Treatment of scaphoid nonunion

Indications

• Operative treatment of scaphoid nonunion varies based on the timing of the injury, bone loss at the fracture site, location of the fracture, presence of humpback deformity or an increased intrascaphoid angle, and the vascularity of the proximal pole.

• Humpback deformity results from collapse of the distal pole of the scaphoid. Normal intrascaphoid angle is 30 degrees plus or minus 5 degrees. Humpback deformity is present when the intrascaphoid angle measured on lateral x-ray or computed tomography (CT) scan is greater than 35 degrees ( Fig. 26.1 ).

  

• Table 26.1 highlights our treatment algorithm for scaphoid nonunion based on specific fracture characteristics.

  TABLE 26.1

  Treatment Algorithm for Scaphoid Nonunion Based on Specific Fracture

  Type of Fracture	Treatment
  Delayed union (< 6 months)	Open reduction and internal fixation with headless compression screw
  Established nonunion without humpback deformity	Open reduction and internal fixation with headless compression screw + bone graft (distal radius, iliac crest cancellous bone graft)
  Nonunion with humpback deformity but no evidence of avascular necrosis	Open reduction via volar approach, corticocancellous bone graft
  Avascular nonunion without humpback deformity	Vascularized bone graft, dorsal or volar approach
  Avascular nonunion with humpback deformity	Vascularized medial femoral condyle bone graft via volar approach

Contraindications

Signs of radiocarpal or intercarpal arthritis, especially patterns indicative of scaphoid nonunion advanced collapse (SNAC; Fig. 26.2 and Table 26.2 ), often confirm that repair/reconstruction are no longer options and salvage should be considered.

TABLE 26.2

Stages of Scaphoid Nonunion Advanced Collapse

Stage	Sites of Osteoarthritis
1	Radial styloid
2	Stage 1 & Scaphocapitate
3	Stage 2 & Lunocapitate
4	Stage 3 & Radiolunate

Clinical examination

• The distal pole of the scaphoid may be tender to palpation, and axial compression of the thumb may reproduce the pain.

• Nagging wrist pain or tenderness in the snuff box months after an injury may indicate a scaphoid fracture that has progressed to a nonunion.

• Decreased wrist motion and grip strength are common findings in patients with a scaphoid nonunion.

• If a patient continues to have radial-sided wrist pain with tenderness over the scaphoid in the anatomic snuff box despite prior treatment, this may reveal progression to nonunion.

Imaging

• A standard three-view wrist x-ray should be obtained. If present, the nonunion is often apparent ( Fig. 26.3 ).

  

• Bone loss, cyst formation, and degree of displacement should be noted.

• Use the lateral view to approximate the lateral intrascaphoid angle to assess for collapse ( Fig. 26.4 ; see also Fig. 26.1 ).

  

• Evaluate for signs of SNAC wrist (posteroanterior [PA] view) and abnormal scapholunate angle (lateral view; see Table 26.2 ).

• X-rays may show previously placed hardware.

• CT and magnetic resonance imaging (MRI) can be useful adjuncts to clinical examination and standard x-ray. Humpback deformity, joint incongruity, and structure of the proximal pole are best appreciated on CT scan. MRI may be used to assess the vascularity of the proximal pole, although there remains no diagnostic gold standard for avascular necrosis ( Fig. 26.5 ).

  

Indications

• Indications for ulna bone grafting:

  • Established nonunion with or without humpback deformity

  • No evidence of avascular necrosis of the proximal scaphoid pole

  • Minimal cystic change, displacement, or carpal malalignment

Positioning

Both the ulna donor site and scaphoid recipient site are prepped and draped into the same operative field.

Exposures

• The decision to use a volar or dorsal approach to the scaphoid is guided by the location of the nonunion, the presence of humpback deformity, and the planned procedure.

  • A proximal nonunion is treated via a dorsal approach for better exposure and for the trailing screw head to purchase the proximal pole.

  • The volar approach improves visualization of more distal fracture/nonunion locations.

  • A notable humpback deformity is generally corrected via a volar approach.

• Recipient site:

  • For the volar approach, the scaphoid is exposed via a curvilinear wrist incision. This incision extends from the radial aspect of the thenar eminence, across the wrist, parallel and radial to the flexor carpi radialis (FCR) tendon ( Fig. 26.6 ).

    

  • For a dorsal approach, a longitudinal or curved incision over the interval between the third and fourth extensor compartments (use Lister tubercle as a landmark) is used. Branches of the superficial radial nerve and the extensor pollicis longus tendon must be protected during this approach.

    • If using a corticocancellous graft, this incision can be somewhat limited ( Fig. 26.7A–B ).

      

    • If planning for vascularized bone options (see the section on “Pedicled Vascularized Bone Graft From Dorsal Distal Radius [1,2 Intercompartmental Supraretinacular Artery]”), a wider approach is used.

• Donor site: A 5-cm longitudinal incision over the ulna, starting 1 cm distal to the olecranon, is used to expose the flat portion of the proximal ulna in preparation for bone graft harvest. The advantage of the proximal bone graft is that the exposure is relatively avascular and the bone is easily accessible.

  • Other graft sites (i.e., iliac crest) can also be used, but we prefer the ulna to keep the procedure to one surgical limb.

Surgical anatomy

• The dominant blood supply to the scaphoid is via a branch from the radial artery that enters through the dorsal ridge and supplies 70% to 80% of the intraosseous vascularity to the proximal pole. This vessel and its branches enter distally and dorsally and travel retrograde through the scaphoid ( Fig. 26.8 ).

  

• The scaphoid proximal pole is uniquely susceptible to avascular necrosis after fracture because of the high dependence on a dominant retrograde-traveling intraosseous vessel.

• A volar branch of the radial artery supplies 20% to 30% of the scaphoid in the region of the distal tuberosity.

• Corticocancellous bone is harvested from the ulna, just proximal to the tip of the olecranon. A 5-mm-wide by 10-mm-long by 5-mm-deep bone graft is usually all that is needed for the scaphoid, but up to 20 mm by 30 mm by 10 mm can be harvested as long as both cortices of the ulna are not violated.

Procedure

Indications

• Indications for pedicled vascularized bone graft:

  • Established nonunion without humpback deformity

  • If a humpback deformity is identified, a volar pedicled bone graft can be considered versus medial femoral condyle (MFC; see later section).

  • Evidence of avascular necrosis of the proximal scaphoid pole

Positioning

• Both the distal radius donor site and scaphoid recipient site are prepped and draped into the same operative field.

Exposures

• A 6-cm curvilinear incision is designed over the dorsoradial wrist in preparation for scaphoid debridement and bone graft harvest ( Fig. 26.16 ).