Quantifying the effect of ischemia on epiphyseal growth in an extremity replant model

2-Butoxyethanol Female-Rat Model of Hemolysis and Disseminated Thrombosis: X-Ray Characterization of Osteonecrosis and Growth-Plate Suppression

We recently proposed a chemically induced rat model for human hemolytic disorders associated with thrombosis. The objective of the present investigation was to apply a noninvasive, high-magnification X-ray analysis, the Faxitron radiography system, to characterize the protracted bone damage associated with this 2-butoxyethanol model and to validate it by histopathology. Groups of female Fischer 344 rats were given 0, 250, or 300 mg of 2-butoxyethanol/kg body weight daily for 4 consecutive days. Groups were then sacrificed 2 hours or 26 days after the final treatment. The treated animals displayed a darkened purple-red discoloration on the distal tail. Histopathological evaluation, including phosphotungstic acid-hematoxylin staining of animals sacrificed 2 hours after the final treatment, revealed disseminated thrombosis and infarction in multiple organs, including bones. The Faxitron MX-20 specimen radiography system was used to image selected bones of rats sacrificed 26 days posttreatment. Premature thinning of the growth plate occurred in the calcaneus, lumbar and coccygeal vertebrae, femur, and ilium of the treated animals. Areas of decreased radiographic densities were seen in the diaphysis of the femur of all treated animals. The bones were then examined histologically and showed a range of changes, including loss or damage to growth plates and necrosis of cortical bone. No thrombi were seen in the animals sacrificed at 30 days, but bone and growth plate changes consistent with prior ischemia were noted. The Faxitron proved to be an excellent noninvasive tool that can be used in future studies with this animal model to examine treatment modalities for the chronic effects of human thrombotic disorders.

Cell proliferation and death of growth plate chondrocyte caused by ischemia and reperfusion

The aim of this study was to assess the short-term response of cell kinetics of growth plate chondrocytes under conditions of warm ischemia and reperfusion. To understand the time-course changes that occur after reperfusion, 0 and 6 h of warm ischemia was produced in the right hindlimb of 35-day-old Wistar rats by isolating the vascular pedicle occlusion. The animals were killed at 12, 24, 48, or 96 h postoperatively after reperfusion, and proximal tibia growth plates were investigated. To investigate the effect of the ischemia period on the kinetics of growth plate chondrocytes, 0, 2, 4, 6, and 8 h of ischemia was induced, and the animals were killed for evaluation 24 h after reperfusion. For evaluation of cell kinetics, BrdU was used to observe the changes in cell proliferation of growth plate chondrocytes, and TUNEL was used to estimate the changes in rate of cell death. In the time-course study, both 0 and 6 h of ischemia increased cell proliferation at 12 and 24 h after reperfusion; however, at 48 and 96 h, the proliferation rate was not further increased. At 12 and 24 h postoperatively, 6 h of ischemia increased chondrocyte proliferation more than 0 h of ischemia with significant differences; 6 h of ischemia led to an increased cell death rate at 12, 24, and 48 h postoperatively, whereas 0 h of ischemia did not affect the cell death rate. In the ischemia time-dependent study, the cell proliferation rate induced by 4 h of ischemia was highest in all controlled periods of ischemia. Cell death rate increased gradually with increases in ischemia time 24 h after reperfusion. This experiment showed that ischemic damage causes short-term postoperative changes in the kinetics of growth plate chondrocytes.

Approaches to study of ischemia in bone

Ischemic osteonecrosis is a complication of certain traumatic and a number of idiopathic conditions. The course of the disease may result in collapse of the convex member of a joint and osteoarthritis, often requiring arthroplasty. Increasing incidence in young adults poses a challenge for development of long-term joint prostheses. Current status of research into the disease is discussed and three new models using intravital microscopy described. The first, an arterial occlusion (AO) model, creates ischemia by occluding the common iliac artery exclusively, avoiding direct trauma on other tissues in the limb. The second, a total occlusion (TO) model utilizes classical tourniquet occlusion of the thigh vessels. The third, a venous occlusion (VO) model, is also a tourniquet procedure but it blocks occlusion of the femoral artery with a protective sheath. Preliminary results from AO and TO studies are reported which show that reperfusion injury is detectible after ischemia doses as short as 4 h. This complication was confirmed by observation of leukocyte adherence, secondary ischemia, and abnormal vessel leakage. Also, a new quantitation of osteonecrosis is introduced whereby fluorescently-tagged dead osteocytes and computer-based image processing provide values for an "osteonecrosis index." Viewing of all vascular events is made possible by intravital microscopy through a bone chamber window implanted in rabbit tibias. It is proposed that such chronic visual techniques allow quantitation of events leading to osteonecrosis as well as the revascularization, resorption and bone apposition of creeping substitution which characterizes postischemia recovery.

Growth factor modulation of the formation of a molded vascularized bone graft in vivo

Peptide growth factors are potent regulators of osteoblast differentiation, proliferation, and maturation. Two of these growth factors, transforming growth factor beta (TGF-beta) and basic fibroblast growth factor (bFGF), were used in an attempt to stimulate osteoneogenesis and angiogenesis in a molded vascularized bone graft in the rat. Custom chambers containing cancellous autograft bone and agarose beads and incubated with TGF-beta, bFGF, or a control solution, were closed around the femoral artery/vein pedicle for 2-4 weeks. Control grafts were completely necrotic and without mechanical integrity. TGF-beta grafts demonstrated active osteogenesis around necrotic bone, osteoclastic activity, and limited angiogenesis. Basic FGF grafts demonstrated substantial angiogenesis with limited osteoblastic activity. This study suggests that TGF-beta and bFGF stimulate populations of cells in the formation of a molded vascularized bone graft. TGF-beta induces the proliferation and/or activity of osteoblastic cells, while bFGF stimulates cells involved in angiogenesis. Despite these findings, an insoluble demineralized matrix component may be required for complete transformation and graft consolidation.

Effect of ischemia and three different perfusion solutions on the rabbit epiphyseal growth plate

An isolated vascularized knee joint model was used (1) to determine the minimum ischemia time that produced growth retarding damage to the epiphyseal plate and (2) to evaluate whether intra-arterial perfusion could reduce the ischemia damage. Experiment 1 consisted of 31 rabbits in 5 groups: 0, 2,4,6, and 8 hr of warm ischemia produced by clamping the pedicle. Experiment 2 consisted of 18 rabbits in which 10 ml of one of (1) Euro-Collins, (2) University of Wisconsin solution, or (3) heparinized blood were perfused through the joint without ischemia. Experiment 3 consisted of 21 rabbits in which one of the three solutions was perfused for a short period during 6 hr of ischemia. Growth of the tibia was followed radiographically every month over 3 months, and the growth plates were evaluated histologically after sacrifice. Results showed that at least 6 hr of ischemia was needed before longitudinal growth was reduced; less ischemia time caused overgrowth. Histologic damage was found in all animals to some degree. Perfusion alone without ischemia had no detrimental effect on growth or histology. The growth reduction at 6 hr of ischemia was minimized by perfusion with every solution. Heparinized blood was the most effective and Euro-collins was the least effective.

Longitudinal growth after replantation of immature extremities on rats

Replantation of right hindlimbs in 76 immature rats was performed to study the factors affecting longitudinal growth of replanted extremities. There was a significant difference in tibia length between the replanted limb and the contralateral normal limb. The difference was significantly influenced by the ischemic interval (2 vs 4 hours), but not by suture method (intact vessels, vascular anastomosis with 10-0 nylon or 11-0 nylon). The replantation of immature extremities should be promptly undertaken because of the vulnerability of the epiphysis to ischemic insult.