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Biomedical subjects

A U Daniels

Publications and source records attributed to A U Daniels.

At least 19 recordsLinked to original sources
PubMed1991

A new method for assessing relative dynamic motion of vertebral bodies during cyclic loading in vitro.

A new experimental technique for measuring generalized three-dimensional motion of vertebral bodies during cyclic loading in vitro is presented. The system consists of an orthogonal array of three lasers mounted rigidly to one vertebra, and a set of three mutually orthogonal charge-coupled devices mounted rigidly to an adjacent vertebra. Each laser strikes a corresponding charge-coupled device screen. The mathematical model of the system is reduced to a linear set of equations with consequent matrix algebra allowing fast real-time data reduction during cyclic movements of the spine. The range and accuracy of the system is well suited for studying thoracolumbar motion segments. Distinct advantages of the system include miniaturization of the components, the elimination of the need for mechanical linkages between the bodies, and a high degree of accuracy which is not dependent on viewing volume as found in photogrammetric systems. More generally, the spectrum of potential applications of systems of this type to the real-time measurement of the relative motion of two bodies is extremely broad.

Equipment Design↗
PubMed1991

The effect of test methodology on apparent compressive stiffness of tibiofemoral joint specimens.

Several investigators have analysed the compressive load bearing properties of the knee. Careful review of these force/displacement data showed considerable variation, with some investigators reporting displacements 12-15 x higher than others for nearly identical testing conditions using the same animal model. In this study, we sought to determine if this variability was inherent in the tibiofemoral joint or if differences in experimental methodology explained the variation. Compressive force/displacement curves were obtained from 39 normal canine tibiofemoral specimens mounted in a universal testing machine. Two commonly reported methods of measuring compressive displacement were used simultaneously. The testing machine crosshead displacement was used as one measure of displacement of the joint. The other method consisted of extensometers mounted to bone at the joint line. Resultant joint rotation in the parasagittal plane was also measured. Using either approach, we found comparatively little variation among the 39 specimens tested. However, the crosshead displacement measurements diverged from the extensometer measurements as the compressive load increased. At 770 N, the crosshead measurement was nearly twice the extensometer displacement. Further analysis showed that the compliances differed by a uniform amount. Parasagittal joint rotation, as measured by the extensometers, was minimal--less than one half of one degree. Although our loading fixtures were expected to be rigid under the loads used, these data suggest that the deformation of the bone and loading fixtures was responsible for the differences we observed, and may be responsible for the variation in compressive displacement results among several published studies. A model is presented which uses a simple elastic element to represent this deformation.

Animals↗
PubMed1991

Compressive strength mapping of femoral head trabecular bone.

The purpose of this study was to develop a test protocol and complete a relative three-dimensional mapping of the local trabecular bone compressive strengths in healthy and osteoarthritic femoral heads. Five fresh frozen cadaveric femoral heads were compared to five fresh frozen osteoarthritic femoral heads obtained from patients undergoing total hip replacement. Each femoral head was coronally sectioned into eight 5 mm slices, which were compression-tested at 20 sites using a hydraulic testing machine. The results of the femoral head compressive strengths were normalized, mapped, and evaluated. The test protocol produced reproducible results and allowed the determination of diseased portions of osteoarthritic bone. The regions of high compressive strength were similar for normal and diseased bone and were located in the superior medial portions of the head. Ultimate stress was higher in diseased bone than in normal bone, while the yield point and stiffness of diseased bone was lower than for healthy bone.

Biomechanical Phenomena↗
PubMed1990

Bone scans after total knee arthroplasty in asymptomatic patients. Cemented versus cementless.

The natural history of bone scans after total knee arthroplasty (TKA) was studied in 26 patients with 28 cemented TKAs and 29 patients with 31 cementless TKAs. The bone scans were examined at specified postoperative intervals. Radionuclide activity of the femoral, tibial, and patellar regions was measured. Six patients who developed pain postoperatively were excluded. Bone scans immediately postoperative and at three months demonstrated increased uptake, which gradually decreased to baseline levels at ten to 12 months. Radioisotope uptake was comparable in the cemented and cementless groups, but was highly variable in individual patients and in each of the follow-up periods. A single postoperative bone scan cannot differentiate component loosening from early bone remodeling. Sequential bone scans, as a supplement to the clinical examination and conventional radiography, may prove useful in the diagnosis of TKA failure.

Aged↗
PubMed1989

Applied biomaterials standards report.

The purpose of my column is to provide readers with current information on biomaterials-related standards produced by both private groups and government agencies, and standards-related activities. Standards are descriptive documents given official status by their producers and, in the case of biomaterials, they are generally intended to provide formalized descriptions of (a) materials used in the construction of medical devices, (b) materials used directly in surgical repairs, (c) test methods to evaluate materials for such applications, and (d) methods for handling or processing such materials. Please consider this column not only a place to obtain biomaterials standards information but also a place to submit news of biomaterials standards developments in order to get the information before the public. This invitation extends to all members of any and all professional organizations and government agencies in the United States and abroad who are active in standards development and would like specific activities or standards publicized. I will present the information in this column to the extent that allotted space allows. And last, a caveat--since this is a column, it contains both factual information and opinions. I will make every effort to make it clear which is which. Also, as a frame of reference, please note that this column was written and submitted in January, 1989.

Biocompatible Materials↗
PubMed1989

The effect of medial meniscectomy and coronal plane angulation on in vitro load transmission in the canine stifle joint.

The purpose of this study was to determine the in vitro load transmission characteristics of the canine stifle joint, paying particular attention to the positioning effect of the meniscus in the coronal plane. The intact joint was first loaded, and then tested under two different loading conditions after a complete medial meniscectomy. The first set of test conditions attempted to simulate those used by previous investigators, by ignoring the spacer effect of the meniscus and not repositioning the joint after its removal. The second set of tests was carried out after the joint was repositioned in the coronal plane to allow initial contact to occur in both tibiofemoral compartments. It is presumed that this occurs subsequent to a meniscectomy in vivo, following the application of any weight-bearing load. As with previous investigators, it was found that after meniscectomy the joints produced slightly larger displacements and lower stiffnesses than when intact (no significant differences from intact). However, repositioning the meniscectomized joint produced markedly smaller displacements (35-49%, p less than 0.01) and greater stiffnesses (47-123%, p less than 0.05) over the range of forces analyzed, compared with the intact joint. The ratio of dissipated to input energy was 42% for the intact joint, and rose following meniscectomy to 54% (p less than 0.05) with repositioning and 55% (p less than 0.05) without repositioning. Measured contact area decreased by 17% (p less than 0.05) following meniscectomy alone, and by 12% (p less than 0.05) following meniscectomy with repositioning. Since repositioning of the joint subsequent to meniscectomy (accounting for the loss of the meniscal spacer) resulted in an increase in structural stiffness, it was concluded that the medial meniscus decreases the structural stiffness of the intact stifle joint. In addition, the meniscus has a role in elastic energy storage and increasing contact area. This study is intended to serve as a baseline comparison for future in vivo studies on meniscectomy, meniscal repair, and meniscal replacement, in addition to more fully elucidating the mechanism of load transmission. A model is presented to explain both the decrease in stiffness after meniscectomy without repositioning and the increase in stiffness after meniscectomy with repositioning, employing linear springs of unequal length and different stiffnesses. After removal of the softer meniscal element and allowing joint approximation to occur, loading of the stiffer articular element results in an initially stiffer preparation.

Animals↗
PubMed1989

Initial effect of collarless stem stiffness on femoral bone strain.

Stress shielding resulting from a stiffness mismatch between bone and femoral prosthesis stems (leading to bone resorption in the proximal femur) is believed to contribute to failure in total hip arthroplasty. In this study, strains were measured under compressive femoral head loads both in the intact femur and after implanting first a collarless steel stem and then a geometrically identical fiber-reinforced polymer composite stem 64% less stiff. Decreasing stem stiffness would be expected increase load transfer from the stem to the proximal medial femur, decreasing the degree of stress shielding. The authors found that proximal medial bone strains were significantly lower with either the steel or composite stem implanted than in the intact case. However, there were no significant differences in strain patterns between the steel and composite stem cases. This apparent insensitivity to prosthesis stiffness may result from factors related to implant geometry and fit.

Adult↗
PubMed1989

Endosteal bone loss after total hip arthroplasty.

Femoral endosteal bone loss has been shown to be part of the natural aging process and may be a factor in femoral component loosening following total hip arthroplasty (THA). In this study, changes in the femoral medullary canal width in 30 patients with aseptic femoral loosening following primary THA were compared with 30 matched control patients. The rate of canal expansion on the operated side was twice that of the nonoperated side and four times that of the control. After the onset of symptoms in the failure group, the rate of femoral expansion of the operated side doubled. Iliac crest biopsies showed a decrease in male patients for osteoid surface and appositional and bone formation rates when compared with literature controls. These results suggest that femoral medullary canal expansion may be a factor in femoral component loosening following THA. The increased rate of canal expansion after the onset of symptoms demonstrates the need for early surgical intervention to avoid excessive bone loss.

Adult↗
PubMed1987

BoneMech database.

Explore the source record for details and available documents.

Biomechanical Phenomena↗
PubMed1986

The stability of internal fixation in the proximal phalanx.

A biomechanical study was performed to assess quantitative differences in the stability obtained with five commonly used types of internal fixation used in proximal phalangeal fractures. The techniques included dorsal plating, dorsal plating combined with an interfragmentary lag screw, two interfragmentary lag screws, tension-band technique, and crossed Kirschner wires. Rigidity and strength in apex palmar bending were determined after oblique osteotomy and fixation of the proximal phalanx. The failure modes for each fixation technique were also observed and described. The results showed that both of the techniques that used interfragmentary lag screws across the oblique osteotomies provided significantly more rigidity than did dorsal plating alone or the wired configurations but that measurements of strength were similar between all techniques tested. Dorsal plates were at a mechanical disadvantage on the compression surface in our apex palmar bend test and consequently provided no more rigidity and strength than did the wired techniques. The tension band technique represented a combination of stiff and flexible intraosseous wires without strict application of tension band principles and provided intermediate rigidity and strength. Rigidity and strength in intact proximal phalanges in the controls were significantly greater than in all techniques tested.

Biomechanical Phenomena↗
PubMed1985

Comparison of internal fixation techniques in metacarpal fractures.

A biomechanical study assessed quantitative differences in the stability that was obtained by five commonly used types of internal fixation employed in metacarpal fractures. The techniques included dorsal plating, dorsal plating combined with an interfragmentary lag screw, crossed Kirschner wires, a single intraosseous wire combined with a single oblique Kirschner wire, and a single intraosseous wire alone. Rigidity and strength in torsion and bending were determined after transverse osteotomy and fixation of the metacarpal were performed. The failure modes for each fixation technique were also observed and described. Significant differences in rigidity were found between the plated configurations (with or without an interfragmentary lag screw) and the wired configurations in both apex dorsal bending and axial torsion. The three wired configurations were not significantly different from each other except in torsion. Analysis of the bending moments that were required to produce both yield and failure in apex dorsal bending and also the energy absorbed to yield showed similar disparity between plated and wired techniques. For metacarpal fixation, dorsal plating with or without lag screws provides significantly more stability than do wired techniques and approaches that provided by intact bones.

Biomechanical Phenomena↗
PubMed1985

Computerized tomographic determination of vertebral density after total hip arthroplasty.

Computerized tomography (CT) provides the capability to determine vertebral bone density with a high degree of accuracy and precision, detecting density changes as small as 5% in serial testing. In this pilot study, CT was used to determine the effects of total hip arthroplasty and its consequent alterations in physical activity levels on the vertebral bone density of 13 postoperative patients. Vertebral bone density was also evaluated in six preoperative patients with degenerative joint disease of the hip and five control patients. The preoperative group and controls were then compared with the postoperative patients, who were divided into two groups--those who had achieved good activity levels and those whose levels of activity remained poor. CT measurement of bone density in the central bodies of T12, L1, and L2 showed that the preoperative group was similar to controls. This suggests that patients accept total hip arthroplasty rather than endure significant activity limitations for extended periods of time. When activity level was restored by arthroplasty, vertebral bone density was preserved. If the patient continued at a poor activity level postoperation, significant loss of bone density occurred secondary to disuse.

Aged↗
PubMed1984

A new method for continuous intraoperative measurement of Harrington rod loading patterns.

A new method has been developed for continuous intra-operative monitoring of bone and implant loading patterns in the operative correction of scoliosis using the Harrington distraction rod. The method incorporates a strain gauge instrumented, distal Harrington hook and similarly equipped Harrington operating instruments (outrigger and distractor). These latter instruments are used to calibrate the hook's response to bone loads under existing operative conditions. Alternative methods of monitoring loading patterns were explored and rejected because they were noncontinuous, more difficult to use, altered the mechanics of the system, or required more expensive components. The method established is being used to avoid bone rupture or rod damage while gaining maximum spinal correction and to determine the effect of auxiliary implant components on loading patterns.

Biomedical Engineering↗
PubMed1983

Simultaneous quantitation of knee ligament forces.

An apparatus and experimental technique have been developed which allow the simultaneous quantitation of human cadaver knee ligament forces with the knee in various positions and subjected to various loads. The methodology permits all the major ligaments of the knee to be kept intact, thus preserving much of their normal relative load-bearing function. A novel measurement technique was employed for ligament force measurement. Strain gauges were placed at the ligamentous insertions and origins either on cortical bone or the cancellous/cortical transition. Gauge output was subsequently calibrated quantitatively by cutting the ligaments and subjecting them to known loads. The gauging technique was thermally stable, and the method as a whole yielded reproducible relative ligament force data when knee positions and loads were repeated for a given knee specimen. Three fresh human cadaver knee specimens have been subjected to testing thus far with gauges at six ligamentous sites. Initial evaluation of the data indicate that ligamentous loading patterns were quite different from those reported in the literature as determined by other methods.

Humans↗