A comparative study of porous coatings in a weight-bearing total hip-arthroplasty model.

The purposes of this study were to compare ingrowth of bone into three types of porous coating and to determine the effect of the type of porous coating and the degree of coverage of the stem on the remodeling of bone on the femoral side in cementless hip arthroplasty. A left total hip arthroplasty was performed in forty dogs. Thirty of the dogs had a titanium-alloy femoral prosthesis that had had one of three types of commercially pure titanium porous material applied along the length of the anterior and posterior surfaces of the stem: ten with sintered fiber-metal, ten with sintered beads, and ten with plasma flame-spray coating. The remaining ten dogs had a femoral component that was circumferentially coated with commercially pure titanium that was plasma flame-sprayed along the length of the stem. In each group, five animals were killed at one month and five were killed at six months. Ingrowth of bone into all three types of porous coating was observed, indicating secure fixation of all components. By six months, there was more ingrowth of bone and new medullary bone adjacent to the proximal and distal aspects of the stems compared with the middle level of the stems in all groups. No significant difference in ingrowth of bone was observed in the beaded surface (25.2 per cent) and the fiber-metal surface (16.6 per cent) at one month, but at six months there was significantly less ingrowth into the beaded surface (23.3 per cent) than into the fiber-metal surface (37.3 per cent). In all groups, a proximal-to-distal gradient of loss of cortical bone was observed by six months. The group of dogs that had the stem with the circumferential coating experienced more severe loss of bone than did the three groups that had a stem with a partial coating. The magnitude of loss of bone was dependent on the extent rather than the type of porous coating.

Revision total hip arthroplasty without cement: subsidence of proximally porous-coated femoral components.

We prospectively studied the intermediate-term results of forty-nine revision total hip arthroplasties without cement that were performed because of aseptic loosening of a cemented femoral component in forty-five consecutive patients; the mean duration of follow-up was sixty-five months (range, forty-five to eighty-seven months). A curved, long-stem, titanium-alloy, non-circumferentially porous-coated femoral component was implanted in each hip. Preoperatively, a staging system was used to classify deficiencies of femoral bone stock according to the loss of cancellous or cortical bone in the metaphysis and diaphysis. Forty-one hips (84 per cent) had cortical or ectatic cavitary bone loss in the metaphysis. The mean Harris hip score significantly improved from 54 points preoperatively to 84 points at the time of the latest follow-up examination (p < 0.001). Twenty-seven patients (twenty-eight hips; 57 per cent) had at least two millimeters of subsidence of the femoral component during the first postoperative year. Eight patients (eight hips; 16 per cent) had no further progression of subsidence. Twenty-one patients (twenty-two hips; 45 per cent) had at least two millimeters of subsidence on two separate postoperative evaluations and therefore were considered to have progressive subsidence. Seventeen patients (nineteen hips; 39 per cent) had no measurable subsidence and were considered to have a stable femoral component. One of these seventeen patients had had a bilateral femoral revision and had progressive subsidence on one side. There was a positive trend for an association between subsidence and the degree of preoperative femoral bone deficiency (p = 0.10), but there was no association between subsidence and the fit of the prosthesis in the metaphysis and diaphysis or the fill of the canal of the femur (p > 0.50). There was no significant loss of bone in the hips with either a stable or a subsided femoral component (p > 0.50), and qualitative reconstitution of the cortex was noted in eleven (52 per cent) of the twenty-one most severely deficient (stage-III) femora. Survivorship analysis showed that, at seventy-two months, there was a 96 per cent chance of survival of the component (95 per cent confidence limits, 0.89 to 1.0) with revision as the end point but only a 37 per cent chance of survival (95 per cent confidence limits, 0.15 to 0.59) with revision or progressive subsidence as the end point.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of disodium etidronate (EHDP) on bone ingrowth in a porous material.

This study evaluated the effect of disodium etidronate (EHDP) on biomechanical and histologic characteristics of bone ingrowth in a porous material. EHDP was administered parenterally to six adult mongrel dogs at a dose of 2 mg/kg/day for eight weeks. Six additional dogs served as controls and were injected with saline. Porous titanium fiber composites were inserted into the proximal humeri and the left olecranons of all animals after the first four weeks of treatment. Upon completing a total of eight weeks of treatment, all animals were sacrificed and the bone-porous implant interfacial shear strength was determined by a pull-out test to failure. Mean shear strength of fixation for the EHDP-treated group was reduced by 76% compared to the control group (p less than 0.001). Bone ingrowth was mineralized in all of the control specimens. Mineralization of tissue ingrowth was inhibited, however, in all specimens from EHDP-treated animals. These findings suggest that cementless skeletal fixation of porous-coated implants by bone ingrowth may be delayed or prevented by the administration of EHDP.

Calcium phosphate-coated porous titanium implants for enhanced skeletal fixation.

Porous titanium fiber implants for cementless skeletal fixation by bone ingrowth were treated with a calcium phosphate coating applied by a plasma flame-spray technique. In a paired experiment, treated and control implants were inserted in the humeri and olecranons of 36 adult dogs for periods of 1, 2, 4, and 6 weeks. After the animals were sacrificed, a biomechanical evaluation of the strength of skeletal fixation of the implants and a histologic evaluation of bone ingrowth was done. The mean shear strength of skeletal fixation at four weeks for the calcium phosphate-coated implants was 24% greater (P less than .01) than for paired controls. No difference in strength of fixation between treated and control implants was present at other time periods. The osteoconductive properties of the ceramic coating were demonstrated by bone forming in direct contact with the calcium phosphate coating on the metal fibers of the treated implants. No significant increase for the volume of bone ingrowth was established for treated implants compared to paired controls at any time period.