Healing of tibial fractures is not impaired after acute hindlimb ischemia in rats

Autologous minced muscle grafts improve endogenous fracture healing and muscle strength after musculoskeletal trauma

The deleterious impact of concomitant muscle injury on fracture healing and limb function is commonly considered part of the natural sequela of orthopedic trauma. Recent reports suggest that heightened inflammation in the surrounding traumatized musculature is a primary determinant of fracture healing. Relatedly, there are emerging potential therapeutic approaches for severe muscle trauma (e.g., volumetric muscle loss [VML] injury), such as autologous minced muscle grafts (1 mm3 pieces of muscle; GRAFT), that can partially prevent chronic functional deficits and appear to have an immunomodulatory effect within VML injured muscle. The primary goal of this study was to determine if repair of VML injury with GRAFT rescues impaired fracture healing and improves the strength of the traumatized muscle in a male Lewis rat model of tibia open fracture. The most salient findings of the study were: (1) tibialis anterior (TA) muscle repair with GRAFT improved endogenous healing of fractured tibia and improved the functional outcome of muscle regeneration; (2) GRAFT repair attenuated the monocyte/macrophage (CD45+CDllb+) and T lymphocyte (CD3+) response to VML injury; (3) TA muscle protein concentrations of MCP1, IL-10, and IGF-1 were augmented in a proregenerative manner by GRAFT repair; (4) VML injury concomitant with osteotomy induced a heightened systemic presence of alarmins (e.g., soluble RAGE) and leukocytes (e.g., monocytes), and depressed IGF-1 concentration, which GRAFT repair ameliorated. Collectively, these data indicate that repair of VML injury with a regenerative therapy can modulate the inflammatory and regenerative phenotype of the treated muscle and in association improve musculoskeletal healing.

Recovery from hind limb ischemia enhances rhBMP-2-mediated segmental bone defect repair in a rat composite injury model

Although severe extremity trauma is often inclusive of skeletal and vascular damage in combination, segmental bone defect repair with concomitant vascular injury has yet to be experimentally investigated. To this end, we developed a novel rat composite limb injury model by combining a critically-sized segmental bone defect with surgically-induced hind limb ischemia (HLI). Unilateral 8mm femoral defects were created alone (BD) or in combination with HLI (BD + HLI), and all defects were treated with rhBMP-2 via a hybrid biomaterial delivery system. Based on reported clinical and experimental observations on the importance of vascular networks in bone repair, we hypothesized that HLI would impair bone regeneration. Interestingly, the BD+HLI group displayed improved radiographic bridging, and quantitative micro-CT analysis revealed enhanced bone regeneration as early as week 4 (p < 0.01) that was sustained through week 12 (p < 0.001) and confirmed histologically. This effect was observed in two independent studies and at two different doses of rhBMP-2. Micro-CT angiography was used to quantitatively evaluate vascular networks at week 12 in both the thigh and the regenerated bone defect. No differences were found between groups in total blood vessel volume in the thigh, but clear differences in morphology were present as the BD+HLI group possessed a more interconnected network of smaller diameter vessels (p < 0.001). Accordingly, while the overall thigh vessel volume was comparable between groups, the contributions to vessel volume based on vessel diameter differed significantly. Despite this evidence of a robust neovascular response in the thigh of the BD + HLI group, differences were not observed between groups for bone defect blood vessel volume or morphology. In total, our results demonstrate that a transient ischemic insult and the subsequent recovery response to HLI significantly enhanced BMP-2-mediated segmental bone defect repair, providing additional complexity to the relationship between vascular tissue networks and bone healing. Ultimately, a better understanding of the coupling mechanisms may reveal important new strategies for promoting bone healing in challenging clinical scenarios.

Effect of preconditioned hyperbaric oxygen and ozone on ischemia-reperfusion induced tourniquet in skeletal bone of rats

BACKGROUND

The aim of the study was to investigate effect of I/R injury on bone tissue and protective role of hyperbaric oxygen precondition (HBO-PC) and ozone precondition (O(3)-PC) on I/R injury by using biochemical analysis.

MATERIALS AND METHODS

Thirty-two rats were included in study. The animals were divided into four equal groups: sham operation, I/R, I/R+HBO and I/R+O(3). One session of 60 min, 3 ATA, 3-4 L/min, 100% oxygenation was defined as one dose of HBO. First dose of HBO was administrated 72 h before ischemia. Subsequent, one-dose of HBO administrated per 12 hours until ischemia time (total seven doses); 0.7 mg/kg ozone/oxygen mixture intraperitoneally was defined as one dose of ozone. First dose of O(3) was administered 72 h before ischemia (total four doses). I/R model was induced in anesthetized rats by unilateral (right) femoral artery clipping for 2 h followed by 22 h of reperfusion. The right tibia and were harvested. Tissue was assayed for levels of malondialdehyde (MDA) and protein carbonyl (PCO), activities of superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px).

RESULTS

MDA and PCO levels were increased in I/R group. SOD activity was increased; GSH-Px activity was decreased in I/R group. MDA and PCO levels were decreased, SOD and GSH-Px activities were increased in both HBO+I/R and O(3)+I/R groups.

CONCLUSION

It has been shown that levels of MDA and PCO in bone were increased followed by 2 h of ischemia and 22 h of reperfusion period. Ozone-PC and HBO-PC has protective effect against skeletal bone I/R injury by decreasing levels of MDA and PCO, increasing activities of SOD and GSH-Px in rats.

Ischemia leads to delayed union during fracture healing: a mouse model

Vascular damage accompanying skeletal injury leads to an ischemic environment, and in clinical settings the extent of vascular damage is directly correlated with failure of skeletal repair. However, the exact mechanism(s) underlying ischemia-related defects in bone healing are not well understood. To better understand the mechanism and to facilitate development of novel interventions to treat ischemic fractures, a mouse model of long bone fracture healing in an ischemic environment was created. Ischemia was induced by femoral artery resection prior to tibia fracture. Fractures were left unstabilized or were stabilized with custom-designed external fixators. Animals with intact femoral vessels served as controls. Tissues from non-stabilized fractures were analyzed at various times from 3 to 28 days after injury (n = 5/time point). Femoral artery resection severely impaired blood supply to the fractured limbs, and perfusion to the fracture sites did not recover until 14 days post-injury. Ischemia significantly decreased the callus size (p < 0.05), and decreased bone (p < 0.05) and cartilage (p < 0.05) matrix production during healing of non-stabilized fracture. The decreased formation of skeletal tissues in ischemic limbs was accompanied by decreased cell proliferation and increased apoptosis at early time points, and increased fibrous and fatty tissues adjacent to the fracture site during the third and fourth week after injury. These alterations led to a delayed-union. Complete fracture healing was not achieved in the majority (day 21 = 4/5; day 28 = 5/5) of ischemic animals, while all control mice (n = 5/5) had evidence of bony bridging by day 21. The ratio of cartilage to bone was similar in ischemic and control limbs at days 7 and 10 in non-stabilized fractures. In stabilized fractures, which healed through direct bone formation in the nonischemic controls, ischemia decreased the amount of bone formation at days 10 and 14 (n = 5/time point) but did not induce cartilage formation. These data reveal that an ischemic insult in the hind limb prior to fracture leads to a delayed union or a nonunion, but does not favor formation of cartilage over bone. This model will be useful for testing novel therapeutic regimens to stimulate fracture healing.

Does long-term ischemia affect the oxidant status during fracture healing?

INTRODUCTION

The influence of transient circulatory arrest on oxidant status during the healing of a tibial fracture was investigated in rats by the use of a hindlimb tourniquet technique.

MATERIALS AND METHODS

One of the most reliable indicators for cytological damage is lipid peroxidation, which can be demonstrated by malondialdehyde (MDA) levels. Fifty-eight Wistar rats were used in this study. To determine the basal MDA levels of bone, 10 rats not exposed to ischemia were killed by an overdose of ether. The remaining 48 rats were randomly divided into two groups (control and ischemia). The control and ischemia groups were then randomly divided into 4 groups of 6 rats each. In 48 rats, the left tibia was fractured and fixed intramedullarly. In the ischemic group, complete acute transient ischemia for 4.5 h was imposed after the fracture. In the control group, no other intervention except the fracture was done. Rats from the control and ischemic groups were killed on days 3, 7, 14, and 28, and MDA levels were determined in tibial bone and callus tissue. The MDA levels of the control and ischemic groups were compared with basal MDA levels in the bone of 10 rats.

RESULTS

There was an apparent difference between the basal and control group MDA levels on days 3 and 7 (p < 0.01), between the basal and ischemic group MDA levels on days 3, 7, and 14 (p < 0.01). In addition, the ischemic group showed a statistically significant increase in MDA levels on days 3, 7 and 14 compared with the control group (p < 0.01).

CONCLUSION

We conclude that complete acute transient ischemia affects the oxidant status during fracture healing. This effect especially occurs during the ischemic period, inflammation, and callus formation of fracture healing.