27 Dorsal Vascularized Graft from the Radius for Scaphoid Nonunio
▪ Rationale and Basic Science
The risk of a delay or nonunion of a scaphoid fracture has long been recognized due to its precarious blood supply. Scaphoid nonunions have been estimated to occur in 5 to 15% of scaphoid fractures. The risk of a nonunion increases with proximal pole fractures and with the development of avascular necrosis (AVN). Union rates following conventional bone grafting of scaphoid nonunions has ranged between 47 and 90% in various publications. To address the problem of scaphoid nonunion, vascularized bone graft rotated on a volar pedicle was introduced in the 1980s.1 Subsequently, Zaidemberg et al in 1991 identified a reliable vascularized bone graft based on a dorsal arterial branch of the radial artery, which they described as the “ascending irrigating branch” of the radial artery. In their initial description, Zaidemberg et al harvested this bone graft with an overlying skin paddle for monitoring and reported a 100% union rate in 11 patients with longstanding nonunions of the scaphoid who underwent this procedure.2
Following this report, the arterial anatomy of the dorsal distal radius was elegantly described by Sheetz et al.3 The authors described several dorsal arterial pedicles with their arcs of rotation and potential uses throughout the carpus for bone defects and AVN. The “ascending irrigating branch of the radial artery” was more anatomically described as the 1,2 intercompartmental supraretinacular artery (1,2 ICSRA) ( Fig. 27.1 ). The ease of identification and arc of rotation of a vascularized bone graft that was pedicled on this arterial branch made it ideally suited to the treatment of problems of the scaphoid, including fracture nonunion, benign tumors, and Preiser disease.
Since the initial early success reported with this treatment method, subsequent studies have shown a high failure rate with very small proximal pole nonunions with AVN and those that are associated with a carpal instability pattern, which has led to more careful patient selection for this procedure.4 – 6
The ideal candidates for this procedure are young (16 to 40 years), healthy patients with an established scaphoid nonunion with an avascular proximal pole but without carpal collapse.
This procedure has been described for patients ranging in age from 14 through 66 years. We do not recommend this procedure for children or adolescents with significant remaining growth potential from the distal radial physis. There are no absolute upper age limits for this procedure.
The timing of surgery is dependent upon the diagnosis for which the procedure is being used. For scaphoid fractures, the procedure is indicated for an established nonunion in which there are no signs of bridging callus after 3 months on radiographs or computed tomographic (CT) scan, sclerosis at the fracture site, cyst formation, or radiographic or magnetic resonance imaging (MRI) evidence of AVN.
Time Limits for Procedure
No absolute time limits have been established for this procedure. Successful union has been reported in scaphoid nonunions treated up to 10 years after the initial injury.2
Very small proximal pole fractures, especially those with fragmentation
Scaphoid fractures with substantial bone loss and a humpback deformity
Patients with ongoing tobacco use
Patients who cannot tolerate cast immobilization.
Patients with previous dorsal wrist surgery or previous fracture of the distal radius
Presence of complex regional pain syndrome
Patients with an absent radial artery
Patients with vascular disease or those with Raynaud disease or phenomenon
Radiographic evaluation of the scaphoid should include standard posteroanterior (PA) and lateral radiographs; a semisupinated anteroposterior (AP) radiograph, which best demonstrates the presence of a humpback deformity; and a “scaphoid view,” which is a PA view taken with the fingers flexed and the wrist in ulnar deviation. Comparison views of the opposite wrist, specifically the scaphoid view and comparison lateral view, allow determination of the normal length and height of the scaphoid and the normal scapholunate angle. MRI evaluation is useful for evaluating the vascularity of both the proximal and the distal poles of scaphoid fracture nonunions. Fracture healing is most accurately assessed with CT scan or tomography.
▪ Surgical Technique
One advantage of this technique is the relative simplicity of the surgical instrumentation. Because this is a pedicled vascularized graft, this procedure can be performed under loupe magnification, and it does not require the use of an operating microscope.
The patient is positioned supine on the operating table, with the hand positioned on an arm table. The ipsilateral iliac crest should also be prepped if it is anticipated that this will be needed for additional nonvascularized graft. Fluoroscopy is used throughout the procedure. The monitor should be positioned at the end of the hand table so that it can be seen by both the surgeon and the assistant.
A nonsterile tourniquet is used for the procedure. However, exsanguination of the limb should be done with elevation rather than an Esmarch to allow better visualization of the supraretinacular artery. The tourniquet is deflated after harvesting and rotating the vascularized bone to assure there is bleeding from the graft. The tourniquet can then be reinflated if needed to facilitate visualization during the remainder of the procedure.
A gentle dorsal curvilinear incision is made beginning on the dorsal base of the first metacarpal. It is curved proximally over the scaphoid toward the radial side of the fourth extensor compartment, continuing proximally to the metadiaphyseal junction of the radius ( Fig. 27.2 ). The skin and subcutaneous tissue are elevated as a single layer over the extensor compartment while protecting branches of the superficial radial nerve ( Fig. 27.3 ).
Careful dissection over the extensor retinaculum is performed. The 1,2 ICSRA is fairly well protected such that subcutaneous dissection over the retinaculum should not cause injury to the vessel. Two parallel longitudinal incisions are along the radial and ulnar sides of the 1,2 ICRSA, which travels down the longitudinal ridge that separates the first and second extensor compartments. The incisions should be separated by at least 5 mm. The pedicle should be dissected with a cuff of retinaculum distally and mobilized away from the capsule so that it can be protected during the exposure of the scaphoid.
The site of the bone graft is from the radial metaphysis, ∼1.5 to 2.0 cm proximal to the radioscaphoid articulation. The first compartment tendons (extensor pollicis brevis and abductor pollicis longus) are retracted radially and the second compartment tendons (extensor carpi radialis longus and brevis) ulnarly. The radial metaphysis is exposed, preserving the periosteum around the planned site of the bone graft. The bone graft is not harvested until the scaphoid is exposed and the defect size is determined.
Attention is then directed to the scaphoid. The proximal portion of the scaphoid is best approached between the second and third compartment tendons. The midscaphoid and distal scaphoid is approached between the first compartment tendons and the third compartment tendon (the anatomical snuffbox). The 1,2 ICSRA must be protected during the mobilization of the extensor tendons to expose the dorsal capsule. A capsulotomy is made overlying the scaphoid. The capsulotomy can be made transversely as a ligament-sparing incision or longitudinally. It may be necessary to use a T-shaped incision to provide adequate exposure of the nonunion site.
The nonunion is opened with a small osteotome or Freer elevator. Microcurettes are used to remove all fibrotic tissue and necrotic bone until punctate bleeding is seen. The absence of punctate bleeding is indicative of hypovascularity. We prefer to use curettes and sharp osteotomes in preparing the defect site rather than a burr because the heat generated from a high-speed burr can cause local bone necrosis.
When there is an avascular proximal, the necrotic bone should be removed down to the subchondral bone supporting the articular surface. Foreshortening of the scaphoid is not a common problem with proximal pole nonunions, which are typically treated with an onlay graft. A defect size of at least 7 mm × 7 mm should be created at the nonunion site to allow adequate debridement of the nonunion site as well as placement of an adequately sized vascular graft. If more bone needs to be removed, this should be done from the distal pole fragment. Two K-wires are prepositioned prior to placement of the graft. The fixation for a proximal pole fracture differs from that for a midwaist fracture. The entry point for the K-wires is just distal to the radial styloid and more dorsal than those typically used to stabilize mid-waist fractures. The K-wires are angled such that they can be advanced through the proximal pole and into the lunate ( Fig. 27.4 ). Once the K-wire position has been established in multiple views under fluoroscopy, the K-wires are retracted into the distal pole prior to graft placement. If additional stability is needed, a supplemental K-wire can be placed from the radius into the lunate.
For midwaist fractures, fibrotic tissue, necrotic bone, and the dorsal osteophyte if present should be removed. A small sagittal saw (with a 5 mm blade) can be used on low speed to help prepare the defect site. In cases of long-standing nonunion, if there is synovial proliferation present, this should be sharply removed. Spurring (beaking) of the radial styloid should also be removed when present.
Midwaist fractures are frequently associated with scaphoid collapse. The normal scaphoid length is best determined from preoperative comparison films with the contralateral wrist. It may not always be possible to completely restore the anatomical length. In particular, when approaching a midwaist scaphoid nonunion from the dorsal side, it can be difficult to correct the volar collapse of the scaphoid. A useful technique is to volar flex the wrist until the lunate is corrected to a neutral alignment with respect to the radius. A 0.045-in. K-wire is placed from the radius into the corrected lunate ( Fig. 27.5 ). The wrist is then brought into extension. Provided that the scapholunate ligament is intact, the proximal pole will remain in alignment with the lunate, and the distal pole of the scaphoid will be reduced close to anatomical length. A second 0.045-in. 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 ( Fig. 27.5 ). Now the defect size can be determined.
For scaphoid waist nonunions the K-wires are placed from the distal pole into the proximal pole, with the skin entry point just distal to the volar tubercle of the scaphoid. The first K-wire is placed more distal and ulnar. The second K-wire is placed slightly more proximal and radial. Parallel or convergent pin placement is acceptable ( Fig. 27.6 ). The pin position is checked in multiple planes under fluoroscopy. If the scaphoid reduction and pin position are acceptable, then harvesting of the vascularized bone graft may proceed.
The necessary graft size is marked on the distal radius and centered over the 1,2 ICSRA pedicle, with the center of the graft ∼1.5 cm proximal to the radioscaphoid joint. The marking of the donor site should be at least 2 mm oversized relative to the defect size. The 1,2 ICSRA pedicle is ligated at the proximal edge of the planned graft using an 8–0 or 9–0 suture. The distal portion of the pedicle (distal to the distal edge of the graft) is mobilized subperiosteally off of the dorsal surface of the radius along with a cuff of retinaculum. The periosteum is sharply incised around the planned graft, and a 0.035-in. or 0.045-in. sharp-tipped K-wire is used circumferentially around the donor site to perforate the cortical bone. When perforating the cortex on the distal edge of the graft, the pedicle must be protected. Only one or two drill holes should be made on either side of the pedicle to facilitate breakage of the cortex ( Fig. 27.7A ). A small, sharp, straight osteotome is then used on the radial, ulnar, and proximal edges of the graft to a depth of no more than 8 mm. The distal osteotomy should be done in two stages, moving the pedicle radial and ulnarward to protect it from injury. A curved osteotome is then placed at the proximal osteotomy site and used to gently elevate the graft from the radial metaphysis. The pedicle with its periosteal and retinacular cuffis completely separated from the radius and joint capsule, allowing the bone graft to rotate on this mobilized pedicle ( Fig. 27.7B ).
The graft is then resized to fit the area of defect within the scaphoid. We ideally try to achieve a good press-fit within the area of the defect. The graft is then removed from the scaphoid defect and the tourniquet is released. It may take up to 5 minutes to identify bleeding from the edges of the graft. Irrigation with warm saline can be useful to confirm graft vascularity. Once the graft has been allowed to perfuse for around 10 minutes, the graft is inset into the scaphoid defect. The previously placed K-wires can be advanced through the graft into the proximal pole or lunate as described earlier. Correction of volar collapse (humpback deformity) is better achieved by rotation of the graft such that the cortical bone is rotated into a volar position. Careful attention is needed to prevent twisting of the vascular pedicle. A limited radial styloidectomy, even in the absence of significant beaking of the radial styloid, can facilitate exposure, decrease tension on the vascular pedicle, and prevent radiocarpal impingement. When there is a large defect that cannot be adequately filled by the vascularized graft, supplemental bone grafting from the iliac crest may be necessary to fill the remainder of the defect. This is particularly important for nonunions that have significant intraosseous cyst formation or significant areas of avascular bone that have been removed from both the proximal and the distal fragments of the scaphoid. We prefer to use iliac crest bone graft rather than harvesting additional metaphyseal bone from the radius, due to the better osteogenic potential of the iliac crest bone. The cancellous bone graft should be morcellized into 1 mm pieces and tightly packed into the cavity of the defect, filling any space between the intact scaphoid and the vascularized bone graft.
Screw fixation can be used if following debridement of all necrotic bone there remains more than a cortical shell for obtaining screw purchase in the bone. Also, screw fixation can fragment the vascularized bone graft and should be used only when dense metaphyseal bone is obtained from the harvested graft site. It is important to make sure that there is adequate capture of the proximal and distal fragments as well as the graft to assure stable fixation and reduce risk of graft extrusion. Several studies indicated a higher union rate with screw fixation.5 , 7 , 8
The capsule is then closed as much as possible without any compression or tension on the pedicle. The radial bone donor site can be left alone or can be packed with Gelfoam or cadaveric cancellous bone allograft. Skin and subcutaneous tissue layers can be closed per surgeon preference.
The patient is immobilized in a sugartong thumb spica splint until the first follow-up visit. After this, the patient is placed in an above-elbow thumb spica splint for an additional 4 weeks. A short-arm thumb spica cast is then applied until there is fracture healing. Cast changes should be performed every 2 to 3 weeks to prevent cast loosening and pin irritation.
If a radiolunate pin has been used, this is removed between 2 and 4 weeks. Scaphocapitate pins (if used) are removed between 4 and 6 weeks. All other K-wires are left in place until fracture union. Earlier removal is indicated if the pins become loose or infected.
Fracture healing is assessed through serial radiographic examination for bridging trabeculae crossing the proximal and distal graft sites. Cyst formation at the graft site or evidence of implant loosening suggests treatment failure. CT scan can be used after 3 to 4 months for definitive fracture evaluation.