AVASCULAR NECROSIS OF THE TALUS: THE EXTENSOR DIGITORUM BREVIS MUSCLE PEDICLE BONE GRAFT, A NEW VASCULARIZED BONE GRAFT
January 1st, 2003
Steven K. Neufeld, MD; Mark S. Myerson, MD; Lew C. Schon, MD;
ABSTRACT
Treatment for symptomatic early-stage avascular necrosis of the talus is controversial. This is a two-part study in which a unique vascularized pedicle bone graft is described with short-term clinical results. A consistent vascularized bone graft source from the extensor digitorum brevis muscle and its bony origin is defined, with the use of standard latex injection techniques and vascular filling of 0.1-mm-diameter vessels in 16 fresh-frozen cadaveric dissections. This vascularized bone graft source has been used with good initial results in four patients with symptomatic avascular necrosis of the talus. This new vascularized pedicle bone graft appears to offer the advantages of providing bone stock, stability, and vascularity so as to enhance bone healing.
INTRODUCTION
Avascular necrosis (AVN) of the talar body has been considered to be the most devastating long-term sequela after talar neck fractures.8,15,27,36,38,54,55 In addition, talar AVN has been reported to occur in patients sustaining trauma to their ankle,5,18,29,62 has been associated with alcoholism,24,65 mucolipidosis, 1 systemic lupus erythematosis, pancreatitis,1,14,40,42,46,53,63 steroid use,1,14,40,46,63 hyperlipidemia,23 sickle cell disease,34 hyperuricemia,21,42,43,53 and has even been reported after strenuous physical activity.62
Methods of treatment for symptomatic avascular necrosis of the talus are restricted to salvage of arthritis and collapse. Nonoperative treatments include long-term use of a protective brace without bearing of weight. Autogenous bone grafting, replacement with an implant,46 and arthrodesis37,42 have been used to treat advanced necrosis. However, the functional results of these treatments are unpredictable. Another option is to promote revascularization of the talus in order to prevent collapse and advancement of the disease. Transferring vascularized pedicle bone for avascular nonunion of the scaphoid66 and avascular humeral head7,58 and revascularization of a talus using a free vascularized bone graft have been reported.32
The extensor digitorum brevis muscle is a small, discrete muscle with a consistent vascular pedicle that allows transplantation as well as rotation as an island muscle flap. We report on using this pedicled vascularized bone graft from the extensor digitorum brevis muscle and its calcaneal origin for use in cases of talar body avascular necrosis.
ANATOMIC STUDY
Eight fresh-frozen cadaveric feet were dissected from above the ankle. An incision was made approximately 2 cm anterior to the tip of the lateral malleolus, curving the tip toward the base of the third metatarsal. The calcaneal cuboid joint along with the overlying origin of the extensor digitorum brevis muscle was identified. A ¼-inch osteotome was used to elevate the dorsal 3 mm of the anterior calcaneal tuberosity along with its attached extensor digitorum brevis muscle attachment. Care was taken to minimize the disruption of the calcaneocuboid articulation.
The anterior tibial artery was identified at the lower margin of the inferior extensor retinaculum. The lateral tarsal artery passing deep to the extensor digitorum muscle belly was also identified. The anterior tibial artery was cannulated with a 14-french angiocath just proximal to the extensor retinaculum. Batson’s compound (Polysciences, Inc. Warrington, PA),46 a partially polymerized monomer that hardens into a plaster cast, was then injected with manual pressure until the digit pulp vessels demonstrated complete filling by tissue coloration and turgor.
The specimens were then refrigerated for 24 hours to allow the curing of the Batson’s compound. To facilitate soft tissue digestion, the skin was dissected from each specimen along with bone and soft tissue surrounding the extensor digitorum muscle. The specimens were then placed in 10% formalin for 24 hours followed by a decalcifying agent for 8 hours. Thin slices of the extensor digitorum muscle-calcaneal bone interface were made, placed on a glass slide, and examined for the presence of vessels going directly into the bone or periosteum. Photomicrographs were taken to demonstrate the vascularity of the bone plug (Fig. 1 and 2).
SURGICAL PROCEDURE
The surgical procedure on the four patients included an incision made approximately 2 cm anterior to the tip of the lateral malleolus, curving the tip toward the base of the third metatarsal. Deep dissection was carried down through the extensor retinaculum and lateral to the extensor digitorum brevis muscle. Carefully avoiding the peroneal tendons, we identified the calcaneal cuboid joint along with the overlying extensor digitorum brevis muscle. As described above, an osteotomy of the anterior tubercle of the calcaneus was performed, preserving the extensor digitorum brevis muscle attachment. If the muscle was short, it was lengthened by subperiosteal stripping distally and cutting the epimysium (Fig. 3).
A bore hole was made in the lateral half of the talar neck extending into the talar body. Subsequently, thorough curettage of the subchondral necrotic bone through the tunnel was done. The vascularized bone graft was then contoured using a ronguer to fit snugly into the talar body. The bone plug along with the extensor digitorum muscle was introduced through the tunnel into the talar body and was sunk far enough into the talus to allow full ankle dorsiflexion and prevent impingement (Fig. 4). A tight interference fit was established obviating the need for internal fixation.
CLINICAL EXPERIENCE
We have performed four extensor digitorum brevis muscle pedicle bone graft transfers for symptomatic avascular necrosis of the talus. In all four patients, the indications for the vascularized bone graft were long-standing symptomatic avascular necrosis of the talus unresponsive to a minimum of 3 months of conservative treatment that included activity modification, bracing and immobilization, and analgesics. All patients had early radiographic talar AVN verified with magnetic resonance imaging (MRI) with no subchondral collapse.
The patients included three men and one woman. The diagnoses leading to avascular necrosis were long-term steroid use for Crohn’s disease in one male, mild ankle trauma in one male, and idiopathic in the woman and in the other male.
The diagnosis of osteonecrosis was made by clinical history and radiographic evaluation and confirmed by biopsy in all cases. Magnetic resonance imaging also confirmed the diagnosis in all cases and was utilized to attempt to localize the extent of the lesion. All patients had either radiological stage I (normal radiologic appearance) or II (cystic and/or osteosclerotic lesions, normal contour of talus and no subchondral fracture) avascular necrosis according the modified Ficat and Arlet scale.51 All four patients had severe pain on weightbearing, which affected their activities of daily living.
The operation was performed as described above. Ankle arthroscopy was performed on one patient to verify that the avascular lesion did not compromise the articular surface. Ankle arthroscopy was not part of the standard protocol in each patient. Intraoperative fluoroscopy verified entrance into the avascular portions of the talar body and correct placement of the vascularized pedicle bone graft. The grafts were introduced into the talar neck/body tunnel so as not to compress the vascular pedicle. The extensor digitorum muscle was secured to the recipient via soft tissue suture attachment. All grafts were noted to be stable with good bony abutment within the host talus.
The average age at time of surgery was 38.5 years (range, 29 - 46 years). The mean follow-up time was 14 months (range, 12.5 - 17 months). Donor site morbidity included a mild skin slough in two patients who were treated successfully with local wound care. A third patient had persistent drainage from an ankle arthroscopy portal site that cleared up with 10 days of antibiotics, and local wound care.
All four patients were followed radiographically for signs of graft incorporation. Standard weightbearing anteroposterior and lateral radiographs as well as anteroposterior talar radiographs were reviewed to assess the interval until fusion. Incorporation was defined as 50% or greater trabeculation bridging across the bone graft. Delayed incorporation was defined as lack of radiographic trabeculation 6 months after surgery.
An MRI was obtained on the first three patients at 3 months postoperatively. An MRI could not be attained on the fourth patient. These early MRIs did not show further avascular changes and suggested early graft incorporation (Fig. 5a, b).
Pain was relieved in all four patients. At 3 months postoperatively, one patient, a former semi-professional tennis player, was back to full activities with only mild complaints of stiffness in the morning (Fig. 6a-d).
It is too early to definitively assess the clinical and radiologic results of these patients. However, at the latest follow-up, they have no clinical or roentgenographic progression of the avascular necrosis.
DISCUSSION
In cases of symptomatic talar avascular necrosis, a combination of immobilization and long-term nonweightbearing on the involved side in order to prevent collapse is recommended.9,45 If conservative treatment fails, the only options are ankle joint arthrodesis, tibiocalcaneal fusion,10,11,18,35,37,59 conventional bone grafting or prosthetic replacement.6,46,49 Hindfoot fusions in patients with avascular necrosis of the talus are technically demanding, however, and require longer operative times to achieve bleeding bony surfaces essential for successful fusion.63 In addition, these patients require a longer time to fusion than those without talar AVN.5,63
Recently, several papers described techniques to promote vascularization of the necrotic talus. Mont et al. reported on 11 patients treated with core decompression for symptomatic avascular necrosis of the talus. At a mean follow-up of 7 years, 82% had excellent or good outcomes. Three ankles required a tibiotalar fusion after failed core decompression44 Doi and Sakai described a technique of using a vascularized corticoperiosteal graft from the supracondylar area of the femur to revascularize three patients with posttraumatic avascular necrosis of the body of the talus. At an average of 22.6 months, the anastomosed vessels were patent and verified by angiogram or skin flap survival. In addition, two of three patients achieved bony union by 6 months after surgery with a normal appearing talar MRI. The third patient, who preoperatively had collapse of the talus with osteoarthritic changes of the ankle, had further collapse postoperatively that necessitated arthrodesis. The authors concluded that vascularized bone grafting cannot replace chondral lesions or collapsed chondral bone but can revascularize the subchondral bone.33 Hussl et al. published one case of an avascular talus successfully revascularized with an iliac crest corticocancellous bone graft containing its vascular pedicle; however, their long-term results have not been reported.32 In an earlier study, that group showed the ability to revascularize a tissue segment consisting of cartilage, subcutaneous tissue, and skin over a transferred muscular-vascular pedicle.31 When a vascular bundle was transplanted into an isolated or necrotic bone, active proliferation of blood vessels and new bone formation occurred.30
Vascularized bone transplantation procedures have been performed for many years by orthopaedic surgeons and offer distinct advantages in the treatment of bone defects and avascular bone as compared with nonvascularized bone grafts. Sliding of bone with attached soft tissue is a form of vascularized bone grafting that has been used to obtain ankle fusions and to address nonunions of the femoral neck and scaphoid.41,50,56 This type of bone grafting provides structural support immediately and provides additional blood flow and living cells to the area with good osteoinductive qualities. Healing of the vascularized bone occurs more rapidly, and therefore allows earlier return of function, including weightbearing and motion.57,64
Furthermore, early studies of muscle-pedicle bone grafts showed that the bone attached to the muscle pedicle remained alive after being transferred as long as the viability of the muscle pedicle was maintained. The osteocytes survived through collateral vascular supply between the pedicle and bone.16,25 Later studies demonstrated that bone grafts with a vascular pedicle not only survive better, but also have superior osteogenic potential and unite more rapidly than free bone graft.19,26,61 Further studies demonstrated new bone formation from the flap’s active periosteum and superior healing as compared with free grafts. It has been proposed that the vascularized bone accelerates the resorption of areas of dead bone and speeds up new bone formation by creeping substitution.4,61 The new blood supply that is brought into the defect, and the capability of the transplanted bone to undergo hypertrophy and form new bone further enhances the healing process.57
The extensor digitorum muscle flap is a well-studied and commonly used vascularized flap in orthopaedic and plastic surgery literature. As an island muscle flap, it can be rotated over the distal third of the tibia anteriorly and over either of the malleoli. It is commonly used for soft tissue coverage in the upper and lower extremity, metacarpal reconstruction, and Achilles tendon reconstruction with little morbidity to the donor site.2,3,17,22,28,39,52,60 In addition, the muscle’s soft tissue origin is commonly transferred and used as an interposition for tarsal coalitions.12,13,20 This muscle is expendable because it is a synergist with the long extensor tendons.48 The extensor digitorum brevis is invaluable in reconstructing problems in the distal third of the tibia, an area particularly difficult to cover with muscle flaps from the calf. It has a large arc of rotation, and fractures of the distal tibia or the ankle, as well as chronic infections, burns, radiation defects, and pressure ulcers, can be resurfaced using this island muscle flap.
The relevant anatomy of extensor digitorum brevis muscle has been previously described in detail.17,47 Just below the inferior extensor retinaculum, the lateral tarsal artery branches from either the anterior tibial artery or dorsalis pedis artery to enter medially and deeply to supply the undersurface of the extensor digitorum brevis muscle along with perforating branches from the peroneal artery. The muscle originates from the lateral and superior aspects of the calcaneus, the surrounding joint capsules, and the extensor retinaculum. It courses obliquely across the dorsum of the foot to insert into the lateral side of the extensor digitorum longus tendons. A medial slip, often called the extensor hallucis brevis, inserts into the base of the proximal phalanx of the great toe.3
The muscle with its attached calcaneal or cuboid origin may be elevated fairly easily by stripping subperiosteally across the dorsum of the foot. The muscle will retain its perfusion via retrograde blood flow through the lateral tarsal artery and anastomotic network.47 By adequately releasing the muscle from the dorsum of the foot and cutting the epimysium when necessary, the graft can be pivoted and inserted relatively easily into a talar body.
These qualities provide a reasonable justification for the use of the extensor digitorum brevis muscle pedicle bone graft as an osteoconductive and osteoinductive source in cases of avascular necrosis of the talus, in talus nonunions, or in limited hindfoot fusions.
CONCLUSIONS
Avascular necrosis of the talus continues to be an unsolved problem for orthopaedic surgeons. Methods of treatment for symptomatic avascular necrosis of the talus are limited, and if conservative treatment fails, options include arthrodesis or core decompression with unpredictable results. The preliminary results from this small study suggest that the extensor digitorum brevis muscle with its calcaneal bony origin can be used as a vascularized pedicle bone graft to treat avascular necrosis. It is proposed that the extensor digitorum brevis vascularized pedicle bone graft may prevent the necrotic talar body from progressive collapse by directly promoting restored vascularization and new bone formation. Therefore, this technique is especially applicable to the early stages of avascular necrosis of the talus to promote revascularization of the subchondral bone and prevent advancement of the disease. Due to the small incidence of symptomatic talar avascular necrosis, we did not attempt to carry out a randomized, controlled study of this vascularized flap compared to other methods of treatment. In addition, the follow-up in this initial study is short. Longer-term follow-up and evaluation of the viability of this procedure should provide additional useful results.
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