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Biomedical subjects

H B Skinner

Publications and source records attributed to H B Skinner.

At least 91 records · Page 5Linked to original sources
PubMed1986

Variations in the density of bone cement after centrifugation.

Barium sulfate added to bone cement to provide radiopacity has a density about four times greater than that of polymerized radiolucent bone cement. Because centrifugation might make a clinically significant change in the distribution of barium sulfate, this process was studied. Radiolucent and radiopaque Simplex-P bone cement (Howmedica, Inc., Rutherford, New Jersey) were mixed with and without cooling and centrifuged for two or four minutes at 2,000 g or 1,000 g (gravity acceleration). The density of sections of the hardened bone cement was measured using the Archimedes principle. Erythromycin and colistin were added to cement batches to test whether or not centrifugation affected the distribution of antibiotics. Direct and radiographic observation and density measurements (cooled specimens, 2,000 g, p less than 0.01) verified that barium sulfate does accumulate at the bottom of the centrifugation tubes. Thin sections of the bone cement revealed that only larger particles (20-100 micron) of barium sulfate were deposited at the bottom. No evidence of redistribution of antibiotics after centrifugation was seen. It is recommended that Simplex-P bone cement be reformulated to eliminate concern about inhomogeneities that arise from centrifugation. Further, it is recommended that cooled, centrifuged antibiotic cement be used for long-stem revision hip surgery, where longer setting times are necessary, and room temperature cement for "fresh" hip surgery. A total centrifuge time of two minutes with a 2,000 g maximum force is recommended.

Anti-Bacterial Agents↗
PubMed1985

An analysis of failed Harrington rods.

Eight mechanically failed Harrington rods have been retrieved and examined clinically, metallurgically, and biomechanically to characterize the mode of instrument failure and to determine how future failure rates might be minimized. The results of the study indicated fatigue to be the mode of mechanical failure in all cases, however, in only one case was any significant metallurgical defect observed. Failure occurred at the ratchet-shaft junction in seven of eight cases with the remaining failure occurring at the midshaft region. This occurred in the rod with the metallurgical defect. The possibility of fatigue failure can be lowered by implementing both clinical and design considerations. Clinically, stress on the rod can be lowered by placing the ratchet-shaft junction as close to the hook as possible and by using the shortest rod possible. Both of these will minimize the moment arm at the vulnerable ratchet-shaft junction. Design modifications, including increased rod diameter, polishing the ratchet-shaft interface and material changes, can also be used to lower the stress on the rods and thus reduce the risk of mechanical failure.

Equipment Failure↗
PubMed1985

Prescription options for the below knee amputee. A review.

In 1973 a workshop sponsored by the National Academy of Sciences recommended that "efforts to develop prescription criteria for use of the numerous variants of the BK prosthesis should be intensified." This paper provides a review of the important considerations in the prescription of a below-knee prosthesis. It is intended that this information would assist the physician to make better informed decisions regarding the specific type of prosthesis for a particular patient. No attempt has been made to describe all prosthetic options since a majority of amputees are fit with only a few prescriptions. Thus, socket design, suspension, shank type, and foot specification may be optimized for individual patients through mutual agreement of the prosthetist and the knowledgeable physician. This paper will present some of the more difficult prescription solutions to the various fitting problems that are representative of our nation's amputee population. This is done with the knowledge that there may be other and equally successful solutions to these problems. Several illustrative examples are provided.

Adult↗
PubMed1985

Static load response of the heels of SACH feet.

Excessive heel hardness in the prosthetic foot is a frequent problem that may contribute to decreased function in the above knee and below knee amputee. Optimal mechanical characteristics of the SACH (solid ankle cushion heel) foot have not been defined. In an effort to characterize the mechanical properties of the heels of these feet, we performed static load-deformation tests on the heels of SACH feet at stimulated heelstrike. These data were interpreted using least squares fitting of the natural logarithms of the load-deformation data. Statistical comparison of these data revealed no significant difference in the static response of the "medium" and "regular" grades of foot. A difference at the 1% level of confidence was found between the "soft" grade and the two firmer grades. Consistency within a grade of foot was quite good. Comparison of feet from another manufacturer revealed no difference in static response, suggesting consistency in static performance among manufactures. It was our clinical impression that all grades of SACH heels are too stiff.

Artificial Limbs↗
PubMed1985

Gait analysis in amputees.

There are marked differences from normal in both AK and BK gait. Forward velocity of walking is significantly lower in the amputee and is lower in the AK than in the BK subjects. Traumatic AK amputees ambulate with time-distance parameters of velocity, cadence, stride length and gait cycle which are all two standard deviations below normal. The same parameters for the traumatic BK amputee are only one standard deviation below normal. The symmetry of walking seen in the normal subject is not present in the lower extremity amputee. Measurements of single limb support times and motion analysis of the lower extremities as well as of the head, arms and trunk bear this out. This asymmetry of motion increases the excursion of the center of mass during each cycle and thereby increases the energy cost of ambulation. Energy cost of amputee gait often places the dysvascular AK amputee at his limits and strains other amputees severely. Further research is necessary to enable amputees to approach the walking capabilities of normal people.

Adult↗
PubMed1984

Joint position sense in total knee arthroplasty.

Seventeen postoperative total knee arthroplasty (TKA) patients were evaluated using two tests of knee joint position sense. Young controls and age-matched controls underwent identical tests. The TKA patients also underwent gait analysis, including foot switch stride analysis, and clinical evaluation using a standard scoring system. Results showed statistically significant decreases in joint position sense from young controls to old controls, and further significant decreases with joint disease; however, no further worsening was noted as a result of TKA. The abnormal gait parameters seen in TKA patients correlated as well with position sense as with clinical score. Strongest correlations were seen when a combined clinical and proprioceptive score was compared with gait parameters. In spite of alleviation of pain and correction of deformity, normal gait and function are not typically achieved after total knee replacement. Irreversible loss of joint proprioceptive function due to the disease process may be a major factor in the discrepancy between clinical and functional outcomes of total joint arthroplasty. Furthermore, loss of proprioception and the resulting abnormal gait patterns may place increased stress on components and contribute to loosening. In addition, an association between degenerative joint disease and decline in proprioception is suggested.

Adult↗
PubMed1984

Bone remodeling due to continuously applied loads.

It has long been known that the stress history of bone tissue influences its structure; however, the nature of this relationship remains largely uncharacterized. The objective of this work was to induce a quantifiable change in the stress history of in vivo bone tissue and examine subsequent changes in structural and material properties that might occur. Continuous compressive loads were applied to the diaphysis of adult mongrel dogs for 2 months. The loads, ranging from 12-130 N, were superposed on the normal activity of the animals by implanting spring loading devices on the diaphysis of the femur. After the animals were sacrificed, mid-diaphysial specimens were subjected to compression testing to determine a structural bulk stiffness. The cross-sectional areas of original bone tissue and new bone deposition were then determined. The ash weights of selected specimens were also determined. The results indicate that a positive correlation between the increase in cross-sectional area and the superposed stress does exist. The new bone apposition was found almost entirely on the periosteal surface. Very little evidence of internal remodeling or endosteal movement was observed. The new tissue was found to have a lower ash weight and appeared to have a disorganized microstructure. Mechanical testing also suggests that the newly deposited tissue is far less stiff than the mature original bone.

Adaptation, Physiological↗
PubMed1984

Proprioception of the knee joint. Paradoxical effect of training.

Two tests frequently used to measure joint proprioception were performed on the knees of twelve members of a professional ballet company to determine the effect of extensive athletic training on this sensation. These tests measured the threshold of perception of joint motion and the ability of a subject to reproduce a joint position. A healthy, active age-matched control group was also tested. Results show that dancers performed significantly better on the threshold test (p less than 0.05) and significantly worse when reproducing a joint position (p less than 0.05) than the control group. The strong implication is that athletic training can affect joint proprioception and that these two tests are in fact, dependent on different neural mechanisms.

Adult↗
PubMed1984

Age-related decline in proprioception.

Joint-position sense of the knee was measured in 29 subjects with normal knee joints ranging in age from 20 to 82 years. Joint-position sense was determined by two common techniques that measure the threshold to detection of motion and the ability to reproduce passive knee positioning. Joint-position sense was found to deteriorate with increasing age as measured by both tests, with a correlation coefficient that was significant at the p less than 0.001 level for each test. The two tests were found to correlate at the p less than 0.025 level, indicating that the same biologic parameter was being measured by both tests. Deterioration of proprioception, or joint-position sense, as measured may be a sensitive indicator of subclinical degenerative joint disease of the knee, as well as a means of quantitating proprioception in suspected neuropathic joints.

Adult↗
PubMed1983

Ambulatory function in total knee arthroplasty.

Through the use of gait analysis, this study attempts to characterize gait after total knee arthroplasty as a function of postoperative time to quantify the effectiveness of the surgery and to evaluate prostheses of several different designs. Gait analysis on 32 preoperative and 50 postoperative patients included measurement of velocity, cadence, stride length, and gait cycle. Postoperative data were collected at various intervals from 0.7 to 111 months after knee surgery (average postoperative time, 45.3 months). Linear regression analysis of velocity, cadence, stride length, gait cycle, and the ratio of contralateral to pathologic single limb support time as a function of postoperative time are reported with statistical error limits. Extrapolation of these results to zero postoperative time indicates that the patients who had had total knee arthroplasty had a slight improvement in all gait parameters compared to the preoperative control group. This was not statistically significant, however, except for cadence (P less than .05). Although velocity and stride length increased slightly toward more normal values with increased postoperative time, gait parameters at no time approached normal values.

Adult↗
PubMed1983

A biomechanical analysis of the etiology of tibia vara.

To elucidate the cause of tibia vara, finite element analysis of the proximal tibia was used to investigate the stresses occurring in the physeal plate during one-legged stance in 2- and 5-year-old children. A modification of the method of Kettlekamp and Chao was used to assign forces to the medial and lateral plateaus and lateral ligament. Stresses were calculated in the physeal plate for the two age groups as a function of degree of varus and body weight. Our results show that increasing varus resulted in increasing compressive stress in the medial tibial physis to a level seven times normal at 30 degrees of varus. Further, tensile stresses determined in the lateral tibial physis were increased above normal. Changes were more marked in the obese child and in the 5 year old. Using the data from Strobino et al. it appears that in the 2 year old 20 degrees of varus resulted in forces sufficient to retard growth. In the 5 year old, however, 10 degrees of varus resulted in borderline forces in a child of normal weight, but forces exceeding those necessary to retard physeal growth were calculated in the model of the obese child. Our data are consistent with the hypothesis that Blount's disease is primarily the result of the proximal tibial epiphysis responding to physical phenomena.

Biomechanical Phenomena↗
PubMed1983

Effect of articular disease and total knee arthroplasty on knee joint-position sense.

Joint proprioception in the human knee has been studied using two previously described tests. Threshold of detection of slow, constant, passive motion and ability to reproduce angles to which the knee was passively placed were accurately measured. A group of postoperative total knee arthroplasty (TKA) patients were examined. All patients also had documented articular disease in the unoperated knee. Results were compared to age-matched controls. In addition, a young control group was studied for comparison to both groups. A significant difference was seen between the young control group and the older control group in both tests performed. Age-matched controls and the postoperative patients demonstrated an even greater difference. There was, however, no difference between the operated and unoperated knee among the TKA patients. It is concluded that joint proprioception declines to some degree with normal aging. A more marked decline is associated with degenerative joint disease. Total joint replacement, however, did not lead to a further decrease in sensation.

Age Factors↗
PubMed1983

Femoral head stresses following cortical bone grafting for aseptic necrosis. A finite element study.

A two-dimensional finite element model was used to compare the femoral head stress distribution of an intact femur with that of a femur following core biopsy and biopsy with cortical grafting. There was a decrease in superior and lateral femoral head stresses of up to 50% by an incorporated and properly placed cortical graft. Core biopsy and cortical grafting short of the subchondral plate produced stress-concentrating effects. A medially placed cortical graft did not stress-relieve the superolateral femoral head. Thus, if cortical grafting is to be undertaken, the graft should extend from the lateral cortex to the subchondral plate, transfixing the length of the necrotic segment. Because of deleterious effects on femoral head stress distribution, core biopsy without cortical grafting should be discouraged or only very cautiously used.

Bone Transplantation↗
PubMed1983

A quantitative histologic study of osteoporosis produced by nutritional secondary hyperparathyroidism in dogs.

Nutritional secondary hyperparathyroidism (NSH) was induced in adult beagle dogs through nutritional control by a diet high in phosphorus (1.20%) and low in calcium (0.12%). A control group was fed a diet containing 0.42% phosphorus and 0.54% calcium. A statistically significant increase in iPTH level was observed at ten and 20 weeks. The femoral heads of experimental (NSH) animals showed increased osteoclastic activity and an approximately 20%-30% reduction in volume fraction cancellous bone. No abnormal osteoid seam was found in the cancellous bone of the experimental animals, and no statistically significant differences were observed in either the calcium-to-phosphorus or mineral-to-matrix ratios of the bone tissue for the two groups. Data obtained from histologic sections on the number of trabecular bone intercepts per unit length and thickness of trabeculae in the femoral head indicated a uniform, rather than specific loss of bone mass in the experimental sections. Histologic sections from the proximal femoral shaft revealed increased endosteal and periosteal diameters in the experimental group compared with the control group.

Animals↗