Biomedical subjects

D T Davy

Publications and source records attributed to D T Davy.

At least 19 recordsLinked to original sources

PubMed1995

Reduction of patellofemoral contact forces following anterior displacement of the tibial tubercle.

Retropatellar pain often accompanies malalignment syndromes and frequently is attributed to excessive patellofemoral contact stresses. Elevation (anterior displacement) of the tibial tubercle has been recommended to relieve these conditions. The degree to which patellar contact forces are decreased and the extent to which elevation alters medial-lateral forces have not been studied directly. We performed anterior translation of the tibial tubercle in knees from cadavers and measured the effect on the magnitude of the three-dimensional patellofemoral contact force with use of a specially designed 6-degrees-of-freedom force transducer, with the natural patellar articular surface in place. Measurements were made in nine knees (average age 67 years, range 46-92 years). The resultant contact force decreased linearly with increasing tubercle elevations of as much as 2.5 cm. The average reduction per centimeter of elevation was 17% of the force measured with no elevation. Elevation of the tubercle had an inconsistent effect on the medial-lateral component of the contact force. As the elevation was increased, six knees exhibited an increase in the medial-lateral component of the contact force acting medially on the knee and three knees exhibited a decrease in this force component. The results of this study show that, while elevation of the tubercle without medialization reduced the total contact force on the patella, the medial-lateral component of this force was altered in an unpredictable way.

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PubMed1995

Torsional loads in the early postoperative period following total hip replacement.

Torques generated in one subject during the early postoperative period were measured with a telemeterized total hip component. The patient was examined during gait, stair ascent, rising from a chair, and single-limb stance. The torques were plotted against both the resultant joint contact force and the force component directed along the stem axis. During gait, the maximum torque was 35 Nm, recorded at a walking velocity of 1.7 m/sec. The peak torques during stair ascent and during rising from a seated position were found to be 23 and 15 Nm, respectively. The maximum value for torque measured in this study was 37 Nm during one attempt at single-limb stance. Comparison of plots for torque versus stem-axis component for the four activities shows that the torque increased more rapidly for chair exits than for gait up to resultant contact force values of as much as 1,000 N. For stair ascent, the same was true to values of 1,400 N. Within any given activity, the relationship between stem torque and resultant or stem-axis force showed considerable variability. These results indicate that experiments evaluating the stability of femoral components in total hip arthroplasty should incorporate a component directed along the stem axis, as well as a component normal to the plane of the prosthesis. The results also suggest that theoretical stress analysis models should consider the broad variability in the orientation of the joint force at the hip.

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PubMed1995

Direct in vitro determination of the patellofemoral contact force for normal knees.

Results of the direct in vitro measurement of the full three-dimensional representation of the patellofemoral contact force and the point of application on the patella of the resultant contact force for eleven normal knees are presented. The applied knee moment versus flexion angle pattern was similar to that experienced when rising from a chair. There was a wide variability of the details of the patellofemoral force interaction among the specimens tested. The magnitude of the resultant contact force increased approximately linearly with flexion angle for some knees while in others the force leveled off or decreased at higher flexion angles. The change in direction of the resultant contact force with respect to the patella was relatively small compared to the angular rotation of the patella. The medial-lateral component of the contact force exhibited substantial variability among knees. The direction of this force (medially or laterally directed) varied among knees and, in some knees, changed direction as a function of flexion angle. The point of application on the patella of the resultant contact force migrated superiorly from 20 to 90 deg flexion. About 90 deg flexion this point tended to migrate inferiorly. The only significant and consistent effect of varying the direction of the quadriceps extension force was a change in the medial-lateral component of the contact force. In all cases, the tendency to sublux laterally increased when the extensor force was rotated 10 deg laterally and decreased when the extensor force was rotated 10 deg medially.

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PubMed1994

A six-degree-of-freedom transducer for in vitro measurement of patellofemoral contact forces.

A satisfactory design of the patellar component used in total knee arthroplasty and a general understanding of the effects of orthopedic procedures require, in part, an accurate description of patellofemoral contact forces. Experimental determination of the contact stress distribution requires integration to estimate the contact forces. Due to complex patellar geometry, the determination of the components of the resultant load is difficult. Current techniques for the direct measurement of contact loads either report a single load component or require sequential experiments to fully describe the contact force. The present study describes the development of a six-degree-of-freedom patellofemoral force transducer. This transducer allows the simultaneous determination of the three components of the contact force with an increase in accuracy over available devices. The contact forces components are accurate to 1% of full scale (900 N anterior-posterior, +/- 200 N medial-lateral and inferior-superior). The location on the patella where the resultant force acts is determined to within 1 mm. Relative movement of this point as a function of either normal change in knee flexion angle or as a result of a typical orthopedic procedure is determined to within 0.1 mm. A protocol is presented that allows the contact forces to be determined for either the anatomically normal patella or a patella following total knee arthroplasty.

Calibration↗

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.

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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.

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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.

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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↗

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.

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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.

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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.

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