PubMed Health⌕ Search

Biomedical subjects

S D Cook

Publications and source records attributed to S D Cook.

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

Wear characteristics of the canine acetabulum against different femoral prostheses.

We studied cartilage degeneration in 45 canine acetabula after implantation of prostheses with articulating surfaces of low-temperature isotropic (LTI) pyrolytic carbon, cobalt-chromium-molybdenum alloy and titanium alloy for periods ranging from two weeks to 18 months. Gross specimens and histological sections were compared with the nonoperated (control) acetabulum of the same animal. Cartilage articulating with LTI pyrolytic carbon exhibited significantly lower levels of gross wear, fibrillation, eburnation, glycosaminoglycan loss, and subchondral bone change than with metallic surfaces. Survivorship analysis showed a 92% probability of survival for cartilage articulating with LTI pyrolytic carbon at 18 months, as compared to only a 20% probability of survival for cartilage articulating with either of the metallic alloys.

Acetabulum↗
PubMed1989

The effects of calcium on bone mineral density in postmenopausal women with colles fractures.

The increased incidence of fracture in postmenopausal women may be attributable, in part, to osteoporosis. Prediposing factors other than age include genetic constitution, physical activity, alcohol and caffeine abuse, and dietary calcium deficiency. A group of 15 postmenopausal women between the ages of 43 and 85 years were analyzed for bone mineral density within 4 weeks of an acute fracture of the distal radius. Dual photon absorptiometry scanning was performed on the first through fourth lumbar vertebrae. Results indicate that bone mineral densities below the fracture threshold (0.965 g/cm2) were seen in 9 of 15 (60%) patients. Each woman was given 1500 mg/day calcium supplementation for 1 year. At 1 year, each woman was contacted for a follow-up bone mineral density analysis. While no significant increase in bone mineral density was seen, calcium supplementation appeared to inhibit further bone loss. The results of this study support previous work which has indicated that supplemental calcium may be beneficial in combatting age-related bone loss.

Adult↗
PubMed1989

Roentgenographic measurement of pedicle screw penetration.

Potential complications due to pedicle screw penetration of the anterior cortex include injury to vascular, visceral, ureteral, sympathetic, and neural structures. This study examined the accuracy of lateral roentgenographic techniques in determining actual screw penetration in vertebral levels T12 through S1 of ten unilateral sets of pedicles in five anatomic specimens. A true lateral roentgenogram alone was inaccurate for determining the penetration of the anterior cortex by a pedicle screw. The greatest discrepancy between roentgenographically apparent and actual screw penetration was found at the L4 and L5 levels. Deviation from a true lateral roentgenographic axis resulted in the most pronounced change in roentgenographically apparent screw penetration at L4 and L5. The roentgenographic axes resulting in the closest approximation of actual screw penetrations were 5 degrees and 10 degrees above the true lateral axis for the T12-L3 and the L4-S1 levels, respectively. At 50% apparent penetration, the screw may be safely assumed to not be penetrating the anterior cortex using a true lateral roentgenogram. At 80% apparent penetration, 30% and 10% probabilities of actual screw penetration of the anterior cortex exist at L4 and L5, respectively. At 100% apparent penetration, there is an almost 100% probability that the screw is actually protruding through the anterior cortex.

Biomechanical Phenomena↗
PubMed1988

The effect of post-sintering heat treatments on the fatigue properties of porous coated Ti-6Al-4V alloy.

Porous coated Ti-6Al-4V alloy implant systems provide a biocompatible interface between implant and bone, resulting in firm fixation and potential long-term retention via bony ingrowth. In order to achieve an acceptable porous coating structure, the sintering protocol for Ti-6Al-4V alloy systems often requires that the material be heat treated above the beta transus. This transforms the as-received equiaxed microstructure, recommended for surgical implants, to a lamellar alpha-beta distribution, which has been shown to have the worst fatigue properties of the most common structures attainable in Ti-6Al-4V alloy. However, post-sintering heat treatments may be used to improve these properties by producing microstructures more resistant to crack initiation and propagation. This study investigated the influence of microstructural variations on the fatigue properties of porous coated Ti-6Al-4V alloy material. Nonporous coated and porous coated Ti-6Al-4V alloy fatigue specimens were subjected to a standard sintering heat treatment to produce a lamellar microstructure. In addition, two post-sintering heat treatments were used to produce coarse and fine acicular microstructures. Rotating beam (reversed bending) fatigue testing was performed and the endurance limits determined for the noncoated and porous coated microstructures. The values determined were 668 MPa (noncoated as-received equiaxed), 394 MPa (noncoated lamellar), 488 MPa (non-coated coarse acicular), 494 MPa (noncoated fine acicular), 140 MPa (porous coated lamellar), 161 MPa (porous coated coarse acicular), and 162 MPa (porous coated fine acicular). The noncoated coarse and fine acicular specimens displayed an approximate 25% increase over the noncoated lamellar specimens. The porous coated coarse and fine acicular specimens showed an approximate 15% improvement over the porous coated lamellar specimens.

Alloys↗
PubMed1988

Measles virus L protein evidences elements of ancestral RNA polymerase.

We have determined the nucleotide sequence of the measles virus (MV) L gene using a cDNA library encompassing the entire MV genome (J. Crowley et al. (1987) Intervirology, 28, 65-77). The L gene is 6639 nucleotides in length, and contains a single long open reading frame that could code for a protein of 247,611 kDa. Both the L gene and in particular the predicted L protein of MV bear substantial homology to their counterparts in Sendai virus and Newcastle disease virus, suggesting that the multifunctional nature of paramyxovirus L proteins imposes strong evolutionary constraints. The predicted MV L protein also contains distinct elements of a postulated ancestral RNA polymerase.

Amino Acid Sequence↗
PubMed1988

Sequence variability and function of measles virus 3' and 5' ends and intercistronic regions.

Sequences critical for the activity of the measles virus (MV) RNA polymerase in transcription and replication were analyzed using a MV genomic cDNA library containing overlapping clones encompassing the entire MV genome. Clones corresponding to the 3' and 5' ends of the MV genome were identified and sequenced, and these sequences were confirmed by primer extension experiments. Neither (+) nor (-) strand leader RNAs were detected in MV-infected cell extracts, using high specific activity riboprobes made form these clones. Clones representing each of the MV gene boundaries were also sequenced, and variations including point mutations, insertions, and deletions were noted. Together with the sequence of the MV L gene region, this report completes the sequence determination of the MV genome.

Base Sequence↗
PubMed1988

Total lymphoid irradiation for multiple sclerosis.

Although chemical immunosuppression has been shown to benefit patients with chronic progressive multiple sclerosis (MS), it appears that chemotherapy has an appreciable oncogenic potential in patients with multiple sclerosis. Accordingly, we developed a modified total lymphoid irradiation (TLI) regimen designed to reduce toxicity and applied it to a randomized double blind trial of TLI or sham irradiation in MS. Standard TLI regimens were modified to reduce dose to 1,980 rad, lowering the superior mantle margin to midway between the thyroid cartilage and angle of the mandible (to avert xerostomia) and the lower margin of the mantle field to the inferior margin of L1 (to reduce gastrointestinal toxicity by dividing abdominal radiation between mantle and inverted Y), limiting spinal cord dose to 1,000 rad by custom-made spine blocks in the mantle and upper 2 cm of inverted Y fields, and also protecting the left kidney even if part of the spleen were shielded. Clinical efficacy was documented by the less frequent functional scale deterioration of 20 TLI treated patients with chronic progressive MS compared to to 20 sham-irradiated progressive MS patients after 12 months (16% versus 55%, p less than 0.03), 18 months (28% versus 63%, p less than 0.03), and 24 months (44% versus 74%, N.S.). Therapeutic benefit during 3 years follow-up was related to the reduction in lymphocyte count 3 months post-irradiation (p less than 0.02). Toxicity was generally mild and transient, with no instance of xerostomia, pericarditis, herpes zoster, or need to terminate treatment in TLI patients. However, menopause was induced in 2 patients and staphylococcal pneumonia in one. Our data suggest that this modified TLI regimen has clinical efficacy and sufficiently low toxicity to make it suitable for investigative immunosuppressive treatment of patients with progressive MS or other non-malignant conditions.

Adult↗
PubMed1988

Comparative mechanical analysis of a looped-suture tendon repair.

The in vitro breaking force of a braided nylon looped-suture tendon juncture designed to decrease tying time was compared with the breaking force of the modified Kessler and Bunnell techniques. Repaired with either braided nylon or tetrafluoroethylene, porcine digiti quarti propius tendons were tested to single cycle failure on a MTS hydraulic testing machine. The results showed that the looped-suture technique had a mean breaking force that was statistically indistinguishable from that of the Bunnell technique regardless of suture material. However, the breaking forces for the looped suture and Bunnell techniques were statistically greater for both suture materials when compared with the modified Kessler technique. The resistance to gap formation for the looped suture was found to be intermediate between the Bunnell technique and the modified Kessler technique.

Animals↗
PubMed1988

Quantitative analysis of tissue growth into human porous total hip components.

Histologic and radiographic analysis was performed on 36 porous-coated total hip components (22 femoral and 14 acetabular) retrieved from 30 patients. The average patient age was 53.0 years (range, 28-78 years) for femoral components and 56.9 years (range, 28-78 years) for acetabular components. The average time in situ was 13.6 months (range, 2-36 months) for femoral components and 5.5 months (range, 1-18 months) for acetabular components. Fourteen implants were retrieved for instability or dislocation, 12 for late infection, and 8 for persistent pain, and 2 were retrieved after the patient died. Radiographs were reviewed for Singh index, heterotopic bone, implant fit, subsidence, and presence of lucent and sclerotic zones. Histologic and microradiographic sections of the implant and adherent tissue were examined for type, amount, and anatomic distribution of tissue ingrowth. Four femoral stems had no bone ingrowth, 10 had minimal bone growth into the available pore volume (less than 2%), 3 had moderate bone ingrowth (2-5%), and 5 had more extensive bone ingrowth (5-10%). Bone ingrowth tended to occur where the implant made direct contact with the endosteal cortical surface and was rarely seen in proximal metaphyseal bone. Bone ingrowth was completely absent in eight acetabular components, minimal (less than 2%) in three, moderate (2-5%) in two, and more extensive (5-10%) in one and tended to occur adjacent to fixation pegs, spikes, or screws. Radiographic or clinical findings were unreliable in predicting the presence or extent of bone ingrowth in either femoral or acetabular components.

Acetabulum↗
PubMed1988

Tissue response to porous-coated implants lacking initial bone apposition.

Although initial bone apposition of a porous-surfaced implant is desirable, it is not always achieved surgically. A model to study the effect of a gap on the quantity and quality of bone growth in both the cancellous and cortical regions has been developed. Implants were surgically placed in the intramedullary canals of adult dogs producing uniform gap spaces 0.0-2.0 mm wide. Histologic and microradiographic evaluations were conducted after 3, 6, and 12 weeks in situ. The results demonstrate that the initial apposition of a porous implant to the surrounding bone surface is not necessary for fixation by bone ingrowth. New bone will grow up to and within the porous structure of an implant even when there is a gap as large as 2.0 mm. However, the rate and degree of maturity and mineralization is enhanced when the gap width is 0.5 mm or less. The amount of bone activity in the cortical region was greater than in the cancellous region at 3 and 6 weeks after operation. After 12 weeks in situ bone growth in gap spaces and into the porous coating was approximately equal.

Animals↗
PubMed1988

Multiple sclerosis in the Shetland Islands: an update.

Annual incidence rates of multiple sclerosis (MS) in the Shetland Islands have been updated from 1938 to 1986. These reveal a significant decline in MS incidence beginning between 1951 and 1968. No significant change in prevalence, age-specific prevalence, duration of MS, or mean age of the MS population in Shetland has been found since the last survey in 1974, although a trend towards an older MS population was noted.

Adult↗
PubMed1988

T cell subsets and disease progression after total lymphoid irradiation in chronic progressive multiple sclerosis.

T lymphocyte subset percentages were determined in 16 total lymphoid irradiation (TLI) treated and 18 sham treated control patients with chronic progressive multiple sclerosis. During the first year after treatment, the ratio of T helper/inducer to T suppressor/cytotoxic cells (Th/Ts ratio) was significantly higher in sham treated multiple sclerosis patients who worsened clinically compared with TLI treated and sham treated multiple sclerosis patients who remained clinically stable. TLI caused a fall in the percentage of T helper cells in treated patients, while the percentage of T suppressor cells remained stable during the first year after treatment. In contrast, the percentage of T suppressor cells fell in sham treated multiple sclerosis patients who worsened clinically.

Follow-Up Studies↗
PubMed1988

Tissue reaction to implant corrosion in 38 internal fixation devices.

The corrosion characteristics, metallurgical properties, and clinical performance of 38 retrieved internal fixation devices were correlated with the tissue reaction to these devices. Metallurgical parameters included thin and heavy inclusion content, Rockwell hardness, and grain size. The excised fibrous tissue strip was directly overlying each plate at removal and sectioned between screw-hole sites. The material studied from the 38 plates consisted of 201 screw-hole junctions with associated tissue biopsy sites. Clinical histories were obtained on all 38 patients with hardware removal. The average age at the time of plate insertion was 35.6 years (range, 4 to 75 years). Insertion diagnoses included acute trauma (35 patients), joint dislocations (two patients), and fracture nonunion (one patient). The devices included seven upper extremity bone plates, 19 lower extremity bone plates, and 12 hip screw plates. The devices remained in situ an average of 20.4 months (range, 3 to 60 months). Routine asymptomatic removals were performed on 17 of the patients, while the remaining 21 patients were symptomatic at the time of removal. Included in the reasons for symptomatic removal were pain associated with the implant (eight patients), nonunion (four patients), bursae prominence (three patients), and implant breakage (two patients). Significant correlations were found between average tissue reaction scores and average crevice corrosion scores; a trend of increasing average tissue reaction scores with increasing average screw surface corrosion scores also was observed for the 38 devices, although this relationship was not significant. Average crevice corrosion scores and average screw surface corrosion scores were highly correlated for all removals, and for the asymptomatic and symptomatic removal groups. The metallurgical parameters of thin inclusion content and heavy inclusion content also were significantly correlated for all removals, as well as for symptomatic removals. Similarly, significant correlations were found between the individual tissue reaction scores and crevice corrosion scores from the 201 individual sites, again for all devices and for the asymptomatic and symptomatic removal groups. Tissue reaction scores and time in situ showed significant correlation, with tissue reaction decreasing over time. Crevice corrosion and screw surface corrosion scores were not significantly related to time in situ. The results of this study indicate that there is considerable tissue reaction to the corrosion products of this material.(ABSTRACT TRUNCATED AT 400 WORDS)

Adolescent↗
PubMed1988

A chronically dislocating prosthetic patella. A case report.

A 63-year-old white woman was evaluated for a chronically dislocating right patella 6 months following total knee arthroplasty. At the time of our initial evaluation, her knee would not extend beyond 35 degrees and her patella was dislocated and irreducible. At arthrotomy, when the patella was everted, the patellar component was oriented with the facet ridge rotated 90 degrees to the trochlear groove of the femoral component. The patellar template guide indicated that the fixation pegs had been drilled properly, and thus, the patellar component had been assembled improperly during manufacturing. After dome-type patellar prosthesis replacement and proximal and distal extensor realignments were performed, 2 months post-revision the patient had a range of motion from 5 degrees to 95 degrees and ambulated with no patellar instability or pain.

Equipment Failure↗
PubMed1988

Hydroxyapatite-coated porous titanium for use as an orthopedic biologic attachment system.

The biologic attachment characteristics of hydroxyapatite (HA)-coated porous titanium and uncoated porous titanium implants were investigated. The implants were placed transcortically in the femora of adult mongrel dogs and evaluated after periods of three, six, and 12 weeks. The HA coating was applied using a modified plasma spray process to samples with pore volume and pore size of the porous coating expanded to equal the pore morphology of uncoated porous specimens. Mechanical push-out testing revealed that the bone-porous material interface shear strength increased with time in situ for both the uncoated and HA-coated implants. The use of the HA coating on porous titanium, however, did not significantly increase attachment strength. Histologic and microradiographic sections yielded similar qualitative results in the amount of bone grown into each system. After three weeks, both systems displayed primarily woven bone occupying approximately 50% of the available porous structure. Six and 12 weeks postimplantation, each system displayed more extensive bone ingrowth, organization, and mineralization, with only limited areas of immature bone. Histologically, differences were noted at the ingrown bone-porous material interface between the two implant types. The HA coating supported mineralization directly onto its surface, and a thin osseous layer was found lining all HA-coated surfaces. An extremely thin fibrous layer was observed separating the uncoated titanium particle surface from ingrown bone. There was no extensive direct apposition or lining of the ingrown bone to the uncoated porous titanium particle surfaces.

Animals↗
PubMed1988

Hydroxyapatite-coated titanium for orthopedic implant applications.

The interface mechanical characteristics and histology of commercially pure (CP) titanium- and hydroxyapatite- (HA) coated Ti-6Al-4V alloy were investigated. Interface shear strength was determined using a transcortical push-out model in dogs after periods of three, five, six, ten, and 32 weeks. Undecalcified histologic techniques with implants in situ were used to interpret differences in mechanical response. The HA-coated titanium alloy implants developed five to seven times the mean interface strength of the uncoated, beadblasted CP titanium implants. The mean values for interface shear strength increased up to 7.27 megaPascals (MPa) for the HA-coated implants after ten weeks of implantation, and the maximum mean value of interface shear strength for the uncoated CP titanium implants was 1.54 MPa. For both implant types there was a slight decrease in mean shear strength from the maximum value to that obtained after the longest implantation period (32 weeks). Histologic evaluations in all cases revealed mineralization of interface bone directly onto the HA-coated implant surface, with no fibrous tissue layer interposed between the bone and HA visible at the light microscopic level. The uncoated titanium implants had projections of bone to the implant surface with apparent direct bone-implant apposition observed in some locations. Measurements of the HA coating material made from histologic sections showed no evidence of significant HA resorption in vivo after periods of up to 32 weeks.

Alloys↗