Rat Osteotomy Research Articles

Temporal Variation in Fixation Stiffness Affects Healing by Differential Cartilage Formation in a Rat Osteotomy Model

Dynamization involves a reduction in fixation construct stiffness during bone healing, allowing increased interfragmentary movement of the fracture through physiologic weightbearing and muscle contraction. Within some optimal range, interfragmentary movement stimulates healing, but this range likely varies across stages of bone healing. How does the time of dynamization affect the cartilage formation, bony bridging, and bone resorption in a rat fracture-healing model? Unilateral external fixators, stabilizing a 1-mm gap, were dynamized at 1 (D1 group, n = 10), 3 (D3 group, n = 11), or 4 (D4 group, n = 11) weeks postoperatively. Continuously 5 weeks stiff (S group, n = 10) and flexible (F group, n = 11) fixation were included for comparison. After 5 weeks, healing was evaluated by histomorphometric methods. Advanced healing, indicated by less cartilage and a greater rate of bony bridging, was observed in the S group compared to the D1 or F group. In contrast, the D3 and D4 groups had less cartilage and more bridging compared to the S group. Also, the S group had less cortical resorption than the F and D1 groups. These data suggest late dynamization at the onset of bony bridging led to enhanced healing, whereas dynamization at the early stage of cartilage differentiation delayed healing. Although our observations from this small-animal study cannot be directly transferred to humans, these data suggest, once bony bridging begins, dynamization may stimulate bone healing and accelerate remodeling.

Characterization of a rat osteotomy model with impaired healing

BackgroundDelayed union or nonunion are frequent and feared complications in fracture treatment. Animal models of impaired bone healing are rare. Moreover, specific descriptions are limited although understanding of the biological course of pathogenesis of fracture nonunion is essential for therapeutic approaches.MethodsA rat tibial osteotomy model with subsequent intramedullary stabilization was performed. The healing progress of the osteotomy model was compared to a previously described closed fracture model. Histological analyses, biomechanical testing and radiological screening were undertaken during the observation period of 84 days (d) to verify the status of the healing process. In this context, particular attention was paid to a comparison of bone slices by histological and immunohistological (IHC) methods at early points in time, i.e. at 5 and 10 d post bone defect.ResultsIn contrast to the closed fracture technique osteotomy led to delayed union or nonunion until 84 d post intervention. The dimensions of whole reactive callus and the amounts of vessels in defined regions of the callus differed significantly between osteotomized and fractured animals at 10 d post surgery. A lower fraction of newly formed bone and cartilaginous tissue was obvious during this period in osteotomized animals and more inflammatory cells were observed in the callus. Newly formed bone tissue accumulated slowly on the anterior tibial side with both techniques. New formation of reparative cartilage was obviously inhibited on the anterior side, the surgical approach side, in osteotomized animals only.ConclusionTibial osteotomy with intramedullary stabilisation in rats leads to pronounced delayed union and nonunion until 84 d post intervention. The early onset of this delay can already be detected histologically within 10 d post surgery. Moreover, the osteotomy technique is associated with cellular and vascular signs of persistent inflammation within the first 10 d after bone defect and may be a contributory factor to impaired healing. The model would be excellent to test agents to promote fracture healing.

Knochenreaktion auf Metall- und Knochenzement-Implantation bei immunologischer Reaktionslage, bei Ratten

After the fact that femoral osteotomy in rats results in destruction of the entire bone (in the majority of experimental animals) due to an immunological reaction by means of Complete Freund's Adjuvant, we have investigated whether or not the implantation of bone cement or Kirschner wires affects additionally the condition of the bone. We have found that bone cement or metallic material within the bone cavity aggravates osteolysis if there is an immunologic reaction present. The conditions of the immunologic mechanism and the applied orthopedic procedures are discussed and an attempt has been made to explain the phenomenon.

Intermittent administration of human parathyroid hormone enhances bone formation and union at the site of cancellous bone osteotomy in normal and ovariectomized rats

Intermittent administration of human parathyroid hormone (hPTH) has an anabolic effect on bone in animals and humans and is expected to be a potent agent for the treatment of osteoporosis. However, little is known about the effects of hPTH on cancellous bone healing after cancellous bone fractures or osteotomies. We evaluated whether hPTH enhanced bone union at the site of cancellous bone osteotomy and further elucidated the possible mechanisms of hPTH effects on cancellous bone healing. After a bilateral ovariectomy (OVX) or sham operation in mature female rats, cancellous bone osteotomy was performed on the right proximal tibia. After once-a-week administration of hPTH (1–34) (100 μg/kg) or its vehicle for 4 weeks, bilateral tibiae including osteotomy and non-osteotomy sites were harvested. Along with conventional bone histomorphometry, cancellous bone union at the osteotomy site and the rate of proliferating cells immunostained with proliferating cell nuclear antigen (PCNA) and adipocytes in the surrounding bone marrow were evaluated. hPTH increased cancellous bone volume by stimulating bone formation in both normal and OVX rats and suppressed adipocyte volume ( p < 0.05). The percentage of PCNA-positive cells at the osteotomy site after PTH treatment was 2- to 3-fold higher than that of vehicle treatment controls both in sham-operated and OVX rats ( p < 0.05). The magnitude of increase in the percentage of PCNA-positive cells after PTH treatment at the osteotomy site was two times higher than that at the non-osteotomy site. Furthermore, PTH treatment increased cancellous bone union after osteotomy both in sham-operated and OVX rats ( p < 0.05). These results suggest that hPTH enhances cancellous bone healing at the site of osteotomy with, at least in part, a local regulating action that increases osteoblastogenesis and decreases adipocytogenesis at and around the osteotomy.

Mesenchymal Stem Cell-mediated Gene Delivery of Bone Morphogenetic Protein-2 in an Articular Fracture Model

In articular fractures, both bone and cartilage are injured. We tested whether stem cells transduced with bone morphogenetic protein 2 (BMP2) can promote bone and cartilage repair. Distal femoral articular osteotomies in nude rats were treated with stem cells, either wild-type or transduced with an adenoviral (Ad) BMP2. Cells were delivered in alginate (ALG) carrier or by direct injection in saline solution. Gene expression of these cells at the osteotomy site was confirmed by in vivo imaging. At day 14, only the group that received AdBMP2 stem cells by direct injection showed completely healed osteotomies, while other groups remained unhealed (P < 0.0003). In ALG groups, bone healing was impeded by the development of a chondroid mass, most pronounced in the AdBMP2 ALG group (P < 0.002). We were successful in achieving repair of both bone and cartilage in vivousing direct stem cell injection. Our data suggests that BMP2 augmentation might be critically important in achieving this effect.

The effect of low-intensity pulsed ultrasound on bone healing in SR-PLLA rod fixed experimental distal femur osteotomy in rat

The effects of low-intensity pulsed ultrasound (30 mW/cm2) were investigated in experimental cancellous bone fracture healing in bioabsorbable self-reinforced poly-L-lactide (SR-PLLA) rod fixed distal femur osteotomy in rats. A transverse transcondylar osteotomy was fixed with one SR-PLLA rod in 32 male Wistar rats of the age of 20 weeks. Half of the rats had a daily 20-min ultrasound exposure for three weeks. The follow-up times were three, six, and 12 weeks. Radiographical, histological, microradiographical, oxytetracycline labeling, and histomorphometrical analyses were performed. No foreign-body reactions were noted. The biocompatibility of SR-PLLA and ultrasound was found to be good. In the radiological and histological assessments there was a slight tendency for enhanced healing in the ultrasound group at three weeks, but at six and 12 weeks no differences were observed. The histomorphometrical and oxytetracycline labeling analyses showed that ultrasound exposure had no significant effects on bone healing. The present study shows that there were no obvious findings to support the hypothesis that low-intensity pulsed ultrasound enhances bone healing in self-reinforced poly-L-lactide (SR-PLLA) rod fixed experimental metaphyseal distal femur osteotomy in rats. The observed good biocompatibility provides a safe starting-point for clinical trials on bioabsorbable fixation combined with low-intensity ultrasound.

Effects of vitamin K1 supplementation on vascular responsiveness and oxidative stress in a rat femoral osteotomy model

The main function of vitamin K1 is to act a co-factor for gamma-glutamyl carboxylase. However, it has also been shown to lessen oxidative stress. This study was aimed to evaluate the effect of vitamin K1 supplementation on vascular responsiveness and oxidative status in rats that underwent femoral osteotomy. Twenty-four male rats were divided into three groups to serve as sham, osteotomy and vitamin K1 groups. Indices of oxidative stress (catalase), and oxidative damage (malondialdehyde) were analysed in erythrocytes. In order to evaluate vascular reactivity, concentration-response curves to phenylephrine, angiotensin II, 5-hydroxytryptamine, bradykinin and histamine were constructed. The findings of this study clearly show that oxidative stress clearly increases after femoral osteotomy in rats. Also, this operation causes a significant depression in vascular responsiveness to contracting agents and endothelium-dependent vasodilators. However, vitamin K1 supplementation prevents vascular hyporeactivity by reducing oxidative stress and may represent a novel approach during osteotomy healing.

Arteriovenous fistula and bone healing: experimental study in the rat.

The incidence of fractures is greater in patients with hemodialysis than in the general population. Surgically created arteriovenous fistulas are widely used in end-stage renal failure patients for the vascular access of hemodialysis. Despite occurrence of fracture at the fistula site in the forearm, bone mineral density is similar in both arms. The effects of arteriovenous fistulas on fracture healing have not been widely studied. The goal of this study was to test the hypothesis that a fracture distal to a surgically-created arteriovenous fistula has negative effects in a rat osteotomy model. The tibial bones were fractured in a monocortical fashion bilaterally. No fixation method was used. The right side was used as control. On the left side of the rat, a side-to-side arteriovenous anastomosis was done between the common femoral vessels proximal to the fracture line under magnification with the operating microscope. Three weeks later, bone segments, including the monocortical osteotomy line, were removed and examined histopathologically. Although the gross appearance of callus formation was not different in both groups, histopathologically, there were more dead medullary bone and less cartilage cells around the osteotomy line in the bone associated with the arteriovenous fistula. But with short-term evaluation of the fracture sites after opening an arteriovenous connection proximal to the fracture site, no real difference was noted related to fracture healing.

Fixation of distal femoral osteotomies with self-reinforced poly(desamino tyrosyl–tyrosine ethyl ester carbonate) rods: an experimental study on rats

AbstractSelf-reinforced poly(desamino tyrosyl–tyrosine ethyl ester carbonate) poly(DTE carbonate) rods (diameter, 2 mm; length, 26 mm) were implanted into the dorsal subcutaneous tissue of 16 rats. Osteotomies of the distal femur were fixed with these rods (2mm by 15mm) in 64 other rats. The follow-up times varied from 1 week to 1 year. After sacrifice, three-point bending and shear tests and molecular weight measurements were performed for subcutaneously placed rods. Radiological, histological, histomorphometrical, microradiographic, and oxytetracycline-fluorescence studies of the osteotomized and intact control femurs were performed. At 36 weeks, the bending strength of the rods was nearly at the same level as the initial value, and the shear strength was decreased to about one quarter of the initial value. One of the 64 evaluated osteotomies showed signs of infection at 24 weeks, and there were five failures of fixation. Fifty-eight osteotomies healed uneventfully. No gross signs of inflammatory or foreign-body reactions were observed. The present investigation showed that the mechanical strength and fixation properties of SR-poly(DTE carbonate) rods are suitable for fixation of cancellous bone osteotomies in rats. The present article is the first report on successful application of SR-poly(DTE carbonate) rods for fixation of cancellous bone osteotomies.

Strength retention of drawn self-reinforced polyglycolide rods and fixation properties of the distal femoral osteotomies with these rods. An experimental study on rats.

Drawn self-reinforced polyglycolide (SR-PGA) rods, Ø 2 mm and 26 mm long, were implanted in the dorsal subcutaneus tissue of 16 rats. Osteotomies of the distal femur were fixed with SR-PGA rods (2 mm by 15 mm) in another 38 rats. The follow-up times varied from one week to one year. After sacrifice, three-point bending and shear tests were performed for subcutaneously placed rods. Radiological, histological, histomorphometrical, microradiographic, and oxytetracycline-fluorescence studies of osteotomized and intact control femora were also performed. At three weeks the flexural strength of the rods was 50% of the initial value, and the flexural modulus was 46% of the initial value. Five osteotomy specimens had to be excluded due to dislocation or non-union. One of the 33 evaluated osteotomy specimens showed signs of postoperative infection. Thirty-two osteotomies healed uneventfully. No gross signs of inflammatory or foreign-body reaction were observed. The amount of osteoid surface and active osteoid formation surface reached their highest value in the histomorphometrical analysis at 24 weeks. The present investigation demonstrated that the mechanical strength and fixation properties of the drawn SR-PGA rods are suitable for fixation of cancellous bone osteotomies in rats. The present article is the first report on the successful application of drawn SR-PGA rods for fixation of cancellous bone osteotomies.

Strength retention of self-reinforced drawn poly-L/DL-lactide 70/30 (SR-PLA70) rods and fixation properties of distal femoral osteotomies with these rods. An experimental study on rats

Self-reinforced polylevo-dextro-lactic acid(SR-PLA)70 composite rods,(2 mm×26 mm) were implanted in the dorsal subcutaneus tissue of sixteen rats. Osteotomies of the distal femur were fixed with SR-PLA70 composite rods (2 mm × 15 mm) in 39 rats. The follow-up times varied from 1 week to 1 year. After sacrifice three-point bending and shear tests were performed for subcutaneously placed rods, and radiological, histological, histomorphometrical, microradiographic, and oxytetracycline-fluorescence studies of osteotomized and intact control femora were performed. At 52 weeks the shear strength and flexural modulus of the rods were 41% of the initial value, and the flexural strength was 43% of the initial value. In the osteotomies seven specimens had to be excluded due to postoperative infection or dislocation of the fragment. Six of the thirty-two evaluated osteotomies showed signs of postoperative infection. Twenty-six osteotomies healed uneventfully. No signs of inflammatory or foreign-body reaction were observed. The present investigation demonstrated that the mechanical strength and fixation properties of the SR-PLA70 rods are suitable for fixation of cancellous bone osteotomies in rats. The present article is the first report on successful application of SR-PLA70 rods for fixation of cancellous bone osteotomies studied.

Gene transfection using biodegradable nanospheres: results in tissue culture and a rat osteotomy model

In this paper, we have investigated sustained release biodegradable nanospheres for the delivery of plasmid DNA. The nanospheres were formulated using a proprietary co-polymer emulsion technique to encapsulate plasmid DNA. Gene transfection with nanospheres containing reporter genes (human placental alkaline phosphatase (AP) or Luciferase) was demonstrated in tissue culture (293T and COS-7 cells), and also in vivo in a nonunion femoral fracture (osteotomy) rat model. The bone gap was filled with nanospheres and gene expression in the implantation site was measured five weeks after the initial surgery. The nanospheres had a mean diameter of 230 nm, with a DNA loading of 0.7%w/w. These nanospheres demonstrated sustained release of the encapsulated DNA under in vitro physiologic conditions with an 82% cumulative DNA release over 17 days. The transfection efficiency of the nanospheres in tissue culture was two to five orders of magnitude greater than the gene expression with the same amount of plasmid DNA in solution. In the rat studies, the mean AP activity in the tissue retrieved from the osteotomy site in the experimental group was 291.8±52.5 cpm Versus 54.1±26.5 cpm (mean±S.E.M., P=0.03) in the sham control group. In conclusion, plasmid DNA nanospheres could be used as an effective nonviral method of gene delivery. In the future, nanospheres containing therapeutic genes, such as those encoding parathyroid hormone peptide, 1–34 amino acids (PTH-34) or Bone Morphogenic Protein-4 (BMP-4), could be used for the healing of nonunion bone fracture sites.

An experimental model for non-union using a muscle tissue interposition without osteotomy in rats

s from the Sixth Meeting of the International Society for Fracture Repair; September 23-26, 1998; Strasbourg, France

Erb:YAG and Hol:YAG Laser Osteotomy: The Effect of Laser Ablation on Bone Healing

Sixty-nine male Sprague Dawley rats were divided into three groups of 23 animals each and osteotomies were performed in group 1 with a power saw, in group 2 with the Erb:Yag laser, and in group 3 with the Hol:YAG laser. Two animals of each group were sacrificed 1 week, 4, 8, and 12 weeks after operation for histologic investigation, and five animals of each group at 4, 8, and 12 weeks after osteotomy for torque testing. Anterior-posterior (AP) radiographs were taken at the same time points and investigated for callus formation and development of pseudoarthrosis. All tibiae osteotomied with the Hol:YAG laser (group 3) developed pseudoarthrosis within 12 weeks and, therefore, torque testing could not be performed for this group. Biomechanical measurements of bone treated by power saw or Erb:YAG laser osteotomies, respectively, showed no significant statistical difference in the stability of bone between the two groups. Histologic examination after 1 week exhibited fibrous tissue at the site of osteotomy in rats of all three groups and additionally carbonization in rats of group 3. Saw osteotomies resulted in more callus formation than Erb:YAG osteotomies, but both techniques provoked a certain reunion within 8 weeks. Hol:YAG laser-treated osteotomies, however, exhibited formation of dense fibrous tissue, carbonization and no callus formation within 12 weeks. Radiographic pictures showed more callus formation for saw osteotomies as compared to those performed with the Erb:YAG laser. For Hol:YAG laser osteotomies pseudoarthrosis was identified also radiologically.

Changes in temporomandibular joint after mandibular subcondylar osteotomy: An experimental study in rats

The objective of this study was to analyze the changes in the different components of the temporomandibular joint and their relation with age after subcondylar osteotomy. For this purpose 149 Wistar rats were divided into three groups: osteotomy, sham operation, and control. Two experimental ages (30 and 70 days) and radiologic, morphometric, macroscopic, and histologic methods of analysis were used. Different changes were observed in young and adult animals. Subcondylar mandibular osteotomy in growing rats caused anteroinferior displacement of the temporal and mandibular component of the joint. At the end of the experimental period only condylar displacement was maintained. Other changes were flattening of the mandibular condyle, which was transient, and lateral thickening of the articular disc. Subcondylar mandibular osteotomy in adult rats caused slight anterior displacement of the joint components at the end of the experimental period. At this age, although changes similar to those in growing animals were observed in some cases, in other cases the presence of pathologic findings, such as deformation of the condylar cartilage, thickening of the disc, intra-articular adherences, and osteolysis of the temporal fossa, were observed. Changes in the joint components were more marked in growing rats than in adults. In growing rats they affected the form of the condylar process to a greater extent, but the majority of these changes were transient. In adult rats, alterations in the joints were less pronounced, but they affected a greater number of joint components and were permanent.

Release of prostaglandins from bone and muscle after femoral osteotomy in rats

In rats after nonstabilized femoral osteotomies, the changes in the release of prostaglandins (PGs) during bone healing (from bone and surrounding muscle tissue) were determined for PGE2, PGF2 alpha, 6-keto-PGF1 alpha, and thromboxane B2. A unilateral osteotomy, with contralateral soft-tissue dissection, was performed. After 4 or 10 days, the rats were killed and soft tissue and femoral bone were incubated, and the release of PGs was measured with specific radioimmunoassays. The release of PGs from rat femurs without previous surgery and from the sham-operated on side did not differ after 180 minutes' incubation. The release of PGE2, 6-keto-PGF1 alpha, and thromboxane-B2 from the osteotomy site was increased for bone on Day 4 and for muscle on Day 10 when compared with the controls. The release of PGF2 alpha from bone and muscle was about the same on both days, but increased as compared with the controls on Day 10 for bone. On Day 10, the other PGs for muscle and bone tissue were decreased as compared with Day 4. The most pronounced release of PGs occurred during the early healing phase after osteotomy; as early as 10 days after surgery, most of the PGs were not increased when compared with the sham-operated on side.

Mechanical effects of intramedullary reaming in pinned osteotomies in rats.

The biomechanical effects of intramedullary reaming on the healing of femoral osteotomies were studied. In rats, transverse osteotomies at the midshaft of both femurs were made. On the left side only, reaming of the medullary cavity was performed, and the osteotomies were then stabilized by intramedullary pinning. At 15, 30, 60, and 90 days after osteotomy, the production of callus, the bending moment, and the bending rigidity were evaluated. There were no significant differences in these biomechanical parameters between the right unreamed and the left reamed femurs during the experimental period. The results indicate that reaming of the medullary cavity of diaphyseal bone does not significantly impair or improve the healing of pinned osteotomies in rats.

Mechanical effects of intramedullary acrylic cement on osteotomy healing in rats.

The medullary cavities of both femora in 35 rats were reamed, and bone cement was injected on the left side. A partial transverse osteotomy of the midshaft of both femora was then performed. At 0, 15, 30, 60, and 90 days following operation, the bending moment and elastic stiffness of the osteotomies were evaluated. No significant differences were found between the right and left femora. It is concluded that acrylic bone cement injected into the medullary cavity does not significantly impair the healing of osteotomies in rats.

Healing of stable and unstable osteotomies in rats.

In two groups of rats a partial, transverse osteotomy at the mid-shaft of the femur was made. The osteotomy was manually broken in one of the groups after the operation. The healing process of the osteotomies was evaluated at 15, 30, 60, and 90 days following operation. The unstable osteotomies healed by the formation of external callus, in contrast to the stable osteotomies, which healed by so-called primary bone union. At 90 days the bending moment and rigidity of the instable osteotomies were regained as compared to the intact right femurs. The stable osteotomies were only 67% as strong as the intact bones (P less than 0.01). The bending rigidity of the stable osteotomies was equal to that of the intact bones during the experimental period. It is concluded that instability at the fracture site is conducive to fast healing.

Fracture Healing in Rats Exposed to Extremely Low-Frequency Electric Fields

Fibular osteotomies in rats were exposed to an extremely low frequency field for 14 days. By histologic evaluation it was found that the healing rate was retarded by the field. The effect (which was replicated) occurred at much lower power levels than are presently employed in electircal osteogenesis.