- Small avulsion fractures are common, easily missed and are functionally important. Avulsions may be seen:
- On the DP view - at the head or base of the phalanges and head of the adjacent metacarpal. This is at the insertion of the medial and lateral collateral ligaments, and the resultant avulsed fragment may be very subtle:
- On the lateral view: anterior aspect - at the head or base of the phalanges or adjacent metacarpal (most commonly at the base of the middle phalanx). This is at the insertion of the volar plate (which refers to the joint capsule). This injury is caused by hyperextension:
- Again on the lateral, but on the dorsal aspect, at the insertion of the extensor tendon:
This tendon may rupture without an attached bone fragment and the resulting flexion deformity at the distal interphalangeal joint is called a mallet finger:
It is impotant to obtain a lateral view of the affected finger when injury to the phalanges is suspected, as an oblique does not demonstrate small avulsions or the extent of displacement of larger avulsion fractures:
- Dislocations to the interphalangeal joints are common. The dislocation is described by which joint is affected and by the direction of the phalanx distal to the joint relative to the phalanx proximal to the dislocated joint (eg, dorsal dislocation at the PIPJ). It is important to assess for any associated fractures pre- and post-reduction:
- Fractures to the shaft, neck or head, particularly of the 4th or 5th metacarpal are common. Most often caused by punching injuries. and are rarely missed as they are usually displaced:
- More subtle, and yet clinically significant, are fractures to the base of the 4th or 5th metacarpal:
- These are often associated with dislocation to the 4th or 5th carpo-metacarpal joints. A dislocation can be identified by recognising loss of the normal joint space (2mm) at the metacarpal base:
- Another associated injury is to the hamate, often evident on the oblique image:
Mechanism of injury is similar to the 5th metacarpal neck fracture so, when index of suspicion is high and a fracture to the head or neck isn't present, scrutinise the base
of the 4th and 5th metacarpals, and the adjacent hamate.
- A common fracture at the base of the 1st metacarpal is an oblique intra-articular fracture, usually with dorsal subluxation of the shaft. This is the Bennett's fracture-dislocation:
- Similar to the Bennett's fracture-dislocation, but comminuted, is the Rolando's fracture-dislocation. Both are unstable injuries:
- Ligament injuries are also common around the thumb, especially at the insertion of the ulnar collateral ligament. This is at the medial aspect of the base of the proximal phalanx. This is termed "skier's thumb":
- Salter-Harris fractures involving the physeal growth plate and adjacent metaphysis and/or epiphysis are common. An injury to this area will cause a fracture to the weakest point, which is the cartilaginous growth plate, and spare the stronger joint capsule, ligaments and tendons. Depending on the involvement of the adjacent metaphysis and epiphysis, determines the classification:
- Salter-Harris Type I = Injury through the physeal growth plate only, usually with displacement. No involvement of the adjacent metaphysis or epiphysis.
- Salter-Harris Type II = Fracture extending through the physeal growth plate and adjacent metaphysis:
- Salter-Harris Type III = Fracture line running through the growth plate and adjacent epiphysis. This is intra-articular, and usually occurs at the site of ligamentous insertion:
- A benign lytic lesion, often seen within the phalanges. Usually asymptomatic and an incidental finding, but can fracture. Characteristically lobulated, slightly expansile with endosteal scalloping and cortical thinning. Multiple enchondromas also commonly seen (Ollier's disease).
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