Biomedical subjects

D T Davy

Publications and source records attributed to D T Davy.

At least 37 records · Page 2Linked to original sources

PubMed1994

Effects of patella alta and patella infera on patellofemoral contact forces.

The relationship between patella alta and patellar subluxation may, in part, reflect the relationship between the height of the patella above the tibiofemoral joint line and the patellofemoral contact force. This study reports on the direct in vitro measurement of the patellofemoral contact force, and its point of application on the patella, as a function of patellar height. The contact force was measured by a specially designed six-degree-of-freedom force transducer under loading simulating rising from a chair. The magnitude of the resultant contact force increased significantly with superior displacement of the patella. The magnitude of the resultant contact force changed as much as 3% per millimeter of change in patellar height. The details of this response varied among the knees tested and depended on the original anatomical patellar height. For a high-riding patella, the onset of tendofemoral contact is delayed and the magnitude of the patellofemoral contact continues to increase with increasing flexion angle. Early onset of tendofemoral contact associated with a low-riding patella results in a concomitant reduction in the magnitude of the contact force. The medially directed component of the contact force acting on the patella resists lateral subluxation of the patella. This force component increased with superior displacement of the patella. This may explain in part the tendency for a high-riding patella to sublux. For all seven specimens tested the point of application of the resultant contact force migrated superiorly with inferior displacement of the patella.

Aged↗

PubMed1994

Comparison of hip force calculations and measurements in the same patient.

Many investigations report hip-contact-force estimates based either on mathematical models or on the output of instrumented implants. Data from instrumented implants have been consistently lower than mathematical predictions. The authors compared mathematical estimates derived from gait laboratory observations made in a patient with an instrumented hip implant. Appropriate modifications to past models resulted in force predictions that were reasonably similar to the output of the instrumented implant. Peak resultant forces were in the range of 2.5-3.5 body weight during level walking at a freely selected speed, while peak out-of-plane forces ranged from 0.6 to 0.9 body weight. Previous parametric hip-force predictions resulting from mathematically modeled surgical alterations may be high insofar as absolute peak values, but trends are likely correct.

Aged↗

PubMed1992

The effects of vascularity and cyclosporin A on the mechanical properties of canine fibular autografts.

We studied the biomechanical behavior of orthotopic canine autografts as influenced by vascularized supply and the administration of cyclosporin A at three months and six months post-surgery. The model was the proximal 8 cm of the fibula in young adult dogs. In vascularized grafts, blood supply was re-established by microvascular re-anastomosis. Experimental controls were sham-operated and unoperated bones. Mid-graft test sections were subjected to loading-to-failure in torsion to determine the strength and stiffness. In both three- and six-month groups, vascularized grafts were significantly stronger and stiffer than contralateral nonvascularized grafts. Vascularized grafts were not significantly different from sham-operated bones. A 30-day regimen of cyclosporin A was found to have no measurable effect on mechanical properties for any individual treatment group. The results indicate that re-established blood supply can be a major factor in maintaining the mechanical integrity in large-segment cortical autografts.

Animals↗

PubMed1991

Pressure erosion of the femoral trochlea, patella baja, and altered patellar surfaces.

As knee flexion increases, so do tendofemoral and patellofemoral compression forces. Three cases of long-standing uncorrected flexion contractures of the knees are presented that resulted in marked erosion of the femoral trochlea, patella baja, and remodeled patellar articular surfaces likely reflecting increased angles of flexion. It is probable that the deep femoral grooves are the result of adaptation under high-level persistent contact loads from the quadriceps tendon. These examples expand our knowledge of bone remodeling and offer information of potential use in studying ancient skeletal samples.

Adult↗

PubMed1991

Telemeterized in vivo hip joint force data: a report on two patients after total hip surgery.

Two telemeterized femoral components were implanted in two patients as part of normal total hip replacement procedures. The two components were instrumented to measure the three force components directed along: (a) the neck axis, (b) transverse to the neck axis and in the plane of the prosthesis, and (c) transverse to the neck axis and perpendicular to the plane of the prosthesis. Data were collected at multiple sessions during the early postoperative period for a number of standard activities, including gait, stair climbing, rising from a chair, single leg stance, double leg stance, ipsilateral and contralateral straight leg lifts while supine, ipsilateral flexion and extension while standing, and ipsilateral abduction while standing and lying on the contralateral side. These data are summarized and compared with the published results from analytic studies and with the results from previous studies using instrumented femoral components. Peak loads for gait during the period of study were roughly 2.7 body weights (BW) when the patients walked at their normal pace. Contact forces at the hip during stationary single leg stance approximated the peak loads during gait with values ranging from 2.1 to 2.8 BW. The highest forces recorded reached values approaching 5.5 BW and occurred during periods of instability while the patient engaged in stationary single leg stance. Our in vivo data indicate that forces generated during the above activities increase in magnitude quite rapidly during the early postoperative period and that during this period the patients have the ability to perform the activities of daily living without generating the high amplitude joint contact forces suggested by the results of dynamic studies. Joint contact forces during gait were found to depend on speed, but the high absolute magnitudes predicted by model studies were not supported by the in vivo data.

Aged↗

PubMed1991

Differential patterns of incorporation and remodeling among various types of bone grafts.

The early (3 months) and later (6 months) patterns of incorporation and bone formation have been evaluated histomorphometrically for different types of bone grafts; that is, vascularized and nonvascularized autografts with and without ciclosporin, and vascularized and nonvascularized dog leukocyte antigen (DLA)-mismatched allografts with and without ciclosporin. The vascularized bones were superior to the nonvascularized ones in healing and remodeling their grafted segments. In the autograft bones, ciclosporin did not alter the incorporation process 3 months after transplantation but delayed and increased the remodeling activities in the long run (6 months). Nonvascularized allografts underwent vigorous resorption, and were markedly porotic. Ciclosporin administration significantly reduced resorption and enhanced remodeling in nonvascularized allografts. The remodeling of allografts was similar to that of autografts in the presence of ciclosporin, but stopped soon after the administration of ciclosporin ceased.

Animals↗

PubMed1991

Adaptation of NASA technology for the optimum design of orthopedic knee implants.

NASA technology originally developed for designing aircraft turbine-engine blades has been adapted and applied to orthopedic knee implants. This article describes a method for tailoring an implant for optimal interaction with the environment of the tibia. The implant components are designed to control stresses in the bone for minimizing bone degradation and preventing failures. Engineers expect the tailoring system to improve knee prosthesis design and allow customized implants for individual patients.

Aerospace Medicine↗

PubMed1990

Cyclosporin A and tissue antigen matching in bone transplantation. Fibular allografts studied in the dog.

We studied the mechanical, metabolic, and histologic properties of short-term nonvascularized cortical bone grafts in a canine fibular graft model. Sham operated nonvascularized autotransplanted and allotransplanted bones were compared. The allografts were performed between dog leukocyte antigen (DLA) class I and II matched; DLA class I and II mismatched; and cyclosporin A (CsA) treated, DLA class I and II mismatched animals. Cyclosporin was given for 1 month, and all the animals were followed for 3 months after surgery. Mechanical properties were investigated using standard torsional tests, metabolic kinetics were assessed using isotopic prelabeling techniques, and histomorphometric analysis of cross-sectional area properties and sequential fluorochrome labels were performed. Autografts were mechanically stronger and stiffer than all the types of allograft. CsA-treated, DLA-mismatched allografts performed better than matched allografts. These in turn were stronger than non-CsA-treated, mismatched allografts, which underwent nearly complete resorption. These relationships were preserved in the metabolic and histologic analyses. In this short-term animal study, although DLA matching resulted in a slight improvement in graft outcome, mismatched grafts in dogs receiving a short course of cyclosporin A fared even better.

Animals↗

PubMed1989

Temporal analysis of vascularized and nonvascularized rib grafts in canine spine surgery.

The authors have previously reported work demonstrating the superiority of vascularized vs. nonvascularized rib grafts, which were inlaid to bridge three vertebral bodies studied at 3 months postoperatively. They questioned whether the mechanical and biologic properties of the nonvascular grafts would improve over time to approach the performance of the vascularized grafts by 6 months. They found that, with increased time, the vascularized grafts continued to improve, showing hypertrophy, maintenance of cortical integrity, and bonding to the recipient vertebral bodies. The nonvascularized grafts, however, showed porosity, fragmentation, and replacement by spongiosa. Mechanical properties showed increased performance in the vascularized vs. nonvascularized grafts, and no improvement was seen between the nonvascularized grafts from 3 to 6 months.

Animals↗

PubMed1988

Some viscoplastic characteristics of bovine and human cortical bone.

Multiple cycle tensile creep tests were performed on human and bovine cortical bone specimens. The tests enabled total strain to be decomposed into elastic, linear viscoelastic, creep and permanent plastic components. The results indicate that a stress threshold exists; above which time dependent effects dominate material response and below which the behavior is primarily linear viscoelastic, with time effects playing only a secondary role. A constant stress above the threshold produces a constant steady state creep rate, with the magnitude of the creep rate being an exponential function of the stress magnitude. Additionally, it was found that a major portion of the inelastic strain is always recovered on unloading and that the accumulation of creep strain increases the material compliance on subsequent loadings below the threshold. These two factors suggest that a damage mechanism is responsible for the nonlinear behavior.

Adult↗

PubMed1988

The superiority of vascularized compared to nonvascularized rib grafts in spine surgery shown by biological and physical methods.

Eleven canine experiments were performed to demonstrate the advantages of immediate vascular preservation in ribs used to fill a surgically created osseous gap bridging three vertebral bodies. In the five vascular rib grafts, mean blood flow was retained and measured at .101/ml/min/ml bone tissue. At autopsy 3 months post-operatively, vascularized grafts were more robust and hypertrophic. Mechanical testing in six stiffness modes confirmed the advantage of vascularized grafts. The experimental results indicate that vascularized grafts retain greater viability and better mechanical properties during graft incorporation. Providing a vascularized construct may be helpful in reconstructing large vertebral osseous gaps.

Animals↗

PubMed1988

Telemetric force measurements across the hip after total arthroplasty.

A telemeterized total hip prosthesis was implanted in one patient and force-data were obtained. Thirty-one days postoperatively, the magnitude of the joint-contact force during double-limb stance was 1.0 times body weight. During ipsilateral single-limb stance the joint-contact force was 2.1 times body weight, and during the stance phase of gait the peak force typically was 2.6 to 2.8 times body weight, with the resultant force located on the anterosuperior portion of the ball. During stair-climbing, the force was 2.6 times body weight. At peak loads, the angle between the resultant force and the axis of the neck was 30 to 35 degrees and that between the resultant force and the plane of the prosthesis was 20 degrees. During stair-climbing or straight-leg raising, the out-of-plane orientation of the resultant force increased substantially. These data provide information concerning the forces that must be sustained by prosthetic hip joints during a number of common activities of daily living within the first month after implantation. The results also provide insight into the progression of early recovery and demonstrate the variety of forces that are generated during this period.

Aged↗

PubMed1987

A dynamic optimization technique for predicting muscle forces in the swing phase of gait.

The muscle force sharing problem was solved for the swing phase of gait using a dynamic optimization algorithm. For comparison purposes the problem was also solved using a typical static optimization algorithm. The objective function for the dynamic optimization algorithm was a combination of the tracking error and the metabolic energy consumption. The latter quantity was taken to be the sum of the total work done by the muscles and the enthalpy change during the contraction. The objective function for the static optimization problem was the sum of the cubes of the muscle stresses. To solve the problem using the static approach, the inverse dynamics problem was first solved in order to determine the resultant joint torques required to generate the given hip, knee and ankle trajectories. To this effect the angular velocities and accelerations were obtained by numerical differentiation using a low-pass digital filter. The dynamic optimization problem was solved using the Fletcher-Reeves conjugate gradient algorithm, and the static optimization problem was solved using the Gradient-restoration algorithm. The results show influence of internal muscle dynamics on muscle control histories vis a vis muscle forces. They also illustrate the strong sensitivity of the results to the differentiation procedure used in the static optimization approach.

Algorithms↗

PubMed1987

Biology of vascularized bone grafts.

Vascularized canine fibular autografts demonstrated improved biologic and mechanical characteristics 3 months after surgery when compared with nonvascularized controls. The vascularized proximal fibula maintained its overall architecture without bony collapse or significant bone turnover. The strength and stiffness of these grafts were approximately 40 per cent and 56 per cent more than nonvascularized grafts, respectively.

Animals↗

PubMed1986

The effects of tibial-femoral angle on the failure mechanics of the canine anterior cruciate ligament.

A series of canine femur-ACL-tibia complexes were subjected to tensile tests with axial tibial orientation and 0 degree, 45 degrees or 90 degrees femoral orientation with respect to load direction. A deflection rate of 51.0 cm min-1 was used in all tests. Marked differences occurred in ultimate loads, deflection and energy absorbed as a consequence of differences in femoral-tibial orientation. The mode of structural failure, as determined by post-test examination, also varied markedly as a function of femoral-tibial orientation. It is concluded that differences both in measured mechanical properties and observed failure details are a consequence of varying the loading pattern of the fiber bundles across the finite breadth of the ligament.

Animals↗

PubMed1985

Anisotropic yield behavior of bone under combined axial force and torque.

In this study the yield behavior of cortical bone was determined under combined loading conditions involving tension, compression and torsion. The axis of each test sample coincided with the long bone axis. To minimize viscoelastic behavior, tests were conducted using an effective strain rate in the range of 0.01-0.06 s-1. Experimental yield loci for bovine and human cortical bone were determined using a strain offset technique to determine the 'common yield point' for combined loading. Several failure criteria which have been used for composite materials were examined for applicability to the experimental results. Data were obtained for bovine and human tibial and femoral bone. The Tsai-Wu criterion was in best agreement to the test data, although Hill's criterion could describe the individual compression-torsion or tension-torsion regimes with good accuracy.

Animals↗

PubMed1985

The influence of muscle model complexity in musculoskeletal motion modeling.

A comparative study of four different muscle models in a musculoskeletal motion problem is made. The models vary in complexity from the simple input-output model to the more complex model of Hatze [1]. These models are used to solve a minimum time kicking problem using an optimal control algorithm. The results demonstrate the strong influence of the model choice on the various predicted kinematic and kinetic parameters in the problem. The study illustrates some of the advantages and disadvantages involved in trade-offs between model complexity and practicability in musculoskeletal motion studies. The results also illustrate the importance of appropriate detailed parameter estimation studies in the mathematical modeling of the musculoskeletal system.

Humans↗

PubMed1984

Mathematical modeling and numerical solutions for functionally dependent bone remodeling.

The phenomenon of bone remodeling is a complex biological process which is dependent on genetic, hormonal, metabolic, and age-related factors as well as functional requirements. The possibility of successfully developing a mathematical model to describe and predict the adaptive response of bone to load will be significantly increased after identification of the nature of the transducer(s) which senses functional requirements and provides signals for the cellular processes responsible for bone synthesis and bone removal. In spite of the present limitations in knowledge about the functional dependence of bone remodeling, a phenomenological model has been developed that assumes that the output signal from the (as yet unspecified) transducer is a remodeling potential that can be modulated by genetic, hormonal, and metabolic factors. An attempt has been made to cast the mathematical model in such a form that the constants and variables appearing in the equations are not mere abstractions, but can be related to biological parameters. In order to use the adaptive hypothesis with specific structural model examples, a numerical procedure has been developed to determine the strain distribution, predict the remodeling (assuming that the remodeling rate is related to the strain history), and update the model by changing the geometry and material properties in response to the remodeling. This numerical procedure is repeatedly iterated to determine the structural architecture at subsequent times. The numerical approach allows use of the remodeling concepts with models of irregular geometry, inhomogeneous material distribution, and anisotropic material properties.

Adaptation, Physiological↗