Experimental free vascularized epiphyseal transplants

Vascularized epiphyseal transplant

In skeletally immature patients, the transfer of vascularized epiphysis along with a variable amount of adjoining diaphysis may provide the potential for growth of such a graft, preventing future limb length discrepancy. This article describes the authors' experience with the vascularized transfer of the proximal fibular epiphysis in the reconstruction of large bone defects including the epiphysis in a series of 27 patients ranging in age from 2 to 11 years. The follow-up, ranging from 2 to 14 years, has been long enough to allow some evaluation of the validity, indications, and limits of this reconstructive option.

Vascularized bone allotransplantation: current state and implications for future reconstructive surgery

This article focuses on current advances in musculoskeletal tissue allotransplantation, including strategies for maintaining tissue viability in the face of histocompatibility mismatch and resulting acute and chronic rejection responses. In particular, it introduces a novel concept developed in the authors' laboratory and currently under evaluation that may obviate the problem of chronic rejection. The authors have used therapeutic angiogenesis to develop a host-derived neoangiogenic circulation that maintains blood flow regardless of rejection. The replacement of the allogeneic vessels together with bone remodeling from host-derived cells eventually may largely replace the allogeneic osteocytes and bone with native bone.

Epiphyseal transplant: Harvesting technique of the proximal fibula based on the anterior tibial artery

Epiphyseal transplants in children were introduced into clinical practice about 20 years ago. Among possible donor sites, the proximal fibula is definitely the most popular choice, and has been used mainly for reconstruction of the proximal humerus and distal radius. Provided that an adequate blood supply both to the physis and to the diaphysis must be restored in order to obtain acceptable axial growth of the transferred fibula and a bone fusion at the osteotomy site, the choice of feeding pedicle is still a controversial issue. Our contribution involves a homogeneous series of 24 patients under 11 years of age who had skeletal reconstruction in the upper limb by means of a vascularized transfer of the proximal fibula based on the anterior tibial artery. The aim of the present paper is to describe in detail the harvesting technique which has been partially modified and gradually refined in our 10-year experience.

Vascularized proximal fibular epiphyseal transfer for distal radial reconstruction

BACKGROUND

Treatment of the loss of the distal part of the radius, including the physis and epiphysis, in a skeletally immature patient requires both replacement of the osseous defect and restoration of longitudinal growth. Autologous vascularized epiphyseal transfer is the only possible procedure that can meet both requirements.

METHODS

Between 1993 and 2002, six patients with a mean age of 8.4 years (range, six to eleven years) who had a malignant bone tumor in the distal part of the radius underwent microsurgical reconstruction of the distal part of the radius with a vascularized proximal fibular transfer, including the physis and a variable length of the diaphysis. All of the grafts were supplied by the anterior tibial vascular network. The rate of survival and bone union of the graft, the growth rate per year, the ratio between the lengths of the ulna and the reconstructed radius, and the range of motion of the wrist were evaluated for five of the six patients who had been followed for three years or more.

RESULTS

The mean duration of follow-up of the six patients was 4.4 years (range, eight months to nine years). All six transfers survived and united with the host bone within two months postoperatively. The five patients who were followed for three years or more had consistent and predictable longitudinal growth. Serial radiographs revealed remodeling of the articular surface. The functional result was rated as excellent for all but one patient, in whom the distal part of the ulna had also been resected because of neoplastic involvement. No major complication occurred at the recipient site, whereas a peroneal nerve palsy occurred at the donor site in three patients. The palsy was transient in two patients, but it persisted in one. No instability of the knee joint was observed.

CONCLUSIONS

After radical resection of the distal part of the radius because of a neoplasm in children, vascularized proximal fibular transfer, based on the anterior tibial artery, permits a one-stage skeletal and joint reconstruction, provides excellent function, and minimizes the discrepancy between the distal radial and ulnar lengths.

Survival of microvascular physeal allograft transplants following withdrawal of short-term postoperative immunosuppression

BACKGROUND

Physeal necrosis following vascularized allograft transplantation occurs because of vascular rejection. The effect of immunosuppression withdrawal on physeal viability after bone-healing to the recipient site was investigated with use of a validated model for heterotopic microvascular transplantation of rabbit tibial physeal allografts. Our hypothesis was that an allograft survives after withdrawal of immunosuppression only if bone-healing, and therefore epiphyseal and metaphyseal vascular continuity, occurs between the transplanted physis and the recipient bone.

METHODS

Physeal grafts with adjacent exposed epiphyseal and metaphyseal bone were transplanted to allogeneic recipients. Graft circulation was restored microsurgically. The immunosuppression regimen consisted of cyclosporine, administered for six weeks, followed by withdrawal of immunosuppression for four weeks. The animals were killed at ten weeks postoperatively. Group I consisted of twelve allografts that were transferred with bone contact between the transplanted graft and the iliac crest recipient site, whereas group II consisted of twelve allografts transplanted without bone contact. Control groups had identical surgical procedures without immunosuppression. Longitudinal growth was assessed by fine-detail radiography, and osseous union was evaluated histologically. Transplanted physes were evaluated histologically, and cellular viability was quantified by bromodeoxyuridine uptake. Two-way analysis of variance was used to compare physeal viability between groups.

RESULTS

Following immunosuppression withdrawal, the physeal grafts with bone contact had significantly greater viability indices (16.0 +/- 2.9 compared with 0.0 +/- 0.0, p < 0.005) and decreased longitudinal growth (5.1 +/- 1.9 mm compared with 10.3 +/- 3.5 mm, p < 0.05), and they demonstrated histological features that were consistent with continued viability associated with mild rejection compared with grafts transplanted without bone contact. Abnormalities of physeal architecture, however, were seen routinely. All control physes transferred without immunosuppression were nonviable and did not grow.

CONCLUSIONS

The viability of physeal allograft transplants is preserved following the withdrawal of immunosuppression, provided that the graft design and recipient site preparation allow for epiphyseal and metaphyseal neovascularization mediated by bone-healing between graft and recipient.

Epiphyseal plate transplantation: an historical review

Non-vascularized and vascularized transplantation of epiphyseal plate autografts have been performed both clinically and experimentally for over 100 years. However, the ultimate clinical goal of vascularized transplantation of epiphyseal plate allografts for paediatric extremity reconstruction remains elusive, due primarily to the lack of suitably nontoxic techniques to prevent graft rejection. We have summarized the published clinical and experimental investigations of vascularized epiphyseal plate transplantation, and organized the experiments and clinical operations into four main groups: (1) local vascular studies on unmanipulated epiphyseal plates, (2) studies of epiphyseal plate behaviour after orthotopic replantation, (3) studies of epiphyseal plate behaviour after heterotopic transplantation, and (4) studies of epiphyseal plate behaviour after allograft transplantation. Prior investigations into the non-vascularized transplantation of epiphyseal plate autografts and allografts are presented as background. These groups of studies serve as the building blocks for the more clinically applicable experimental investigations outlined in the final section of this review.

Short-term response of epiphyseal plate cell populations following selective devascularization and microsurgical revascularization

The distal femoral epiphyseal plates of 21 8-week-old New Zealand white rabbits were totally or partially (nutrient artery only) devascularized, or devascularized and then microsurgically revascularized. Sacrifice was at 24, 48 or 72 hours postoperatively. The heights of the proliferative and hypertrophic zones of the epiphyseal plates operated upon were compared with the contralateral control epiphyseal plates for both the central and the peripheral regions of the epiphyseal plate. Neither extent of devascularization nor revascularization had a significant effect on the height of the proliferative zone of chondrocytes at any of the follow-up intervals. Selective devascularization of the nutrient artery led to a significant increase in height of the central region of the hypertrophic zone of chondrocytes at 48 and 72 hours. Microsurgical revascularization did not lead to a significant change in the height of either the central or the peripheral regions of the hypertrophic zone of chondrocytes at any of the follow-up intervals. This study is another 'building block' experiment toward vascularized epiphyseal plate transplantation in humans.

Effects of free perichondrial graft replacement of epiphyseal cartilage on bone growth

An experimental study in 24 lambs was carried out to find an alternative tissue for the distal epiphyseal cartilage of the femur. The animals were divided into three groups. In the first group (n = 12) the left femoral distal epiphyseal cartilage was completely removed and replaced by a free perichondrial graft taken from the distal half of the scapula. In the second group (n = 6) the epiphyseal cartilage was removed and was not replaced by any tissue. The third group (n = 6) was used as control. After six months the legs in the first and third groups were of the same normal length while the legs in the second group were significantly shorter. We conclude that free perichondrial graft seems to be able to replace the epiphyseal cartilage and prevent retardation of growth.

Physeal replacement with cultured chondrocytes of varying developmental time: failure to reconstruct a functional or structural physis

Reconstruction of physeal regions excised from the distal femoral chondroepiphysis was attempted in a murine model. Cultured chondrocytes of varying developmental time from the same inbred strain of mice were used for replacement. Vascularity, matrix formation, and cell division, as well as growth, were assessed. The cultured chondrocytes did not produce growth. Consistent with this, cell division, as assessed with incorporation of tritiated thymidine, was not normal. However, the cultured chondrocytes did receive a nutritional supply from the host and did continue matrix formation after transplantation.

Hemiepiphyseal reconstruction using tissue donated from fetal limbs in a murine model

Epiphyseal reconstruction in the immature skeleton could have great clinical significance. Hemiepiphyseal reconstruction was performed in a murine model by transplanting fetal tissue to surgically created defects in postnatal mice. Reconstruction is facilitated by the existence of inbred strains. While the reconstruction as performed here did not completely restore the growth characteristics of the epiphysis, the model represents a potentially fruitful interface between basic and clinical biology.

Epiphyseal replacement using developing tissue donors in a murine model: a combined histologic and radiographic study

Epiphyseal transplantation has long been a goal of orthopaedic surgeons. While microvascular surgery has raised hopes that this goal could be achieved, factors other than blood supply also appear capable of affecting the function of the epiphysis. Basic research into the biology of the epiphysis appears to be required. This would be facilitated with a model of epiphyseal transplantation using a small mammal. The purpose of this experiment was to develop such a model in the mouse. Developing CD1 mouse or Lewis rat limb tissue was used to replace knee tissue that had been resected from CD1 postnatal mouse hosts. Donor tissue ranged from 14-day embryonic mouse to 9-day postnatal mouse or 18- and 19-day fetal rat, which has a gestation similar to the mouse. The murine tissue is known to be avascular prior to the sixth postnatal day. The limbs were analyzed radiographically and histologically. The results show that epiphyseal replacement could be studied using developing tissue donors in a murine model. The results suggest that donor tissue prior to vascularization and tissue combinations with the least developmental time mismatch (the least heterochronicity) produced relatively the best, although still abnormal epiphyses.