Papers by Kenneth St. John
Journal of Spinal Disorders, 1994
Anterior cervical discectomy and interbody grafting provide excellent results in treating cervica... more Anterior cervical discectomy and interbody grafting provide excellent results in treating cervical radiculopathy. This prospective study compares the results of the technique obtaining autogenous bone from the cervical vertebrae for grafting to the modified Smith-Robinson technique using autogenous iliac crest graft. Seven levels in six patients were fused using the vertebral body autograft technique and 43 levels in 40 patients using the standard technique. All patients had radiculopathy and neck pain. Statistically significant differences in fusion rate (4/7 vertebral body autograft; 40/43 modified Smith-Robinson) (p = 0.029), disc height maintenance (p = 0.001), and neck pain improvement (p = 0.05) occurred between the techniques. We do not recommend vertebral body autograft over the modified Smith-Robinson technique for anterior cervical fusion following discectomy.
Southern Medical Journal, Jan 1, 1993
Journal of Biomaterials Applications, Jan 1, 2011
Acetabular hip joint components manufactured from gamma-sterilized ultra high molecular weight po... more Acetabular hip joint components manufactured from gamma-sterilized ultra high molecular weight polyethylene (UHMWPE), gamma cross-linked UHMWPE, or polycarbonate-urethane (PCU) polymers were evaluated in a hip joint simulator, using cobalt alloy femoral components, for at least 5 million cycles. The volume of material losses due to wear was calculated for each type of sample, based upon mass loss measurements, every 500,000 cycles. The loss of material for the conventional UHMWPE was much higher than for the cross-linked UHMWPE, showing about a 70% reduction in wear due to cross-linking. The material loss for the PCU samples appears to have been at least 24% lower than for the cross-linked UHMWPE. Based upon these results, the PCU material seems to have potential for use as an alternative bearing material to UHMWPE for total hip replacement surgeries.
Journal of biomaterials applications, Jan 1, 2010
Ultra high molecular weight polyethylene cups, 22 mm in diameter, were aged for 5 years in the no... more Ultra high molecular weight polyethylene cups, 22 mm in diameter, were aged for 5 years in the normal laboratory environment. Half of the samples had been processed by the standard radiation sterilization techniques, while the remainder had been cross-linked by a technique involving higher radiation doses and controlled temperature at the time of irradiation. The samples had been tested in a hip simulator for 5,000,000 cycles using a lubricant that had been diluted 1:1 with deionized water. Once that testing was completed, further testing was conducted using lubricant with greater and lesser serum protein concentrations, and the results compared with those that had already been recorded. Comparison of the wear rates within the study as well as to published data concerning the effect of serum concentration showed results that were consistent with assumed differences in lubrication ability at different concentrations. The results of other published studies were found to be inconsistent with each other and different from some of the results of this study. There is shown to be a need for carefully controlled and conducted studies to agree, if possible, on the importance of the serum concentration and the appropriate parameters to be used in testing, as well as variations that may be necessary with different bearing material characteristics.
Clinical Materials, Jan 1, 1993
A model simulating a spiral diaphyseal fracture with butterfly fragments and bone loss was utiliz... more A model simulating a spiral diaphyseal fracture with butterfly fragments and bone loss was utilized to evaluate an hydroxyapatite/tricalcium phosphate, and collagen composite bone graft substitute in twelve dogs. The resultant grafted and contralateral control femora were tested in torsion at one year. This study examines the histological response to the graft material as well as crack propagation and fracture surface morphology using light microscopy and SEM. SEM and gross evaluation of the grafted bones revealed that 8/12 had fractured through bone outside the osteotomy site and all fractures included bone outside the graft site. No graft material was demonstrated at the points of initiation or termination of fracture for any of the bones. It was apparent that recorticalization had begun to occur at the graft site but the canal had not yet fully formed. The HA/TCP was seen to be tightly bound in tissue which had the appearance of new bone. Bone was found to be in direct apposition to the surface of the ceramic and within pores with no intervening soft tissue. Much of the new bone had remodeled into well organized Haversian systems with some patchy areas of woven bone and osteoid seen with polarized light illumination.
Dental Clinics of North America, Jan 1, 2007
With the long history of use of many materials in dental surgery, biocompatibility concerns are n... more With the long history of use of many materials in dental surgery, biocompatibility concerns are not as great a concern as other issues, such as long-term degradation, mechanical strength problems, and prevention of secondary caries. It is important, however, not to forget that the potential exists for adverse tissue responses to synthetic materials used in repair, augmentation, and repair of natural tissue structures. As new materials and repair techniques become available and the sophistication of cell-level and subcellular response evaluations increases, the concerns to be addressed and the methods to be used may change. The advent of tissue-engineered medical products may mean that new questions must be addressed.
Journal of Applied …, Jan 1, 1994
The need for alternatives to autogenous bone grafts is widely recognized. This study compared the... more The need for alternatives to autogenous bone grafts is widely recognized. This study compared the torsional strength of canine femora 1 year after grafting with one of three forms of a collagen/hydroxyapatite/tricalcium phosphate bone grafting material (COLLAGRAFTTM), autogenous bone, or no graft. The groups were compared to each other and to the unoperated contralateral femora. Results of torsional testing were evaluated for torsional strength, torsional displacement, total energy to fracture and White fracture mode. Data analysis showed lower torsional strength of the operated vs. unoperated femora with the exception of morsellized COLLAGRAFTTM material, which had higher strength. However, the only difference in the operated groups was that the morsellized COLLAGRAFTTM had greater strength than several groups including the autogenous bone group. There was no difference found in angular displacement between any of the groups. However, there was a difference in the energy to fracture in both strip forms of the C0LLAGRAFTTM. The final conclusion is that in this model, grafting with COLLAGRAFTTM provided torsional properties at one year postoperatively at least equivalent to autogenous bone.
Journal of Biomedical …, Jan 1, 2004
Wear of the polyethylene in total joint prostheses has been a source of morbidity and early devic... more Wear of the polyethylene in total joint prostheses has been a source of morbidity and early device failure, which has been extensively reported in the last 20 years. Although research continues to attempt to reduce the wear of polyethylene joint-bearing surfaces by modifications in polymer processing, there is a renewed interest in the use of metal-on-metal bearing couples for hip prostheses. Wear testing of total hip replacement systems involving the couple of metal or ceramic heads on polymeric acetabular components has been performed and reported, but, until recently, there has been little data published for pin-on-disk or hip-simulator wear studies involving the combination of a metallic femoral head component with an acetabular cup composed of the same or a dissimilar metal. This study investigated the in vitro wear resistance of two cobalt/chromium/molybdenum alloys, which differed primarily in the carbon content, as potential alloys for use in a metal-on-metal hip-bearing couple. The results of pin-on-disk testing showed that the alloy with the higher (0.25%) carbon content was more wear resistant, and this alloy was therefore chosen for testing in a hip-simulator system, which modeled the loads and motions that might be exerted clinically. Comparison of the results of metal-on-polyethylene samples to metal-on-metal samples showed that the volumetric wear of the metal-on-polyethylene bearing couple after 5,000,000 cycles was 110 -180 times that for the metal-bearing couple. Polyethylene and metal particles retrieved from either the lubricant for pin-on-disk testing or hip simulator testing were characterized and compared with particles retrieved from periprosthetic tissues by other researchers, and found to be similar. Based upon the results of this study, metal-on-metal hip prostheses manufactured from the high carbon cobalt/chromium alloy that was investigated hold sufficient promise to justify human clinical trials.
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Papers by Kenneth St. John