Prediction of three-dimensional contact stress and ligament tension in the ankle during stance determined from computational modeling.

BACKGROUND: Our goal was to quantify and visualize the three-dimensional loading relationship between the ligaments and articular surfaces of the ankle to identify and determine the stabilizing roles of these anatomical structures during the stance phase of gait. MATERIALS AND METHODS: We applied discrete element analysis to computationally model the three-dimensional contact characteristics and ligament loading of the ankle joint. Physiologic loads approximating those at five positions in the stance phase of a normal walk cycle were applied. We analyzed joint contact pressures and periankle ligament tension concurrently. RESULTS: Most ankle joint loading during the stance phase occurred across the articular surfaces of the joint, and the amount of ligament tension was small. The tibiotalar articulation showed full congruency throughout most of the stance phase, with peak pressure developing anteriorly toward the toe-off frame. Of the periankle ligaments, the deep deltoid ligament transferred the most force during the stance phase (57.2%); the superficial deltoid ligament transferred the second-most force (26.1%). The anterior talofibular ligament transferred force between the talus and fibula continuously, whereas the calcaneofibular ligament did not carry force during gait. The distal tibiofibular ligaments and the interosseous membrane were loaded throughout the stance phase. CONCLUSION: Force transmission through the ankle joint during the stance phase is predominantly through the articular surfaces, and the periankle ligaments do not play a major stabilizing role in constraining ankle motion. The medial ligaments have a more important role than do the lateral ligaments in stabilizing the ankle joint. CLINICAL RELEVANCE: In addition to ligament insufficiency, other factors, such as varus tilt of the tibial plafond, may be important in the development of recurrent instability. Continuous loading of syndesmosis ligaments provides a theoretical basis for evidence of syndesmosis screw breakage or loosening. The analysis method has potential applications for clarifying ankle joint function and providing a basis for comparison between normal and abnormal joint conditions.

Upper tibia osteotomy: long term results - realignment analysis using OASIS computer software.

BACKGROUND: The normal values for axial alignment and joint line obliquity of the knee that indicate a successful valgus upper tibial osteotomy have not been established and reported in the literature. METHODS: To identify those parameters we prospectively followed 51 patients with 54 lateral closing wedge upper tibial osteotomies performed after preoperative and postoperative analysis of standardized hip-to-ankle radiographs with a software computer program (OASIS). RESULTS: Of the 54 knees, 18 (33.3%) underwent additional surgery. The average follow-up of the remaining 36 knees was 10 years (range 6.9-13.8 years). The cumulative osteotomy survival rate was 89% at 5 years and 76% at 10 years. Compared with patients whose postoperative femorotibial angle was 174 degrees -180 degrees , the patients whose postoperative femorotibial angle was <174 degrees or >180 degrees did worse with respect to osteotomy failure. Ten knees were at a decreased risk of failure. These knees had a postoperative femorotibial angle of 174 degrees -180 degrees , lateral joint line obliquity of <4 degrees , and a medial plateau force distribution of 40%-60%. The knees that met these criteria had 100% survival at 5 and 10 years, whereas the rest of the knees had survival rates of 86% and 70%, respectively. CONCLUSIONS: We believe that using these criteria during preoperative planning may improve the survival of upper tibial osteotomy provided a precise, reproducible surgical technique and rigid fixation can be performed.

Extracortical bone-bridging fixation with use of cortical allograft and recombinant human osteogenic protein-1.

BACKGROUND: Prosthetic reconstruction with extracortical bone-bridging fixation is an effective method for the treatment of massive bone loss. We evaluated the effect of the use of recombinant human osteogenic protein-1 (rhOP-1) combined with allogenic cortical bone strips as a substitute for an autogenous bone graft for extracortical bone-bridging. METHODS: Eight skeletally mature adult male dogs underwent a bilateral resection of a 6-cm segment of the femoral diaphysis and reconstruction with a porous segmental prosthesis. On the experimental side, an allogenic cortical onlay graft in the form of bone strips combined with rhOP-1 mixed with bovine type-I-collagen putty (OP-1 putty) was applied. On the control side, allogenic cortical bone strips augmented with autogenous cancellous bone chips and bone marrow were used. The reconstructions were followed for twelve weeks with biweekly evaluations of load-bearing gait and radiographs. The animals were killed twelve weeks after the surgery, and the reconstructed femora were studied biomechanically, histologically, and with microradiographs. RESULTS: One animal was excluded from the analysis because a fracture of the proximal part of the femur on the control side was observed radiographically twelve weeks after the surgery. There were no significant differences in load-bearing gait between the experimental and control sides throughout the experimental period. Serial radiographs revealed a 1.9-fold (p<0.04), 2.7-fold (p<0.01), and 2.4-fold (p<0.03) increase in mineralized area on the experimental side at two, four, and six weeks, respectively. The torsional stiffness and strength of the fixation attributed to the extracortical bridging bone alone were 2.3-fold (p<0.03) and 2.2-fold (p=0.058) greater on the experimental side, respectively. The allograft porosity on the experimental side was 3.8-fold (p<0.02) greater than that on the control side. With the number of samples available, there was no significant difference in mineral apposition rate between the experimental and control sides. CONCLUSIONS: In an animal model of segmental bone-replacement prosthetic fixation with use of the extracortical bone-bridging principle, an allogenic onlay cortical graft combined with rhOP-1 was an effective substitute for autogenous bone graft.

Virtual Interactive Musculoskeletal System (VIMS) in orthopaedic research, education and clinical patient care.

The ability to combine physiology and engineering analyses with computer sciences has opened the door to the possibility of creating the "Virtual Human" reality. This paper presents a broad foundation for a full-featured biomechanical simulator for the human musculoskeletal system physiology. This simulation technology unites the expertise in biomechanical analysis and graphic modeling to investigate joint and connective tissue mechanics at the structural level and to visualize the results in both static and animated forms together with the model. Adaptable anatomical models including prosthetic implants and fracture fixation devices and a robust computational infrastructure for static, kinematic, kinetic, and stress analyses under varying boundary and loading conditions are incorporated on a common platform, the VIMS (Virtual Interactive Musculoskeletal System). Within this software system, a manageable database containing long bone dimensions, connective tissue material properties and a library of skeletal joint system functional activities and loading conditions are also available and they can easily be modified, updated and expanded. Application software is also available to allow end-users to perform biomechanical analyses interactively. Examples using these models and the computational algorithms in a virtual laboratory environment are used to demonstrate the utility of these unique database and simulation technology. This integrated system, model library and database will impact on orthopaedic education, basic research, device development and application, and clinical patient care related to musculoskeletal joint system reconstruction, trauma management, and rehabilitation.

Effect of pulsed electromagnetic fields on maturation of regenerate bone in a rabbit limb lengthening model.

To study the effect of applying pulsed electromagnetic fields (PEMF) during the consolidation phase of limb lengthening, a mid-tibial osteotomy was performed in 18 adult New Zealand White rabbits and an external fixator was applied anteromedially. Animals were randomly assigned to treatment and control groups. After a 7-day latency period, the tibiae were distracted 0.5 mm every 12 h for 10 days. The treatment group received a 20-day course of PEMF for 60 min daily, coinciding with initiation of the consolidation phase. The control group received sham PEMF. Radiographs were performed weekly after distraction. Animals were euthanized 3 weeks after the end of distraction. Radiographic analysis revealed no significant difference in regenerate callus area between treatment and control tibiae immediately after distraction, at 1 week, 2 weeks, or 3 weeks after distraction ( p = 0.71, 0.22, 0.44, and 0.50, respectively). There was also no significant difference in percent callus mineralization ( p = 0.96, 0.69, 0.99, and 0.99, respectively). There was no significant difference between groups with respect to structural stiffness ( p = 0.80) or maximal torque to failure ( p = 0.62). However, there was a significant positive difference in mineral apposition rate between groups during the interval 1-2 weeks post-distraction ( p < 0.05). This difference was no longer evident by the interval 2-3 weeks post-distraction. While PEMF applied during the consolidation phase of limb lengthening did not appear to have a positive effect on bone regenerate, it increased osteoblastic activity in the cortical bone adjacent to the distraction site. Since the same PEMF signal was reported to be beneficial in the rabbit distraction osteogenesis when applied during distraction phase and consolidation phase, application of PEMF in the early phase may be more effective. Further work is necessary to determine optimal timing of the PEMF stimulation during distraction osteogenesis.

Three-dimensional dynamic hip contact area and pressure distribution during activities of daily living.

Estimation of the hip joint contact area and pressure distribution during activities of daily living is important in predicting joint degeneration mechanism, prosthetic implant wear, providing biomechanical rationales for preoperative planning and postoperative rehabilitation. These biomechanical data were estimated utilizing a generic hip model, the Discrete Element Analysis technique, and the in vivo hip joint contact force data. The three-dimensional joint potential contact area was obtained from the anteroposterior radiograph of a subject and the actual joint contact area and pressure distribution in eight activities of daily living were calculated. During fast, normal, and slow walking, the peak pressure of moderate magnitude was located at the lateral roof of the acetabulum during mid-stance. In standing up and sitting down, and during knee bending, the peak pressures were located at the edge of the posterior horn and the magnitude of the peak pressure during sitting down was 2.8 times that of normal walking. The peak pressure was found at the lateral roof in climbing up stairs which was higher than that in going down stairs. These results can be used to rationalize rehabilitation protocols, functional restrictions after complex acetabular reconstructions, and prosthetic component wear and fatigue test set up. The same model and analysis can provide further insight to soft tissue loading and pathology such as labral injury. When the pressure distribution on the acetabulum is inverted onto the femoral head, prediction of subchondral bone collapse associated with avascular necrosis can be achieved with improved accuracy.

Tendon reattachment to a metallic implant using an allogenic bone plate augmented with rhOP-1 vs. autogenous cancellous bone and marrow in a canine model.

Functionality of endoprosthetic reconstruction may be improved through secure and lasting soft tissue reattachment directly to the metallic implant surface. Tendon reattachment to the metallic surface of a titanium implant (enhanced tendon anchor, ETA) using autogenous bone plate as an interpositional structure between the tendon and metal, augmented with autogenous bone chips and marrow, provided successful mechanical and functional outcome. However, preparation of the autogenous bone plate is not practical in a clinical setting, but application of an allogenic bone plate could be an alternative. The autogenous cancellous bone and marrow may also be substituted by bone growth factors so that no autogenous bone graft is required. We hypothesized that the reconstitution of the direct tendon-bone insertion morphology in tendon reattachment to metallic implant could be achieved using allogenic cancellous bone plate augmented with autogenous cancellous bone and marrow, and that the autogenous bone grafts could be replaced by recombinant human osteogenic protein-1 (rhOP-1). In two canine groups the supraspinatus tendon was reattached unilaterally to a modified ETA implant with a highly porous metallic surface known as Tritanium Dimensionalized Metal. Allogenic bone plates saturated with rhOP-1-collagen putty were used in the OP-1 (OP) group, while plates saturated with autogenous cancellous bone and marrow were used in the bone marrow (BM) group. Functional, radiographical, mechanical and histomorphological analysis results were compared between both groups. At 15 weeks, gait analysis showed 78% and 81% recovery of preoperative weight-bearing in OP and BM groups, respectively. The calcified area around the tendon in OP group was 5.2 times larger than that in BM group (p<0.001). The ultimate tensile strength of the reattachment was 24% and 38% of the intact contralateral side in OP and BM groups, respectively, without significant difference between them. There was evidence of tendon-bone insertion transitional zones, tissue ingrowth and adhesion to the metallic surface in both groups. In conclusion, the use of the allograft combined with rhOP-1 had a similar effect as combined with autogenous cancellous bone and marrow in the tendon reattachment to the metallic surface.

Quantification of the microstructural anisotropy of distraction osteogenesis in the rabbit tibia.

A longitudinal orientation of fibers and trabeculae has been observed histologically within distracted callus. This study quantified the intensity and angle of orientation of trabeculae within a distracted callus. Sixteen New Zealand white rabbits underwent unilateral tibial callus distraction with an external fixator across a mid-diaphyseal osteotomy. Included were: a seven-day postoperative latency period, ten days of distraction at 0.5 mm every 12 hours, and 20 days of post-distraction consolidation before euthanasia. Tibiae were removed, stripped of soft tissue, sectioned, and processed for decalcified histology. Micrographs of mid-coronal sections of the callus were evenly divided into 12 regions and underwent Fast Fourier Transform (FFT) analysis of the digitized image to determine the angle and intensity of the orientation of the bony trabeculae within the callus. The microstructure of the regenerate callus demonstrated an angle of orientation that uniformly matched that of cortical bone in all of regions of the callus and an intensity of orientation which approached that of cortical bone.

Use of virtual, interactive, musculoskeletal system (VIMS) in modeling and analysis of shoulder throwing activity.

Our purpose in this study was to apply the virtual, interactive, musculoskeletal system (VIMS) software for modeling and biomechanical analysis of the glenohumeral joint during a baseball pitching activity. The skeletal model was from VIMS library and muscle fiber attachment sites were derived from the visible human dataset. The muscular moment arms and function changes are mainly due to the large humeral motion involved during baseball pitching. The graphic animation of the anatomic system using VIMS software is an effective tool to model and visualize the complex anatomical structure of the shoulder for biomechanical analysis.

The effect of multidrug chemotherapy on bone graft augmented prosthesis fixation.

Use of combination adjuvant chemotherapies have improved the disease free survival rate of tumor patients significantly. However, studies have shown that chemotherapeutic agents have negative effects on bone graft incorporation and fixation of porous-coated prostheses needed for reconstruction of bone defects after wide resection of malignant tumors. Unilateral resection of a 6-cm segment of the femoral diaphysis and reconstruction with a porous-coated segmental prosthesis was performed in eight mixed-breed dogs under perioperative chemotherapy with doxorubicin, cisplatin, and ifosfamide. Eight strips of autogenous cortical bone were evenly placed around the junctions between the femur and the prosthetic surface. Autogenous cancellous bone was placed under and between the strips of cortical bone. Two cycles of the chemotherapy were given preoperatively, and three cycles postoperatively. The animals were followed for 12 weeks, with sequential assessments of weight-bearing and radiographic evaluation. Biomechanical, histological, and microradiographic analyses of the retrieved specimens were performed. Doxorubicin, cisplatin, and ifosfamide combination chemotherapy showed a significant effect on new bone formation as seen in reduced callus size and lower ultimate strength of extracortical fixation. However, the onlay corticocancellous grafting method provided better biologic fixation of the prosthesis compared with fixation without any bone grafting under non-chemotherapy condition in a previous study. Extracortical bone grafting is an effective modality for implant fixation even under intensive chemotherapy.

Linear increase in axial stiffness of regenerate callus during limb lengthening.

Distraction osteogenesis is a powerful tool for addressing segmental defects and limb-length discrepancies. Guidelines for the rate and rhythm of distraction have been described. The possibilities of early consolidation or nonunion threaten clinical success. A quantifiable method for monitoring the distraction gap would be useful. Previous methods to measure regenerate callus stiffness have not gained widespread clinical acceptance, largely because of cumbersome instrumentation. A rabbit tibial lengthening model was used to show the clinical utility of a digital torque wrench in monitoring axial stiffness of the regenerate bone callus during distraction osteogenesis. We confirmed the linear increase in peak torsional stiffness with time, which has been reported by others. This relationship may prove to be a useful clinical adjunct in guiding the rate and rhythm of distraction during limb lengthening.

Computational simulation of axial dynamization on long bone fractures.

BACKGROUND: Axial dynamization has been shown in previous studies to promote callus formation, improve bone healing at fracture sites, and enhance bone remodeling. However, the possibility of non-axial movements or uniform fracture site compression during dynamization, and the appropriate relaxation of fixator joints to achieve such function, have not been investigated. METHODS: This study used previously developed computational models based on two commercially available unilateral external fixators (Dynafix and Orthofix) to analyze the fixator joint adjustments used and the fracture site movements generated during dynamization. FINDINGS: When none of the fixator's sliding joints were parallel to the long bone axis, significant non-axial movements occurred during dynamization. The dual sliding joint design of the Dynafix fixator was beneficial in reducing these non-axial movements. When all of the fixator joints were allowed to adjust simultaneously during dynamization, exact axial movement or uniform compression at a complicated fracture site was achievable. INTERPRETATION: This study revealed that significant non-axial movements may occur during dynamization, and that such a deficiency can be corrected by relaxing certain fixator joints in addition to the sliding mechanism. The same modeling technique can also be applied in bone lengthening application to assure desirable limb alignment during the distraction process. These analysis results can aid the performance assessment of an external fixator and facilitate appropriate application of such a device to achieve either active or controlled axial movement.

Biomechanical considerations of fracture treatment and bone quality maintenance in elderly patients and patients with osteoporosis.

Osteoporosis is a major public health problem that is characterized by low bone mass and structural deterioration of bone tissue, leading to bone fragility and an increased susceptibility to fractures of the hip, spine, and wrist. Poor bone quality in patients with osteoporosis presents the surgeon with difficult treatment decisions. Bone fracture repair has more pathways with combinations of bone formation mechanisms, which depend on the type of fracture fixation to be applied to achieve the desirable immobilization. There only may be one remodeling principle and in less than ideal conditions, mechanical and biophysical stimuli may provide effective augmentation of fracture healing in elderly patients. A different stimulus may limit its association to a specific healing mechanism. However, no matter which fixation method is used, an accurate reduction is a requisite for bone healing. Failure to realign the fracture site would result in delayed union, malunion, or nonunion. Therefore, a basic understanding of the biomechanics of osteoporotic bone and its treatment is necessary for clinicians to establish appropriate clinical treatment principles to minimize complications and enhance the patient's quality of life. We describe the biomechanical considerations of osteoporosis and fracture treatment from various aspects. First, bone structure and strength characterization are discussed using a hierarchical approach, followed by an innovative knowledge-based approach for fracture reduction planning and execution, which particularly is beneficial to osteoporotic fracture. Finally, a brief review of the results of several experimental animal models under different fracture types, gap morphologic features, rigidity of fixation devices, subsequent loading conditions, and biophysical stimulation is given to elucidate adverse mechanical conditions associated with different bone immobilization techniques that can compromise normal bone fracture healing significantly.

Long-term results of segmental prosthesis fixation by extracortical bone-bridging and ingrowth.

BACKGROUND: The technique of extracortical bone-bridging and ingrowth fixation with a porous coating over the shoulder region of the implant and augmentation by autogenous bone-grafting was introduced to improve the longevity of implant fixation. The potential advantages of this technique are that new-bone formation across the bone-prosthesis junction may share stress and may prevent osteolysis by sealing off this critical region against the infiltration of wear particles. The objectives of this study were to examine the prevalence of stem-loosening with use of the extracortical bone-bridging and ingrowth technique, the amount of bone formation over the porous-coated region of this prosthesis, and the characteristics of bone formation over the porous-coated region and adjacent bone. METHODS: Forty-three patients who had prosthetic reconstruction with the extracortical bone-bridging and ingrowth technique from 1976 to 1990 were included in this retrospective study. The mean length of follow-up was 9.7 years (range, two to twenty-one years). All but one patient were managed with autogenous bone graft; five, with allograft and autograft; and one, with allograft only. Extracortical bone formation was measured over a 2-cm length of the porous-coated region of the prosthesis in four zones (the medial and lateral aspects on anteroposterior radiographs and the anterior and posterior aspects on lateral radiographs) and was reported as the percentage of the total length (8 cm) covered by extracortical bone with a thickness of >1 mm. The Spearman rank coefficient was used to assess the correlation between pairs of continuous variables. RESULTS: The final average percentage of the porous-coated region that was covered by extracortical bone formation was 76% +/- 34% for all patients and anatomical sites of reconstruction. Use of bone cement was associated with less bone formation (p = 0.04), and this value remained lower at the final measurement (p = 0.06). One stem had aseptic loosening, but no sign of osteolysis was found. The radiographic appearance of the bone formation had stabilized at two years of follow-up. All patients with allograft augmentation had greater bone formation. The amount of extracortical bone formation did not differ in relation to the type of porous coating, anatomical sites, pathological disorder, sex or age of the patient, or length of reconstruction. CONCLUSIONS: As shown by the low prevalence of stem-loosening (two of fifty-six stems or one of forty-three patients), the use of the extracortical bone-bridging and ingrowth fixation technique is associated with improved stem fixation in segmental bone-replacement prostheses applied for limb salvage. In the demanding biomechanical environment and with the risk of stress and particle-related bone resorption, the extracortical bone-bridging and ingrowth fixation is an attractive method to provide long-lasting implant fixation.

The use of Novabone and Norian in cranioplasty: a comparative study.

Bone replacement products have enhanced the ease of reconstructing bone while improving morbidity related to bone harvest. Although these products are successfully used, studies of bone healing and biomechanical strength are lacking. We aimed to compare how Norian CRS (cranial replacement substance) and Novabone C/M heal in a cranial defect. Adult New Zealand rabbits underwent removal of a critical size cranial defect. The defect was filled with Novabone (n = 8), Novabone plus demineralized bone matrix (n = 8), or Norian (n = 8), or it was left empty (n = 8). Rabbits were euthanized at 8 weeks. Cranial specimens were harvested and soft radiographs, contact microradiographs, and biomechanical testing were done. Soft radiographs revealed opacification like adjacent bone with Novabone, which was augmented when Novabone was combined with demineralized bone matrix. Norian maintained an opaque appearance. The control group did not heal. Contact microradiographs demonstrated bone within the healing defect with Novabone, which was augmented by demineralized bone matrix. Norian was not replaced with bone but served as a scaffold for bone formation. Biomechanical indentation testing demonstrated that the stiffness of Norian was the highest. Novabone plus demineralized bone matrix had a higher stiffness than Novabone alone. All experimental groups had a statistically significant difference compared with Norian. None of the groups achieved the strength of unoperated native bone. Studying two popular products, we found evidence that Novabone was incorporated into cranial bone, regenerating the bone. Novabone healed at a faster rate, creating a stronger product, with demineralized bone matrix. The biomechanical strength of the healed defect was higher in the Norian group, because the bone cement remained solid and was not incorporated, unlike crania reconstructed with Novabone.

Graphic-based musculoskeletal model for biomechanical analyses and animation.

The ability to combine physiology and engineering analyses with computer sciences has opened the door to the possibility of creating the 'Virtual Human' reality. This paper presents a broad foundation for a full-featured biomechanical simulator for the human musculoskeletal system physiology. This simulation technology unites the expertise in biomechanical analysis and graphic modeling to investigate joint and connective tissue mechanics at the structural level and to visualize the results in both static and animated forms together with the model. Adaptable anatomical models including prosthetic implants and fracture fixation devices and a robust computational infrastructure for static, kinematic, kinetic, and stress analyses under varying boundary and loading conditions are incorporated on a common platform, the VIMS (Virtual Interactive Musculoskeletal System). Within this software system, a manageable database containing long bone dimensions, connective tissue material properties and a library of skeletal joint system functional activities and loading conditions are also available and they can easily be modified, updated and expanded. Application software is also available to allow end-users to perform biomechanical analyses interactively. This paper details the design, capabilities, and features of the VIMS development at Johns Hopkins University, an effort possible only through academic and commercial collaborations. Examples using these models and the computational algorithms in a virtual laboratory environment are used to demonstrate the utility of this unique database and simulation technology. This integrated system will impact on medical education, basic research, device development and application, and clinical patient care related to musculoskeletal diseases, trauma, and rehabilitation.

Assessment of external fixator reusability using load- and cycle-dependent tests.

No standard method has been established for investigating repeated use of an external fixator. The purpose of the current study was to establish a fatigue testing method for assessing fixator frame reuse. A unilateral DynaFix trade mark external fixator system was tested using high-load and low-cycle (900-150 N at 5 Hz) and low-load and high-cycle (450-100 N at 10 Hz) tests (assumed one use of 500,000 and 1 million cycles, respectively). These loading conditions were selected to simulate single clinical use and to satisfy Food and Drug Administration requirements. In the high-load low-cycle test, substantial failure of the serrated joint occurred before completion of the first simulated use. In the low-load high-cycle test, all fixators completed three simulated clinical uses without failure, although (1/4) of the serrated joint components had hairline cracks. The high-load low-cycle test identified the fixator components which should be examined and replaced if reuse of the fixator is to be considered. Wear and deformation of the set screw on the rotary joint and telescoping mechanisms were observed in the low-load high-cycle test but not in the high-load low-cycle test. Therefore, if the unilateral DynaFix trade mark fixators are being considered for reusability, the number of reuses should be limited as the whole structure of the device will experience fatigue damage as the loading cycle increases.

Biophysical stimulation of bone fracture repair, regeneration and remodelling.

Biophysical stimulation to enhance bone fracture repair and bone regenerate maturation to restore its structural strength must rely on both the biological and biomechanical principle according to the local tissue environment and the type of mechanical stress to be born by the skeletal joint system. This paper reviews the possible interactions between biophysical stimuli and cellular responses in healing bone fractures and proceeds to speculate the prospects and limitations of different experimental models in evaluating and optimising such non-invasive interventions. It is important to realize that bone fracture repair has several pathways with various combinations of bone formation mechanisms, but there may only be one bone remodeling principle regulated by the hypothesis proposed by Wolff. There are different mechanical and biophysical stimuli that could provide effective augmentation of fracture healing and bone regenerate maturation. The key requirements of establishing these positive interactions are to define the precise cellular response to the stimulation signal in an in vitro environment and to use well-established animal models to quantify and optimise the therapeutic regimen in a time-dependent manner. This can only be achieved through research collaboration among different disciplines using scientific methodologies. In addition, the specific forms of biophysical stimulation and its dose effect and application timing must be carefully determined and validated. Technological advances in achieving focalized stimulus delivery with adjustable signal type and intensity, in the ability to monitor healing callus mechanical property non-invasively, and in the establishment of a robust knowledge base to develop effective and reliable treatment protocols are the essential pre-requisites to make biophysical stimulation acceptable in the main arena of health care. Finally, it is important to bear in mind that successful fracture repair or bone regeneration through callus distraction without adequate remodeling process through physiological loading would seriously undermine the value of biophysical stimulation in meeting the biomechanical demand of a long bone.

The effect of recombinant human osteogenic protein-1 (bone morphogenetic protein-7) impregnation on allografts in a canine intercalary bone defect.

The utility of cortical allografts in repairing large bone defects is limited by their slow and incomplete incorporation into host bone. In order to determine the effects of recombinant human osteogenic protein-1 (rhOP-1) impregnation on allograft incorporation, we used a canine intercalary bone defect model. Bilateral resection of a 4 cm segment of the femoral diaphysis and reconstruction with structural bone allografts were performed. In one limb, the allograft was soaked in solution with rhOP-1 for 1 h before implantation. In the other limb, the allograft was soaked in the same solution without rhOP-1. Dynamic load-bearing, radiographic analysis, biomechanical testing, and histomorphometric analysis were conducted. Radiographic analysis showed significantly larger periosteal callus area in the rhOP-1 treated group at week 2. The rhOP-1 significantly increased allograft bone porosity and significantly increased the number of active osteons in the allografts. There were no significant differences between the rhOP-1 treated and non-treated allografts in load bearing and biomechanical analyses. These findings indicate that rhOP- I increases intercalary allograft remodeling without deleterious effects in mechanical and functional strength.

The effect of low intensity pulsed ultrasound on regenerate bone in a less-than-rigid biomechanical environment.

The purpose of this study was to investigate effects of low intensity pulsed ultrasound (LIPU) on distraction osteogenesis in a less-than-rigid biomechanical environment in a rabbit model. A less-rigid mini-lengthener was applied and a mid-tibial osteotomy performed in 20 New Zealand White rabbits. After a 7 day latency period, the tibiae were distracted 0.5 mm every 12 hours for 10 days. Ten of the rabbits received LIPU for 20 min/day (ultrasound group) and 10 received sham LIPU (control group) from day 17 until sacrifice on day 37. Radiographs were taken weekly after distraction and the callus area was measured. After sacrifice, dual-energy X-ray absorptiometry (DEXA), torsional testing to failure, and histomorphometry were performed. On radiographs, all the treatment tibiae displayed persistent radiolucencies; however, only one of the control tibiae displayed a radiolucent interzone. Torsional strength of the treatment group was 54% of the contralateral tibia compared to 139% in the control group (p<0.008). Bone density and callus size were not significantly different between the 2 groups; however, the ultrasound group displayed a tendency towards more cartilage and fibrous tissue formation (p<0.16) and less bone (p<0.16) than controls. In a biomechanically unstable environment, LIPU appears to stimulate more cartilage formation in regenerated callus than in controls. This callus is biomechanically inferior to unstimulated callus at the early stage of healing tested. During distraction osteogenesis a sound biomechanical environment is important to achieving anticipated results.