Norwich Image Interpretation Course

Heidi Nunn (Advanced Practice Reporting Radiographer)


The Wrist

Fracture prevalence Normal anatomy PA Normal anatomy lateral
Colles'/Smith's Radial styloid Paediatric Scaphoid Triquetrum Hamate Lunate Pisiform Capitate Trapezium Trapezoid
Carpal dislocations Zone of Vulnerability Carpal Instability Galeazzi

(hover over images to zoom, click to enlarge)
Learning outcomes
  • Assess skeletal radiographs using a systematic approach on the DP and lateral
  • Describe carpal anatomy
  • Understand mechanisms of injury and the likely fractures/dislocations which may result
  • Recognise less common fractures to the individual carpal bones
  • Accurately describe carpal dislocations and associated fractures within the zone of vulnerability
  • Understand common eponyms
  • Recognise potential ligament injuries
  • Understand paediatric fractures – torus/greenstick terminology
Fracture prevalence

A fall on the out-stretched hand (FOOSH) tends to result in specific injuries depending on the general age of the patient:

  • 4-10 years - Torus fracture of the distal radial metaphysis
  • 11-16 years - Salter-Harris II fracture involving the physeal plate
  • 17-40 years - Scaphoid fracture
  • Over 40 years - Colles'-type fracture
Normal anatomy - PA radiograph
  • Distal radial articular surface tilts 17 degrees towards the ulna.
  • Medially the radius articulates with the head of the ulna at the ulnar notch. The head of the ulna is usually 2mm shorter than the radius and either touches or slightly overlaps the radius at the distal radioulnar joint.
  • The width of the intercarpal joints is uniform, approximately 2mm.
  • Three carpal arcs should be traced:
    1. along the proximal row of carpal bones; proximal aspect.
    2. along the proximal row of carpal bones; distal aspect.
    3. along the capitate and hamate proximally.
  • These three lines should remain unbroken:
Normal DP wrist    Normal DP wrist
  • The distal radial epiphyseal line may remain as a linear density, with a spur-like projection laterally, simulating a fracture due to the break in the cortex. However, this is a normal variant.
Epiphyseal spur
Normal anatomy - Lateral radiograph
  • The distal articular surface is angled 10-15 degrees anteriorly. This is useful when identifying subtle fractures at the distal radius with flattening of this angle.
  • Articular surfaces of radius, lunate and capitate should be in a straight line and be congruent (parallel). The "apple" (capitate) should sit in the "cup" (lunate), which should sit in the "saucer" (radius):
Normal lateral wrist    Normal lateral wrist
Colles' / Smith's fracture
  • Fractures of the distal radius are classified depending on which direction the distal fragment is displaced. If displaced posteriorly, it is referred to as a Colles' fracture. The term "Colles" was originally used to describe a very specific injury, but the term is now used more generally.
Colles' fracture
  • If the distal fragment is displaced anteriorly, the fracture is classified as a "Smith's" fracture:
Smith's fracture
  • A Barton's fracture refers to an intra-articular shearing fracture with subluxation at the radio-carpal joint. It is described by the direction of displacement. The volar type is most common:
Volar type Barton's - fracture volar rim radius (and ulna) with anterior subluxation radiocarpal joint
  • If the distal radius fracture is displaced, the attachment of the triangular fibrocartilage tends to result in an avulsion fracture of the ulnar styloid process:
Avulsion fracture of ulnar styloid (and Colles' fracture)
Radial Styloid Fracture
  • Fractures are common due to blunt trauma directly to the radial styloid process. Fractures are oblique, intra-articular and are usually minimally displaced:
Radial styloid fracture
Paediatric fractures
  • Most common, but often subtle, are torus fractures of the distal radial metaphysis, usually dorsally (due to a FOOSH). The torus fracture will be evident by a buckling of the cortex with little displacement:
Torus fracture
  • Greenstick fractures of the radial and ulnar shaft are demonstrated by a break in one cortex only (incomplete), with displacement/angulation. An increase in the force will result in a complete fracture.
Greenstick fracture
  • Salter-Harris fractures involving the physeal growth plate are common, particularly Salter-Harris type II through the dorsal aspect of the distal radial metaphysis (again due to FOOSH):
Salter-Harris I    Salter-Harris II
Scaphoid
  • Majority of fractures are at the waist and are non-displaced. Can be difficult to see initially, therefore if clinically suspected repeat radiographs are taken at 10-14 days to demonstrate sclerosis or resorption at the fracture line:
Scaphoid - fracture demonstrated on follow up images (bottom)
  • Fractures at the distal pole are usually avulsion injuries caused by the radial collateral ligament. The distal pole has its own blood supply, so healing is quick.
Fracture distal pole scaphoid
  • Blood supply to the proximal pole enters at the waist. This supply may be cut off by a fracture through the waist. The proximal pole is consequently at risk from delayed union or avascular necrosis, where the proximal fragment collapses and becomes radiographically denser:
AVN proximal pole of scaphoid
  • Clinical assessment of the injured scaphoid includes compression by axial loading which causes pain to the anatomical snuff-box. However, fractures to both the base of the 1st metacarpal and to the radial styloid will also produce pain to the anatomical snuff-box with this clinical assessment. It is therefore important to assess these areas carefully on the scaphoid views:
Bennett's fracture-dislocation
Triquetrum
  • This is the second most common carpal bone to be fractured.
  • An avulsed bony fragment will be demonstrated on the lateral radiograph, dorsal to the proximal row of carpal bones:
Triquetral fracture
Hamate
  • Associated with fracture-dislocations at the base of the 4th and 5th metacarpals. Important to spot but often subtle.
  • Ensure there is a 2mm joint space with the adjacent metacarpals on the DP view.
  • Scrutinise the cortex of the hamate, particularly on an oblique view:

Fracture hamate

Lunate
  • Fractures are rare. Lunate dislocations may occur following high impact trauma. A sclerotic lunate is sometimes seen, which is due to avascular necrosis (decreased blood supply), known as Keinbock's disease. The lunate becomes denser radiographically, fragments and collapses:
AVN lunate
Pisiform
  • Fractures very occasionally seen due to direct trauma to the antero-medial aspect of the carpus:
Fracture pisiform
Capitate
  • Isolated fractures are rare, but as part of complex carpal fractures and lunate/perilunate fracture-dislocations, a fracture of the capitate may be seen.
Comminuted fractures proximal capitate and lunate, with impaction and rotation    Comminuted fractures proximal capitate and lunate, with impaction and rotation
Trapezium
  • Fractures are rare. The 1st carpo-metacarpal joint is a very common site for arthritic changes.
Fracture trapezium, fracture triquetral
Trapezoid
  • Fractures are rare.
Carpal Dislocations
  • Lunate dislocation - Lunate loses its articulation with both the capitate and the radius and is displaced volarly with up to 90 degrees rotation. The capitate remains aligned with the radius but sinks proximally:
Lunate dislocation    Lunate dislocation    Lunate dislocation
  • Perilunate dislocation - The lunate maintains its normal articulation with the radius, but the capitate articular surface is dislocated from the lunate, normally dorsally:
Perilunate dislocation, fracture scaphoid    Perilunate dislocation    Perilunate dislocation
  • Midcarpal dislocation - The lunate tilts volarly but is not dislocated from the radius. The capitate is dislocated from the lunate but not as dorsally as seen in a perilunate dislocation:
Midcarpal dislocation, fracture radial styloid    Midcarpal dislocation    Midcarpal dislocation
Zone of vulnerability
  • Most fracture-dislocations fall within the "zone of vulnerability".
  • When identifying a fracture or dislocation, it is helpful to understand that likely associated fractures will be within this zone, i.e., radial styloid, waist of the scaphoid or capitate, proximal pole of the hamate, triquetrum or ulnar styloid.
  • With progression from the radial to the ulnar side of the arch, the severity of the injury increases and the frequency of the injury decreases:
Zone of vulnerability
Carpal instability
  • Refers to ligament rupture within the carpal bones, most commonly at the scapho-lunate joint.
  • Scapholunate dissociation is demonstrated by the gap between the scaphoid and lunate increasing in size more than 2mm. It may also become triangular in appearance on the PA radiograph.
  • There is foreshortening of the scaphoid and a cortical "ring sign" is seen at the distal pole:
Carpal instability
  • A 'clenched fist' view is sometimes helpful to demonstrate the widening at the joint:
Clenched fist view
Galeazzi fracture-dislocation
  • Refers to a displaced fracture of the distal radial shaft accompanied by a dislocation to the distal radioulnar joint:
Galeazzi fracture-dislocation
  • Similar pattern seen at the elbow where a displaced fracture to the proximal ulna is accompanied by a dislocation of the radial head. This is termed a "Monteggia" fracture-dislocation.

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