THE USE OF STRUCTURAL ALLOGRAFT FOR SURGICAL PROCEDURES OF THE FOOT AND ANKLE
January 1st, 2003
Myerson MS, Neufeld, SK, Uribe, J
ABSTRACT
Background: The purpose of this retrospective study was to review the results of using structural fresh frozen femoral head allograft in foot and ankle procedures. The indications for the use of structural graft were to restore more normal dimensions of the foot and ankle following prior surgery or trauma and for the management of arthritis or deformity where conventional cancellous graft would not be sufficient. For each patient, structural iliac crest autograft was presented as an alternative treatment.
Methods: Between January 1995 and December 1998, 75 foot and ankle surgeries were performed using structural allograft in 73 patients (32 male and 41 female patients) whose average age was 46 years (range, 9 to 82 years). The bone graft was used in conjunction with arthrodesis of the subtalar joint (twenty eight procedures), hallux metatarsophalangeal (eight procedures), calcaneocuboid (six procedures), tibiocalcaneal (six procedures), ankle (six procedures), and tarsometatarsal joints (three procedures), and with osteotomy of the calcaneus (eleven procedures), fibula (four procedures) and medial cuneiform (three procedures). Risk factors were identified preoperatively that could adversely affect the outcome of surgery, including diabetes and neuropathy (seven cases), smoking (fourteen cases), avascular necrosis of bone (eight cases), and multiple prior surgeries (56 procedures in 35 patients). Each surgery was performed in a standardized manner determined by the deformity presented, and rigid internal fixation was used in all extremities. Although it was not possible to measure the volume of each graft, the mean structural dimension (height or length) of the graft was 1.85 centimeters (range, 1.2 to 4.5 centimeters).
Results: Healing was determined by the absence of swelling and warmth and by the presence of trabeculation across the arthrodesis or osteotomy on both sides of the allograft. Healing occurred at a mean of 4.0 months (range, 2 to 10 months) in 92 % (69 of 75) of the procedures performed. Once the graft was integrated, there was no evidence of graft resorption or subsidence at a mean of 3.5 years following surgery (range, 2.5 to 5 years). There was a 12 % incidence of superficial wound complications (nine of seventy-three patients) including dehiscence and infection, and two patients (2.7 %) developed a deep infection.
Conclusions: Structural allograft is appropriate for reconstructive procedures of the foot and ankle and may be used successfully in patients with risk factors for bone healing with a relatively low complication rate.
INTRODUCTION
Bone is the second most frequently transplanted tissue, with more than 200,000 procedures performed in the United States annually27. Bone graft is used as a framework to provide stability and to augment healing in multiple settings including nonunion or delayed union, filling of osseous defects or cavities, and arthrodesis. Bone grafts can be classified according to their origin: autograft, allograft, xenograft, and bone graft substitutes and can be cortical, cancellous, or corticocancellous, each of which has advantages and disadvantages. Although cancellous grafts do not withstand heavy mechanical stresses, revascularization occurs more predictably than with solid or cortical bone grafts23. Structural grafts are therefore used mostly where greater mechanical stress is present because the cortical component of the graft facilitates support as well as rigid fixation. Traditionally, corticocancellous bone grafts have been harvested from the iliac crest31,32, and although defects of the foot or ankle may be spanned in this way, numerous potential complications may occur with this type of graft 3,5,19.
Many studies suggest similar results when substituting allograft for autograft 18,31-33. Its use in spinal arthrodesis and in the treatment of benign and malignant bone tumors, wrist arthrodesis, and large defects in fractures is well documented 2,10,16,20,30. There are limited reports on the use of these grafts in foot and ankle surgery 12,18,33. The purpose of this study was therefore to evaluate the suitability of structural allograft for these foot and ankle procedures.
MATERIALS AND METHODS
The study population consisted of 73 patients who were operated on between January 1995 and December 1998. All patients were eligible for inclusion in this study if their surgery was performed with a structural allograft. Patients who had been treated with structural allograft prior to 1995 and who were the subject of a prior study were excluded from this investigation.17 11,15,42 We retrospectively reviewed the records of these patients who underwent 75 foot and ankle surgeries using structural fresh frozen femoral head allograft. There were 41 female patients and 32 male patients with an average age of 46 years (range, 9 to 82 years). The indications for the use of a structural graft were to restore more normal dimensions of the foot and ankle following prior surgery or trauma and for the management of arthritis or deformity where conventional cancellous graft would not be sufficient. Structural graft was also indicated where we wanted to avoid the shortening that is associated with the use of cancellous graft even if union could be obtained24. The alternative choices for structural bone graft were presented to each patient preoperatively, and appropriate informed consent was obtained after a full discussion regarding the risks and benefits of allograft versus autograft.
A subtalar arthrodesis was performed in the 27 patients for salvage following failed treatment of calcaneus fractures in 28 feet. (Table 1) There were 13 patients with flatfoot deformity, for whom lengthening of the lateral foot was performed either with calcaneus osteotomy (eleven feet in ten patients) which was combined with an osteotomy of the medial cuneiform (3 feet in 3 patients), or a calcaneocuboid arthrodesis (3 feet in 3 patients).(Fig 1) The remaining three patients who were treated with calcaneocuboid arthrodesis had sustained trauma with crushing of the cuboid and distal calcaneus. Eight patients were treated with arthrodesis of the hallux MTP joint for failure of prior correction of hallux valgus with marked shortening or avascular necrosis of the first metatarsal. (Fig 2) The six ankle arthrodeses included four patients who had sustained an ankle fracture, followed by collapse of the joint with either avascular necrosis or severe bone loss. The remaining two patients who were treated with ankle arthrodesis had diabetic neuroarthropathy. (Fig 3, Tibiocalcaneal arthrodesis was performed in five patients with diabetic neuroarthropathy, and for one patient with rheumatoid arthritis and avascular necrosis of the talus. Fibula osteotomy was performed in four patients for restoration of length following malunion after ankle fracture. Tarsometatarsal arthrodesis was performed in two patients following trauma and in one patient with deformity after attempted correction of hallux valgus. The height, weight, activity level, occupation, history of systemic illness, prior surgical procedures, and smoking status were determined for each patient.
The choice of anesthesia was determined by the magnitude of the surgery and patient comfort. Of the 75 procedures, 58 were performed with the use of intravenous sedation and a regional ankle or popliteal nerve block, and the remainder was done under general anesthesia. Preoperatively, each patient received a prophylactic dose of cephalosporin antibiotics intravenously. No tourniquet was used in 56 procedures; a thigh tourniquet was used for 14, and an Esmarch bandage was used for five procedures.
All allograft was taken as a corticocancellous block from fresh frozen cadaveric femoral head and neck specimens and thawed in normal saline for 10 minutes before use. The femoral head was cut according to the location of the arthrodesis or osteotomy . If possible, the thicker cortical calcar region of the femoral neck was used, and the size and shape of the graft was contoured using a reciprocating saw (Fig. 4 The site of the arthrodesis or osteotomy also determined the shape of the graft. For example, the graft for an arthrodesis of the hallux MTP joint was obtained from the margin of the neck of the femoral head, and appropriate dorsiflexion of the hallux was maintained by the contour of the harvested graft. (Fig 5, 6). The size of the structural bone graft was determined following resection and debridement of all sclerotic and avascular bone to bleeding margins. A lamina spreader was inserted into the defect and the spreader adjusted until the desired correction was noted fluoroscopically. A ruler or piece of foil from a suture pack was used to measure the exact size of the graft needed, although minor adjustments to the size of the graft were often made following insertion. Once the desired correction was obtained, the graft was impacted into place and the smooth lamina spreader was withdrawn from the osteotomy or arthrodesis site. A variety of internal fixation devices were used determined by the size and shape of the bone graft, the adjacent bone structure, and the requirements for obtaining stability in each case. The size of the bone graft used (height or length) averaged 1.85 centimeters (range, 1.2 to 4.5 centimeters).
The postoperative course was standardized according to the procedure performed. The limb was immobilized postoperatively in a posterior plaster splint, and sutures were removed once wound healing had occurred, between 10 and 20 days. Patients who underwent surgery of the midfoot and forefoot were then immobilized in a below-the-knee cast with weightbearing of 20 kilograms for 6 weeks, followed by gradual progression of their weightbearing in a removable boot or cast until union was noted. Where hindfoot or ankle surgery was performed, bearing of weight was not permitted until 8 weeks. Patients with neuropathy did not begin bearing of weight for 12 weeks, followed by the use of a below-the-knee cast bearing weight for an additional 12 weeks, and then a weightbearing boot until arthrodesis was noted by radiograph, as well as the absence of warmth and swelling of the foot.
RESULTS
Arthrodesis
Sixty-nine of 75 (92%) of the foot and ankle procedures healed successfully (Table II). Nonunion occurred with arthrodesis of the calcaneocuboid (2 procedures), subtalar (1 procedure), hallux MTP (1 procedure), and tarsometatarsal joints (1 procedure) and with a fibula osteotomy (1 procedure). Four of these six nonunions were revised successfully. One of the two patients with a nonunion after calcaneocuboid arthrodesis was minimally symptomatic, no resorption or collapse of the graft occurred, and no further surgery was performed. For the second patient with a calcaneocuboid nonunion, fusion occurred between the graft and the calcaneus, and revision of the arthrodesis was performed successfully with cancellous autograft. The subtalar nonunion occurred in a patient who smoked two packs of cigarettes per day, had two previous surgeries on the hindfoot, and was noted to have hard dense sclerotic and avascular bone the time of the arthrodesis (Table III). Partial collapse with resorption of the graft occurred, and revision was attempted with cancellous autograft unsuccessfully. Ultimately a triple arthrodesis was successfully accomplished with cancellous autograft and a direct current internal bone stimulator (EBI Medical Systems, Parsipanny NJ). The patient with the hallux MTP joint nonunion had undergone three prior surgeries and smoked 10 cigarettes a day. The nonunion occurred in the distal host-graft interface with maintenance of the length of the hallux, and revision arthrodesis was performed with cancellous autograft harvested from the ipsilateral calcaneus6. The failure of the tarsometatarsal arthrodesis occurred at the proximal host-graft interface and was successfully revised with cancellous autograft harvested from the calcaneus. This patient had two previous surgeries on the foot and smoked one pack of cigarettes a day. The patient with nonunion of the fibular osteotomy developed a deep infection 1 month postoperatively, and was treated with debridement and removal of the allograft. This patient was a smoker (two packs of cigarettes daily) who had one prior surgery. Once the infection was successfully treated, the patient did not wish to have any further treatment.
Time to Union
The average time to union for the study group was 4 months (range, 2 to 10 months) (Table II). Union of the tibiocalcaneal, ankle, and hallux MTP joints took longer (average, 5.6 months, range, 3 to 10 months). Osteotomies of the calcaneus, medial cuneiform and fibula, and subtalar arthrodeses, healed relatively more quickly (average, 3 months, range 2 to 4.5 months). Healing was judged by the absence of swelling and pain, and the presence of trabeculation across the arthrodesis or osteotomy on both sides of the graft, as determined by radiograph. Once the graft was integrated, there was no evidence of graft resorption or collapse at a mean of 3.5 years following surgery (range, 2 to 5 years).
Delayed Union
Union delayed to over 4 months from the arthrodesis was present in 22 of 75 procedures (Table II). This figure does not include four of the six patients with a nonunion, where the graft was noted to have resorbed either partially or completely prior to 4 months. Resorption occurred in one patient each after a tarsometatarsal, subtalar, and calcaneocuboid arthrodesis and after a fibula osteotomy. The patient with the hallux MTP fusion and the patient with the calcaneocuboid arthrodesis were included in the 22 patients with delayed union above. For each of the patients with delayed union, immobilization was continued and an external bone stimulator (EBI Medical Systems, Inc., Parsippany, NJ) was applied for 16 of the 22 patients at a mean of 4.5 months (range, 4 to 5.5 months). Two of these patients (hallux MTP and calcaneocuboid arthrodesis) did not demonstrate any further bone healing despite immobilization and the use of an external bone stimulator, there was partial graft resorption which occurred at 5 and 6 months, and a nonunion was noted. Once union had occurred, there was no evidence of graft resorption or subsidence at a mean of 3.5 years following surgery (range, 2.5 to 5 years). No fracture of the graft was noted during the study period for these patients.
Infection
Seven patients (seven procedures) developed wound problems after subtalar arthrodesis, including one deep infection, four superficial infections, and two incidences of minor wound dehiscence. There were fewer complications with the other procedures, where there was one deep infection (with fibula osteotomy), one superficial infection (with ankle arthrodesis), and one uninfected wound dehiscence (with tibiocalcaneal arthrodesis). Two patients developed a deep infection (Table II). The first was in a 61-year-old smoker who had a fibular osteotomy for a prior malunion after an open reduction internal fixation of her ankle fracture. One month following surgery, a wound dehiscence occurred with a deep infection evident. Staphylococcus aureus was cultured, and the patient was treated with debridement of the allograft, and 6 weeks of intravenous cephalosporin antibiotics. The second deep infection occurred in a patient who had a subtalar arthrodesis at 2 weeks following surgery. There was a wound dehiscence, which was treated with irrigation and debridement of devitalized deep tissue and coverage with a local rotation abductor digiti minimi muscle flap. Staphylococcus aureus was initially cultured, and this patient was treated with 6 weeks of intravenous cephalosporin antibiotics. Successful union occurred at 4 months following the arthrodesis procedure.
Risk Factors
Smoking (Table III), diabetes, avascular necrosis, and prior surgery (Table I) were the main risk factors in the current study21,40. Of the seven patients with diabetes, two had a superficial infection, and all seven had problems with bony consolidation (either a delayed or nonunion). Avascular necrosis was a risk factor for patients undergoing ankle, tibiocalcaneal, and subtalar arthrodeses25. There were seventeen extremities with avascular necrosis of the distal tibia, the talus, the dorsal surface of the posterior calcaneus, or the first metatarsal, present in patients undergoing ankle (3), tibiocalcaneal (6), subtalar (5) and hallux MP (3) arthrodeses. Of these patients, one had a nonunion of a subtalar arthrodesis and an additional 11 had delayed union of a subtalar (3), ankle (3), and tibiocalcaneal (5) arthrodesis.
There were 35 patients with a history of prior foot and ankle procedures (average, 2.4 procedures, range, 1 to 7 procedures). Of the six patients in this study who developed a nonunion, five had undergone multiple procedures (average, 2.5 procedures per patient, range, 1 to 7 procedures). Of the seven patients with wound problems in this study, three patients undergoing subtalar arthrodesis had multiple surgeries with an average of 3.6 procedures (range, 2 to 7 procedures).
DISCUSSION
The use of allograft bone dates back to the early 1900s13,29. The first long-term follow-up evaluation showed that these grafts were partially replaced and incorporated by the host and that joints could be preserved for as long as 20 years after surgery37. Allografts provide the form and matrix of bone tissue, but no viable cells are transplanted. In addition, bone allografts are more slowly incorporated into the host and induce an immune response, which may delay the osteoinductive phase of bone graft incorporation22,34. Although structural autograft is widely used, it is not without problems. There may not be a sufficient volume of bone to span a structural defect. More importantly, there is a substantial risk of morbidity at the donor iliac crest site (fracture, hemorrhage, pain, nerve or arterial injury, and cosmetic deformity)19,46. One study32 noted that autograft, in comparison with demineralized bone matrix allograft, resulted in a longer operative time, substantially greater blood loss, and overall higher cost to patients. Flemister et al.18 showed a statistically shorter hospital stay in patients undergoing a subtalar arthrodesis who did not receive an autogenous bone graft.
Concerns with Allograft Use
Studies have shown that freezing of cortical grafts may improve their incorporation22. Overt graft rejection is extremely rare, and clinical studies have not shown adverse effects secondary to the immunogenicity of allografts8,9,28. Allograft is weakest during revascularization, and the mechanical property of the bone graft may be affected by preservation techniques. For example, freeze-dried allograft is weaker in its torsional and bending strength when compared with frozen allograft, whereas the compressive strengths of these grafts are equivalent. Loss of hoop stress and cracking of the allograft has been observed after surface drying9,31,38,39. These factors, however, may not apply to the small size of the grafts used in this study and no fracture of a graft was noted during the period of study these patients were studied.
Another concern with the use of structural allografts is the possible transmission of infection. Although extremely rare, transmission of disease is possible. An audit from a bone bank in Leicester, England26, showed contamination of femoral head grafts from both live and cadaver donors, and one clinical infection was documented in the nine large allografts implanted36. In another review of 303 procedures, there was one case in which a contaminated allograft was responsible for a clinical infection44. A few case reports note viral transmission through allografts, with the risks apparently related to the type of allograft used14. For example, the risk of viral transmission through processed, freeze-dried allograft chips is practically zero, whereas the risk of transmission through transplantation of a frozen, unprocessed femoral head is similar to the risk of transmission of a disease through transfusion of a unit of blood43. The deep infection that occurred in two patients in our study appeared unrelated to the use of the femoral head allograft in that there was no infection in any other bone tissue processed from the donor sources used for these two cases. The incidence of wound problems and infections with subtalar fusion was high. Nonetheless, the 25 % incidence of wound problems in these patients (seven of 28) was likely a result of the inherent risk associated with distraction of poor-quality skin in patients who were smokers and who had been treated with multiple prior surgeries.
For the surgical procedures in this study, structural and rather than cancellous graft was felt necessary to obtain arthrodesis and maintain length. Although structurally strong, allograft does not provide the osteoinductive elements to an arthrodesis site that are provided by autograft. Although not relevant to our study where structural allograft only was used, the use of cancellous allograft versus autograft has been compared in hindfoot arthrodeses31, demonstrating a longer healing time and greater occurrence of pseudoarthrosis in patients who received allograft. These authors found that one of 17 patients receiving autograft went on to nonunion, whereas three of 24 patients with allograft had a nonunion. In another study of cancellous graft procedures by Thoran et al.41, a comparison was made between the uses of autogenous graft versus allograft dowels in talonavicular joint arthrodeses. In that study, all four allogenic dowels developed fibrous nonunions. In another series of 86 subtalar arthrodeses after calcaneal fractures18, there was a union rate of 96 %, and all of the seven cases for which cancellous allograft was used went on to successful union.
The use of structural allograft is supported in the spine, hand, and tumor surgery literature, concluding that there is no significant difference in the incidence of nonunion between patients treated with allograft and autograft4,10. Zasacki47 reviewed the use of allogenic bone in 36 primary joint arthrodeses. Ten cases involved interpositional allograft in a subtalar joint arthrodesis, and three of those did not fuse. Myerson et al.35 reported on the results of arthrodesis of the hallux MTP joint using structural bone graft for restoration of length. In their study of 24 patients, five nonunions occurred, of which four were treated with iliac crest autograft and one with structural allograft. Brodsky et al.7 reported on interposition iliac crest autograft for salvage of the hallux MTP joint in 12 patients with arthrodesis in 11 of them. The results of interposition of structural iliac crest autograft for distraction subtalar arthrodesis has been reported by Carr et al.11 (arthrodesis in 13 of 16 patients), by Amendola and Lammens1 (arthrodesis in all of 15 patients), Easley et al.17 (arthrodesis in all of 24), and Trnka et al.45 (arthrodesis in 32 of 37).
Although there was a limited number of nonunions, there was a high incidence of delayed union in the current study. It is not clear whether these delayed unions were the result of a relatively high-risk patient population or a factor inherent to these procedures, such as use of structural allograft. These are complex procedures, and, as noted previously, the literature does not report any substantially greater success with structural autograft harvested from the iliac crest.
CONCLUSION
The use of structural allograft to correct deformity and fill in bone voids is an attractive alternative in reconstructive surgery of the foot and ankle, and avoids the potential for complications associated with harvesting autograft, reduces operative time and cost and can fill large voids that cannot be filled with autograft. The techniques should be used cautiously in high-risk patients such as smokers and in patients with multiple prior surgeries. The current results suggest that structural allograft can be used successfully in surgical reconstruction of the foot and ankle.
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