Biocompatibility of Delrin 150: a creep-resistant polymer for total joint prostheses.

A thermoplastic polymer, Delrin 150 (polyoxymethylene homopolymer), with creep resistance ten times that of ultrahigh-molecular-weight polyethylene, is used as a material for total joint prostheses. A study was made of the local and systemic host response to this polymer when implanted in three different mammalian species. 316 LC stainless steel was used as a control.

Total surface hip arthroplasty in dogs using a fiber metal composite as a fixation method.

A total hip surface replacement was performed on 13 adult mongrel dogs using a porous fiber metal composite for fixation to bone. Titanium fiber composite rings were molded onto cylindrical acetabular prostheses, and cobalt-chrome fiber inserts were sintered onto the cast cobalt-chrome femoral components. The animals were allowed unrestricted walking.

A canine cementless total hip prosthesis model.

To evaluate a porous fiber titanium composite as a fixation method, total hip arthroplasty was performed in 13 large male mongrel dogs. In seven both acetabular and femoral composites were fixed with a porous titanium fiber composite, and in the other six the acetabulum was fixed with acrylic cement. The animals were killed one, three, and six months following implantation.

Segmental replacement of long bones using titanium fiber metal composite following tumor resection.

A series of 17 long bone defects following tumor resections were reconstructed using titanium fiber metal implants with adequate bone grafts. There were nine diaphyseal segmental arthroplasties and eight arthrodeses of the knee. The results were excellent in 11 and satisfactory in five, and there was one failure.

The influence of early weight-bearing on experimental total hip arthroplasties in dogs.

The bone-cement interface is an area of concern in the long-term fixation of endoprostheses. The effect of early weight-bearing on the interface has been discussed as an important parameter influencing the characteristics of the interface. In this study, a total hip arthroplasty was performed in two groups of six dogs each.

Development of a new endosseous dental implant. Part II: Human studies.

The development of an endosseous implant has followed a logical and formal plan. 1. Extensive experiments with animals provided preliminary statistics of successful function, extensive histologic studies, evaluation of biocompatibility, and a preliminary assessment of contraindications.

Segmental replacement of the femur in baboons with fiber metal implants and autologous bone grafts of different particle size.

A study was made of bone ingrowth into fiber metal composite prostheses used to replace large segments of the femur in baboons. Bone grafts of two different types were used to cover the segment: chips of bone with large particle size and ground bone with a smaller particle size. The prosthetic segment was bridged by bone at 3 and 6 months in all cases irrespective of the structure of the transplant.

Evaluation of sintered titanium fiber composite as a subperiosteal implant.

Seventy-two sintered titanium fiber composite implants were placed subperiosteally and anchored intraosseously on the lateral aspect of 12 dog mandibles. The implants were covered with either Millipore filter, silicone, or left uncovered. Analysis after the animals were killed showed that bone growth into the subperiosteal portion of the implants was maximal at three to six weeks after implantation and remained at a depth of 380 mu through 24 weeks in a majority of the implants.

Contact pressure dependence of wear rates of ultra high molecular weight polyethylene.

Wear rates of orthopaedic polyethylene in 37 degrees C water are not very contact stress dependent below 1000 psi (6.9 MPa) but above that level they accelerate substantially. The pressure dependence overall follows an exponential function.

The influence of grain size on the fatigue behavior of annealed 316 LVM stainless steel.

Experimental tests demonstrate that there is a sharp drop in resistance to fatigue fracture when the grain size is increased from 75 to 150 micrometers. This is at least a partial explanation for fatigue fractures of the stems of total hip-joint prostheses reported in the literature. It is also shown that plastic strains associated with fatigue stressing increase with increasing grain size so that loosening of the bone cement embedment may also be part of the premature failure process.

Effect of an in vivo environment on the strength of bone cement.

Bar-shaped polymethylmethacrylate test specimens removed from rabbits after implantation for times up to 26 months showed a significant change in fracture stress as determined by three-point bending in the period between 12 and 26 months. There were no adverse findings in the tissue which developed around the bone-cement test bars.

Evaluation of couple/crevice corrosion by prosthetic alloys under in vivo conditions.

Alloys of cast Co-Cr-Mo, wrought Co-Cr-W, wrought, Co-Ni-Cr-Mo(MP35N), Ti-60% Al-4% V, and graphite were incorporated in specimens which simulated both a couple and a crevice corrosion condition. These specimens were implanted in a dog for 30 months. Post-sacrifice examination showed no substantial evidence of corrosion activity on the surfaces of the metals except for a tarnish film on the titanium alloy specimens.

Defects in failed stems of hip prostheses.

A study has been made of the fractures and associated material from 34 prostheses broken in service. All the fractures appear to be of the fatigue type. Search by metallographic analysis for cracklike generating defects in material near the fracture reveals such conditions as abnormally coarse crystals, large nonmetallic inclusions, large inclusion population, undissolved master alloy particles, abnormal carbide segregation, interdendritic segregation, shrinkage, and gas porosity.

The appearances of wear on polyethylene--a comparison of in vivo and in vitro wear surfaces.

An examination has been made of the wear surfaces of 21 ultra-high-molecular-weight polyethylene components of hip and knee joint prostheses removed from patients. Both light optics and scanning electron microscope systems of examination have been used. The appearances are compared with specimens subjected to two different in vitro wear tests.