70 Scaphoid Nonunion with Avascular Necrosis
70.1 Patient History Leading to the Specific Problem
A 31-year-old woman presents with left radial-sided wrist pain. The patient is an avid motorcyclist and fell off her dirt bike 1 year prior to presentation. At the time of her accident, she was diagnosed with a displaced left scaphoid waist fracture (▶Fig. 70.1a–c) for which she was treated with an open reduction and internal fixation (ORIF) surgery with a compression screw placed through a volar approach (▶Fig. 70.1d–f). Six months after surgery, radiographs and a CT scan failed to show signs of bridging across the fracture sight (▶Fig. 70.2). In addition, sclerosis of the proximal pole of the scaphoid was then evident on CT scan, suggestive of proximal fragment avascular necrosis (AVN).
70.2 Anatomic Description of the Patient’s Current Status
The patient suffered a scaphoid waist nonunion with suspected AVN of the proximal fragment with hardware in place. Fractures of the scaphoid waist often occur through a fall onto an outstretched hand, resulting in injury from a combination of hyperdorsiflexion and loading of the radial side of the wrist. The proximal fragment blood supply is tenuous and susceptible to AVN. The proximal pole is encompassed in the articular cartilage and receives inflow solely from the dorsal carpal branches of the radial artery entering its dorsal ridge to travel proximally in a retrograde fashion. Placement of a cannulated screw through a volar approach typically does not compromise the blood supply, and it is probable that AVN resulted from proximal fragment vascular disruption secondary to the displaced fracture rather than the initial failed surgical treatment. Although this patient does not currently display signs of radiographic arthrosis, the natural history of scaphoid nonunion is well described with a predictable progressive pattern of arthritic changes. Although treatment is recommended for symptomatic and asymptomatic nonunions, it is unclear whether the progression to arthritis is influenced.
70.3 Recommended Solution to the Problem
Scaphoid nonunion with AVN of the proximal fragment can be challenging for the hand surgeon, especially in the setting of a previous failed surgery. Treatment options differ based upon the absence or presence of arthritic changes. For patients with arthritic changes, several salvage options exist including scaphoidectomy with limited intercarpal arthrodesis, proximal row carpectomy, total wrist arthrodesis, and total wrist arthroplasty. In the absence of arthritic changes, the mainstay treatment comprises nonunion repair with vascularized bone grafting, as this is thought to afford higher rates of treatment success as compared to nonvascularized grafting (union rates of 88 vs. 47%, respectively). Although both pedicled bone grafts and microvascular bone transfers have been described, recent evidence suggests that treatment with the medial femoral condyle (MFC) flap may provide the highest rate of union. A retrospective cohort study demonstrated a greater union rate and decreased time to union with the MFC flap relative to a pedicled distal radial vascularized bone graft. To assess union rates for MFC and iliac crest free flaps, a systematic review was performed demonstrating superiority of the MFC flap (union rates of 100 vs. 88%). Other treatments include excision and replacement of the proximal pole with an osteochondral MFC or rib flap; however, partial or complete scapholunate ligament excision may lead to carpal collapse and compromised wrist kinematics. Proximal pole replacement with an implant arthroplasty has been described with good mid-term results, although long-term follow-up is required to determine the durability of this procedure.
Based on aforementioned considerations and recent evidence suggesting minimal donor site morbidity results from MFC harvest, a treatment solution utilizing an MFC corticoperiosteal free flap was proposed with the following points of surgical technique as previously detailed.
70.4 Technique
Remove the prior compression screw through the previous volar approach. Expose the nonunion site (▶Fig. 70.3a) and curettage of the proximal fragment necrotic bone, leaving behind a subchondral shell of approximately 2 mm. Verify integrity of the proximal pole cartilage cap and absence of arthritic changes. Deflate the tourniquet to confirm lack of punctate bleeding from the proximal pole (preoperative MRI does not reliably predict proximal fragment AVN). Dissect free the descending genicular artery (DGA) and elevate a small corticoperiosteal bone block based upon the DGA. While doing so, identify cutaneous perforators based upon the saphenous artery or a DGA communicating branch at the level of the femoral condyle (▶Fig. 70.3b), and elevate a chimeric flap (▶video 70.1). Administer 2,500 U of intravenous heparin prior to pedicle sectioning (▶Fig. 70.3c).
Curettage a small cavity in the distal fragment to accommodate the bone block. Trim then inset the bone block into the volar scaphoid while distracting the volar aspect of the scaphoid to restore its normal length. Ensure that the cortical portion of the bone block resides within the scaphoid, similar to the Russe technique. Pin the scaphoid to secure the bone block (▶Fig. 70.4). Expose the radial artery and venae comitantes in the distal forearm, and preserve any sizable superficial veins encountered during the exposure as potential outflow options. Perform microvascular anastomosis (end-to-end radial artery following normal intraoperative Allen testing; end-to-end to venae comitantes and/or cephalic vein branches).
