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Biomedical subjects

R Shahar

Publications and source records attributed to R Shahar.

At least 19 recordsLinked to original sources
PubMed2006

A method for patient-specific evaluation of vertebral cancellous bone strength: in vitro validation.

BACKGROUND: In the context of osteoporosis, important determinants of the fracture risk are the apparent strength and stiffness of cancellous bone, as well as its brittleness and energy absorption capacity. Standard medical imaging, however, cannot measure these mechanical properties directly. Consequently, an estimation of the risk for fracture is made by correlating relative density or mineral density at a skeletal site with statistics of fracture occurrence, which provides limited and partial indications on fracture risks. A better method for evaluating the patient-specific mechanical properties of cancellous bone is therefore required. METHODS: In order to asses the mechanical properties of vertebral cancellous bone, we developed a finite element parametric model of lattice trabecular architecture that, in the future, will be suitable for use with bone imaging modalities. The model inputs are apparent morphological parameters (trabecular thickness and trabecular separation) and the bone mineral density. We conducted uniaxial compression tests on 36 canine vertebral cancellous bone specimens (C7 and L1) to validate model predictions of strength and stiffness in vitro. FINDINGS: Predictions of strength and stiffness matched the experimental results within relative absolute errors of 17.7% and 12.8%, respectively (average of differences between model-predicted and measured values, divided by the average of measured values). We also employed the model for evaluation of strength and stiffness of human L1 and L5 vertebrae and found mean strength of 1.67 MPa (confidence interval 0.42 MPa) and mean elastic modulus of 190 MPa (confidence interval 50 MPa), which are well within the range of previously reported apparent strength and stiffness properties. INTERPRETATION: The present model can be used to improve medical imaging-based evaluation of the spine in osteoporotic individuals by providing more specific information on the individual bone's susceptibility to fracture once clinical bone scans will be able to provide more reliable measures of trabecular thickness and separation.

Animals↗
PubMed2006

Anisotropic Poisson's ratio and compression modulus of cortical bone determined by speckle interferometry.

Young's modulus and Poisson's ratios of 6mm-sized cubes of equine cortical bone were measured in compression using a micro-mechanical loading device. Surface displacements were determined by electronic speckle pattern-correlation interferometry. This method allows for non-destructive testing of very small samples in water. Analyses of standard materials showed that the method is accurate and precise for determining both Young's modulus and Poisson's ratio. Material properties were determined concurrently in three orthogonal anatomic directions (axial, radial and transverse). Young's modulus values were found to be anisotropic and consistent with values of equine cortical bone reported in the literature. Poisson's ratios were also found to be anisotropic, but lower than those previously reported. Poisson's ratios for the radial-transverse and transverse-radial directions were 0.15+/-0.02, for the axial-transverse and axial-radial directions 0.19+/-0.04, and for the transverse-axial and radial-axial direction 0.09+/-0.02 (mean+/-SD). Cubes located only millimetres apart had significantly different elastic properties, showing that significant spatial variation occurs in equine cortical bone.

Animals↗
PubMed2006

Femoral compartment syndrome due to haemangiosarcoma in the semimembranosus muscle in a dog.

A five-year-old, entire male German shepherd dog was presented to the Veterinary Teaching Hospital-Koret School of Veterinary Medicine because of an acute, painful swelling of the right thigh and severe lameness of two-weeks duration. On physical examination, a firm and painful mass was detected in the hamstring region. Radiography and ultrasonography revealed a soft tissue mass, with a 250 cc fluid accumulation craniomedial to it. Intracompartmental pressure measurement with a Wick catheter demonstrated significantly elevated pressure within the right caudal femoral compartment (25 to 28 mmHg compared with 5 to 7 mmHg in the unaffected leg). Surgical exploration of the area was undertaken, fasciotomy and mass excision were performed, and resolution of the clinical signs was achieved. The mass was identified by histopathology results as haemangiosarcoma. Two and a half months after surgery, which was followed by adjunct chemotherapy (doxorubicin), the dog was readmitted with a subcutaneous mass in the same area, although he was not lame at this time. Radiographs of the thoracic cavity demonstrated widely disseminated metastases in the lungs. At that point, the owner elected to have the dog euthanased.

Animals↗
PubMed2006

Arthrodesis of the tarsometatarsal joint, using type II ESF with acrylic connecting bars in four dogs.

Hyperextension injury of the tarsometatarsal joint (TMTJ) is a debilitating injury and arthrodesis of this joint is often the only procedure that can result in full return to function. Most surgical procedures described for arthrodesis of the tarsometatarsal joint necessitate the use of external, splint or cast, to protect the implants used from fatigue failure. This report describes the successful use of type II external fixator that spans the tarsometatarsal joint in four dogs with hyperextension injury of the tarsometatarsal joint. This technique enables the patient to bear weight on the limb immediately after surgery until bony fusion is achieved, without the need for an additional protecting splint.

Animals↗
PubMed2005

How to select the elastic modulus for cancellous bone in patient-specific continuum models of the spine.

Patient-specific finite element (FE) modelling is a promising technology that is expected to support clinical assessment of the spine in the near future. To allow rapid, robust and economic patient-specific modelling of the whole spine or of large spine segments, it is practicable to consider vertebral cancellous bone in the spine as a continuum material, but the elastic modulus of that continuum material must reflect the quality of the individual vertebral bone. A numerical parametric model of lattice trabecular architecture has been developed for determining the apparent elastic modulus of cancellous bone Ecb in vertebrae. The model inputs were apparent morphological parameters (trabecular thickness TbTh and trabecular separation TbSp) and the bone mineral density (BMD), which can all be measured in vivo, using the spatial resolution of current clinical quantitative computed tomography (QCT) commercial whole-body scanners. The model predicted that Ecb values between 30 and 110 MPa represent normal morphology and BMD of human spinal cancellous bone. The present Ecb to TbTh, TbSp and BMD relationships pave the way for automatic generation of patient-specific continuum FE spine models that consider the individual's osteoporotic or other degenerative condition of cancellous bone.

Bone Density↗
PubMed2005

Chondrosarcoma of the proximal humerus in a cat.

Chondrosarcoma of the proximal humerus was diagnosed in a four-year-old, castrated male, domestic shorthair cat that was presented with a slowly growing solid mass in the region of the proximal humerus. Forequarter amputation was advised, but declined by the owners. Following surgical debulking clinical signs resolved, but two months after surgery the cat was readmitted because the mass had recurred in the same region. The forequarter was amputated. Histopathological evaluation of the tumour confirmed the diagnosis of chondrosarcoma. Follow-up examinations performed over a period of 15 months from initial presentation revealed that the cat was doing well and had no signs of metastatic disease. To the authors' knowledge, this is the first reported case of chondrosarcoma of the proximal humerus in a cat to be diagnosed and surgically treated. This case demonstrates that animals with such tumours may recover well after complete excision.

Amputation, Surgical↗
PubMed2004

A quasi-static three-dimensional, mathematical, three-body segment model of the canine knee.

A mathematical, three-dimensional, anatomically accurate model of the canine knee was created to determine the forces in the knee ligaments and the knee joint reaction forces during the stance phase of a slow walk. This quasi-static model considered both the tibio-femoral and patello-femoral articulations. The geometric and morphometric data of the hind limb were obtained from cadaver data. Muscle forces acting on the femur and the hip joint reaction force were determined by numerical optimization. Ligaments were modeled as non-linear-springs. Ligament material properties were obtained from the literature pertaining to the human knee. The model consists of-28 non-linear algebraic equations describing equilibrium of the femur and the patella, and geometric constraints. This system of equations was solved by a non-linear least-squares method. Results are presented for a knee with an intact cranial cruciate ligament (CCL) and for a knee with a ruptured CCL. Forces predicted to occur in the CCL by analysis of the model were found to be very similar to reported results of CCL forces measured in vivo in goats.

Animals↗
PubMed2003

Stress and strain distribution in the intact canine femur: finite element analysis.

Information regarding the stresses and strains in the canine femur during various activities is important for veterinary orthopaedic surgeons, engineers designing implants for dogs, and researchers of human orthopaedics who use dogs as models. Nevertheless, such information is currently unavailable. The objective of this study is to determine the stress and strain distribution in the canine femur during mid-stance, for two loading scenarios. Three-dimensional finite element models of the canine femur were created. Two loading cases were considered: the hip joint reaction force alone, and the hip joint reaction force with all muscle forces acting on the femur. Force directions and magnitudes were obtained from the literature. Analyses were performed with NASTRAN for Windows software. When all muscle forces were considered, stresses and strains were significantly reduced, peak compressive stresses were found to occur in the medial diaphysis, and peak tensile stresses occurred in the lateral diaphysis. While the canine femur seems to be loaded primarily in bending when only the hip joint reaction force is considered, the bending moment is significantly decreased when all muscle forces are considered as well. Further in vivo and in vitro experiments are needed to validate the results of the calculations described in this paper. It is expected that future studies will be carried out, in which the stress and strain distributions in femora with different types of implants and stems will be compared to those in the normal femur.

Animals↗
PubMed2002

The effect of short-duration, high-intensity electromagnetic pulses on fresh ulnar fractures in rats.

Pulsed electromagnetic fields (PEMFs) have been found to be beneficial to a wide variety of biological phenomena. In particular, PEMFs have been shown to be useful in the promotion of healing of ununited fractures. Conflicting information exists regarding the benefit of using PEMFs to accelerate the healing of fresh fractures. This paper reports on the evaluation of the effect of a new PEMF generator (PAP IMI) on the healing of fresh ulnar fractures in rats. This device is unique by virtue of the extremely high power output of each of the pulses it generates. Ulnar fractures were created in rats by using a bone cutter, thus producing a 2-3 mm bone defect. Rats were then randomly divided into treatment and control groups. The treatment group underwent periodic treatments with the PAP IMI, and the control group received no treatment. Radiographs of rats from both groups were taken at 1-week intervals. Histological evaluation was performed at the end of the study. Radiographic and histopathological evaluations were scored, and scores were used to assess both rate and quality of healing. The radiographic results demonstrated gradual bridging callus formation in both control and treatment groups, however, the healing process was faster in rats that were not treated by PEMF. Histological evaluation demonstrated that the fibrous content of the callus in rats belonging to the treatment group was significantly higher than that in rats belonging to the control group. The results of this study do not support the claim that PEMF generated by the PAP-IMI stimulate osteogenesis and bone healing after the creation of fresh ulnar fractures in rats.

Animals↗
PubMed2001

Morphometric and anatomic study of the hind limb of a dog.

OBJECTIVE: To obtain the anatomic and morphometric data required for biomechanical analysis of the hind limb in dogs. ANIMALS: A healthy adult mixed-breed 23-kg male dog. PROCEDURE: Following euthanasia of the dog, all muscles of the right hind limb were identified and meticulously removed. Physiologic cross-sectional areas (PCSA) and architectural indices (AI) were calculated. The coordinates for the origin and insertion of each muscle were determined, using orthogonal right-handed coordinate systems embedded in the pelvis, femur, and tibia. RESULTS: PCSA and AI were calculated for 29 muscles, and coordinates for the origins and insertions of these muscles were determined. CONCLUSIONS: Results provide the morphometric and anatomic data necessary for 3-dimensional biomechanical studies of the hind limb in dogs.

Animals↗
PubMed1999

Free skin grafting for treatment of distal limb skin defects in cats.

The technique and results of free skin grafts have been described in dogs, horses, rabbits, goats and mice. The procedure in cats is, however, described only indirectly in papers relating to dogs. A standard technique has been developed by the authors for use in cats, and is reported for 17 grafts in 16 cats with traumatic injury to the legs resulting in large areas of skin loss. This paper describes the preparation of the wound for grafting, the harvesting of the graft, graft placement, postoperative care and the results of the application of this technique. The success rate in this series of cases was high. This was attributed to proper preparation of the recipient site, collection of the graft and postoperative bandaging. The results suggest that the success rate of free skin grafts in cats is considerably higher than that achieved by the present authors in dogs, and reported for dogs by other surgeons in the literature.

Animals↗
PubMed1997

Immunoreactivity of canine mammary neoplasms with monoclonal antibody CC49.

Monoclonal antibody (MAb) CC49 binds to human tumour-associated glycoprotein termed TAG-72. CC49 is a second-generation MAb with higher affinity to TAG-72 than the original MAb B72.3. CC49 was applied to 42 samples from different canine mammary tumours, belonging to seven different histopathological types. Immunoreactivity was detected by the use of an avidin-biotin complex immunoperoxidase method. Most sections from all types of mammary neoplasm reacted with this MAb. Normal tissue did not stain or stained only weakly. The results of this study suggest CC49 has selective immunoreactivity for a variety of canine mammary tumours, which seems superior to that reported with MAb 72.3. These results support the proposal for further study of diagnostic and therapeutic uses of CC49 in the management of canine mammary tumours.

Adenocarcinoma↗
PubMed1985

Pleural dialysis in the management of acute renal failure in two dogs.

Pleural dialysis, as an alternative to peritoneal dialysis and hemodialysis, was shown in a limited number of cases to be an inexpensive and easily applied technique for use in dogs. It is a viable modality for the management of acute renal failure in dogs that have suffered an acute but reversible renal insult, in which volume replacement and dopamine/furosemide infusion fails to reverse the oliguric state.

Acute Kidney Injury↗
PubMed1985

Peripheral polyneuropathy in a dog with functional islet B-cell tumor and widespread metastasis.

A 12-year-old female Irish Setter was examined because of recurrent episodes of hindlimb weakness. The dog was not ataxic, but had generalized muscular atrophy, decreased patellar reflexes, and slow proprioception. Blood glucose content was low (32 mg/dl) and the amended insulin-glucose ratio was high (9,600). Electromyographic studies showed evidence of polyneuropathy. The diagnosis was functional islet B-cell tumor with peripheral neuropathy. Exploratory laparotomy was performed. Widespread metastases were observed and the dog was euthanatized because of the poor prognosis. The dog was necropsied and the diagnosis was confirmed on the basis of microscopic findings.

Adenoma, Islet Cell↗
PubMedDate not supplied

A technique for management of bite wounds of the thoracic wall in small dogs.

Bite wounds of the chest wall in small dogs can extend into the thorax and can be associated with severe damage to chest wall muscles, ribs, and lungs. Two major problems associated with the management of these wounds are lack of sufficient muscle tissue for chest wall reconstruction, and difficulty draining the extensive dead space created in the chest wall. We describe a simple method to overcome these problems. The bite wound areas were surgically explored and all devitalized soft tissue was debrided. The pleural cavity was explored, intrathoracic injuries repaired, and a thoracic drainage tube was placed. Ribs in the injured area were stabilized in anatomic position by means of heavy gauge sutures passed around pairs of adjacent ribs, thus creating a scaffolding for soft tissues. Viable muscle and subcutaneous tissues were apposed as much as possible and the skin closed over the defect. Eleven small dogs were treated using this technique. All dogs had severe injuries to the thoracic wall muscles and eight dogs had multiple rib fractures. There was no evidence of chest wall instability in any of the dogs after surgery. Nine dogs survived the injury and were reevaluated 3 to 32 months after surgery. All were clinically normal. One dog developed wound infection and pyothorax, caused by insufficient debridement of injured muscle tissue, and died 10 days after surgery. A second dog died 24 hours postoperatively of undetermined causes.

Animals↗
PubMedDate not supplied

Relative stiffness and stress of type I and type II external fixators: acrylic versus stainless-steel connecting bars--a theoretical approach.

OBJECTIVE: To compare the stiffness and pin stresses of three sizes of external fixator systems with stainless-steel and acrylic connecting bars. STUDY DESIGN: Finite element analysis. METHODS: Small, medium, and large external fixator systems of type I and type II configurations were modeled for finite element analysis. Each model was evaluated with a standard stainless-steel and three different diameters of acrylic connecting bar. Displacements and stresses were calculated for the loading modes of axial compression, medio-lateral bending, cranio-caudal bending, and torsion. The location of the pin experiencing maximum stress was determined for all configurations and loading modes. RESULTS: Acrylic column diameters of 9.53 mm for the small external fixator system and 15.9 mm for the medium external fixator system provide equivalent stiffness and maximum pin stresses to those provided by the standard stainless-steel connecting bars (3.2- and 4.8-mm diameter, respectively). The largest diameter acrylic column tested (31.75-mm) produced lower stiffness and higher maximum pin stresses than the standard stainless-steel connecting bar (11.1-mm diameter). CONCLUSIONS: When applying a small or medium external fixator, an acrylic column of 9.53-mm or 15.9-mm diameter, respectively, can be used. For a large external fixator system, an acrylic column of diameter >31.75 mm is required. CLINICAL RELEVANCE: The sizes of acrylic connecting bars for use in small and medium external fixator systems have been determined. Large systems should incorporate the standard stainless-steel connecting bar.

Acrylic Resins↗
PubMedDate not supplied

Semirigid external fixation for repair of fractures in young animals.

An alternative method for external coaptation of fractures in young animals utilizes tongue depressors incorporated in a bandage consisting of a thick layer of cotton padding, gauze bandaging, and adhesive tape. This method was used in 13 cases with fractures of the tibia or the radius and ulna, some of which were open. Five cases (four dogs and a cat) had displaced fractures, and eight cases had either nondisplaced or only mildly displaced fractures. Size of the animal was not considered a limiting factor. Bandages were examined periodically. All fractures healed uneventfully, and the splints were removed 21-to-44 days after application. This method of external coaptation proved to be easy to apply and modify during the healing process and was applicable to a wide variety of fractures with good results.

Animals↗