Image Interpretation Course

by Heidi Gable DCR(R) PgCert

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The Wrist

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

(click on images to enlarge)

Fracture prevalence

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

  4-10years – Torus fracture of the distal radial metaphysis.
  11-16years – Salter-Harris II fracture involving the physeal plate.
  17-40years – Scaphoid fracture.
  Over 40years – Colles-type fracture.
  

Normal anatomy - PA film

• 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:

• 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.

Normal anatomy - Lateral film

• 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):

  

Colles / Smiths fracture

• Fractures of the distal radius are classified depending on which direction the distal fragment is displaced. If displaced posteriorly, it is refered 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.
  
  
     
• If the distal fragment is displaced anteriorly, the fracture is classified as a Smith's fracture:
  
  
     
• If a shearing fracture is intra-articular with posterior displacement of the distal fragment, along with the carpus, then it is termed a Bartons. A reverse Bartons refers to anterior displacement of the fragment along with the carpus.
• 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:
  
  
  
  
  

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:
  
  
    
• Greenstick fractures of the radial and ulna 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.
  
  
    
• 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):

   

Scaphoid

• Majority of fractures are at the waist and are non-displaced. Can be difficult to see initially, therefore if clinically suspected repeat films are taken at 10-14 days to demonstrate sclerosis or resorption at the fracture line:

      

• 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.

• 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:

• 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:
  
  

  

Triquetrum

• This is the second most common carpal bone to be fractured.
• An avulsed bony fragment will be demonstrated on the lateral film, dorsal to the proximal row of carpal bones:

Hamate

• Associated with fracture-dislocations at the base of the 4th and 5th metacarpals. Important to spot but often subtle.
• Scrutinise the cortex of the hamate, particularly on an oblique view.
• Ensure there is a 2mm joint space with the adjacent metacarpals on the DP view:

Trapezium

Trapezoid

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:

   

• Perilunate dislocation - The lunate maintains its normal articulation with the radius, but the capitate articular surface is dislocated from the lunate, normally dorsally:

   

• 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:

  

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:

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 film.
• There is foreshortening of the scaphoid and a cortical “ring sign” is seen at the distal pole:

• A 'clenched fist' view is sometimes helpful to demonstrate the widening at the joint:

Galeazzi fracture-dislocation

• Refers to a displaced fracture of the distal radial shaft accompanied by a dislocation to the distal radio-ulnar joint:

   

• 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 the Monteggia fracture-dislocation.

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