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J D Bobyn

Publications and source records attributed to J D Bobyn.

68 records · Page 4Linked to original sources
PubMed1986

Principles, techniques, results, and complications with a porous-coated sintered metal system.

Experience with biologic fixation hip arthroplasty using the powder-made sintered porous system has been very encouraging over the past 8 years. With simple implant design, accurate instrumentation, and careful attention to surgical technique, the results of surgery can be made equal to those obtained with conventional cemented arthroplasty (using the current improved implant designs and cementing techniques). Most of the problems associated with this new technology have been recognized and solved. The most serious problem is probably that of stress shielding and disuse osteoporosis, and this may well be overcome through judicious design modification. It is the next decade that will determine whether the incidence of late aseptic loosening is reduced through design for a "living" interface between implant and bone.

Acetabulum↗
PubMed1985

Spaceflight results in formation of defective bone.

Growing rats were flown on 19 day spaceflights aboard Cosmos 782 and 936 biosatellites. Spaceflight resulted in a prominent skeletal defect at the periosteal surface of the tibia diaphysis. The defect, termed an arrest line, was approximately 3 micron across and separated the bone formed in space from that formed following spaceflight. The bone matrix at the arrest line region was abnormal in that collagen fibers were preferentially orientated parallel to the periosteal surface. In addition, the bone matrix was hypomineralized. The altered bone was inferior to normal bone in resistance to abrasion and may be partially responsible for the decrease in torsional strength observed after spaceflight.

Animals↗
PubMed1985

Biologic fixation arthroplasty in the treatment of osteonecrosis.

To provide a possible solution to the problem of aseptic loosening of prosthetic hip replacement components, the authors treated selected patients who had stage IV, V, or VI osteonecrosis with uncemented, porous-coated components on the femoral side. These stems are designed for bone ingrowth, with the goal of attaining a more viable and permanent interlocking bone between the implant and host bone. This article presents the necessary surgical principles and techniques for biologic fixation arthroplasty and reports the early results that have been obtained.

Acetabulum↗
PubMed1982

Effect of pore size on the peel strength of attachment of fibrous tissue to porous-surfaced implants.

Twenty-four rectangular metal plates were fabricated with surface regions in three different pore size ranges (5-20 microns, 20-50 microns, 50-200 microns). The plates were implanted into the dorsal subcutaneous tissue of 12 adult mongrel dogs for periods of 4, 8, 12, and 16 weeks. After animal sacrifice, the fibrous tissue which adhered to the porous-surfaced regions of each plate was mechanically peeled off to give an indication of the strength of tissue attachment. The tissue was examined by both transmitted light and scanning electron microscopy. At each time period, the tissue that contacted the porous regions was found to be collagenized fibroconnective tissue. The mechanical tests indicated an increasing strength of tissue attachment with increasing implantation time and pore size range. The largest pore size range of approximately 50-200 microns produced a mean peel strength of attachment of 27.5 g/mm at the 16-week period.

Animals↗
PubMed1982

Biologic fixation and bone modeling with an unconstrained canine total knee prosthesis.

To study the effects of dynamic loading on biologic fixation, an unconstrained type of prosthesis was designed for total replacement of the knee joint of dogs. The femoral component was fabricated from cast cobalt-based surgical alloy. The tibial component was fabricated from surgical grade, ultra-high molecular weight, high density polyethylene. Both components were designed for initial stabilization at surgery by mechanical interlock with bone. In addition, the bone-interfacing surface of the metal component was made porous and the stem of the polymer component was grooved to permit the subsequent ingrowth of tissue. Knee arthroplasty was performed on a total of six beagles. The prostheses were monitored for periods of 20 months and demonstrated an overall excellent stability and functionality. Each tibial component became stabilized by the formation of a thin, surrounding shell of osseous tissue. Interposed between this bone and the implant was usually a thin layer of fibrous tissue, suggesting micromovement during loading. Each femoral component became solidly fixed by bone growth into the porous surface. The altered stress state in the region of the implant eventually resulted in reactive bone modeling, with both bone formation and resorption occurring along the length of the implant.

Animals↗
PubMed1981

Osteogenic phenomena across endosteal bone-implant spaces with porous surfaced intramedullary implants.

Porous surfaced femoral components of hip prostheses stabilized by tissue ingrowth are often situated a certain distance away from the endosteal cortex in the diaphysis. The purpose of this study was to examine the significance of this space between an implant and the cortex on bone growth into the porous surface of the implant. Intramedullary rods of different diameters with porous surface regions made of powder metal were inserted into the femurs of adult beagles. The rods had outside diameters of 2.5, 3.2, 4.5, and 5.5 millimeters; this variation produced endosteal bone-implant surface spaces ranging from 0 to 4 millimeters. The animals were sacrificed at 4, 8, 12, and 16 weeks. Histological sections revealed that by 12 weeks the implants became generally surrounded by a thin shell of spongy bone which was joined to the endosteal cortex by bony trabeculae. This feature was most prominent for implants which were approximately 2 millimeters or less from the endosteum. Denser, more haversian-like bone developed up to and within those areas of implants which were in contact with the cortex. The development of this intramedullary type of bone could significantly contribute to the fixation strength of clinical porous surfaced prostheses whose stems do not completely fill the medulla.

Alloys↗
PubMed1980

The effect of porous surface configuration on the tensile strength of fixation of implants by bone ingrowth.

In an attempt to gain information that could be directly applied to the design of clinical porous-surfaced prostheses intended for biological attachment by bone ingrowth, the tensile strength of the bone-implant interface was expressed as a function of 2 fundamentally different porous-surface configurations. Using powder metallurgy techniques, standard 3-hole fracture fixation plates were prepared with both a single and a multiple layer of spherically shaped metal powder particles on the bone-contacting surface to produce implants with different porous surfaces. These plates were implanted onto the lateral aspect of canine femurs for periods of 4, 6, 8, 12, 18, and 24 weeks. Mechanical tests were performed to measure the tensile strength of fixation of the implants by the ingrowth of bone. The results of the mechanical tests indicated that implants with the multiple particle layer surfce configuration develop a greater tensile strength of fixation than do implants with the single particle layer surface configuration. In addition, this fixation strength develops more quickly if the cortical bone is petaled prior to implantation. These findings should be considered when designing porous-surfaced implants intended for fixation by bone ingrowth.

Animals↗
PubMed1979

The porous-surfaced electrode: a new concept in pacemaker lead design.

Three major problems which may be encountered with endocardial pacemaker electrodes are a lack of stable position, a chronic increase in stimulation threshold, and a diminishing magnitude of the sensed endocardial signal. These problems are particularly manifest in the atrium. Having previously shown that porous metal surfaces can support stable tissue ingrowth in both bloodstream and soft tissue environments, we set out todetermine the performance of porous-surfaced endocardial pacing electrodes in the atrial position. In two groups of six dogs each, J-shaped atrial leads with Elgiloy electrode tips (2.3 mm. in diameter, 2.3 mm. in length), having either conventional smooth surfaces (control) or porous surfaces (20 to 50 micron particle size) produced by powder metallurgy techniques, were positioned in the right atrial a-pendage. Stimulation thresholds and P-wave amplitude were repeatedly measured until the dogs were put to death 30 w-eks following implantation. The presence or absence of electrode fixation was observed and the atrial tissue reaction was examined grossly and by both light and scanning electron microscopy (SEM). The porous-surfaced electrodes demonstrated superior long-term stimulation thresholds which, at 30 weeks, averaged less then one third of those in the control group. In addition, the porous group showed a small but significant improvement in the amplitude of the sensed P wave. None of the smooth-surfaced electrodes showed fixation, and the tissue reaction consisted of a thick layer of granulation and fibrous tissue on the underlying endocardium, widely separating the electrode from the myocardium. In contrast, all of the porous-surfaced electrodes were fexed to the endocardium by fibrous tissue ingrowth into the surface pores. This tissue fixation of the electrode tip in close proximity to underlying myocytes explains their superior performance.

Animals↗
PubMedDate not supplied

The optimum pore size for the fixation of porous-surfaced metal implants by the ingrowth of bone.

For a study on the effects of pore size variation on the rate of bone growth into porous-surfaced metallic implants and on the strength of fixation resulting from this ingrowth, 4 distinct pore size ranges were prepared on cobalt-base alloy implants with cobalt-base alloy powder particles of different dimensions. The porous implants were placed into canine femurs for periods of 4, 8, and 12 weeks. Mechanical tests were performed to measure the shear strength of fixation of the implants to cortical bone. For implants with powder-made porous surfaces, a pore size range of approximately 50 to 400 microns provided the optimum or maximum fixation strength (17 MPa) in the shortest time period (8 weeks).

Animals↗