Vascularized Distal Radius Grafts
Vascularized distal radius bone grafts are an established treatment for carpal pathology. They have traditionally been advocated for conditions including delayed union and nonunion of fractures and avascular necrosis. The basic science associated with their use has demonstrated superior blood flow as compared with nonvascularized grafts.1,2 The bone heals via creeping substitution and osteocytes are preserved, resulting in more rapid osseous union.3 In a canine study, vascularized bone grafts (VBGs) showed superior union rates compared with nonvascularized bone grafts, but the literature is mixed on this point in human studies.4 In 1991, Zaidemberg et al described a pedicled VBG source from the dorsoradial aspect of the radius based on an ascending irrigating branch of the radial artery. The group reported a 100% union rate in 11 patients with a scaphoid nonunion treated with this graft, at an average time to union of 6.2 weeks.5 The blood supply to the dorsal aspect of the carpus has been extensively described by Sheetz et al. They described several pedicles from which potential VBGs may be harvested from the dorsum of the distal radius. The most common of these pedicles is the 1,2 intercompartmental supraretinacular artery (12 ICSRA, also known as the ascending irrigating branch of the radial artery).
Pedicled VBGs are technically less demanding than free VBGs and are associated with less morbidity. Sheetz et al helped define an anatomically based nomenclature for distal radius pedicled VBGs. Some commonly utilized donor grafts include the 1,2 ICSRA, the 2,3 ICSRA, the fourth extensor compartment artery (fourth ECA), and 5 ECA.6 A 4 + 5 ECA combination graft has been described to provide a longer pedicle.
The most common indications for pedicled VBGs have been for scaphoid nonunion, scaphoid osteonecrosis, and lunatomalacia (Kienböck disease).
Scaphoid fractures/nonunions, especially with a small proximal pole, are fairly well-established indications for a pedicled VBG.
Additional indications may include patients with a scaphoid nonunion who have failed prior surgery. The most commonly utilized graft choice for scaphoid pathology is the 1,2 ICSRA graft. The 2,3 ICSRA could be utilized as well.
The rationale for pedicled VBGs in the treatment of lunate osteonecrosis is primarily to help revascularize the bone. While indications continue to evolve, most would agree that the best indications for VBG are in lunates that have not collapsed and have an intact cartilaginous shell. In addition, pedicled vascularized bone grafting can be utilized in conjunction with traditional treatments for Kienböck disease, such as joint leveling and unloading procedures.
The rationale and indications for VBG in the treatment of Preiser disease are similar to those in Kienböck disease and are also still being defined. It appears that they are more appropriately utilized in early-stage disease. Preserving the cartilage shell, while removing the osteonecrotic bone, can be challenging when treating scaphoid osteonecrosis.
Relative contraindications to a distal radius pedicled VBG for scaphoid nonunion include the presence of arthritic changes and an inability to restore the scaphoid height. However, VBGs may be used in conjunction with structural bone grafts.
For Kienböck and Preiser diseases, contraindications include collapse of the bone and destruction of the cartilaginous shell. In addition, the presence of arthritic changes and carpal malalignment are considered contraindications.
Injuries to the radial artery in the snuffbox or dorsal carpal arch are contraindications. Caution should be taken in the presence of prior surgery on the dorsal wrist.
Patient-related factors that are considered relative contraindications to a VBG include smoking and tobacco use, clotting disorders, and osteomalacia.
Plain films and computed tomography (CT) scans are helpful in delineating the bony anatomy and can shed some light on the vascularity of the bone.
Magnetic resonance imaging (MRI) will be more sensitive in detecting avascular bone.
Doppler can be helpful in delineating the anatomy of the dorsal vessels but is not mandatory.
The vessels that supply dorsal distal radius bone grafts ( Fig. 30.1a–c ) arise from the radial, ulnar anterior interosseous and posterior interosseous vessels. They form three dorsal arches: (1) a dorsal intercarpal arch, (2) a dorsal radiocarpal arch, and (3) a dorsal supraretinacular arch.
An anatomic study by Sheetz et al noted that the 1,2 ICSRA was present in 94% of specimens, the 2,3 ICSRA was present in 100% of specimens, and the 4 and 5 ECA were also noted to exist in 100% of wrists.6?
The nutrient artery for the 1,2 ICSRA branches from the radial artery at an average of 1.9 mm proximal to the styloid (range –6.3 to 3.2 mm). The internal diameter of the vessel averages 0.30 mm (range 0.14–0.58). The pedicle length averages 22.5 mm (range 15–31). The graft is located about 1 cm (range 8–18 mm) proximal to articular surface, where it incorporates the largest number of perforators.
The nutrient artery for the 2,3 ICSRA is 13 mm from the joint line and is slightly larger than 0.1 mm in diameter. The 4 ECA is ~ 11 mm from the joint line and has a diameter of 0.16 mm.
1,2 ICSRA for Scaphoid Pathology
This procedure is shown in Fig. 30.2a–v .
The patient is positioned supine with an arm board.
Loupe magnification is sufficient for performing this procedure.
The tourniquet is inflated after arm elevation (without Esmarch bandaging) and is inflated to 175–200 mm Hg. This will allow better visualization of the donor vessels.
Skin lines are drawn demarcating the relevant anatomy and anticipated locations of the vessels and scaphoid nonunion.
A curvilinear incision will facilitate exposure of the fracture and the 1,2 ICSRA.
The superficial branch of the radial nerve is identified and protected with a vessel loop.
The 1,2 ICSRA is identified between the first and second dorsal compartments, and the 2,3 ICSRA lies between the second and third compartments. The skin and subcutaneous tissue are elevated as a single layer over the extensor compartment while protecting the superficial radial nerve branches. The 1,2 ICSRA can be identified running proximally and superficially down a longitudinal ridge that separates the first and second extensor compartments. Two parallel longitudinal incisions are made at least 5 mm apart along the radial and ulnar sides of the 1,2 ICRSA. The bone graft is outlined over the radial metaphysis 1.5 to 2.0 cm proximal to the radial styloid after retracting the extensor pollicis brevis (EPB) and abductor pollicis longus (APL) radially and the extensor carpi radialis longus (ECRL) and brevis ulnarly.
A longitudinal capsulotomy is now made over the scaphoid, and the nonunion is exposed. An undisplaced fibrous nonunion is curetted to remove all fibrous tissue, taking care not to destabilize the fragments. When there is an avascular proximal pole, the necrotic bone should be removed down to the subchondral bone supporting the articular surface.
While keeping the wrist flexed, one volar guide wire and one dorsal Kirschner wire (K-wire) are placed down the longitudinal scaphoid axis under fluoroscopic control. When the VBG is used as an onlay graft, a small (2.5 mm to 3.2 mm) cannulated headless screw is first inserted over the volar guide wire to provide provisional fixation of the nonunion and so as not to interfere with the VBG onlay. The dorsal K-wire is advanced distally and prepositioned in the distal fragment in preparation for capturing the onlay graft. A 1 cm square defect is outlined with an osteotome at right angles to the nonunion site and is removed.
In the case of scaphoid collapse, a useful technique is to flex the wrist volarly until the lunate is corrected to a neutral alignment with respect to the radius. A 1.1 mm (0.045) K-wire is driven from the radius into the corrected lunate. The wrist is then brought into extension. A second 0.045 K-wire can then be placed from the distal pole into the capitate to maintain the reduction of the distal pole prior to placement of the bone graft.
A dorsal cortical window is created across the non-union site to house the bone graft. In the case of a fibrous nonunion, care is taken not to destabilize the two fragments, since it makes fixation more difficult. The screw can be inserted to stabilize the nonunion prior to making the dorsal cortical window. A smaller than normal headless screw is inserted in a more volar position than normal to accommodate the onlay graft.
The graft is harvested by first sharply dissecting in line with the supraretinacular artery.
A slightly oversized graft, centered over the 1,2 ICSRA pedicle, is then osteotomized to a depth of 8 mm on its radial, ulnar, and distal aspects after the pedicle is ligated at the proximal edge. The distal portion of the pedicle is mobilized subperiosteally off of the dorsal surface of the radius along with a cuff of retinaculum. A curved osteotome is then placed at the proximal osteotomy site and used to pry the graft gently from the radial metaphysis. The pedicle with its periosteal and retinacular cuff is completely separated from the radius and joint capsule. The graft is rotated 180 degrees and press fitted into the dorsal defect over the nonunion site and held in place by driving a prepositioned dorsal K-wire proximally. The capsule is closed without any compression or tension on the pedicle. The tourniquet can be released at this point to check flap vascularity and achieve hemostasis prior to skin closure.
Postoperative care includes thumb spica immobilization until clinical and radiographic signs of healing, which is typically 8–12 weeks and up to 8 months in some cases. CT scanning is used to evaluate the amount of bony union. Some authors insist on 50% bridging bone on three CT cuts before declaring union.