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Biomedical subjects

E L Radin

Publications and source records attributed to E L Radin.

At least 37 records · Page 2Linked to original sources
PubMed1990

A dynamic finite element analysis of impulsive loading of the extension-splinted rabbit knee.

A dynamic nonlinear finite element model was developed to study juxtarticular stresses in the splinted rabbit knee, an established laboratory model for creating osteoarthrosis due to impulsive loading. Plane strain finite element results were validated by comparison with corresponding experimental data. Parametric effects studied included the input tibial displacement speed, the local bone density distribution, and the modulus of cartilage and subchondral bone. While the computed resultant contact force magnitude was sensitive to a number of model parameters, the stress patterns, when normalized to a given resultant force magnitude, were not. Despite comparable force peaks, the finite element results showed approximately six-fold higher effective strain rate levels for a severely impulsive loading protocol known to induce rapid osteoarthrosis, versus those for a mildly impulsive loading protocol not usually associated with cartilage damage. A propensity for elevated shear in the deep cartilage layer near the contact periphery, observed in nearly all computed stress distributions, is consistent with previous experimental findings of fissuring at that level in the impulsively loaded rabbit knee.

Animals↗
PubMed1990

The role of the quadriceps in controlling impulsive forces around heel strike.

The damaging effect of transient loads on joints has been observed in vitro and in vivo, and may be an aetiological factor in osteoarthrosis. The events around heel strike, when the velocity of the foot is brought rapidly to zero, may be a source of such loads in normal activity. By modifying the rate at which the limb descends to the ground, quadriceps action influences the magnitude of the heel strike transient. Experiments were carried out to analyse the occurrence of these transients, and a two-dimensional mathematical model of the knee joint and lower leg was used to calculate the forces developed at the knee in response to them. Paralysis of the quadriceps resulted in a large increase in the heel strike transient.

Biomechanical Phenomena↗
PubMed1990

Experimental stress fractures of the tibia. Biological and mechanical aetiology in rabbits.

We have shown that stress fractures can be induced in the tibial diaphysis of an animal model by the repeated application of non-traumatic impulsive loads. The right hind limbs of 31 rabbits were loaded for three to nine weeks and changes in the bone were monitored by radiography and bone scintigraphy. The presence of stress fractures was confirmed histologically in some cases. Most animals sustained a stress fracture within six weeks and there was a positive correspondence between scintigraphic change and radiological evidence. Microscopic damage was evident at the sites of positive bone scans. The progression, location, and time of onset of stress fractures in this animal model were similar to those in clinical reports, making the model a useful one for the study of the aetiology of stress fractures.

Animals↗
PubMed1990

A prognosis for ultra high molecular weight polyethylene.

Ultra high molecular weight polyethylene (UHMPWE) is now the material of choice for total joint replacement prostheses, in combination with a metal surface against which the polymer articulates. As this material has now been in use in this application for approximately three decades and other limiting factors (e.g. loosening of the prosthesis) have been improved upon, it is appropriate to attempt a long-term prognosis.

Joint Prosthesis↗
PubMed1989

Mechanical and morphological effects of strain rate on fatigue of compact bone.

Compact bone specimens were cyclically loaded in uniaxial tension for one million cycles; loading was performed at either of two physiological strain rates (0.01 s-1 or 0.03 s-1) and a physiological strain range (0-1200 microstrain). Microdamage in loaded and nonloaded control specimens was then assessed histomorphometrically. Fatigue, evidence by stiffness loss, was observed at both strain rates and was significantly greater in specimens loaded at the high experimental strain rate than in specimens loaded at the low strain rate. Morphologically, this fatigue corresponded to increased numbers of microcracks in the bone. These data show that fatigue and resultant microdamage are realistic expectations of cyclic loading within the physiological strain range. The rate at which strains are developed influences the fatigue behavior of compact bone, suggesting that cyclic loading at high physiological strain rates, characteristic of vigorous activities, is more damaging to compact bone than loading at lower physiological strain rates.

Animals↗
PubMed1989

The effects of altered strain environments on bone tissue kinetics.

This study defines the alteration in bone tissue kinetics responsible for the "adaptive remodeling" response to altered strain environments. Adult beagle dogs were separated into three experimental groups: ulnar osteotomy, ulnar osteotomy with fracture fixation plate spanning the gap and sham surgery. Four sets of double fluorochrome labels were administered. Prior to sacrifice at 1, 3, and 6 months, strains were measured through rosette strain gages on the cranial and caudal surfaces of the intact radius. Histomorphometric analysis indicated that the increased bone mass in response to elevated strain results from increased activation frequency of modeling with more sites undergoing formation processes than resorption processes on periosteal and endocortical surfaces. Increased remodeling activation did not lead to increased bone mass. There was no evidence that elevated strain changes the individual vigor of osteoclasts or osteoblasts, or that the sigma period was altered by elevated strain.

Adaptation, Physiological↗
PubMed1989

Skeletal change in response to altered strain environments: is woven bone a response to elevated strain?

Studies demonstrate that geometric changes in bone architecture in response to altered mechanical strain occur through the formation of woven bone. The goal of this study was to test the hypothesis that these changes are partly the result of surgical manipulation rather than a true adaptive response to altered strain. Beagle dogs were subjected to either an ulnar osteotomy, an osteotomy with plate fixation, or sham operation. Strains on the radius were measured just prior to sacrifice 1, 3 or 6 months after surgery. Our results support the idea that woven bone can be a normal response to an abnormal strain environment if the mechanical challenge is intense enough; that elevated mechanical strains can cause the endocortical bone envelope to revert to a state of net formation; and that "adaptive remodeling" in adults in response to a change in mechanical strain may be a special case of modeling in which resorption is not required prior to formation at a particular skeletal site.

Adaptation, Physiological↗
PubMed1988

Synovial membrane and cartilage changes in experimental osteoarthrosis.

The Hulth instability model was performed on 25 rabbit knee joints. Electron-microscopic, light-microscopic, and histomorphometric data demonstrated consistent chondrocyte alterations and cartilage destruction. The comparison between operated, sham, and control knees shows that surgical intervention without surgically induced instability is followed by changes in the synovial membrane and cartilage. The cartilage destruction is preceded by a synovial reaction, suggesting that the inflammatory response has an important role in the onset of cartilage damage in this model. The damage was more severe in the experimental knees, suggesting that mechanical instability is also a factor in cartilage destruction.

Animals↗
PubMed1988

Global mechanical consequences of reduced cement/bone coupling rigidity in proximal femoral arthroplasty: a three-dimensional finite element analysis.

Component loosening in total hip arthroplasty is often accompanied by substantial bony remodelling, associated initially with reduced stiffness of the cancellous bone bordering the cement, and eventually with the formation and proliferation of a compliant fibrous membrane at the bone/cement interface. An anatomically based three-dimensional finite element model has been developed to explore the salient stress changes occurring with progressive degradation of the stiffness of the cancellous bone in a thin zone bordering the cement. This border zone, modelled as a distinct linearly elastic and isotropic material layer, assumed a geometry and a range of mechanical properties inferred from eventual membrane thickness apparent in recent animal studies of component loosening. The major variables considered were: stiffness (elastic modulus) and compressibility (Poisson ratio) of the border zone, stiffness changes in the outlying cancellous bone, resultant hip contact force, and trochanteric muscle loadings. The results for the limiting case of a non-degraded border zone compared reasonably with previous studies of femoral reconstructions having rigid bone-to-cement attachment. Progressive decay of border zone stiffness produced complex changes in load transmission. Foremost among these were a generalized increase in stress levels (especially of transverse-plane tension) in the proximo-lateral cancellous bone, and a corresponding generalized decrease in stress levels in the proximo-medial cancellous bone. There were also large bending moment increases in the prosthesis and its cement mantle, especially at mid-stem. At almost all sites, the critical stress levels were those developed for peak stance-phase loading, rather than for the lower loads (and different resultant contact force directions) occurring elsewhere in the gait cycle. The elevated proximo-lateral cancellous bone stresses occurring with eventual membrane development, consistent with localized bony hypertrophy seen in recent animal studies, may be a response to hoop stresses occurring during pistoning of the tapered cement mantle.

Bone Cements↗
PubMed1988

[Arthrotomy--a prearthrotic factor?].

UNLABELLED: Light-microscopic and electron microscopic findings of the synovial membrane and cartilage were compared, of rabbit knee joints on which arthrotomy and surgical induced instabilisation operation were performed. The joint opening was followed by an inflammation of the synovial membrane, and cartilage changes were similar in joints of arthrotomy and surgically induced instability. CLINICAL RELEVANCE: To prevent joints from further damage after arthrotomy or arthroscopy, joints should be spared from weight bearing during the time of synovial inflammation.

Animals↗
PubMed1987

Reasons for failure of L5-S1 intervertebral disc excisions.

This study reviews 247 patients who still had preoperative complaints six months to two years after disc excision. In over half, spondylosis of the L5-S1 facets was present, concurrently associated with a pelvic obliquity. A number of other organic causative factors were identified in 18% of the patients. Nonorganic reasons accounted for failure in only 13%. Over 70% of patients with associated spondylosis were improved by treatment directed at this condition.

Adult↗
PubMed1987

The effect of spondylosis on the outcome of chemonucleolysis.

In an attempt to understand the relation between the outcome of chemonucleolysis treatment of lumbar discs and the presence of spondylosis (degenerative process) of the lumbar spine, 40 cases of disc herniation with subsequent intradiscal chymopapain injection (chemonucleolysis) were reviewed. Thirty-eight patients had plain radiographs, 25 had myelography, 28 had computed tomography (CT), and 15 had both myelography and CT. A review of these examinations revealed that 24 patients had minimal or mild spondylosis (group 1) and 13 patients had moderate spondylosis (group 2). Only one patient had a severe spondylosis (group 3). Chemonucleolysis failed in 8/24 (33%) patients from the first group and 2/13 (15%) cases from the second group. Therefore, the presence or absence of even moderate spondylosis did not affect the treatment success rate. A review of the 11 failed cases revealed spinal canal stenosis in three cases and a large disc herniation in two (one case with a myelographic block). Another case had a sequestered disc fragment. In two further cases, the disc herniation was far lateral with complete occlusion of the lateral foramen; another case exhibited severe degenerative changes of facet joints. In two other cases, treatment failure could not be explained by any radiographic finding. Of three patients with large disc herniation, only one responded successfully to intradiscal injection of chymopapain. Chemonucleolysis, however, failed in the only patient in the third group who had severe spondylosis of the facet joint.

Adolescent↗
PubMed1987

Osteoarthrosis. What is known about prevention.

Views of the general nature and cause of osteoarthrosis have changed over the past two decades. Osteoarthrosis is not a condition of relentless progression. It is not a disease, but rather the result of an imbalance between the mechanical stresses on the joint and the ability of the tissues of the joint to withstand those stresses. Effective treatment of osteoarthrosis is generally mechanical. In many cases, the progression of the condition can be halted with appropriate intervention.

Humans↗
PubMed1987

Early vascular changes in rabbit subchondral bone after repetitive impulsive loading.

The sequence of vascular and bony changes that precedes experimental osteoarthrosis was observed in rabbits. The subchondral bone underlying the weight-bearing portion of the medial tibial condyle and the talocalcaneal joint were examined after two, three, and six weeks of 50-ms and 500-ms repetitive loading at 1 Hz for 40 minutes each day. Vascular alterations were evident in the subchondral bone of the talocalcaneal joint after three weeks of a 50-ms load regime. A 10% increase in bone mass and a significant increase in the number of small diameter vessels were observed after six weeks. No changes were observed in the tibial subchondral bone, consistent with the measured attenuation of load distal to this joint. No changes were observed in either tibial or calcaneal subchondral bone in the 500-ms load group. Impulsive loading promotes early vascular changes in subchondral bone, which are developed in response to both the magnitude and the rate of loading.

Animals↗
PubMed1986

Role of muscles in protecting athletes from injury.

Athletics create impact load which can be deleterious to the musculoskeletal system. These impact loads are attenuated by either deformation of materials external to the body, deformation of tissues, or tearing of tissue and fracture of bone. Muscles act to lower the bending stress on bone and to attenuate the peak dynamic loads from unprotected impulsive loads that can damage musculoskeletal tissues. Athletes should be advised to avoid impulsive loads for which they are unprepared, and to not participate in athletics when their muscles are fatigued.

Athletic Injuries↗