragments.
Gamekeeper's/Skier's thumb7
▪ Rupture or severe stretching of the ulnar collateral ligament (p. 155) at the first metacarpophalangeal joint (MCPJ). Occasionally a bone fragment may be avulsed. A complete tear of the ligament requires surgical repair7,8.
□ Usually the ligament alone is torn and the radiographs appear normal.
□ If there is clinical uncertainty as to whether the ligament is torn then stress radiographs can assist in confirming or excluding the diagnosis. Diagnostic ultrasound examination by a skilled practitioner is a reliable alternative to stress radiography7,8.
Skier's thumb.
In most cases the medial collateral ligament is torn and the standard radiographs appear normal.
Occasionally there is an avulsion fracture of the base of the proximal phalanx at the insertion of the ligament.
Skier's thumb.
Fragments have been detached from the base of the proximal phalanx of the thumb. This represents an avulsion (rather than a tear or stretching) of the medial collateral ligament. Result: an unstable joint.
Carpometacarpal (CMC) joint dislocations3,10–14
High velocity motor vehicle trauma can cause a dislocation at any of the CMC joints.In less violent impacts (eg punching a wall) it is the 4th and 5th metacarpals that are most commonly dislocated.
4th or 5th CMC dislocation
Emergency Departments that receive hand injuries due to fist fights will regularly see dislocations involving these CMC joints. The injury commonly results from a transmitted force along the metacarpal shaft when the closed fist hits a solid object. It is often associated with a fracture at the base of the affected metacarpal and/or the adjacent metacarpal and/or the hamate. A fracture of the dorsal surface of the hamate (seen on the oblique view) should always raise the suspicion of a dislocation at the 5th CMC joint.
What to look for on the PA radiograph:
▪ Effacement of the adjacent CMC joint space.
▪ Apply this analogy: can I see “the light of day” (pp. 156–157) between the bases of the 4th and 5th metacarpals and the hamate? In other words, any lack of parallelism between the base of a metacarpal and the articular surface of the adjacent carpal bone (p. 168) is very suggestive of a dislocation.
▪ Has the head of the 5th metacarpal dropped well below the 4th metacarpal head?
How to confirm/refute your suspicion:
▪ Check the oblique radiograph. Then, if there is still continuing doubt, obtain a lateral view. The base of the 5th metacarpal dislocates posteriorly.
The PA image on the left is normal and the “light of day” is evident at the bases of the 4th and 5th metacarpals. The PA image on the right shows (a) fracture of the base of the 5th metacarpal and (b) loss of the joint space at the 5th CMC joint (ie indicating a dislocation). Note that the joint space (“the light of day”) is well seen at the base of the 4th metacarpal indicating that this joint is normal.
The 4th and 5th CMC joints on the PA radiograph
Four different patients, each with a normal PA radiograph. The corresponding artworks show that the normal carpometacarpal (CMC) joints can vary slightly in appearance between patients. The difference is invariably due to the different slope of the articular surfaces between normal patients, as illustrated in (a) and (b) below. However, when you inspect the PA view a joint space (ie a black line) at the base of the 4th and 5th metacarpals will always be visible on a normal PA radiograph, without exception. Visualising this normal zigzag black line may be conceptually difficult for an inexperienced observer. The schematic drawings below explain how a joint (“the light of day”) disappears on the PA view when a 4th or 5th CMC joint is dislocated.
Diagrammatic representation of the 4th and 5th CMC joints. (a) = normal; (b) = normal; (c) = dislocated 5th CMC joint; (d) = Dislocations at 4th and 5th CMC joints.
Pitfalls
Mobile basal joint of the thumb. The exceptional mobility of the basal joint (ie the trapezium–1st metacarpal joint) of the thumb means that it may be entirely normal (above) but appears to be subluxed. Be careful not to make this mistake. Clinical correlation should discount this possibility.
Additional bones. Sesamoid bones adjacent to the first metacarpophalangeal joint (MCPJ) should not be confused with fracture fragments. Most hands usually have five sesamoid bones: two adjacent to the MCPJ of the thumb, one adjacent to the MCPJ of the index finger and one adjacent to the MCPJ of the little finger.
Accessory epiphyses
Sometimes accessory metacarpal epiphyses—or partial epiphyses—are present in young children. The most common of these pseudoepiphyses occur in the head of the 1st (thumb) metacarpal (left and right) and at the base of the 2nd metacarpal (centre and right). Unless the possibility of an accessory epiphysis is considered, particularly at the base of the 2nd metacarpal, then a normal developmental variant may be read as an undisplaced metacarpal fracture.