Control Femurs Research Articles

Transplantation of a vascularized rabbit femoral diaphyseal segment: Mechanical and histologic properties of a new living bone transplantation model

A new vascularized bone transplantation model is described, including the anatomy and surgical technique of isolating a rabbit femoral diaphyseal segment on its nutrient vascular pedicle. The histologic and biomechanical parameters of pedicled vascularized femoral autotransplants were studied following orthotopic reimplantation in the resulting mid-diaphyseal defect. Vascularized femur segments were isolated in 10 rabbits on their nutrient pedicle, and then replaced orthotopically with appropriate internal fixation. Postoperative weightbearing and mobility were unrestricted, and the contralateral femora served as no-treatment controls. After 16 weeks, the bone flaps were evaluated by x-ray (bone healing), mechanical testing (material properties), microangiography (quantification of intraosseous vasculature), histology (bone viability), and histomorphometry (bone remodeling). Bone healing occurred by 2 weeks, with further callus remodeling throughout the survival period. Eight transplants healed completely, while two had a distal pseudarthrosis. Microangiography demonstrated patent pedicles in all transplants. Intraosseous vessel densities were comparable to nonoperated (control) femora. We found ultimate strength and elastic modulus to be significantly reduced when compared to normal controls. Viable bone, increased mineral apposition rate, and bone turnover were demonstrated in all transplants. The method described, and the data provided will be of value for the further study of isolated segments of living bone, and in particular, for investigations of reconstruction of segmental bone loss in weight-bearing animal models. This study also provides important normative data on living autologous bone flap material properties, vascularity, and bone remodeling. We intend to use this method and data for comparison in subsequent studies of large bone vascularized allotransplantation.

Fixation of experimental osteotomies with bioabsorbable SR-polylactide–polyglycolide (80/20) polymeric rods

Self-reinforced polylactide-polyglycolide (80/20) composite rods, 2 mm in diameter and 36 mm in length, were implanted into the dorsal subcutaneous tissue of 20 rabbits. Osteotomies of the distal femur were fixed with these rods (2x15 mm) in the rabbits. The follow-up times varied from 3 to 104 weeks. After sacrifice, three-point bending and shear tests and molecular weight measurements were performed for subcutaneously placed rods. Radiological, histological, microradiographic, oxytetracycline-fluorescence, and histomorphometrical studies of the osteotomized and intact control femora were performed. After 6 weeks the mechanical properties had decreased significantly, but osteotomies had healed uneventfully. The present investigation showed that the mechanical strength and fixation properties of SR-Polylactide-glycolide (80/20) rods are suitable for fixation of cancellous bone osteotomies in rabbits provided that the operative technique is correct. The present article is the first report on the application of these rods for fixation of cancellous bone osteotomies.

Initial stability of circumferential meshes with impacted bone allografts for massive femoral defects

When the proximal femur is absent due to a failed femoral stem in total hip arthroplasty, impacted bone grafts contained within circumferential meshes could be an alternative reconstructive method. The purpose of this study was to analyse the initial resistance to axial and rotational forces in a fresh frozen bovine model with complete loss of the proximal femur reconstructed with a circumferential metal mesh, impacted bone allografts and a long cemented stem. Four bovine femurs with a complete proximal bone defect were reconstructed with a circumferential mesh, impacted bone grafts and a cemented stem. The results were compared with four intact femurs using the same implant. Under axial load, subsidence was observed at an average of 617 kg in the experimental group, and a cortical fracture occured at 1335 kg in the control group. Under rotational load, experimental femurs failed at an average of 79 kg and the control femurs fractured at 260 kg. This model provided 50% of the resistance to axial load and 30% of the resistance to rotational load compared to an intact femur, which is enough to resist physiological load. This stability encourages the use of circumferential meshes, impacted bone allografts and cemented stems in revision hip surgery with massive bone loss.

Combination of platelet‐rich plasma with polycaprolactone‐tricalcium phosphate scaffolds for segmental bone defect repair

Porous scaffold biomaterials may offer a clinical alternative to bone grafts; however, scaffolds alone are typically insufficient to heal large bone defects. Numerous studies have demonstrated that osteoinductive growth factor or gene delivery significantly improves bone repair. However, given the important role of vascularization during bone regeneration, it may also be beneficial to incorporate factors that promote vascular ingrowth into constructs. In this study, a strategy combining structural polycaprolactone-20% tricalcium phosphate (PCL-TCP) composite scaffolds with platelet-rich plasma (PRP) was tested. Following bilateral implantation of constructs into 8 mm rat nonunion femoral defects, 3D vascular and bone ingrowth were quantified at 3 and 12 weeks using contrast-enhanced microcomputed tomography (micro-CT) imaging. At week 3, PRP-treated femurs displayed 70.3% higher vascular volume fraction than control femurs. Interestingly, bone volume fraction (BVF) was significantly higher for the empty scaffold group at the early time point. At 12 weeks, BVF measurements between the two groups were statistically equivalent. However, a greater proportion of PRP-treated femurs (83%) achieved bone union as compared to empty scaffold controls (33%). Consistent with this observation, biomechanical evaluation of functional integration also revealed a significantly higher torsional stiffness observed for PRP-treated defects compared to empty scaffolds. Ultimate torque at failure was not improved, however, perhaps due to the slow resorption profile of the scaffold material. Histological evaluation illustrated infiltration of vascularized connective tissue and bone in both groups. Given that bone ingrowth into untreated defects in this model is minimal, PCL-TCP scaffolds were clearly able to promote bone ingrowth but failed to consistently bridge the defect. The addition of PRP to PCL-TCP scaffolds accelerated early vascular ingrowth and improved longer-term functional integration. Taken together, the results of this study suggest that the use of PRP, alone or in combination with other bioactive components, may be an effective approach to augment the ability of porous biomaterial scaffolds to repair orthotopic defects.

RECOMBINANT HUMAN OSTEOGENIC PROTEIN-1 INDUCES BONE FORMATION IN A CHRONICALLY INFECTED, INTERNALLY STABILIZED SEGMENTAL DEFECT IN THE RAT FEMUR

Background: Recombinant human osteogenic protein-1 (rhOP-1), combined with a collagen carrier, has been shown to induce new-bone formation in a variety of animal models. The purpose of the present investigation was to test the hypotheses that rhOP-1 would accelerate bone formation in an internally stabilized, chronically infected, critical-size defect in the rat femur and that this effect would be enhanced by the administration of systemic antibiotic. Methods: A 6-mm segmental defect was created surgically, stabilized with a polyacetyl plate and six Kirschner wires, and contaminated with 104 colony-forming units of Staphylococcus aureus in one femur in each of 168 Sprague-Dawley rats. After two weeks, these infected defects were débrided surgically and were assigned to one of six treatment groups. The defects in the thirty animals in the first group received lyophilized collagen carrier mixed with 200 μg of rhOP-1 dissolved in buffer, the defects in the thirty animals in the second group received carrier with 20 μg of rhOP-1 in buffer, and the defects in the twenty-four control animals in the third group received carrier mixed with buffer without rhOP-1. The last three groups were treated identically to the first three groups, except that the animals also received the antibiotic ceftriaxone for twenty-eight days after débridement. The animals were killed at two, four, eight, or twelve weeks after débridement. Newly mineralized callus within the defect, and adjacent to and bridging the outside of the defect, was assessed with use of quantitative high-resolution radiography, microcomputed tomography, torsional failure testing, and histological analysis of undecalcified sections. Results: Bacterial cultures confirmed the presence of a chronic infection during the study period in all animals. At the later time-points, significantly more newly mineralized callus was present within and adjacent to the débrided defects that had been treated with 200 μg of rhOP-1, whereas minimal amounts of callus were present within and adjacent to the defects that had been treated without rhOP-1 and with 20 μg of rhOP-1. At eight and twelve weeks after débridement, there was significantly more newly mineralized callus in the group that had been treated with 200 μg of rhOP-1 with antibiotic than in the group that had been treated with 200 μg of rhOP-1 without antibiotic (p < 0.05). At twelve weeks, the values for torque, energy to failure, and linear stiffness for femora that had been treated with 200 μg of rhOP-1 with antibiotic were not significantly different from the values for intact, contralateral control femora, whereas the values for femora that had been treated with 200 μg of rhOP-1 without antibiotic remained significantly lower than those for the intact, contralateral controls (p < 0.05). Conclusions: Recombinant human osteogenic protein-1 maintained its osteoinductive capability in the presence of chronic infection, and this property was enhanced by antibiotic therapy. No substantial callus formed in the infected defects without a sufficiently high dose of rhOP-1. Clinical Relevance: The treatment of an infection at the site of a fracture often necessitates removal of internal fixation. However, internal fixation is needed for fracture stability. This study presents an intervention that may accelerate fracture-healing in the presence of infection and colonized hardware, thereby permitting earlier removal of the hardware and more timely and effective treatment of the infection.

Recombinant Human Osteogenic Protein-1 Induces Bone Formation in a Chronically Infected, Internally Stabilized Segmental Defect in the Rat Femur

Recombinant human osteogenic protein-1 (rhOP-1), combined with a collagen carrier, has been shown to induce new-bone formation in a variety of animal models. The purpose of the present investigation was to test the hypotheses that rhOP-1 would accelerate bone formation in an internally stabilized, chronically infected, critical-size defect in the rat femur and that this effect would be enhanced by the administration of systemic antibiotic. A 6-mm segmental defect was created surgically, stabilized with a polyacetyl plate and six Kirschner wires, and contaminated with 10(4) colony-forming units of Staphylococcus aureus in one femur in each of 168 Sprague-Dawley rats. After two weeks, these infected defects were débrided surgically and were assigned to one of six treatment groups. The defects in the thirty animals in the first group received lyophilized collagen carrier mixed with 200 microg of rhOP-1 dissolved in buffer, the defects in the thirty animals in the second group received carrier with 20 microg of rhOP-1 in buffer, and the defects in the twenty-four control animals in the third group received carrier mixed with buffer without rhOP-1. The last three groups were treated identically to the first three groups, except that the animals also received the antibiotic ceftriaxone for twenty-eight days after débridement. The animals were killed at two, four, eight, or twelve weeks after débridement. Newly mineralized callus within the defect, and adjacent to and bridging the outside of the defect, was assessed with use of quantitative high-resolution radiography, microcomputed tomography, torsional failure testing, and histological analysis of undecalcified sections. Bacterial cultures confirmed the presence of a chronic infection during the study period in all animals. At the later time-points, significantly more newly mineralized callus was present within and adjacent to the débrided defects that had been treated with 200 microg of rhOP-1, whereas minimal amounts of callus were present within and adjacent to the defects that had been treated without rhOP-1 and with 20 microg of rhOP-1. At eight and twelve weeks after débridement, there was significantly more newly mineralized callus in the group that had been treated with 200 microg of rhOP-1 with antibiotic than in the group that had been treated with 200 microg of rhOP-1 without antibiotic (p < 0.05). At twelve weeks, the values for torque, energy to failure, and linear stiffness for femora that had been treated with 200 microg of rhOP-1 with antibiotic were not significantly different from the values for intact, contralateral control femora, whereas the values for femora that had been treated with 200 microg of rhOP-1 without antibiotic remained significantly lower than those for the intact, contralateral controls (p < 0.05). Recombinant human osteogenic protein-1 maintained its osteoinductive capability in the presence of chronic infection, and this property was enhanced by antibiotic therapy. No substantial callus formed in the infected defects without a sufficiently high dose of rhOP-1. The treatment of an infection at the site of a fracture often necessitates removal of internal fixation. However, internal fixation is needed for fracture stability. This study presents an intervention that may accelerate fracture-healing in the presence of infection and colonized hardware, thereby permitting earlier removal of the hardware and more timely and effective treatment of the infection.

Trabecular Bone Contributes to Strength of the Proximal Femur Under Mediolateral Impact in the Avian

Osteoporosis in long bones involves loss of cortical thickness and of the trabecular microarchitecture. Deterioration and weakening of trabecular bone tissue during osteoporosis imposes greater physiological loads on the cortical shell. However, it is unclear whether trabecular bone significantly contributes to the strength of whole bones under non-physiological impact loads. We hypothesize that trabecular tissue in epiphyses of long bones contributes to resisting and distributing impact loads. To test this hypothesis, we caused artificial trabecular bone loss in proximal femora of adult hens but did not alter the bone cortex. Subsequently, we compared the energy required to fracture the proximal part of femora with missing trabecular tissue with the energy required to fracture control femora, by means of a Charpy test. Extensive loss of trabecular bone in hens (over 0.50 grams or approximately 71% weight fraction) significantly reduced the energy required to fracture the whole proximal femur in mediolateral impacts (from approximately 0.37 joule in controls to approximately 0.20 joule after extraction of core trabecular tissue). These findings indicate that trabecular bone in the proximal femur is important for distributing impact loads applied to the cortex, and support the concept that in treating osteoporosis to prevent hip fractures, it is just as important to prevent trabecular bone loss as it is important to prevent loss of cortical thickness.

Fixation of distal femoral osteotomies with self-reinforced poly(L/DL)lactide 70 : 30 and self-reinforced poly(L/DL)lactide 70 : 30/bioactive glass composite rods. An experimental study on rabbits

Two self-reinforced poly(L/DL)lactide 70 : 30 or self-reinforced poly(L/DL)lactide 70 : 30/bioactive glass (SR-P(L/DL)LA/bioactive glass) composite rods (2 mm × 40 mm) were implanted into the dorsal subcutaneous tissue and osteotomies of the distal femur were fixed with these rods (2 mm × 26 mm) in 36 rabbits. The follow-up times varied from 3 to 100 weeks. After the animals were killed, 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 femora were performed. After 12 weeks the SR-P(L/DL)LA rods had fragmented into pieces and the mechanical properties could not be measured. The SR-P(L/DL)LA/bioactive glass rods lost their mechanical properties slower, and at 24 weeks the bending strength had decreased by 39% and the shear strength by 50%. After that the mechanical properties of the SR-P(L/DL)LA/bioactive glass rods could not be measured. All osteotomies healed well, and no gross signs of inflammatory reactions were observed. One slight displacement was seen in the three-week follow-up group with SR-P(L/DL)LA rods. Signs of resorption of the implants were seen after 48 weeks in the SR-P(L/DL)LA group and after 24 weeks in the SR-P(L/DL)LA/bioactive glass group. The SR-P(L/DL)LA/bioactive glass rods were almost totally resorbed from the bone at 100 weeks. The present investigation showed that the mechanical strength and fixation properties of the SR-P(L/DL)LA and the SR-P(L/DL)LA/bioactive glass composite rods are suitable for fixation of cancellous bone osteotomies in rabbits.

Metabolic measurement techniques to assess bone fracture healing: a preliminary study.

The purpose of this study was to project the effectiveness of using positron emission tomography for evaluation of fracture healing using the analogous method of liquid scintillation. A reproducible comminuted fracture model in rabbit femurs was stabilized with external fixation. Thirty-nine rabbits were divided into four groups: Group A had slight distraction, Group B had shortening, Group C had a bone defect, and Group D was the sham control group. At 2 and 4 weeks after fracture, the femurs had liquid scintillation measurements using 2-[14C]-deoxyglucose (2DG C-14). Glucose uptake was significantly elevated in the experimental limb relative to the contralateral control femurs at both times. The distraction group showed a significant decrease in uptake from 2-4 weeks. There was a high correlation between the liquid scintillation measurements and the radiographic fracture healing scores, with higher levels of 2DG C-14 uptake corresponding to lower levels of fracture healing calcification. The high correlation found between 2DG C-14 uptake and radiographic scores suggests that positron emission tomography used in conjunction with a glucose-based radiopharmaceutical such as 2-[18F]fluoro-2-deoxyglucose can monitor the fracture healing process effectively.

Fixation of distal femoral osteotomies with self-reinforced polymer/bioactive glass rods: an experimental study on rabbits

Two self-reinforced poly(desamino tyrosyl–tyrosine ethyl ester carbonate), poly(DTE carbonate) or self-reinforced poly(DTE carbonate)/bioactive glass rods, (2 mm by 40 mm) were implanted into the dorsal subcutaneous tissue and osteotomies of the distal femur were fixed with these rods (2 mm by 26 mm) in 36 rabbits. The follow-up times varied from three to 100 weeks. 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 femora were performed. The initial mechanical properties were higher with the SR-poly(DTE carbonate) rods, but the SR-poly(DTE carbonate)/bioactive glass rods lost their mechanical properties slower. At 100 weeks the bending strength had decreased to 21% of the initial value with the SR-poly(DTE carbonate) rods and to 49% with the SR-poly(DTE carbonate)/bioactive glass rods. The shear strength had decreased to 10% with the SR-poly(DTE carbonate) rods and to 23% of the initial value with the SR-poly(DTE carbonate)/bioactive glass rods. Two slight displacements and one delayed union and one failure of fixation were seen in the SR-poly(DTE carbonate) group. In the SR-poly(DTE carbonate)/bioactive glass group five delayed unions and seven slight displacements were seen. No signs of osteolysis or foreign body reactions were observed. Signs of resorption of the implants were seen at 100 weeks in the SR-poly(DTE carbonate)/bioactive glass group. The present investigation showed that the mechanical strength and fixation properties of SR-poly(DTE carbonate) and SR-poly(DTE carbonate)/bioactive glass rods are suitable for fixation of cancellous bone osteotomies in rabbits.

Fixation of distal femoral osteotomies with self-reinforced polymer/bioactive glass rods: an experimental study on rabbits

Two self-reinforced poly(desamino tyrosyl–tyrosine ethyl ester carbonate), poly(DTE carbonate) or self-reinforced poly(DTE carbonate)/bioactive glass rods, (2 mm by 40 mm) were implanted into the dorsal subcutaneous tissue and osteotomies of the distal femur were fixed with these rods (2 mm by 26 mm) in 36 rabbits. The follow-up times varied from three to 100 weeks. 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 femora were performed. The initial mechanical properties were higher with the SR-poly(DTE carbonate) rods, but the SR-poly(DTE carbonate)/bioactive glass rods lost their mechanical properties slower. At 100 weeks the bending strength had decreased to 21% of the initial value with the SR-poly(DTE carbonate) rods and to 49% with the SR-poly(DTE carbonate)/bioactive glass rods. The shear strength had decreased to 10% with the SR-poly(DTE carbonate) rods and to 23% of the initial value with the SR-poly(DTE carbonate)/bioactive glass rods. Two slight displacements and one delayed union and one failure of fixation were seen in the SR-poly(DTE carbonate) group. In the SR-poly(DTE carbonate)/bioactive glass group five delayed unions and seven slight displacements were seen. No signs of osteolysis or foreign body reactions were observed. Signs of resorption of the implants were seen at 100 weeks in the SR-poly(DTE carbonate)/bioactive glass group. The present investigation showed that the mechanical strength and fixation properties of SR-poly(DTE carbonate) and SR-poly(DTE carbonate)/bioactive glass rods are suitable for fixation of cancellous bone osteotomies in rabbits.

Effects of extracorporeal shock waves on immature rabbit femurs

We hypothesized that extracorporeal shock waves induce overgrowth and local increases in bone mineral content (BMC) in immature long bones. Immature male rabbits (n=14; 9 weeks old) were randomized equally between group I, which received 1000 100 MPa shock waves on the femoral shaft and group II, which received 5000. Unexposed femurs were used as controls. No fractures occurred in group I; three occurred in group II. Six weeks after exposure, the length and width were significantly larger (1.0 and 14.9%, respectively), and the BMC was significantly higher (22.8%) than those of control femurs in group I. These results of differences in width and BMC might be clinically useful.

Effects of extracorporeal shock waves on immature rabbit femurs.

We hypothesized that extracorporeal shock waves induce overgrowth and local increases in bone mineral content (BMC) in immature long bones. Immature male rabbits (n=14; 9 weeks old) were randomized equally between group I, which received 1000 100 MPa shock waves on the femoral shaft and group II, which received 5000. Unexposed femurs were used as controls. No fractures occurred in group I; three occurred in group II. Six weeks after exposure, the length and width were significantly larger (1.0 and 14.9%, respectively), and the BMC was significantly higher (22.8%) than those of control femurs in group I. These results of differences in width and BMC might be clinically useful.

Fixation of distal femoral osteotomies with self-reinforced poly(L/DL)lactide 70:30/bioactive glass composite rods. An experimental study on rats.

Self-reinforced poly(L/DL)lactide 70:30/bioactive glass [SR-P(L/DL)LA/bioactive glass] composite rods, 2 mm in diameter and 36 mm in length, were implanted into the dorsal subcutaneous tissue of 16 rats. Osteotomies of the distal femur were fixed with these rods (2 x 15 mm) in 64 other rats. The follow-up times varied from one week to one 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 femora were performed. At 24 weeks the mechanical properties had decreased significantly. Thirty-nine osteotomies healed uneventfully. One of the 64 evaluated osteotomies showed signs of infection at six weeks, and there were 19 non-unions and six delayed unions. In 20 operations the fixation was loose and out of these 14 non-unions were observed. No gross signs of inflammatory or foreign-body reactions were observed. The present investigation showed that the mechanical strength and fixation properties of SR-P(L/DL)LA/bioactive glass composite rods are suitable for fixation of cancellous bone osteotomies in rats as long as the operative technique is correct. The present article is the first report on the application of SR-P(L/DL)LA/bioactive glass composite rods for fixation of cancellous bone osteotomies.

A longitudinal evaluation of the effect of two doses of tibolone on bone density and metabolism in early postmenopausal women

Tibolone, a steroid with tissue-specific activities, can reduce the bone resorption that takes place after the menopause. The present calcium-controlled, 2-year study aimed to evaluate the effect of two doses of oral tibolone, 1.25 mg and 2.5 mg, on bone loss in early postmenopausal women. The subjects were randomly allocated to one of the three groups, namely tibolone 2.5 mg (n=30), tibolone 1.25 mg (n=30) and a control group (n=30). All subjects received 1000 mg of calcium per day. In the control group, vertebral and femur bone mineral density (BMD) decreased significantly (p<0.05) after 12 and 24 months. In both tibolone groups, vertebral and femur BMD increased significantly (p<0.05) increased after 12 and 24 months. In the control group, bone turnover markers (urinary excretion of hydroxyproline/creatinine and plasma osteocalcin levels) remained constant, while in both tibolone groups these markers showed similar significant decreases (p<0.05) after 12 and 24 months. After 24 months, body weight increased in the control group (p<0.05), while smaller increments were evident in the tibolone groups. Symptom scores in the control group did not show any significant modification during the study. In contrast, the administration of 2.5 mg tibolone was significantly (p<0.05) effective in reducing hot flushes and other symptoms. The tibolone 1.25 mg group yielded similar results (even if it was proportionally less efficient) to the higher dose. It is concluded that tibolone is effective, even at lower doses, in relieving climacteric symptoms and preventing a decrease in spine and femur BMD in early postmenopausal women.

Cryopreservation with dimethyl sulfoxide sustains partially the biological function of osteochondral tissue

The clinical routine use of bone allograft transplants dates back to the discovery that grafts devitalized by freezing bear a reduced antigenicity. Graft failures, caused by a host versus graft reaction, however, remain a clinical problem. Previous investigations on pancreatic islet allografts revealed improved survival and biological function when fast cryopreservation (−70°C/min) was performed in the presence of dimethyl sulfoxide (DMSO). The aim of this study was to determine the effect of fast freezing using DMSO on the biological function of osteochondral tissues. Organ culture was performed with neonatal femora of mice, untreated, rapidly frozen (−70°C/min) with DMSO, or frozen without DMSO. After the culture, tissue morphology, cellular proliferation, osteoblast function, osteoclasts, and the presence of antigen-presenting cells were investigated. In untreated control femora histology appeared normal and proliferating and collagen-synthesizing osteoblasts, osteoclasts, and B-cells and macrophages were present. In frozen femora (with and without DMSO) a disintegration of the periosteum and the epiphyseal growth plate were observed and no active osteoblasts could be detected. Osteoclasts were partially detached from the bone surface. Cell proliferation was fully blocked in femora frozen in the absence of DMSO, while freezing in the presence of DMSO preserved cell proliferation in the medullary canal. The proliferating cells do not express epitopes present on the cells of the B-cell or macrophage lineages. Although the biological function of osteoblasts and osteoclasts was lost upon freezing of osteochondral tissue, DMSO included in freezing protocols preserves some residual cell viability which may be of importance for early graft revascularization as has been previously demonstrated by our group.

The effect of implant overlap on the mechanical properties of the femur.

The most biomechanically stable relationship between the side plate of a compression hip screw (CHS) and retrograde intramedullary (IM) femoral nail has not been described in the literature. This becomes a clinical issue when treating supracondylar femur fractures with a retrograde nail in patients with a history of compression hip screw fixation of intertrochanteric fractures. The proximal end of the nail and the interlocking screws may act as a stress riser in the femoral diaphysis. The purpose of this study is to determine the biomechanical consequences of the amount of implant overlap between a CHS plate and retrograde IM femoral nail. Nine paired fresh-frozen cadaver femora from elderly donors were cleaned of soft tissue and fixed with uniaxial strain gauges. Each femur was loaded three times in a fall-loading configuration to 50 kg at a rate of 1 Hz. The study consisted of two phases. In phase 1, six pair were randomly divided into a control and test femur from each pair. Three states were compared on each test femur: uninstrumented, instrumented with CHS, and instrumented with CHS and retrograde nail. The control femur consisted of the matched femur tested in two states: uninstrumented and instrumented with a CHS. The femora were then loaded to failure. The tests were performed with the retrograde nail and CHS gapped 3 cm, kissing, and overlapping by two screw holes (two pair for each state). In phase 2, each of the remaining three pair were instrumented with a CHS and retrograde nail overlapping in one femur and gapped in the matched femur and tested in the same manner. Data analysis was performed using Pearson's correlation coefficients between groups. Paired samples t tests were used to compare differences within test states and independent samples t tests were used to compare differences between femora. Mean strain at 50-kg load, load-versus-strain patterns, failure patterns, and load and strain at failure were recorded. RESULTS; Correlation coefficients were greater than 0.98 within and between pairs (p < 0.001). There were statistically significant differences (p < 0.05) in strain patterns between the uninstrumented, CHS, and CHS/IM test states. The addition of a side plate significantly (p < 0.05) increased lateral compressive strains in the femoral diaphysis. Mean strain at 50-kg load was significantly (p < 0.05) altered by the addition of the retrograde nail in all three implant orientations. Gapped implants failed at lower loads and strains than femurs with kissing and overlapping implants. Gapped constructs failed at lower loads than control states. Overlapped constructs tolerated the highest loads and strains before failure. Strain patterns are altered by the degree of implant overlap in the proximal femoral diaphysis. Femora with uninstrumented intervals between retrograde nails and side plates fail at lower loads than femora without retrograde nails and those with kissing or overlapping implants. Kissing or overlapping instrumentation increases load to failure and creates a more biomechanically stable construct than gapped implants. The findings of this study suggest an overlapping implant orientation in the femur increases failure load at the implant interface.

Effect of Low-Intensity Ultrasound Stimulation on Consolidation of the Regenerate Zone in a Rat Model of Distraction Osteogenesis

This study was performed to explore the tissue-level changes in mineralization caused by low-intensity ultrasound stimulation after distraction osteogenesis. Unilateral femoral lengthenings (7 mm) were performed on 34 male Sprague-Dawley rats. Half of the animals received daily ultrasound stimulation for 5 weeks; the remaining animals received sham treatments. Healing was assessed with serial radiographs, quantitative micro-computed tomography, and biomechanical testing. Twenty-one animals were evaluated at the conclusion of the study (9 experimental, 12 control). Radiographically, healing of the ultrasound-treated bones preceded that of the sham-treated bones by approximately 1 week. Bone volume fraction and trabecular bone pattern factor were significantly higher in the ultrasound-treated animals, but there were no significant differences in bone mineral content or bone mineral density. The ultrasound-treated femurs were 20% stiffer and 33% stronger than the control femurs, but the differences were not statistically significant. These findings suggest that pulsed, low-intensity ultrasound matures the regenerate by altering the microarchitecture of the newly formed bone.

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.

Shear-load carrying capacities of the distal rat femora after osteotomy fixed with self-reinforced polyglycolic acid and poly-L-lactic acid pins.

Distal femora of 40 rats were osteotomized and fixed with self-reinforced polyglycolide (SR-PGA) and self-reinforced polylactide (SR-PLLA) pin 2.0 mm in diameter and 15 mm in length. The shear-load carrying capacities of the osteotomized bones were compared with each other and with the intact control rat distal femora of the same age of 20 pairs. The follow-up times were 1, 3, 6, 12, 24, 36, 48, and 52 weeks. After killing all operated and control femora were examined macroscopically and radiographically. The shear-load carrying capacities reached their highest values at 24 weeks in the SR-PGA-fixed specimens, after that decreasing to the level where they remained. In the SR-PLLA-fixed specimens the strength values of the pins increased after three weeks, but there was a decrease at 24 weeks. After that the shear-load carrying capacities started to raise because of the influence of the healed osteotomy. In the control bones the shear-load carrying capacities were weaker than in the SR-PGA-and SR-PLLA-fixed specimens except at three weeks, as the osteotomies had not yet healed. During the whole follow-up period the mean shear-load carrying capacity of the SR-PGA-fixed specimens was 199.1 N, in the SR-PLLA-fixed specimens 214.6 N, the corresponding value of the control specimens being 148.2 N.