Volar Carpal Artery Graft for Scaphoid Nonunion and Kienböck Disease
The development of vascularized bone grafts (VBGs) is based on experimental experience. After simple implantation of blood vessels into the bone, angio- and osteoneogenesis was demonstrated. Animal studies showed that VBGs accelerate bone healing, promote new bone formation with normal morphology, and maintain enhanced blood circulation in the long term. Therefore, they are used in conditions where hypovascularity is suspected to be at the origin of the clinical problem, such as in Kienböck disease or in scaphoid nonunion.
Palmar and dorsal pedicled grafts have been proposed. We have demonstrated the utility of using a palmar vascularized distal radius graft pedicle on the palmar carpal arch, which is a bridging artery between the radial and ulnar artery. Prior to surgical application we assessed the anatomical parameters of the vascularized graft, which was first described by Kuhlmann in a separate anatomic study on 40 cadaver upper extremities.1
Indications
VBGs are indicated in scaphoid nonunions with avascularity or hypovascularity of the proximal pole. A VBG may also be employed in scaphoid nonunions without frank signs of hypovascularity as an alternative to simple bone grafts, because of their better healing potential.
VGBs are used in avascular necrosis (AVN) of other carpal bones, especially for Lichtman Stage 3A and B Kienböck disease.
VBGs may also be used in earlier stages of AVN (Lichtman stage 2), instead of waiting for irreversible collapse of the lunate, because of VBGs’ low donor-site morbidity.
Contraindications
Use of VBGs is contraindicated in the presence of radiocarpal and/or midcarpal osteoarthritis.
Injury to the radial or ulnar artery is a relative contraindication because of the risk of hand ischemia from disruption of the collateral blood flow through the palmar carpal arch (PCA).
Previous volar wrist surgery may damage the arterial pedicle and is a relative contraindication.
Examination/Imaging
Standard X-ray images and computed tomography (CT) scans can be performed to assess the scaphoid nonunion. Magnetic resonance imaging (MRI) is performed to rule out AVN of the proximal pole.
MRI is standard in staging Kienböck disease and for evaluating osteonecrosis of other carpal bones.
The Allen test is performed to assess the radial and ulnar artery patency.
Relevant Anatomy
The vascular axis for the pedicle is the PCA, which arises at the radial artery ~ 1.2 cm proximal to the tip of the radial styloid. The artery then lies on the periosteum and runs ulnarly along the distal border of the pronator quadratus muscles toward the distal radioulnar joint (DRUJ) to join the ulnar artery ( Fig. 29.1a,b ).
The anterior branch of the anterior interosseous artery (AIA) runs distally from its origin, lying first on the interosseous membrane and then on the DRUJ. It lies dorsal to the pronator quadratus muscle and joins the palmar carpal arch with a T-shaped anastomosis at the level of the DRUJ.
The AIA and the PCA give off frequent periosteal branches to form a vascular periosteal network.
The bone graft is harvested from the palmar ulnar aspect of the radius, close to the distal radioulnar and radiocarpal joints. The pivot point of the pedicle is its origin from the radial artery.
The median length of the pedicle, measured between its origin and the T point, is 3 (range 2–3.5) cm, which is sufficient to allow the placement of the bone graft within the lunate or the scaphoid bone without flexion of the wrist.
Surgical Technique
The operation is performed under regional anesthesia under tourniquet control as an outpatient procedure. The patient is positioned in the supine position with the arm supported by a hand table, and the wrist is placed in extension.
Scaphoid Nonunion
The scaphoid tubercle is identified and an incision made along the flexor carpi radialis tendon, in the usual Russe palmar approach to the scaphoid. The incision is extended 2 cm proximally to allow exposure of the distal radius. If more exposure is needed, the incision can be extended distally by opening the carpal tunnel ( Fig. 29.2a,b ).
Before inspection of the scaphoid, the vascular pedicle is dissected under loupe magnification. The pronator quadratus muscle fascia is exposed by retracting the flexor tendons ulnarly during wrist flexion. Usually the radial part of the palmar carpal arch can be identified under the muscle fascia just at the distal border of the pronator quadratus.
The muscle fascia is opened a few millimeters proximal to that distal border and the pedicle is exposed.
The wrist is brought back into extension and the scaphoid nonunion is exposed. A limited cortical resection is performed at the margins of the nonunion site, whereas a more aggressive débridement is performed centrally. The subsequent defect defines the dimensions of the graft.
The wrist is brought into flexion and the flexor ten-dons are retracted.
The pedicle is isolated with wide margins by cutting a 3–4 mm strip of periosteum and pericapsular tissue while elevating the pedicle subperiosteally ( Fig. 29.3a,b ). The artery is elevated in a radial direction to increase the length of the pedicle.
If necessary (rarely), the pedicle can be elevated up to its origin at the radial artery. The pedicle becomes more superficial at the level of the radial styloid to run palmarly and terminate in the dorsal aspect of the radial artery. If more pedicle length is needed (extremely rare), the radial artery itself can be mobilized and transposed ulnarly.
The graft margins are outlined on the ulnar palmar edge of the distal radius. The DRUJ and the radiocarpal joint and their inclinations are marked with a thin needle.
The proximal, distal, and ulnar margins of the graft are osteotomized ( Fig. 29.3a,b ). The radial margin is carefully osteotomized through the cortex only, using a very narrow osteotome after carefully elevating the pedicle.
The graft is elevated with a variable amount of cancellous bone. To get more cancellous bone, the osteotome is kept vertical to the cortex with very little rotation. The graft is raised and the pedicle mobilized ( Fig. 29.4a,b ).
If necessary, additional nonvascularized cancellous bone from the distal radius can be harvested in addition to the vascularized graft. The graft is press-fitted and wedged into the nonunion site, followed by internal fixation using a compression screw ( Fig. 29.5a ). If the nonunion is very unstable, the screw can be inserted prior to graft insetting, followed by compression of the graft with a few final turns of the screw. If additional fixation is required, a 0.8-mm Kirschner wire (K-wire) can be inserted.
A limited capsular closure is performed, avoiding compression of the pedicle.
The wrist is immobilized until there are radiographic signs of union.
Pearls
The palmar vascularized graft has a stable vascular pedicle of good caliber and is relatively easy to harvest by the conventional palmar approach to scaphoid nonunions.
The graft can also be used in scaphoid nonunions where AVN is not suspected and avoids the disadvantages of iliac crest bone graft while bringing in a new blood supply for bone healing.
The low morbidity also allows its use in early AVN of the carpal bones, as in Kienböck disease.
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