Scaphoid fracture

Scaphoid fractures (i.e fractures through the scaphoid bone) are common, can in some instances be difficult to diagnose, and can result in significant functional impairment. 

Epidemiology

Scaphoid fractures account for 70-80% of all carpal bone fractures ¹. Although they occur essentially at any age, adolescents and young adults are most commonly affected ¹. Older patients falling in a similar manner are more likely to sustain a distal radial fracture (usually a Colles fracture). 

Clinical presentation

Classically there can be pain in anatomical snuffbox which is thought to have a sensitivity of ~ 90 % and a specificity ~ 40 % ⁴

Mechanism

The usual mechanism is falling on an outstretched hand with resultant hyper-extension of the wrist or purely compressive force ⁷. Occasionally stress fractures are also encountered although these are less common, and only usually seen in athletes (e.g. shot-putters or gymnasts) ⁸.  

Fractures can occur essentially anywhere along the scaphoid, but distribution is not even ⁹:

• distal pole (or so-called scaphoid tubercle) : 10%
• waist of scaphoid : 70-80%
• proximal pole : 20%

Radiographic features

Plain film

Plain radiographs of the wrist, including dedicated scaphoid views are the initial imaging modality of choice. It should however be noted that initial radiograph can miss from 5-20% of fractures in the acute setting ¹. 

If clinically a scaphoid fracture is suspected but plain films are normal, then re-radiograph in 6 weeks may be helpful as a first step. 

Features include:

• visualisation of the fracture +/- displacement
• soft tissue swelling and lateral displacement of the adjacent fat pads
• associated scapholunate ligament disruption (Terry Thomas sign) which can be accentuated with a clenched fist view

If AVN develops the first sign will be slight sclerosis. This can be on account of the rest of the wrist undergoing demineralisation due to immobilisation, whereas the proximal portion being bereft of blood supply retains its calcium. With time the proximal part undergoes osteonecrosis, becomes increasingly sclerotic and can 'implode' and fragment with secondary osteoarthritic changes ⁹. 

Report checklist

In addition to stating that a fracture is present, a number of features should be sought and commented upon:

• fracture
  • location (distal pole, waist, proximal pole)
  • involvement of articular surfaces
  • displacement
  • humpback deformity due to angulation between proximal and distal parts
• alignement
  • scapholunate interval
  • lunate dislocation (trans-scaphoid perilunate dislocation)
• associated fractures (e.g. Colles fracture or other carpal bone fractures)
• evidence of avascular necrosis if the fracture is subacute

Importantly if no fracture is seen it is essential to recommend repeat x-rays (including dedicated scaphoid views) in 7-10 days ¹. If these repeat films are negative also, then MRI (or bone scan if MRI is unavailable) should be recommended if clinical suspicion persists ¹. 

CT

CT is usually not required but can be highly accurate (even more than MRI) in assessing occult cortical injury but are insensitive to trabecular injury ⁵. They are useful however when fractures of the carpus are extensive or complex. CT also is useful in assessing bone union ⁸. 

MRI

MRI is the most sensitive modality for trabecular fractures, and this can detect completely undisplaced fractures ⁹. It is also useful in assessing for avascular necrosis. 

Bone scan

Although bone scans are more sensitive than plain film, they are usually reserved for patients with ongoing pain despite normal serial plain films ⁸. An occult fracture will appear as a region of increased uptake, whereas avascular necrosis will demonstrate a photopaenic region at the lower pole of the scaphoid.   

Treatment and prognosis

Management options can broadly be divided into:

• immobilisation with cast application
• internal fixation for displaced fragments, usually with a headless self-compressing screw ¹⁰
• non-union can be managed with internal fixation and bone grafting ¹⁰

Factors affecting prognosis:

• location ⁹
  • distal pole: excellent likelihood of union (~ 100%)
  • waist: ~ 10-20% chance of non-union
  • proximal pole: ~ 30-40% chance of non-union
• vertically oriented fracture line 
• fragment displacement  of greater than 1mm
• ligamentous instability: increased scapholunate angle (i.e > 60º or radiolunate or capitolunate angle > 15º

In addition to the usual potential non or mal-union and resulting secondary osteoarthritic change, a number of specific complications are encountered from time to time: 

• avascular necrosis - Preiser disease
  • this usually involves the proximal portion as a result of blood supply to the scaphoid entering relatively distally. 
• SNAC wrist - scaphoid non union advanced collapse
• SLAC wrist - scapholunate advanced collapse