Biomedical subjects

R D Coutts

Publications and source records attributed to R D Coutts.

At least 55 records · Page 3Linked to original sources

PubMed1985

Rib perichondrial grafts for the repair of full-thickness articular-cartilage defects. A morphological and biochemical study in rabbits.

The purpose of this study was to investigate the use of perichondrial grafts in articular cartilage defects and to characterize the newly formed cartilage. In a rabbit model, rib perichondrium was used to repair full-thickness defects in the femoral condyle. The quality of repair was then evaluated histologically and biochemically at six and twelve weeks after grafting. Unacceptable results were obtained in 50 per cent of the rabbits. These failures were due to condylar fracture in 20 per cent, failure of graft attachment in 20 per cent, and infection in 10 per cent. The technique of grafting must be improved to increase the percentage of successful grafts in which neocartilage with a relatively normal chemical composition fills the articular cartilage defect. Successful grafts proliferate to fill the full-thickness defect with neocartilage, which has biochemical characteristics that are similar to those of hyaline cartilage.

Animals↗

PubMed1984

Less rigid internal fixation plates: historical perspectives and new concepts.

In the application of "rigid" plates for diaphyseal fractures, lack of callus healing and overprotection of the underlying bone are viewed by many investigators as undesirable consequences. Potential solutions offered to overcome these deficiencies include modification of the timing of plate removal, use of biologically degradable materials for plates so that stress-shielding can be minimized, and use of less rigid plate fixation systems. This study emphasizes the selection of appropriate design criteria for less rigid plate-fixation systems. To accomplish this goal, the axial, bending, and torsional stiffness parameters are considered in place of the oversimplified terms such as "flexible plate" or "elastic fixation." With the aid of finite element modeling and simplified bench experiments, we performed parametric studies and singled out the plate axial stiffness as the dominant factor in altering the bone stresses. As a result, we designed two experimental plates, one a thin Ti-6Al-4V (titanium with 6% aluminum and 4% vanadium) alloy plate with low stiffness in axial and bending directions, and the other a tubular stainless steel plate with low stiffness in the axial direction but moderate stiffness in bending and torsional directions. The low-stiffness Ti-6Al-4V alloy plate was first tested in a demanding bilateral canine midshaft osteotomy, and proved to be inadequate. Both experimental plates were successful in the unilateral osteotomies, with the tubular plate yielding the best results. After 6 months of plating, the bones beneath the tubular plate had superior mechanical and structural properties as compared to those of the control "rigid" stainless steel and the Ti-6Al-4V alloy plates. Application of this plate prolonged for 9 months did not cause reduction in bone properties and strength. The success of the tubular plate is due to its moderate bending and torsional stiffnesses, which provide adequate fixation to achieve callus union, while its low axial stiffness permits the underlying bone to share the physiological stresses needed for bone remodeling. These drastic changes in mechanical demands on the internal fixation plate during the early healing phase and the postunion remodeling phase are discussed.

Alloys↗

PubMed1984

Characterization of arthroplasty tissue after 14 years post-cup arthroplasty: a morphological and biochemical assessment.

The cup arthroplasty has been reported to cause the formation of a fibrocartilaginous joint surface, which may result in a painless, functional joint. The joint surface of a 38-year-old man with a failed cup arthroplasty implanted for 14 years was examined histologically and biochemically. The joint surface tissue of this patient resembled fibrous connective tissue, with major types of collagen being Type I and Type III. No evidence of cartilaginous transformation in the healing scar was demonstrated, despite several years of successful functioning of the cup arthroplasty.

Adult↗

PubMed1984

Technical aspects of perichondrial grafting in the rabbit.

A screening process to determine the most appropriate model for the study of cartilage growth from perichondrium obtained from the rabbit's left tenth costal cartilage has resulted in the following observations: (1) best growth is achieved when fixation of the graft is secure and conformity to the recipient bed is complete; (2) immobilization enhances fixation, but permits fibrous tissue growth onto the graft, and (3) diminishing periods of immobilization enhance perichondrial growth, but have a deleterious effect on fixation.

Animals↗

PubMed1984

Physiology and therapeutic value of passive joint motion.

Despite the long history of therapeutic experience with different types and amounts of passive joint motion, its effects and the principles of its use remain controversial. Through empiric success, a spectrum of passive motion has evolved for various clinical purposes, including joint diagnosis; correction of joint deformities; mobilization of stiff joints; stimulation of joint healing; neuromuscular re-education; and prevention of immobilization complications (e.g., contracture formation, connective tissue atrophy, relative healing inhibition, and associated stasis abnormalities). However, the potential abuses of passive motion (e.g., causing additional tissue trauma, mobilizing unprotected joints, and stretching the wrong joints or tissues) have created serious doubts as to the value of this therapy and raised important questions concerning the lack of proper definition (e.g., force, direction, speed, and duration) and the unknown margins of safety. Clinical and experimental evidence supports the probable effectiveness of passive joint motion on joint and tissue levels, but without a better quantitative understanding of the mechanisms of action, dose-responsiveness, specific tissue effects, and, most important, their controls. Thus, passive motion will continue to be used suboptimally with inconsistent results. When these clinical and research deficiencies are corrected, passive motion will attain its proper place as a powerful and reliable orthopedic tool.

Connective Tissue↗

PubMed1983

A new femoral component design based on the trabecular systems of the proximal femur.

This investigation presents a new design of the femoral component used in total hip arthroplasty. The design utilizes a tensile component which screws into the femoral stem from the lateral side of the femur. The potential advantages of utilizing such a component are 1) PMMA cement may be not needed to hold the implant in place, 2) better stress distribution in the region of the greater trochanter is achieved, 3) reduced stress levels in the implant, and 4) the femoral stem may be shortened to reduce the amount of reaming required. Two dimensional, plane stress finite element models of the proximal end of a normal femur, a femur with the new implant design, and a femur with a control Charnley-Cobra femoral component were developed. Loads simulating a one-legged stance were applied on the models. The normal and shear stresses, the octehedral shearing stress and the directions of principal stress were calculated for comparison with the normal femur. There was distinct improvement in bone stress distribution for the femur with the experimental implant as compared to the femur with the control prosthesis. The stress concentration normally observed in the mid-shaft area of the Charnley femoral stem was also not seen in the new design.

Biomechanical Phenomena↗

PubMed1982

The effect of delayed internal fixation on healing of the osteotomized dog radius.

Delay in surgical intervention has been reported to enhance the process of fracture healing. Quantitative observations or experimental osteotomies were made to investigate the mechanical for such enhancement. Eight mongrel dogs with bilateral radial osteotomies were prepared with immediate plate fixation on the right side, and with delayed fixation two weeks later on the left side. The response to delayed fixation was measured radiographically, mechanically, and by measurement of new bone formation using a quantitative tetracycline incorporation method. A clearly discernible stimulation of new bone formation occurred early in the osteotomy healing process. Delayed fixation has a transient stimulatory effect on the healing process of bone.

Animals↗

PubMed1980

Principles of less rigid internal fixation with plates.

The paradox of internal fixation for treating fractures is that fixation is required to achieve union, while flexibility is necessary to restore normal mechanical properties of bone after union. Three series of experiments were performed to investigate the role of plate rigidity on fracture repair and changes in bone mass. Using plates with tenfold differences in axial and bending rigidities, the authors were able to show some advantages in fracture healing and bone remodelling with less rigid plates.

Animals↗

PubMed1977

Subchondral cysts (geodes) in arthritic disorders: pathologic and radiographic appearance of the hip joint.

A comprehensive study of femoral heads of patients and cadavers with osteoarthritis, rheumatoid arthritis, osteonecrosis, and calcium pyrophosphate dihydrate deposition disease allows insight into the radiographic and pathologic appearance of subchondral radiolucencies in these disorders. The term geode, rather than cyst or pseudocyst, may be a more appropriate decription of these lesions. In osteoarthritis, goedes occur on the pressure segment of the femoral head in association with loss of articular space; in rheumatoid arthritis, they are initially noted at the chondro-osseous junction and subsequently involve the entire femoral head. In osteonecrosis, geodes appear in the necrotic segment of the femoral head. In calcium pyrophosphate deposition disease, geodes resemble those in osteoarthritis but are larger, more numerous, and more widespread.

Arthritis↗

PubMed1976

Stimulation of bone formation in vivo by phosphate supplementation.

The effect of phosphate supplementation on bone remodeling was assessed in six mature, healthy beagle dogs. The phosphate supplement was given in divided doses orally, daily for 12 weeks in the form of a neutral potassium phosphate preparation. The dose averaged 108 mg P/kg per day, which is double the normal canine phosphorus intake. Bone remodeling was assessed by measurement, at sacrifice, of areas of cortical bone containing different color-coded tetracyclines which had been continuously administered during 12-week control and treatment periods; remodeling was assessed kinetically during the control and treatment periods by replicate studies employing 47Ca intravenously. Both techniques demonstrated that the principal effect of phosphate supplementation was a significant stimulation of bone formation. Within cortical bone, formation was doubled, from an average of 2.7% to 5.3% per year. The major location of new bone deposits was endosteal. Whole skeletal mineral accretion, measured kinetically, increased 45% above an average control value of 0.154 g/day. These studies suggest that, in the adult dog, "normal" plasma phosphate levels are suboptimal for new bone formation. Even with this short duration of administration, phosphate produced microscopic calcification of the renal parenchyma. However, there was no biochemical evidence of renal functional impairment.

Animals↗

PubMed1976

The effects of rigidity of internal fixation plates on long bone remodeling. A biomechanical and quantitative histological study.

The effect of rigidity of internal fixation plates on long bone remodeling was studied using two types of plates with considerable differences in stiffness. The plated bones were subjected to bioengineering quantitative histological, and cortical thickness studies after 9 and 12 months. The biomechanical results, together with the quantitative histological measurements of the macroscopic architecture, showed that tissue characteristics of the plated bones were similar. However, because of the larger cortical area, the less regidly plated femora can sustain significantly higher loads and energy before failure. Cortical thickness measurements also showed that rigid plate immobilization results in thinning of the cortex of the underlying bone. The experimental results suggest that cortical bone remodels according to functional stress demands, and the osteoporosis secondary to rigid plate protection is consequent to thinking of its cortex.

Animals↗

PubMed1976

A comparison of cortical bone atrophy secondary to fixation with plates with large differences in bending stiffness.

Two internal-fixation plates with large differences in bending stiffness were applied to pairs of intact femora of six adult mongrel dogs to study the osteoporosis induced by rigid fixation. After nine and twelve months of plate application a significant, increased amount of bone atrophy was seen on the rigidly plated side. Biomechanical measurements of specimens from various segments of both femoral diaphyses showed the bones to have similar mechanical properties (as tissue), but different structural properties (as organ). These findings suggest that the osteoporosis due to rigid plate fixation occurs by thinning of the cortex rather than by reduction of the mechanical properties of the osseous tissue.

Animals↗

PubMed1975

Quantitative histological evaluation of early fracture healing of cortical bones immobilized by stainless steel and composite plates.

Internal fixation devices of less bending stiffness than conventional plates made of stainless steel or vitallium were compared with conventional plates in a study of fracture healing. The material for this investigation was a fine graphite fiber reinforced methyl methacrylate resin composite with a modulus of elasticity approximately ten times less than that of stainless steel. Osteotomies were performed on canine radii. Internal fixation was accomplished by means of a composite plate on the left side, and a stainless steel plate on the right. Clinical assessment, as well as biomechanical and quantitative histological techniques, were used to compare osteotomy healing of the two sides. At four months, all osteotomies had healed and the bioengineering tests showed radii from the two sides had equivalent strength. However, significantly less cortical porosity was found in the side with the composite plate (6.8 per cent), as compared to that of the stainless steel plated side (14 per cent). These results suggest that a less stiff fixation plate may have some advantage in the treatment of long bone fracture if there is no implant failure, and if union rates are equivalent.

Animals↗

PubMed1974