Biomedical subjects

Edmund Y S Chao

Publications and source records attributed to Edmund Y S Chao.

At least 19 recordsLinked to original sources

PubMed2006

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.

Animals↗

PubMed2005

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.

Animals↗

PubMed2005

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.

Animals↗

PubMed2005

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.

Computer Simulation↗

PubMed2005

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.

Animals↗

PubMed2005

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.

Baseball↗

PubMed2005

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.

Animals↗

PubMed2004

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.

Animals↗

PubMed2004

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.

Aged↗

PubMed2004

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.

Adolescent↗

PubMed2003

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.

Animals↗

PubMed2003

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.

Algorithms↗

PubMed2003

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.

Analysis of Variance↗

PubMed2002

Callus stimulation in distraction osteogenesis.

Distraction osteogenesis has been described as in vivo tissue engineering. The ability to stimulate this process for the repair of bony defects or lengthening of congenitally shortened facial structures is likely to significantly impact the field of craniofacial surgery. The purpose of this study was to determine whether mechanical stimulation of the distracted rabbit mandible would accelerate the maturation of the bony callus when applied during the early consolidation period. Twenty adult New Zealand White rabbits underwent unilateral mandibular osteotomy. A uni-directional internal distractor device (Synthes, Paoli, Pa.) was positioned along a plane perpendicular to the line of osteotomy. After a 7-day latency period, distraction was commenced at a rate of 1.0 mm/day for 12 days in all animals. In a control group of 10 rabbits, a consolidation period of 8 weeks was observed before they were killed. In the experimental group of 10 rabbits, daily alternate compression and distraction of 1 mm (sequential compression and distraction) was performed for 3 weeks followed by a 5-week period of rigid fixation. Each animal received a dose of a fluorescent label at three different time points during the study: at the end of the distraction period, 3 weeks after the completion of the distraction phase, and 3 days before it was killed. All animals were killed 8 weeks after the completion of the distraction phase. Undecalcified histologic analysis and 3-point bending tests to failure were performed on the extracted mandibles. The results of the experimental and control groups were compared. Four animals in the control group and three animals in the experimental group were excluded from the study because of screw loosening resulting in distractor dislodgment or because of infection. On histologic analysis, cortical thickness at the center of the callus was found to be significantly greater in the experimental group compared with the control group when normalized to the contralateral hemimandible (83 percent versus 49 percent, respectively; p < 0.007). The ratio of cortical to cancellous bone in the distracted callus was uniformly found to be greater in the experimental specimens. The mineral apposition rate was calculated by using fluorescence microscopy and found to be significantly greater in the experimental group both during the period of sequential compression and distraction (3.2 microm/day versus 2.1 microm/day, p = 0.02) and after the period of sequential compression and distraction (1.4 microm/day versus 1.1 microm/day, p = 0.006). Mechanical testing revealed no significant differences in bending strength or stiffness between experimental or control groups (p = 0.54 and 0.47, respectively). This study has demonstrated that daily alternating compression and distraction of 1 mm amplitude during the early consolidation period has a stimulatory impact on callus formation with respect to osteoblastic activity, remodeling, and maturation of bone. Optimal timing and amplitude of sequential movement, long-term biomechanical differences, and molecular pathways have yet to be elucidated.

Animals↗

PubMed2002

Kinematic simulation of fracture reduction and bone deformity correction under unilateral external fixation.

Combined kinematic analysis and graphic models of two unilateral external fixators are presented to simulate and visualize the correction of bone fracture deformities through systematic adjustments of the fixator joints. The models were developed as rigid linkage systems, and the analysis utilized the 4x4 transformation matrices and the kinematic chain theory to obtain the necessary rotations and translations at each joint of the fixator to correct bone deformities at the fracture site. Three-dimensional malalignments with fracture gaps were simulated to correct the deformities. Due to the redundant pair variables in the fixator joints and other problems in obtaining unique solutions, an optimization technique was used to solve the governing linkage loop equations. For each adjustment solution, the bone correction paths were infinite but a unique and optimal reduction path was obtained by applying corrections to all joints simultaneously and in small increments. When the deformity exceeded a certain range, no admissible solution could be obtained, partially due to the limitation of the unilateral fixator configuration and partially due to the restricted joint rotation and translation in the fixator design. The present models and analysis technique can be used to investigate a fixator's adjustability to correct a 3-D bone deformity at a fracture or lengthening site facilitating patient care planning and medical personnel training.

Biomechanical Phenomena↗

PubMed2002

The effect of low intensity pulsed ultrasound applied to rabbit tibiae during the consolidation phase of distraction osteogenesis.

The purpose of this study was to determine if low intensity pulsed ultrasound (LIPU) accelerated the maturation of regenerate bone when applied after distraction in a rabbit model. A mid-tibial osteotomy was performed in 26 New Zealand white rabbits and an external fixator applied anteromedially. After a seven day latency period, the tibiae were distracted 0.5 mm every 12 h for 10 days. Thirteen of the rabbits received LIPU for 20 min/day (treatment group) and 13 received sham LIPU (control group) from day 17 until sacrifice on day 37. Radiographs were taken weekly after distraction and the total and mineralized areas of the callus were measured. After sacrifice, dual-energy X-ray absorptiometry, torsional testing to failure, and histomorphometry were performed. Ultrasound-treated tibiae were a mean of 68.8 +/- 3.8% as stiff as and 68.2 +/- 6.0% as strong as the contralateral tibiae. Control tibiae were 78.7 +/- 7.0%, as stiff as and 70.2 +/- 7.9% as strong as the contralateral tibiae. The differences in stiffness and strength were not significant (p = 0.39 and 0.81, respectively) with the number of the animals tested in the study. The treatment group was 91.6% as dense as the contralateral side and the control group was 88.5% as dense as the contralateral side (p = 0.84). Radiographs revealed a significantly larger callus in the LIPU-treated tibiae at 1, 2 and 3 weeks after distraction compared to control tibiae (p < 0.01, 0.008 and 0.05, respectively). Histomorphometry revealed significantly less fibrous tissue in the LIPU-treated tibiae (p < 0.05) and a strong trend towards more bone in the LIPU-treated tibiae compared to controls (p = 0.06). LIPU was found to increase the size of the distraction callus and it might alter the composition of regenerate bone but it did not have a positive effect on the mechanical properties or density of regenerate bone when applied during the consolidation phase of distraction osteogenesis.

Animals↗

PubMed2002

Effect of pulsed electromagnetic fields (PEMF) on late-phase osteotomy gap healing in a canine tibial model.

The effects of a pulsed electromagnetic field (PEMF) on late bone healing phases using an osteotomy gap model in the canine mid-tibia were investigated. A transverse mid-diaphyseal tibial osteotomy with a 2-mm gap was performed unilaterally in 12 adult mixed-breed dogs and stabilized with external fixation. Animals in the variable group (n = 6) were treated with PEMF for 1 h daily starting 4 weeks after surgery for a total of 8 weeks, whereas no stimulation signal was generated in the control group (n = 6). Functional load-bearing and radiographic assessments were conducted time-sequentially until euthanasia 12 weeks after surgery. Torsional tests and an analysis of undecalcified histology were performed on the retrieved mid-tibial diaphysis containing the osteotomy site. In the PEMF group, load-bearing of the operated limb recovered earlier when compared to the control group (p < 0.05). Load-bearing in the PEMF group at 8 weeks was greater than in the control group (p < 0.02). The periosteal callus area increased following surgery at 6 weeks (p < 0.05) and thereafter (p < 0.01) in the PEMF group, while a significant increase was observed at 8 and 10 weeks after surgery (p < 0.05) in the control group. Both the normalized maximum torque and torsional stiffness of the PEMF group were significantly greater than those of the control group (p < 0.04 and p < 0.007, respectively). Histomorphometric analyses revealed greater new-bone formation (p < 0.05) in the osteotomy gap tissue and increased mineral apposition rate (p < 0.04) and decreased porosity in the cortex adjacent to the osteotomy line (p < 0.02) in the PEMF group. PEMF stimulation of 1 h per day for 8 weeks provided faster recovery of load-bearing, a significant increase in new bone formation, and a higher mechanical strength of the healing mid-tibial osteotomy. This study revealed enhancing effects of PEMF on callus formation and maturation in the late-phase of bone healing.

Animals↗

PubMed2002

Biologic tendon fixation to metallic implant augmented with autogenous cancellous bone graft and bone marrow in a canine model.

Soft tissue attachment to a metallic prosthesis is required for the improvement of the functional outcome of endoprosthetic reconstructions. Direct tendon attachment to the metallic surface can be achieved through fibrous ingrowth, but such an attachment has a mechanical strength less than one fifth of that of a normal tendon insertion. Regeneration of a transitional structure between the tendon and the metallic surface similar to the normal morphology of a direct tendon insertion may improve the mechanical strength of the new tendon insertion. The objective of the study was to investigate the effect of placement of an interpositional autogenous cancellous bone plate augmented with bone marrow on the mechanical strength of the soft tissue attachment to the metallic surface. The insertion of the supraspinatus tendon was reattached to a porous titanium prosthesis in a canine shoulder model. An autogenous cancellous bone plate supplemented with bone marrow was positioned between the metallic surface and the tendon. Assessment of load-bearing, as a measure of functional recovery, and radiological analysis were performed at 3, 6, 9, 12, and 15 weeks. The animals were euthanized 16 weeks after surgery, and the specimens were subjected to tensile mechanical testing (six animals) and microradiographic-histologic evaluation (three animals). Functional analysis showed a 90.3% recovery of preoperative weight-bearing by 16 weeks (p < 0.05). The mineralized area around the prostheses increased by 63% over time (p < 0.05). Tensile stiffness and strength of the reconstruction were 43.6% and 42.8% of the intact tendon insertion values, respectively. These results were higher than in previous experiments using the direct tendon attachment (p < 0.01, p < 0.05, respectively) or the interpositional bone plate without marrow supplementation (p < 0.05, p < 0.05, respectively). Morphologically, the tendon reattachment site contained the basic tissue transition zones in normal tendon insertion to bone. Inductive bone grafting, supplemented with bone marrow, in the biologic augmentation of tendon anchoring onto a porous metallic prosthesis was an effective technique to increase the mechanical strength of the tendon attachment to the metallic prosthesis.

Animals↗