Clinical experience in allogeneic vascularized bone and joint allografting

The allotransplantation of vascularized femoral diaphyses and total knee joints is a novel approach in orthopedic surgery. Allogeneic femoral diaphyses were transplanted into three patients suffering from chondrosarcoma or posttraumatic defects. Total knee joints allografts were transplanted in five patients with large bone defects of the knee and loss of the extensor apparatus caused either by major trauma alone or infection after a major trauma. Bone segments and total joints were harvested from multi-organ donors, perfused with UW-solution and transplanted within cold ischemia times of 18-25 h. Patients were immunosuppressed postoperatively primarily with cyclosporine (Cyclosporin A) and azathioprine. Two allografts (1 femur, 1 knee) were lost due to infections. Seven of the eight patients are able to walk with full weight-bearing posttransplant. Two of the patients with transplanted joint allografts subsequently received total knee arthroplasty implantations. Vascularized bone and joint allotransplantation may serve as a last line of defense treatment before considering lower limb amputation.     

Experimental vascularized bone transplantations

The postoperative hypertropy of the vascularized fibula graft is of particular interest. In order to clarify the etiology of the hypertrophy, we conducted experimental projects on vascularized bone grafts using fluorochrome bone labelings, his-tomorphometry and measurement of blood flow in rats and rabbits. In the murine vascularized tibio-fibula graft for bone defects of the tibia, where mechanical stress to the graft can be expected, cross-sectional bone growth was maintained with acceleration of new bone formation and an alteration of growth direction at 3 weeks after the transplantation. In vascularized bone grafts where no mechanical stress to the graft is expected, more bone resorption was seen than bone formation. In the murine tail bone graft to a bony defect of the femur, the cancellous bone gradually disappeared, and the trabeculae took on an architecture characteristic of the femur. This process slowly transforms the graft into a femur with the morphologic features of a long bone. These results suggested that remodeling of the graft corresponding with the changes in the dynamic environment was accompanied by adequate resorption. The cross-age transplantation of vascularized tibio-fibula grafts in rats showed that the younger the donor, the faster the hypertrophy. Age is one of the important factors affecting remodeling of the vascularized bone graft. The blood flow of the grafted bone in the rabbits increased immediately after the transplantation as a reaction to surgery. Thereafter the blood flow of the graft may depend on the biological demands for new bone formation in adapting to the biomechanical environment of the recipient site. © 1995 Wiley-Liss, Inc.     

Experimental study of vascularized bone grafts: hypertrophy of the grafted bone

The mechanism underlying hypertrophy of experimentally vascularized bone grafts was studied in 15-week-old rats. The segmental ulna was grafted to the tibial defect with an external fixator. In experiment 1, 24 rats were classified into four groups to evaluate conventional (non-vascularized), cuff (periosteum-encased, non-vascularized), and vascularized bone grafts, and vascularized segmental grafts with fracture. In experiment 2, 12 rats were classified into two groups according to the presence of mechanical loading. This involved vascularized bone grafts with external fixators, and vascularized bone grafts with external fixators removed after bone union. The bone dynamics of the grafts were investigated by several methods, including roentgenographic analysis, histologic studies, and fluorochrome labeling. In experiment 1, a slight bone formation was recognized in the conventional bone graft, while irregular bone formation with creeping substitution was observed in the cuff graft. The vascularized bone graft showed significant hypertrophy; hypertrophy of the vascularized bone with fracture was greater than that without fracture. In experiment 2, markedly circumferential bone formation was observed after removal of the external fixator, while slight new bone formation was observed during the late postoperative period in bone with an external fixator. These results suggest that hypertrophy can be promoted by artificial fracture of the grafted bone, and that mechanical loading is an important factor for remodeling of grafted bone.     

Experimental study on vascularized bone allografts for reconstruction of massive bone defects

To study the healing mechanism of vascularized bone allografts under short-term as well as long-term immunosuppression with cyclosporin A, experimental vascularized intercalary bone allograft transplantation was carried out between inbred rats using the tibiofibula graft model. Bone scintigram and radiographs were used as an indicator for early detection of rejection after transplantation and bone union. In vascularized bone allografts under long-term immunosuppression with cyclosporin A, early bone union and continuous incorporation were similar to that observed in vascularized bone autograft transplantation. When administration of cyclosporin A was discontinued before completion of bone union, the graft was rejected and bone union was delayed. Apparent swelling on the operated limb associated with a decrease in bone scintigram uptake suggested the occurrence of rejection of the allograft. Vascularized bone allograft transplantation is useful for reconstruction of massive bone defects only if immunosuppressants are used and maintained at least until bone union is obtained. © 1994 Wiley-Liss, Inc.     

Experimental study of vascularized bone: quantitative analysis of bone scintigraphy and histology

The purpose of this study was the sequential evaluation of vascularized bone by quantitative analysis of bone scintigraphy with Tc-99m methylene diphosphonate (MDP). The correlation between the uptake of Tc-99m MDP and the morphologic behavior of vascularized bone was investigated, simultaneously with bone labeling, contact microradiogram (CMR), and histology of an undecalcified sample. In this experiment, 41 adult female rabbits were used. An island tibia pedicled with the popliteal vessels was used as the model of vascularized bone. The maximum uptake of Tc-99m MDP was observed at two to four postoperative weeks. When bone marrow was partially exposed, the uptake was significantly large. On the basis of this experimental study, the degree of Tc-99m MDP uptake seemed to depend primarily on the osteoblastic activity of vascularized bone. The newly-formed bone was observed mainly at periosteal sites.     

Experimental study and clinical observations on hypertrophy of vascularized bone grafts

In order to understand the mechanisms involved in the hypertrophy of vascularized bone grafts, a series of animal experiments were carried out and 32 clinical cases were studied. A defect in the tibial shaft was created in puppies and the ipsilateral fibula was transferred into the medullary cavity of the tibia with the anterior tibial artery and vein. The same procedure was performed on a control group but without vessel supply. Radiologically, in the vascularized group mild hypertrophy in the fibula was seen at 2 weeks, became marked by 4 weeks, but in no case did the thickening (hypertrophy) of the graft ever exceed the diameter of the recipient tibia. The control group did not show hypertrophy but fracture callus formed in the recipient tibia at both ends of the graft. On histological evaluation no reactive bone formation was evident in the control group but some reactive bone formation was seen in the vascularized group just beneath the periosteum. There was no change in the periosteum itself. In the clinical cases 47% of patients showed hypertrophy. Hypertrophy was noted mainly in the fibulae but rarely in other bones such as ilium or rib. The important factors were age and good vascularity of the grafted bone. During the period of study, weight-bearing was eliminated, so that the effects of mechanical force did not explain hypertrophy. We conclude from these studies that true hypertrophy is an essentially different process from reactive callus which forms normally in response to fracture healing. Vascularized bone grafts show remarkable hypertrophy of the grafted bone, but the exact mechanism is ill defined. In order to investigate the mechanisms, a series of animal experiments were carried out and clinical cases were studied. © 1994 Wiley-Liss, Inc.     

Cortical bone allografting in femoral head necrosis

Ten femoral heads (six patients) with avascular necrosis were operated on using a fibular allograft. The procedure included core decompression followed by insertion of a cortical bone graft in order to relieve mechanical stresses from the overlying subchondral bone. The presence of the supporting graft should avoid an expected collapse or prevent its worsening if already present. A freeze-dried and processed cortical bone allograft was preferred to an autograft. Weightbearing was normally and fully resumed at the second postoperative month. There were three failures within the first year, four satisfactory results, in which the hip was replaced after 4 years while there are still 3 hips that have been preserved from arthroplasty in young patients after 5 years. The technique is easy and able to substantially delay an arthroplasty in an active patient.     

Current status of allografting for bone tumors.

Over the past 20 years the Orthopaedic Oncology Unit of the Massachusetts General Hospital has performed over 660 massive cadaveric allograft transplantations, mostly for patients with bone tumors. The overall success rate for such procedures is around 80%, with most of the failures occurring in the first 3 years as a result of fracture (19%), nonunion (14%), and infection (10%). With longer follow up, late occurring osteoarthritis has been noted in approximately 17% of those patients at risk, suggesting that the articular surface begins to "wear" at 5 years. Some problems remain with the procedure, and more study of such aspects as the immune mechanism, cryopreservation of cartilage, maintaining the status and safety of the bone banking system, and improving the techniques of surgery ultimately may lead to a more uniform and predictable success rate.     

Experimental study of vascularized bone grafts in rat: Effect of mechanical loading on bone dynamics

We studied the etiology of postoperative hypertrophy of vascularized bone grafts in a murine experimental model. Syngeneic grafting of revascularized ulna to rat tibia was performed with (group 1) or without (group 2) mechanical loading. The effect of simple overloading on intact bone was studied by segmental resection of the radius (group 3). Bone dynamics were examined by histomorphological measurements. Significant hypertrophy was observed in the early postoperative period in both groups 1 and group 2. After the initial phase, bone growth continued and extensive remodeling was observed in group 1, while marked bone resorption was observed in group 2. Adaptive remodeling was also observed in group 3 after surgery, but was slower than that in groups 1 and 2. Early hypertrophy of vascularized grafts did not correspond to mechanical loading. These results suggest that mechanical loading is the principal factor responsible for remodeling in vascularized bone grafts for their adaptation to a new environment.     

Biology of vascularized bone grafts

Vascularized canine fibular autografts demonstrated improved biologic and mechanical characteristics 3 months after surgery when compared with nonvascularized controls. The vascularized proximal fibula maintained its overall architecture without bony collapse or significant bone turnover. The strength and stiffness of these grafts were approximately 40 per cent and 56 per cent more than nonvascularized grafts, respectively.     

A vascularized fibula model to study vascularized canine bone grafts

We have refined the experimental canine vascularized fibula model in 26 dog experiments. Our results have demonstrated that both periosteal and endosteal blood flow are retained following end-to-end anastomosis of the bone graft pedicle artery and vein. The success of this model depends on detailed knowledge of the surgical anatomy and upon meticulous microvascular surgical technique.     

Experimental vascularized bone grafts: histopathologic correlations with postoperative bone scan: the risk of false-positive results

A positive bone scan in an experimental model of bilateral ulna diaphyseal bone grafts demonstrated early bone repair in both vascularized and nonvascularized orthotopic ulna autografts. A positive bone scan did not correlate with the perfusion of the vascularized and nonvascularized grafts as measured by microangiograms done 1 week postoperatively. In this model, if the bone scan is intended to monitor the circulatory status and viability of the bone graft, it must be done earlier than 1 week postoperative prior to the onset of creeping repair in both vascularized and nonvascular ulna autografts.     

Experimental free vascularized epiphyseal transplants

Growth plates have been transferred both clinically and in experimental models since the end of the 19th century. Results have been unpredictable and frequently unsatisfactory due to postoperative ischemia. Modern microvascular techniques have minimized this problem and preservation of growth plate structure and function has been reported after replantation and free tissue transfers in children and immature animals. Experimental revascularized growth plate transplants were first reported in 1979. Viable orthotopic transfers are associated with rapid bony union, maintenance of radiological structure, and continued growth in length at near normal rates. Detailed studies have demonstrated a continuation of cell division, metabolic activities, and normal histology. Technetium bone scans have been a useful postoperative indicator of viability, and ischemic times of more than three hours can be tolerated. The behavior of heterotopic transplants has not yet been fully studied. Early attempts suggest that biomechanical problems may be troublesome.     

Composite vascularized skin/bone graft model: a viable source for vascularized bone marrow transplantation

In this study, we introduce a new model for vascularized skin and bone marrow transplantation. Twenty-five Lewis (RT1(1)) rats were studied. Anatomic dissection studies were performed in 5 animals. In the experimental group, 10 isograft transplantations were performed between Lewis rats. Combined groin skin and femoral bone flaps were transplanted based on the femoral artery and vein. Transplants were evaluated on a daily basis. All flaps survived without problems over 100 days posttransplant. The skin component remained pink and pliable, and grew new hair. Histological examination of the femoral bone (except the femoral head) revealed active hematopoiesis with a viable compact and cancellous bone components on day 100 posttransplant. This model can be applied to tolerance induction studies across the major Histocompatibility (MHC) barrier, where bone will serve as donor of stem and progenitor cells, and the skin flap will serve as a monitor of graft rejection.     

Reperfusion injury in vascularized bone allografts

A vascularized allograft canine tibia was used to evaluate the preservation of the osseous microcirculation. Six pairs of adult tibiae were harvested, and a vascular washout was performed with mannitol solution. The bones then were perfused continuously (0.03 ml/min at 5°C) for 20 hours with University of Wisconsin solution. Following storage, each pair of bones was transplanted, by microvasacular anastomosis, to a recipient dog, and bone blood flow was estimated using the radiolabeled microsphere method. Adreno-receptor control mechanisms were evaluated in one specimen, and endothelial function was evaluated in the contralateral specimen. Alpha₁-adrenoreceptor blockade produced a significant increase (89 ± 80%) in bone blood flow (p < 0.05). A further increase (99 ± 56%) was observed with the addition of alpha₂-blockade (p < 0.01). Acetylcholine produced a decrease (65 ± 65%) in blo od flow (p < 0.1). This effect was inhibited by L -N^G-monomethyl-arginine, which resulted in an increase (53 ± 47%) in bone blood flow (p < 0.05). The no-reflow phenomenon was observed in two vascularized allografts. These results demonstrate that smooth muscle adrenoreceptors were preserved successfully for 24 hours. In contrast, endothelial function was abnormal. There was no evidence that the endothelium was producing endothelium-derived relaxing factor, and the results suggest that an endothelium-derived constricting factor dependent on L -arginine was produced during reperfusion. It is concluded that University of Wisconsin solution does not preserve normal endothelial function in the microcirculation of bone.