29 The Volar Carpal Artery Vascularized Bone Graft for Scaphoid Nonunion
▪ Rationale and Basic Science Pertinent To the Procedure
The problem of scaphoid nonunion is significant. Around 5 to 15% of all scaphoid fractures will progress to nonunion, the rate rising to up to 30% in fractures of the proximal pole.1 Even after nonvascularized bone grafting, the overall rate of persistent nonunion remains at around 30%.2 , 3 Untreated scaphoid nonunions are likely to progress to periscaphoid arthritis and carpal collapse.4 , 5
Treatment of scaphoid nonunion with vascularized bone grafting is associated with improved rates of consolidation in the context of avascular necrosis (AVN) of the proximal pole or secondary scaphoid nonunion, where the initial surgical failure is likely to be related to a poorly vascularized distal fragment. The simpler pedicled techniques are usually preferred to free bone transfer, unless there is a very large bone deficiency. A recent meta-analysis investigating vascularized bone grafting for AVN has shown union rates of 88%, versus 47% with nonvascularized wedge grafting.3
The advantages of vascularized bone in primary scaphoid nonunion are less clear. Authors using nonvascularized bone grafting techniques for primary scaphoid nonunion without AVN have reported union rates of around 80%, whereas those using vascularized grafts report rates greater than 90%, with many as high as 100%.6 Animal studies also suggest that bone healing is improved in the presence of vascularized bone grafting.7 However, a large, randomized study comparing the two methods is lacking. Previous clinical studies have been hampered by difficulties comparing different treatment modalities due to the heterogeneity of terms and measurable parameters. Preoperatively, for example, there are many classifications of scaphoid fracture used by investigators, and each fracture type carries a different risk of nonunion. There are additional difficulties in quantifying bone loss around the fracture and in identifying avascular necrosis of the proximal pole.8 Intraoperatively, a multitude of fixation techniques are used, which are influenced by the operator’s proficiency and the technical difficulties posed by each case. Postoperatively there are varying definitions of bony union used.3 In the absence of unequivocal advantages of vascularized bone, nonvascularized bone grafting is preferred by many surgeons for primary nonunion because pedicled bone grafting is often associated with a greater degree of difficulty, longer duration of surgery, and higher morbidity.
The chosen source of pedicled vascularized bone is varied. Most reports concern the dorsal radius bone graft on the 1,2 intercompartmental supraretinacular artery (1,2 ICSRA) described by Zaidemberg et al9 and Sheetz et al,10 which can be performed through the same dorsal incision as that used for scaphoid exposure, with a proximal extension. Other donor sites include the first or second metacarpal.11 – 13 In 1987 Kuhlmann et al described a volar radial vascularized bone graft from the ulnar distal radius, pedicled on the volar carpal artery as it traverses the distal epiphysis from the radial artery.14
The volar carpal artery bone graft has important advantages over other sources of pedicled vascularized bone. The defect created by correction of the humpback deformity is volar and can be difficult to reach using the 1,2 ICSRA bone graft due to limitations of pedicle length and difficulties accessing the defect from a dorsal approach.15 In contrast, a volar approach allows excellent access for debridement of devitalized bone and insertion of a volar wedge-shaped graft to restore the anterior defect apparent after restoration of scaphoid height. A volar approach is also less likely to disrupt the important dorsal vascular supply of the scaphoid bone. Compared with classic Matti-Russe grafting for primary nonunion, the technique of volar carpal artery bone grafting is simpler because it avoids the iliac crest donor site, allowing a single incision, regional anesthesia, and minimal discomfort for the patient, who may be treated on an outpatient basis. The harvest technique is similar to that used in nonvascularized volar radial bone harvest, and the additional dissection required to mobilize the pedicle is minimal so that the procedure is rapid, technically straightforward, and with no increased morbidity. For these reasons we prefer to use the volar vascularized bone graft to treat not only cases of AVN or secondary nonunion after previously failed surgery, but all cases of primary scaphoid nonunion.
Basic Science: Anatomical Study
In 1965 Judet and Roy-Camille16 suggested using bone graft from the palmar radius, pivoted on the pronator quadratus muscle to repair scaphoid nonunions. In 1987 Kuhlmann et al were the first to describe the branch of the radial artery supplying the bone.14 With this knowledge the muscular pedicle could be narrowed, allowing improved maneuverability and reach and transposition of a larger graft. The reduced bulk of the pedicle also facilitated repair of the radioscaphocapitate ligament over the scaphoid.
Kuhlmann et al’s report prompted us to confirm the anatomy and the reliability of the flap though our own anatomical study. We injected the arterial system of 40 fresh upper limb specimens with colored latex. The distal volar vascular network was then dissected, revealing the radial, ulnar, and anterior interosseous arteries ( Fig. 29.1 ). The volar carpal artery was identified in 100% of the specimens dissected. It was found that the vessel originates from the radial artery at the level of the radial styloid, traversing the palmar aspect of the distal radius in a plane between the periosteum and the distal edge of the pronator quadratus. The vessel travels along the radial third of the distal radius, sends branches to penetrate the radius at the level of the distal epiphysis, then continues medially to form a T-shaped anastomosis with the anterior interosseous artery superficial to the distal radio ulnar joint17 ( Fig. 29.2 ).
Timing (immediate, delayed)
Time limits for the procedure
The indication for the procedure is scaphoid nonunion without periscaphoid arthritis. Patients with radiological or clinical evidence of early radioscaphoid arthritis may require arthroscopy or magnetic resonance imaging (MRI) of the joint surface before proceeding. Radioscaphoid arthritis involving the styloid and distal scaphoid only [scaphoid nonunion advanced collapse (SNAC) wrist grade I] may be managed with styloidectomy in addition to vascularized bone grafting.
Most patients with scaphoid nonunion present in their fourth decade; however, there are no age limitations for the repair, and the senior author (CM) has performed the procedure in patients ranging from 15 to 61 years of age. A recent meta-analysis of treatment of scaphoid nonunion found that patient age had little effect on union rates, but that the chance of secondary nonunion increases with delay to surgery of more than 12 months from injury.3 We have performed volar vascularized bone grafting on patients presenting up to 10 years after the initial injury; however, early surgery is likely to improv-e union rates, there by avoiding further degenerative changes and allowing an earlier return to normal activity for a greater number of patients.