Behavior of the femoral stem in the Bihapro hip prosthesis.

This study evaluated the hydroxyapatite-coated femoral stem of the Bihapro hip prosthesis (Biomet Ltd, Bridgend, United Kingdom) using radiography, TC-99 scintigraphy, and bone densitometry. Thirty stems with >2 years of follow-up (mean: 31 months) were evaluated. No loosening or changes in the position of the implant were seen, and the mean subsidence was 2.2 mm. Radiography revealed a densification in the metaphyseal zone with reconstruction of the trabecular lines in 21 cases, while in 22 patients, radiolucent lines in the distal area of the femoral component were observed. Scintigraphy showed a diaphyseal normo-captation in 19 cases and a hypercaptation <1.4 with a mean index of 1.1 in 10 patients. Metaphyseal hypercaptation >1.4 was seen in 24 patients. Bone densitometry revealed increased density in the metaphyseal zones in 29 patients with a periprosthetic/normal bone quotient of 1.4.

Loosening of threaded acetabular cups in arthroplasty of the hip. The association with different types of coxarthrosis.

Seventy-nine patients underwent hip arthroplasty using a threaded acetabular cup during 1988 and 1989. Out of 71 cups implanted for coxarthrosis, radiographs of 62 have been reviewed at a mean follow up of 69 months. The survival rate at 5.5 years was 77.5%. The mean age at operation was 61 years. Loosening of the cup occurred in 7 cases with pain on walking; 5 had a revision operation. In another 28 patients, radiolucent lines greater than 1 mm were found around the cup and 7 of these were unstable. The previous coxarthrosis was classified as atrophic with 5 loose cups, normotrophic with 2 loose cups and hypertrophic with no loosening. This difference between loosening in the atrophic and hypertrophic types of preexisting coxarthrosis was statistically significant. Radiolucent lines were present in 61% of the atrophic cases, 53.4% of the normotrophic and 25% of the hypertrophic, which was also significant. If the cases of loosening are added to those with radiolucent lines, the types of coxarthrosis show highly significant differences. Threaded cups had a high percentage of failure which was greater in cases with atrophic coxarthrosis.