Carpal Bone Malunions and Nonunions

Paul C. Baldwin III

John R. Fowler

INTRODUCTION

Mechanism of injury
- Scaphoid fractures occur most commonly from a fall onto the outstretched hand, resulting in force transmission of dorsiflexion, ulnar deviation, and intercarpal supination.
Pathoanatomy
- Scaphoid nonunions can result in persistent disability, wrist pain, stiffness, and scaphoid nonunion advanced collapse (SNAC).
- SNAC is a pattern of progressive posttraumatic degenerative arthritis of the radiocarpal and midcarpal joints due to the associated pathomechanics of the scapholunate joint.
- Fracture location determines vascularity and subsequently risk for nonunion.
  - Vascularity—distal pole > waist > proximal pole
- Increasing fracture displacement is a risk factor for nonunion and malunion.
Epidemiology
- Healing rates of 90% to 95% with cast treatment of distal pole and waist fractures.
- Frequency of scaphoid nonunion following surgical fixation is unknown.
  - The union rate greatly depends on the location of the fracture (distal, proximal, waist) and other factors such as chronicity and patient factors (smoking, compliance, etc).
- Proximal pole fractures have higher rates of nonunion due to poor vascularity.

EVALUATION

History
- Injury details
  - Mechanism of injury
  - Estimated chronicity
- Previous treatments
  - Nonoperative
  - Operative
  - Obtain medical records
- Associated symptoms
  - Pain
  - Loss of motion
  - Loss of function
Physical examination
- Inspection—identify for swelling, previous incisions
- Wrist range of motion
- Palpation—anatomic snuffbox, proximal pole, distal pole, axial loading of thumb
- Scaphoid shift test
- Watson test
Diagnostic data
- Plain radiographs:
  - Posteroanterior (Figure 19.1)
  - Lateral
  - 45° pronated and supinated oblique
  - Scaphoid view (posteroanterior in ulnar deviation)
  - Evaluate for sclerosis, cystic formation, bone resorption at the fracture site, hardware loosening, and hardware failure.
  - Evaluate for associated degenerative changes and/or carpal instability.
- Computed tomography scan (with scanning plane parallel to the longitudinal axis of scaphoid)
  - Evaluate for early degenerative changes of wrist
  - Evaluate for fracture displacement
  - Evaluate for technical errors of previous surgeries
    - Hardware placement
    - Fracture reduction
  - Evaluate for fracture fragment sclerosis (osteonecrosis)
- Magnetic resonance imaging
  - Evaluate for vascularity and osteonecrosis.
  - Evaluate for chondromalacia.
  - Evaluate for associated ligamentous injury.
Classifications (radiographic)
- Mack-Lichtman classification
  - Type I—nondisplaced, stable, no significant degenerative changes
  - Type II—unstable, >1 to 2 mm
  - Type III—unstable, early degenerative changes with radial styloid beaking and joint space narrowing of radioscaphoid joint
  - Type IV—unstable, midcarpal arthritis present without radiolunate arthritis
  - Type V—unstable, midcarpal arthritis with radiolunate arthritis
- Scaphoid nonunion advanced collapse
  - Stage I—arthrosis localized to radial side of scaphoid and radial styloid
  - Stage II—Stage I findings in addition to scaphocapitate arthrosis
  - Stage III—periscaphoid arthrosis (proximal capitate and lunate can be maintained)