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Biomedical subjects

H B Skinner

Publications and source records attributed to H B Skinner.

At least 19 recordsLinked to original sources
PubMed1992

Use of hot wire anemometry to measure velocity of the limb during human movement.

Hot film anemometry, x-configuration probes were used in two experiments to evaluate their effectiveness at measurement of limb velocity. Data from tests with a probe attached to the end of a pendulum establish that the hot films measure velocity in the swing phase within 0.098 ms-1. The kinetic energy per unit mass of the pendulum was predicted within +/- 0.005 m2 s-2, from the measured velocity. In gait experiments with one human subject at speeds greater than 0.25 ms-1, the hot film anemometer and a video system predicted speeds within 0.083 ms-1. The hot film data are electronic signals that are easily stored and processed. The results from these experiments demonstrate that hot film anemometry is an effective and efficient method for direct measurement and analysis of the limb velocity.

Biophysical Phenomena↗
PubMed1992

Three-dimensional finite element modelling of bone: effects of element size.

This study quantifies the effects of element size on the stress/strain results of finite element (FE) models of bone that are generated with a previously described automated method. This method uses cube-shaped hexahedral elements, which enabled element shape and aspect ratio to be held constant while the effects of element size were studied. Three models of a human proximal femur, each with a different element size (3.1 mm, 3.8 mm and 4.8 mm), were analysed. Convergence in strain energy of the models had been verified in previous work. The stresses and strains predicted by the models were compared on a pointwise basis using linear regression analysis. There was a general decrease in the level of stress and strain when element size was increased, even though convergence in strain energy had been achieved. An increase in element width from 3.1 mm to 3.8 mm decreased the predicted stresses by 13% to 29% overall; the predicted strains decreased by 4% to 20% for the same increase in element size. These results indicate that linear cube-shaped hexahedral elements must be very small (3 mm on a side or smaller) to represent the sharp variations in mechanical properties that exist in bone, and that use of larger elements decreases the predicted stresses and strains. The elements used in this study are similar to those typically used to represent trabecular bone in conventional (non-automated) FE modelling methods. Therefore, the sensitivity of the stress/strain results to element size that was found for trabecular bone also applies to conventional modelling of such bone.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

Mechanistic insights relevant to protein secretion in yeast.

During the past year, a powerful combination of genetic and biochemical approaches has yielded fascinating information with respect to the question of how proteins cross membranes and subsequently traffic between intracellular compartments of the yeast secretory pathway. Fundamental advances have been made in two specific areas. These include experiments that have provided new perspectives with respect to the nature of the soluble machinery involved in facilitating protein traffic from the cytoplasm to the lumen of the endoplasmic reticulum, and work that has provided a biochemical description of what may in effect represent a membranous ligand-gated channel that is required for protein translocation into the endoplasmic reticulum lumen.

Biological Transport↗
PubMed1992

Compressive mechanical properties of human cancellous bone after gamma irradiation.

The effect of gamma irradiation on the mechanical properties of human bone was examined. Specimens of cancellous bone were cut from the proximal epiphyseal region of fresh-frozen tibiae and divided into control and irradiated groups according to anatomical region. The irradiated groups were exposed to 10,000, 31,000, 51,000, or 60,000 gray (1.0, 3.1, 5.1, or 6.0 megarad). The specimens were tested in compression to failure to determine failure stress, strain to failure, and elastic modulus. Failure stress and elastic modulus were found to be proportional to the square of the density and were normalized with respect to this property. Significant differences in normalized failure stress (p less than 0.001) and normalized elastic modulus (p = 0.003), when compared with the values for matched control specimens, were found only for the specimens that had been irradiated with 60,000 gray (6.0 megarad).

Aged↗
PubMed1991

The effect of ankle constraint on the torsional laxity of the knee during internal-external rotation of the foot.

The in vivo torsional laxity and stiffness of the knee joint are usually determined by rotating the foot and measuring the torque generated at the knee. However, when rotation is applied to the foot, significant three-dimensional forces and moments are produced at the knee. These forces and moments depend upon the external constraint of the ankle complex, and as a result, the observed laxity of the knee also depends on the ankle constraint. Tests are conducted with the foot of a subject in a shoe, with and without the ankle taped, and in a buckled and unbuckled (ski) boot that can effectively constrain ankle rotation. The average laxity of the primary (linear) region of the axial moment vs internal-external rotation is 30% greater when the ankle is constrained by the buckled boot than it is in three other cases of lesser ankle constraint.

Adult↗
PubMed1991

Subtrochanteric osteotomy in total hip revision. Report of two cases.

Revision of the femoral component in a failed total hip arthroplasty can be difficult, tedious, and destructive to the patient's femur. This is particularly true in cases of severe osteolysis or revision of previous revisions. A technique is described whereby visualization of the femoral canal is obtained by subtrochanteric osteotomy. This technique may be useful in selected cases of hip revision.

Femur↗
PubMed1991

A finite helical axis as a landmark for kinematic reference of the knee.

Reference coordinates based on the finite helical axis for flexion of the knee from 0 to 90 deg are proposed. Six degree-of-freedom tracking allows the use of such a helical axis as a kinematic landmark for knee motion representation. Data from five human subjects in vivo are presented as a path of finite helical axes for flexion of the knee from 20 to 80 deg. The finite helical axis rotates by an average of 11.4 deg, the centrode translates an average of 19.8 mm, and the total axial translation averages 0.1 mm during flexion from 20 to 80 deg. Error due to the transducer was measured on a fixed-pivot pendulum and found to be 1.0 deg and 1.9 mm rms for the helical axis orientation and position, respectively, and 0.1 mm for the axial translation. Reproducibility and soft tissue effects on the measurements were repeatable to 4.0 deg and 2.7 mm rms in orientation and position, respectively, and 0.1 mm for the axial translations. Soft tissue errors averaged 4.9 deg and 3.6 mm in position and orientation, and 0.3 mm in the axial translations.

Adult↗
PubMed1991

Analysis of a below-knee patellar tendon-bearing prosthesis: a finite element study.

In this study, a finite element (FE) model of a below-knee prosthesis of patellar tendon-bearing (PTB) design, and several altered variations of the model have been constructed. A load of approximately 1.5 times normal body weight (984 N) was applied at the heel of the model to simulate heelstrike conditions. The "base" model was then analyzed and revised iteratively until a model which provided consistency between soft tissue elastic modulus and socket displacement was developed. The interface normal and shear stresses obtained from the analysis of this revised base model were highest (about 961, and 463 KPa, respectively) at the distal anterior tip of the socket/stump. Proximally, higher normal stresses (72-78 KPa) were found medially and posteriorly. Proximal shear stresses were highest posteriorly (79 KPa), although shear stresses medially (51 KPa), and laterally (43 KPa), were also much higher than anteriorly (10 KPa). FE analyses were performed on the altered models to determine the relative effects on socket/stump interface stresses of altering the FE model of the prosthesis. Results of the analysis indicate that fabricating the prosthesis from a material with an elastic modulus ten times lower than that of the revised base model can produce reductions in the maximum pressure of up to 14 percent. Large decreases in maximum pressures (71 percent) resulted from the use of a suction socket rather than a conventional socket. Small changes in stump length (2 cm) caused relatively large pressure changes (16 to 18 percent).

Amputation, Surgical↗
PubMed1991

Isoelasticity and total hip arthroplasty.

Important parameters in designing an "isoelastic" prosthesis that transfers stress in a more physiologic manner are explored. The effect of material properties and geometry on the mechanical properties of a femoral component are discussed. The bending "stiffnesses" of cortical bone, metal prosthese, and composite prostheses are compared, and the bending rigidities of prosthesis and bone as they might vary with surgical technique are explained. It is shown that the flexural rigidity of a prosthesis stem as presently designed is close to the flexural rigidity of cortical bone, but 200 to 400 times greater than that of the material it replaces, ie, cancellous bone and fatty marrow.

Bone and Bones↗
PubMed1990

Automated three-dimensional finite element modelling of bone: a new method.

Three-dimensional finite element stress analysis of bone is a key to understanding bone remodelling, assessing fracture risk, and designing prostheses; however, the cost and complexity of predicting the stress field in bone with accuracy has precluded the routine use of this method. A new, automated method of generating patient-specific three-dimensional finite element models of bone is presented--it uses digital computed tomographic (CT) scan data to drive the geometry of the bone and to estimate its inhomogeneous material properties. Cubic elements of a user-specified size are automatically defined and then individually assigned the CT scan-derived material properties. The method is demonstrated by predicting the stress, stain, and strain energy in a human proximal femur in vivo. Three-dimensional loading conditions corresponding to the stance phase of gait were taken from the literature and applied to the model. Maximum principal compressive stresses of 8-23 MPa were computed for the medial femoral neck. Automated generation of additional finite element models with larger numbers of elements was used to verify convergence in strain energy.

Adult↗
PubMed1990

Alternatives in the selection of allograft bone.

Many orthopedic surgeons are unfamiliar with the various types of commercially available allograft bones, despite their frequent use in reconstructive and tumor surgery. This report summarizes the mechanical, osteoinduction, and safety data for sterile fresh-frozen, secondarily sterilized, and freeze-dried bone. The orthopedic surgeon can make informed choices about bone alternatives based on the risks and benefits of each type. Data have shown that fresh-frozen sterile-collection bone is the optimal substitute for autogenous bone in most applications.

Biomechanical Phenomena↗
PubMed1990

Decreased pain with lower flexural rigidity of uncemented femoral prostheses.

One hundred one consecutive uncemented hip arthroplasties (87 patients) were analyzed radiographically at 1-year follow up to relate mechanical factors to hip pain as determined by clinical pain scores. The average area moment of inertia and flexural rigidity were greater for the bone than the metal prosthesis for each type of prosthesis (AML, HG, PCA). Normalization of the flexural rigidity ratio (bone to prosthesis) for patient weight yielded a Spearman correlation coefficient of 0.232, significant at P = .02, suggesting that both applied stress and bending stiffness have an effect on pain. No relationship was seen between pain and AP, or average gap between prostheses and bone.

Adult↗
PubMed1990

Ankle weighting effect on gait in able-bodied adults.

Energy expenditure during ambulation was measured in 10 able-bodied subjects wearing symmetrically and asymmetrically added ankle weights. When a 1.82-kg weight was added to one ankle and then both ankles, baseline oxygen consumption per unit distance (0.148 +/- 0.025 mL O2/kg/m) increased significantly by 7.4% (0.159 +/- 0.025 mL O2/kg/m) and 17.6% (0.174 +/- 0.027 mL O2/kg/m), respectively. The rate of oxygen consumption rose by 6.3% to 11.28 +/- 1.57 mL O2/kg/min and by 14.2% to 12.12 +/- 1.75 mL O2/kg/min, respectively, but only the latter increase was significant. When gait was analyzed using the same weight-addition protocol, velocity, cadence, stride length, gait cycle, and double-limb support time showed no change. However, asymmetric weighting decreased single-limb support time, increased the swing phase, and decreased the stance phase of gait in the weighted limb. The unweighted leg was conversely affected. Symmetric ankle weighting caused a significant increase in single-limb support time for both extremities, consistent with previous data.

Adult↗
PubMed1989

The stiffness of cylindrical casts enforced with splint laminations: biomechanical considerations.

Splint lamination is often used to strengthen a plaster cast while minimizing its thickness and weight. We evaluated the following lamination configurations to determine the effectiveness of each relative to a 3-mm-thick short leg cast: anterior-posterior splints, medial-lateral splints, and an anteriorly placed fin. Theoretical stiffness was calculated as a function of the area moment of inertia, and then the actual casts were tested in three-point bending on a servohydraulic apparatus. The experimental results were correlated with the calculated data, and finite element studies were performed to correlate the experimental results with the geometries of the casts. The theoretical and experimental data indicate that anterior-posterior splint lamination reinforcement stiffens a cylindrical cast to flexion-extension bending moments more effectively than does medial-lateral splint placement. An anterior fin can stiffen the cast as effectively as a splint can. However, the fin must be relatively large, which may cause it to accentuate problems with clothing and be difficult to apply.

Biomechanical Phenomena↗
PubMed1979

Evaluation of a commercial, porous stainless steel as a prosthetic implant material.

In the course of evaluating various porous materials as candidates for prosthetic devices, a commercial stainless steel (316L) was found which was designed for porous filtration applications. Small bars (approximately to 3mm x 3mm x 20mm) were implanted in dog extremeties for periods of 10 to 15 weeks. The average tensile strength of the bone/(bone/metal) interface was found to be 0.975 kgf/mm2 (1380 psi) with no indication of variation with time of implantation. Scanning electron microscopy (SEM) combined with X-ray energy dispersive (XRED) analysis indicates production of calcified bone in the bone/metal composite. Inherent strength and porosity characteristic combined with biocompatbility indicate that this commercially available meterial is a viable implant candidate for attachment to the skeletal system.

Animals↗
PubMedDate not supplied

Velocity-diameter relationships of the microcirculation.

An analytical expression for the relationship between velocity (and blood flow) and diameter for vessels in the microcirculatory range up to 900 mum diameter is presented. Both the arterial and venous systems are considered. The analytical expression for these relationships has been derived from computer analysis of data obtained from individual measurements reported in the literature. Computer analysis shows that blood velocity is a nearly linear function of diameter of blood vessels for the arteriolar tree. The relationship for blood flow as a function of diameter is Q = 108d3.101 for arteries, arterioles and capillaries in the diameter range 5 to 900 mum and for the venous system in the range 5 to 115 mum is Q = 334d2.388 where Q is in mum3 per second and d is in mum. Comparison of the results of this study for the arterial system to the Hagen-Poiseuille Law reveals close agreement, if correction is made for geometric factors of blood vessels and for the variation of viscosity with diameter for blood.

Animals↗