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Biomedical subjects

S D Cook

Publications and source records attributed to S D Cook.

At least 235 records · Page 13Linked to original sources
PubMed1985

The measurement of shock waves following heel strike while running.

A non-invasive method for demonstrating the shock wave which propagates through the skeletal system following heel strike is described. This wave was not seen in force plate studies where adequate shock absorption was provided by running shoes. In the present study six subjects ran across a force plate without shoes before and after they were fatigued on a treadmill to demonstrate possible changes in the heel strike transient. Most of the parameters measured were not altered by fatigue, and a relationship between the shock wave and height, but not the weight of the runner was demonstrated. The different mechanisms leading to this phenomenon, and its implication in the areas of osteoarthritic degeneration and running mechanics are discussed.

Adult↗
PubMed1985

The effect of oral corticosteroid dosage on CT enhancing multiple sclerosis plaques.

Fifty high-dose delayed CT scans were performed on 36 patients with definite MS within 4 months of a clinical relapse. The number of enhancing lesions visualized was compared in patients being treated with high- or low-dose oral corticosteroids and untreated controls. High-dose oral corticosteroid treatment significantly but incompletely reduced enhancement of MS plaques. Lower doses were less effective, especially when the latter were given on alternate days.

Administration, Oral↗
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

Declining incidence of multiple sclerosis in the Orkney Islands.

The incidence of MS in the Orkney Islands has been updated from 1941 to September 21, 1983. Since 1965, MS incidence rates have fallen significantly when compared with those for 1941 to 1964. Alterations in age-specific prevalence, mean duration of illness, and mean age of the MS population are consistent with the decline in incidence of MS in recent years. Although the reason for the decreasing incidence is uncertain, it is consistent with the hypothesis that MS may be caused by canine distemper virus.

Adult↗
PubMed1985

Post-sintering heat treatments for porous coated Ti-6A1-4V alloy.

Previous studies have shown that the application of a porous Ti-6A1-4V alloy coating results in a substantial decrease in the substrate material fatigue properties. This phenomenon is due to both a microstructural change from the equiaxed alpha-beta microstructure to a lamellar structure and a notch effect created by the porous coating. The lamellar microstructure has been shown to exhibit the worst fatigue properties of the most common structures obtained in Ti-6A1-4V alloy. This study examined various post-sintering heat treatments which would alter the material microstructure and possibly result in improved fatigue performance. The heat treatments examined produced alternate microstructures to the lamellar structure and some approached the totally transformed acicular alpha structure. The acicular alpha structure has been shown to exhibit the best fatigue properties for Ti-6A1-4V alloy in the notched condition.

Alloys↗
PubMed1985

Interface mechanics and bone growth into porous Co-Cr-Mo alloy implants.

The interface mechanics and bone growth into porous Co-Cr-Mo alloy implants were evaluated. Three mean pore sizes (155, 235, and 350 microns) were studied for implants fabricated with one, two, and three layers of spherical powder particles and totally porous implants. All implants had a pore volume of 38%-40%. Ten implants were inserted transcortically in the femora of six adult mongrel dogs and were allowed to remain in situ for a period of 12 weeks. Postretrieval mechanical testing and histologic and microradiographic analyses were used to evaluate the implant systems. A statistically significant increase in interface shear strength (p less than .05) was determined as the number of powder particle layers was increased from one and two layers to three layers. However, a decrease in interface strength was determined for totally porous implants (seven to 12 particle layers) below the value for the single-porous-layer implants. Pore size, in the range investigated, was not found to influence the interface attachment strength. Neither pore size nor porous layer thickness was found to affect interface stiffness. Histologic and microradiographic sections revealed extensive mineralized bone growth deep into the pores of all implant types and often extending to the core of the one-, two- and three-layered porous-coated implants. Both mature haversian bone and less mature woven bone were found within the porous structure. Extensive but incomplete bone infiltration was found in the totally porous implants, with the remainder of the porosity filled with macrophage-laden connective tissue. No difference in the histologic response was observed as a function of pore size in any of the implant systems. Active bone labels were present at the 12-week time period, indicating continued bone remodeling.

Animals↗
PubMed1985

Clinical and metallurgical analysis of retrieved internal fixation devices.

The clinical performance, corrosion characteristics, and metallurgical properties of 82 retrieved stainless-steel bone plates have been examined. The plates had been in situ for periods ranging from one to 169 months. Only 29% of these devices (24 of 82 plates) were removed on a routine asymptomatic basis, while 62% (51 of 82 plates) were removed for cause-related reasons such as implant-related pain, infection, nonunion or malunion, and so forth; seven plates were removed for unknown reasons. Although most patients who had plates removed for pain reported some improvement in symptoms, others felt no improvement after removal. On examination, over 89% of the recovered implants displayed some degree of either surface (pitting) or screw-plate interface (crevice and fretting) corrosion or both. Statistical analyses revealed that the metallurgical properties of grain size and nonmetallic inclusion content correlated significantly with the degree of both types of corrosion.

Bone Plates↗
PubMed1985

A clinical and metallurgical analysis of retrieved Jewett and Richards hip plate devices.

The metallurgical properties of 61 retrieved 316L stainless steel (ASTM F138-76) hip plate devices used for the treatment of intertrochanteric fractures were examined. Surface and screw-plate interface corrosion characteristics were graded, and grain size, inclusion content, and hardness values were measured. These measurements were then correlated with the clinical performance of the devices. The devices studied included 21 Jewett nail-type and 40 Richards compression screw-type hip plates. The devices had been in situ an average of 26.7 months, with in situ periods ranging from 2.0 to 156.0 months. Cause-related reasons represented the majority of removals (89.8%), while only 10.2% of the hip plates were removed on a routine asymptomatic basis. The data suggest that surgeons consider this type of device as a permanent implant, with removal undertaken only for causative factors. Of all devices removed, 30.6% were retrieved from patients who presented with fracture nonunion. Upon microscopic examination, 97% of the retrieved implants exhibited some degree of either surface of interface corrosion. Statistical analysis revealed significant correlations between corrosion scores and the metallurgical properties of grain size and nonmetallic inclusion content. No statistically significant metallurgical or corrosion differences were discerned between the two types of devices studied. However, four implants of the Jewett design and four of the Richards design were found to be out of ASTM specification F-138-76. It should also be noted that four devices of the Jewett design (19%) fractured in situ, while none of the retrieved Richards designs had fractured. No correlation was observed between the plates' corrosion scores and in situ time.(ABSTRACT TRUNCATED AT 250 WORDS)

Bone Plates↗
PubMed1985

Biomechanics of running shoe performance.

The running shoe provides shock absorption and motion control for the runner. The change in shock-absorption properties has been studied as a function of miles run. Different models of running shoes encompassing various manufacturers' models and price ranges were mechanically tested to simulate the repeated heel strikes of running. The energy absorbed by the shoes was determined from the area under the load deformation curve at various intervals to the equivalent of having run 500 miles. Shoes were also tested at similar intervals after having been worn by volunteers during normal training. A difference of approximately 33 per cent in the initial shock absorption was observed in the different shoe models tested. In general, the mechanically tested shoes retained approximately 75 per cent of their initial shock absorption capability after 50 miles and approximately 67 per cent after 100 to 150 miles. Between 250 and 500 miles, the shoes retained less than 60 per cent of their initial shock-absorption capacity. The shoes tested after having been worn during running by volunteers had similar but less severe degradation characteristics. These shoes tended to retain approximately 70 per cent of the initial shock absorption characteristics were apparent based upon either shoe price or manufacturer. In addition, shoes that exhibited superior initial shock absorption capability often had more rapid degradation characteristics.

Athletic Injuries↗
PubMed1984

Correlation of tissue reaction to corrosion in osteosynthetic devices.

This study evaluated the interaction of osteosynthetic plates to adjacent tissue. Eleven patients had 13 plates removed with simultaneous biopsies of the adjacent soft tissue. Four patients had pain localized to the area of the plate and 11 patients had routine removal or removal for fracture nonunion. Each plate was graded on a 0-5 point scale for the amount and severity of corrosion present at the screw-plate interface. The adjacent tissue was fixed in formalin and stained with hematoxylin and eosin. The tissue reaction was graded on a 0-5 point scale based on the inflammatory response. A positive correlation of corrosion and tissue reaction was found that was significant at p less than 0.005 in the asymptomatic group. The other good correlation showed that tissue reaction tends to decrease with time at p less than 0.005. There was no correlation of corrosion with tissue reaction in the symptomatic removal group. All patients with pain adjacent to the plates were relieved by implant removal. The findings suggest that stainless steel is minimally toxic to human tissue in most circumstances and that the toxic products are well tolerated. There was a significant group (4/11) that showed a different pattern of tissue response which did not appear to be toxic response. We do not recommend routine implant removal to prevent metal toxicity; however, there is a group of patients who have pain in the area of the implant that may be caused by an allergic reaction and is relieved by implant removal.

Adolescent↗
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

CEPHS--a system for computer analysis of cephalometric radiographs.

A system developed for computer-aided analysis of cephalometric radiographs is described. Capabilities of the system include a method to digitize the radiographs using a personal computer and to upload the data to mainframe computer. Extensive cephalometric analysis measurements are performed, and superimposition of plots a series of radiographs is also possible. In addition, the system is capable of generating normal measurement values for various patient groupings, and of producing plots of normal radiographs for these groupings.

Cephalometry↗
PubMed1984

Proprioception in idiopathic scoliosis.

Proprioception testing and gait analysis was performed on a group of 17 patients with idiopathic scoliosis. All curves had documented progression. The average curve was 26.8 degrees, all primary curves being right thoracic. The average age was 14.8 years. Twelve, healthy, age-matched controls underwent identical testing. Results showed that scoliotic subjects had asymmetry in their ability to reproduce angles between their two knees, as well as an absolute deficit in their ability to reproduce angles as compared with controls (P less than 0.01). The threshold of detection of change in angle at the knee was also quantitatively higher than controls (P less than 0.05), although asymmetry was not statistically significant. No significant differences were measured in gait parameters between scoliotics and controls. These joint position tests have been applied previously to young and elderly adults, athletes, and total joint patients. In no group has any asymmetry of response been demonstrated, both extremities showing virtually identical performance in each case. The tests administered measure sensory modalities, which are conducted through the posterior columns. Although the site of damage in the neural pathway cannot be specifically localized by these tests, results of this study support the presence of a neurologic deficit in idiopathic scoliosis.

Adolescent↗
PubMed1984

Tissue reaction to a failed Bion hip prosthesis in a dog.

The tissue reaction in a dog to a failed constrained total hip replacement system with a Bion elastomer component was evaluated. The device consisted of Ti-6A1-4V alloy acetabular and femoral components connected with a Bion component. At necropsy the Bion component was found to have fractured. The tissue surrounding the Bion was granulomatous with numerous blackened regions. Histologically a severe chronic inflammatory response was present in the surrounding tissue with numerous giant cells and Bion laden macrophages.

Alkadienes↗
PubMed1984

The effect of aging and surface modification on the mechanical properties of dense aluminum oxide.

The effect of in vivo aging and surface texturing on the mechanical properties of dense aluminum oxide were studied. The modulus of rupture and Weibull modulus were determined in air and Ringer's solution using a 3-point bend test. The results showed that the in vivo environment sealed off microcracks either chemically or by tissue ingrowth which strengthened the alumina. The surface modification, however, tended to create more microcracks and stress concentrations at the surface indentations which tended to weaken the alumina.

Aluminum↗
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↗