Image Interpretation Course
by Heidi Nunn DCR(R) PgCert
The Hand
Phalanges | Metacarpals | Thumb | Paediatric fractures | Enchondroma
(click on images to enlarge)
Phalanges
- 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 important 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: - 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:
- 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:
Metacarpals
- 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.
Thumb
- 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”:
Paediatric Fractures
- 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:
- Salter-Harris Type IV = Fracture involving the epiphysis, physeal plate and metaphysis.
- Salter-Harris Type V = A compression fracture extending through the physeal growth plate. Often difficult to detect.
- Subtle torus fractures are also common, particularly at the
base of the phalanges. Torus fractures refer to buckling of the cortex, with little displacement:
Enchondroma
- 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).
