Scaphoid Fracture - Hand

Introduction

Scaphoid is most frequently fractured carpal bone, often occurring after a fall onto an outstretched hand
- treatment may require a prolonged period of cast immobilization, percutaneous surgical fixation, or microsurgical graft reconstruction
Epidemiology
- incidence
  - 15% of acute wrist injuries
  - 60% of all carpal fracture
  - 8 per 100,000 females, 38 per 100,000 males
- demographics
  - 2 :1 male : female
  - most common in third decade of life
- location
  - incidence of fracture by location
    - waist -65%
    - proximal third - 25%
    - distal third - 10%
      - Historically the distal pole is most common location in pediatrics due to ossification sequence, however more recently waist fractures have become most common
Pathophysiology
- pathoanatomy
  - most common mechanism of injury is axial load across a hyper-dorsiflexed, pronated and ulnarly-deviated wrist
  - common in contact sports
  - transverse fracture patterns are considered more stable than vertically or obliquely oriented fractures
Associated conditions
- SNAC (Scaphoid Nonunion Advanced Collapse)
Prognosis
- incidence of AVN (without treatment) is directly correlated with proximity of fracture to proximal pole
  - proximal 5th AVN rate of 100%
  - proximal 3rd AVN rate of 33%

Anatomy

Osteology
- complex 3-dimensional structure described as resembling a boat, skiff, and twisted peanut
- oriented obliquely from extremity's long-axis (implications for advanced imaging techniques)
- largest bone in proximal carpal row
- > 75% of scaphoid bone is covered by articular cartilage
- articulates with radius, lunate, trapezium, trapezoid, and capitate
Blood supply
- major blood supply is dorsal carpal branch (branch of the radial artery)
  - enters scaphoid in a nonarticular ridge on the dorsal surface and supplies proximal 80% of scaphoid via retrograde blood flow
- minor blood supply from superficial palmar arch (branch of volar radial artery)
  - enters distal tubercle and supplies distal 20% of scaphoid
- creates vascular watershed and poor fracture healing environment
Biomechanics
- link between proximal and distal carpal row
- both intrinsic and extrinsic ligaments attach and surround the scaphoid
- the scaphoid flexes with wrist flexion and radial deviation and extends during wrist extension and ulnar deviation (same as proximal row)
See Wrist Ligaments and Biomechanics for more detail

Classification

Herbert and Fisher Classification- based on fracture stability
- Type A- stable, acute fractures
- Type B- unstable, acute fractures (distal oblique, complete waist, proximal pole, trans-scaphoid and perilunate associated fractures)
- Type C- delayed union characterized by cyst formation and fracture widening
- Type D- nonunion
Anatomic- Proximal pole, waist, distal pole
Russe, Mayo Classifications- based on fracture pattern orientation
Poor correlation with fracture union and poor inter- and intra-observer reliability

Presentation

History
- high or low energy fall onto outstretched hand
Symptoms
- variable level of pain over wrist
Physical exam
- inspection
  - wrist swelling
  - rarely any ecchymosis, hematoma, or gross deformity
- motion
  - worsened wrist pain with circumduction
- pain with resisted pronation
- provocative tests
  - anatomic snuffbox tenderness dorsally
  - scaphoid tubercle tenderness volarly
  - scaphoid compression test
    - positive test when pain reproduced with axial load applied through thumb metacarpal
  - 87-100% sensitivity and 74% specificity when all three tests positive within 24 hours of injury

Imaging

Radiographs
- recommended views
  - neutral rotation PA and lateral, semi-pronated (45°) oblique view
  - scaphoid view
    - 30 degree wrist extension, 20 degree ulnar deviation
    - waist fractures seen best
- findings
  - if radiographs are negative (27%) and there is a high clinical suspicion
  - repeat radiographs in 14-21 days
Bone scan
- indications
  - occult fractures in acute setting
- sensitivity and specificity
  - specificity of 98%, and sensitivity of 100%, PPV 85% to 93% when done at 72 hours
MRI
- indications
  - most sensitive for diagnosis occult fractures < 24 hours
  - immediate identification of fractures / ligamentous injuries
  - assessment of vascular status of bone (vascularity of proximal pole)
    - proximal pole AVN best determined on T1 sequences
- sensitivity and specificity
  - approach 100% for occult fractures
CT scan with 1mm cuts along scaphoid axis
- indications
  - best modality to evaluate fracture location, angulation, displacement, fragment size, extent of collapse, and progression of nonunion or union after surgery
- sensitivity and specificity
  - 62% sensitivity and 87% specific for determining stability and fracture
  - less effective than bone scan and MRI to diagnose occult fracture

Treatment

Nonoperative
- cast immobilization
  - indications
    - stable nondisplaced fracture (majority of fractures)
    - if patient has normal radiographs but there is a high level of suspicion can immobilize in thumb spica and reevaluate in 12 to 21 days
  - outcomes
    - scaphoid fractures with <1mm displacement have union rate of 90%
Operative
- Percutaneous screw fixation
  - indications
    - unstable fractures as shown by
      - proximal pole fractures
      - displacement > 1 mm without significant angulation or deformity
    - non-displaced waist fractures
      - to allow decreased time to union, faster return to work/sport, similar total costs compared to casting
  - outcomes
    - union rates of 90-95% with operative treatment of scaphoid fractures
      - CT scan is helpful for evaluation of union
- Open reduction internal fixation
  - indications
    - significantly displaced fracture patterns
    - 15° scaphoid humpback deformity
    - radiolunate angle > 15° (DISI)
    - intrascaphoid angle of > 35°
    - scaphoid fractures associated with perilunate dislocation
    - comminuted fractures
    - unstable vertical or oblique fractures
  - outcomes
    - accuracy of reduction correlated with rate of union

Technique

Cast immobilization
- technique
  - start immobilization early
    - nonunion rates increase with delayed immobilization of > 4 weeks after injury
  - long arm spica vs short arm casting is controversial
    - no consensus
    - duration of casting depends on location of fracture and risk of nonunion
    - immobilization maintained until radiographic fracture healing demonstrated, usually no sooner than 8 weeks
    - may be required for up to 12-14 weeks for high-risk fracture patterns/patients
    - athletes should not return to play until imaging shows a healed fracture
  - may opt to augment with pulsed electromagnetic field (studies show beneficial in delayed union)
  - formal therapy following immobilization to regain range of motion

Percutaneous screw fixation
- approach
  - dorsal approach
    - best for proximal pole fractures
    - care must be taken to avoid EPL tendon and to preserve the blood supply when entering the dorsal ridge
      - limit exposure to the proximal half of the scaphoid
    - percutaneous has higher risk of unrecognized screw penetration of subchondral bone
  - volar approach
    - indicated in waist and distal pole fractures
    - fractures with humpback flexion deformities
    - allows exposure of the entire scaphoid
    - avoids jeopardizing scaphoid blood supply
    - uses the interval between the FCR and the radial artery
    - careful capsule management to allow closure and restoration of RSC ligament
  - arthroscopic assisted approach
    - has also been described to aid in anatomic reduction
- technique
  - precise wire placement in central axis to guide cannulated screw
  - do not violate scaphotrapeziotrapezoidal joint cartilage
  - rigidity is optimized by long screw placed down the central axis of the scaphoid
  - oblique fluoroscopic images to confirm placement and appropriate screw length
Open reduction internal fixation
- approach
  - dorsal and volar approaches as above
- technique
  - allows direct visualization and reduction at fracture site
  - screw placement as above

Complications

Scaphoid Nonunion
- incidence
  - 5-10% following immobilization, higher rates for proximal pole fractures
- risk factors
  - vertical oblique fracture pattern, displacement >1mm, advancing age, nicotine use
- treatment
  - vascularized or nonvascularid bone grafting procedures
Osteonecrosis
- incidence
  - 13-50% of all scaphoid fractures
  - many studies showing 100% in proximal fifth fractures with immobilization
Malunion
- flexion of distal fragment and extension of proximal fragment due to pull of scapholunate interosseous ligament creating shortened bone with humpback deformity
- treatment
  - no clear indications supporting operative versus non-operative treatment
Subchondral bone penetration with arthrosis due to prominent hardware
- incidence
  - seen following mini-open fixation techniques
  - incidence has decreased with use of fluoroscopy
- treatment
  - revision surgical fixation versus implant removal following union
SNAC wrist (scaphoid nonunion advanced collapse)