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Biomedical subjects

H B Skinner

Publications and source records attributed to H B Skinner.

At least 73 records · Page 4Linked to original sources
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↗
PubMed1989

Stress analysis of a total hip acetabular component: an FEM study.

A stress analysis of a total hip acetabular component was performed using three-dimensional finite element modeling. The model consisted of 548 four-noded quadrilateral shell elements with 582 nodes. A worst-case support condition was assumed in which bony contact with small areas of the ilium, ischium, and pubis was represented by three-point support. Loads corresponding to the peak pressures developed in the hip when rising from a seated position--the activity contributing most to the fatigue of a prosthesis--were applied to the model. Peak stresses of 490 MPa are predicted around a screw hole in the region of greatest loading; according to the fatigue curve for porous-coated Ti-6Al-4V alloy, this translates into a component life of three years. When the area of bony support for the prosthesis is increased by a factor of 1.5, the fatigue life is more than doubled to seven years. The addition of restraints around the loaded hole to represent the placement of a screw extends the lifetime dramatically to 65 years. Substituting the material properties of cobalt-chromium alloy increases the predicted lifetime of the component to twelve years. We conclude that poor bone support can compromise the service life of titanium alloy acetabular components. Furthermore, we suggest that screw fixation be used to secure the prosthesis in the anterior-superior region if the prosthesis is not well supported by bone in the acetabulum.

Acetabulum↗
PubMed1989

Unicameral bone cysts. A comparison of treatment options.

Thirty-two unicameral bone cyst cases from various hospital centers in the San Francisco Bay Area were reviewed in order to compare the results of different treatment methods. Thirteen of the 32 cysts were latent and 19 were active, judged by their proximity to the growth plate. The average age at presentation was 8.9 years, and average follow-up was 5.6 years. Fifteen patients were treated surgically, 12 were given steroid injections, and five were treated nonoperatively. Comparative analysis of these methods supports previous studies which show that steroid injections are as effective as surgical intervention while having lower morbidity.

Adolescent↗
PubMed1988

Prediction of fatigue failure of a total knee replacement tibial plateau using finite element analysis.

Recent reports of total knee prosthesis fractures have raised concerns over the long-term structural integrity of metal-backed tibial components. Both the development of a fibrous tissue membrane under the tibial plateau of a total knee prosthesis and loading conditions may seriously alter the fatigue life of the metal tibial tray. The effects of the cement and fibrous tissue at the bone-prosthesis interface were studied. Using the method of three-dimensional finite element analysis, peak loads of normal gait were simulated at several locations on the plateau of a generic, single-stemmed, porous-coated, CoCrMo tibial component model, providing information on the effect of abnormal loading patterns. According to the analysis, stresses below the material endurance limit are predicted throughout the prosthesis prior to the development of the fibrous membrane. However, stresses exceeding the yield strength of the material are predicted in a prosthesis that is supported by a fully developed 1 mm membrane, meaning that it has a markedly increased risk of low-cycle fatigue failure. Lateral displacement of the loading is detrimental to prosthesis life because maximum stress increases 100% while posterior displacement of the loading increases maximum stress by only 30%. Anterior loading creates stresses similar to those created by central loading. Because of their susceptibility to low-cycle fatigue failure, simple, single-stemmed prostheses are not recommended in cases of questionable bone stock unless modified. Several design alternatives are proposed.

Bone Cements↗
PubMed1988

Composite technology for total hip arthroplasty.

Composite materials, which can be very strong while having a low modulus of elasticity, are being studied because such materials have potential to be made into isoelastic hip prostheses. Composites intended for medical applications incorporate carbon or polyamide as a fiber component, while polysulfone, polyetheretherketone, or polyethylene is used as a matrix component. Mechanical properties (especially the modulus of elasticity) are emphasized because of the desire to match those properties of the proximal femur. Many of the variables that affect the mechanical properties of these materials are explained. The application of stress to different fiber orientations demonstrates the mechanical properties of the composite, and this is proved mathematically. It is shown that in composites with fibers oriented in the same direction, the modulus of elasticity in the direction of the fibers generally approaches that of the fibers as the amount of matrix decreases. Perpendicular to the fibers, the modulus of elasticity of the composite is only slightly greater than that of the matrix material. For isotropic chopped-fiber composites, the modulus of elasticity approaches that of the matrix as the fiber content decreases; at high-fiber content, the modulus is significantly less than that of oriented long-fiber composites. In general, the modulus of elasticity and fiber content have a linear relationship. Composites have fatigue properties that vary with direction and approach ultimate strength in tension but are lower in compression. The fatigue properties of proposed composites are discussed. Abrasion as a cause of stress concentration sites and wear particles is considered.

Biomechanical Phenomena↗
PubMed1987

Soft-tissue response to total hip surface replacement.

Tissue reaction to prosthesis wear debris and its relationship to prosthetic loosening was investigated. Eighteen dogs underwent hip surface replacement; 6 animals accounted for 6 control and 6 carbon hips, and 13 experimental animals accounted for 13 implanted carbon and 13 cobalt-chromium-molybdenum (CoCrMo) prostheses. Both kinds of prostheses articulated against a high-density polyethylene acetabular component. One year after implantation, tissue response to the prostheses was evaluated according to a semiquantitative method, and a total tissue score indicating the degree of tissue response was obtained. The total tissue score was then compared with the normalized final vertical ground reaction force (GRF) for each hip in the animals with bilateral hip replacements. Compared with the controls, significantly greater tissue response was seen in both kinds of prosthetic hips (p = .001). No statistically significant difference in the tissue response of the two types of hip prostheses was noted, although the tissue response score of the CoCrMo demonstrated a trend toward more severe reaction than the carbon. No statistical difference in tissue reaction was noted for loosened components as compared with tightly fixed components. Amount of wear debris was the best predictor of component loosening. Gait analysis demonstrated a statistically significant negative correlation between GRF and total tissue score (p = .036), and between GRF and wear debris score (p = .034). The results of this study suggest that GRF may predict the amount of wear debris in the tissues surrounding a total hip surface arthroplasty, and that severity of pain is related to the degree of tissue response.

Animals↗
PubMed1987

A library of trimethylguanosine-capped small RNAs in Physarum polycephalum.

We have constructed a cDNA library for the trimethylguanosine-capped small RNAs (sRNAs) in the acellular slime mold Physarum polycephalum. Capped sRNAs were purified from total cellular RNA of vegetative microplasmodia by preparative immunoprecipitation with anti-trimethylguanosine antibody. The purified RNA was analyzed by polyacrylamide gel electrophoresis. Approx. eleven different capped sRNAs were observed with a size range of 70-204 nucleotides (nt). Based on their approximate sizes, the presence of trimethylguanosine cap, and the presence of a lupus type-Sm antigen, molecules U1-U7 (excluding U3) were identified. Further confirmation of the identity of molecule U1a was established by Northern hybridization, U4a by colony hybridization, and U6 and U7a by direct chemical sequence analysis. Purified capped sRNAs were tailed with oligo(A), and inserted into oligo(dT)-tailed plasmid pCDV1. The cDNAs were used to transform Escherichia coli strain HB101. Approx. 1.9 X 10(5) ampicillin-resistant (ApR) transformants were obtained per microgram of tailed sRNA. Dot-blot hybridization, using Physarum RNA precipitated with anti-cap antibody as a probe, indicated that approx. 94% of the ApR colonies contained recombinant DNAs. The library was screened by colony hybridization using heterologous sRNA probes. Clones hybridizing with heterologous sRNAs U1, U2, U4 and U7 were each represented in the library in approximately the same frequency as their relative abundance in the Physarum sRNA population they were derived from. The insert of one Physarum U4 clone was sequenced and was found to have 57.1% homology with nt 1-91 of the published sequence for rat U4 RNA. A 12-nt 'functional' subdomain of the rat U4 molecule was 83.3% conserved in Physarum U4.

Autoantigens↗
PubMed1987

Failure analysis of PCA revision total knee replacement tibial component. A preliminary study using the finite element method.

This report documents the results of a finite element method (FEM) "worst-case" failure analysis of a stemmed, porous-coated tibial revision component that was designed with "slots" to aid in removal. A three-dimensional FEM model of a metal-backed tibial component was subjected to expected peak loads while being restrained at the stem and unsupported under the plateaus. Stresses in the prosthesis plateau adjacent to the stem were found to exceed yield stress in many areas, and to exceed the expected endurance limit in large areas. We conclude that a stemmed prosthesis with slots is flawed and may be expected to fail if implanted without adequate support for the prosthesis plateau. The long-term effects of bone remodeling may further jeopardize the integrity of this prosthesis. We recommend that this prosthesis not be used in its present design.

Biomechanical Phenomena↗
PubMed1987

Soft tissue sarcoma associated with aluminum oxide ceramic total hip arthroplasty. A case report.

Malignant tumors around fracture fixation implants have been reported sporadically for many years. Recently, however, reports of sarcomatous degeneration around a standard cemented hip arthroplasty and around cobalt-chromium-bearing hip arthroplasties raise new questions of the malignant potential of metallic ends prostheses. Sarcomatous changes around aluminum oxide ceramics seem not to have been reported in the literature. The present report may be the first documented case of an aggressive soft tissue sarcoma detected 15 months after the patient had an uncemented ceramic total hip arthroplasty. If a causal relationship exists, the incidence of this phenomenon in the United States is 250 times greater than would be expected from statistics on soft tissue sarcoma at the hip. Because of the similarity on plane roentgenograms of this tumor to lesions known to be caused by wear debris, tumors should be included in the differential diagnosis of cases of total hip loosening.

Adult↗
PubMed1986

Effect of fatigue on joint position sense of the knee.

This study was designed to test position sense of the knee joint before and after fatigue in order to determine whether muscle or capsular receptors are the primary sensors for joint position sense. Reproduction of passive positioning and detection of the onset of motion (kinesthesia) were employed to measure joint position sense. Eleven subjects underwent joint position sense measurement before and after a fatigue protocol. A significant worsening of reproduction of knee joint angle after fatigue was noted (p less than 0.05). Threshold (kinesthesia) showed no statistically significant change after fatigue. A significant correlation of reproduction measurements and threshold measurements prior to fatigue (p less than 0.01) demonstrated that the same neural mechanism is applicable in the rested state, but these variables did not correlate significantly after fatigue. There was a significant correlation between reproduction measurements before and after fatigue (p = 0.018), while no correlation was seen for the pre- and postfatigue threshold measurements, suggesting a change in the neural path after fatigue. Since both tests of joint position sense are affected by fatigue, we conclude that muscle receptors are a prominent, if not primary, determinant of joint position sense, and capsular receptors may have a secondary role. Reproduction ability is decreased, presumably through the loss of efficiency of muscle receptors. The threshold data suggest a change in the mechanism of appreciation after fatigue, possibly due to increased sensitivity of capsular receptors from muscle-fatigue-induced laxity.

Adult↗
PubMed1986

The clinical anatomy of commonly injured muscle bellies.

Injury to a skeletal muscle belly resulting in discontinuity of the muscle fibers is an infrequent but serious occurrence. Early surgical treatment of these injuries may prevent healing of the muscle in a lengthened position. Cadaver specimens of commonly injured muscles of the upper and lower extremities were examined for the presence, location, and extent of the tendons of origin and insertion. Most of the muscle bellies contained tendinous extensions that appeared as flattened fibrous bands. Optimal surgical repair of a muscle belly injury should include re-establishing the continuity of any intramuscular tendinous extensions. This study provides anatomic information as to the approximate location and extent of these tendons to permit optimal repair. In general, operative repair of the tendinous portion within a muscle belly is possible in the proximal third and distal thirds of most muscles, and in the middle third of a few muscles.

Humans↗