Mode of loosening of matt-finished femoral stems in primary total hip replacement.

OBJECTIVE

Major advances have occurred in total hip replacement (THR) surgery aiming at minimizing or delaying loosening of the components. Currently, substantial controversy exists regarding the possible role of the surface finish of cemented femoral stems in the loosening process. Several authors have recently suggested that a roughened surface finish of the femoral component in cemented THR can predispose the implant to early loosening and subsequently severe osteolysis. The aim of this study was to evaluate both the incidence of, and the mode of loosening of the cemented femoral components in a large series of primary THR with matt-finished surface followed over a span of 2 decades. The aim was to assess the behavior of bead-blasted chrome-cobalt cemented femoral stems of the computer assisted design (CAD) and Harris Design-2 (HD-2).

METHODS

From a prospective study of 161 consecutive hips in 140 patients who underwent primary THR using HD-2 or CAD cemented femoral components performed by a single surgeon between 1976 and 1979, all hips were evaluated with special emphasis on the 73 patients (84 hips) who were followed for an average of 18 years. Among the 161 hips, all femoral stems that became loose were studied in detail. The cement technique used in all cases was the so-called 2nd generation cementing technique. No patient was lost to follow-up. We now report on the subset of 10 hips (6%) (9 patients) among the entire 161 hips that had an aseptic failure of fixation of their femoral components.

RESULTS

Ten of 117 CAD stems (8.5%) and none of 44 HD-2 stems became loose. Five percent (8 of 161) of those (all CAD) were revised due to aseptic loosening. Two of those revisions for aseptic femoral loosening were carried out during the first decade (1.2%). One of these 2 loose stems was converted into a resection arthroplasty at another hospital despite not being loose radiographically and having no osteolysis. The other loose stem was removed at 9 years and 10 months for a fracture secondary to lysis below the tip of the stem. The remaining 8 loose stems were not diagnosed as loose until the 2nd decade following the operation. Six of those 8 stems were revised and 2 have not been revised. The average duration until these 6 were revised was 18 years after the operation (range 14-19). The remaining 2 unrevised stems are debonded (<1mm) but functioning well. No stem showed the early type of rapid lysis reported for the Iowa design. There was no consistent relationship between the development of loosening and osteolysis in the 10 hips that became loose. Among the 5 hips that debonded, the debonding was initially noted at an average of 13 years (range 4-21) but in this group, osteolysis was present in 3 hips and was first noticed at an average of 9 years (range 5-12) after the operation. Of those that developed both osteolysis and radiographic evidence of loosening, the lysis preceded the debonding in 2 of the 3 cases.

CONCLUSION

There is no evidence in this series of 161 hips that a matt surface finish was associated with either the premature loosening or the marked progressive osteolysis pattern of the type that has been described with the Iowa stem. The evidence in our report does not support the hypothesis that a bead-blasted surface finish in the 2 designs studied here (CAD and HD-2) lead to a high incidence of early loosening and marked progressive lysis. In general, these stems have functioned well in the long term, both clinically and radiologically. This data raises the question that other factors, such as the design, the offset, the high placement of the medial curvature of the stem, and the large body weight in the patients in the Iowa series may have contributed to the early failure of fixation of those hips in that series in conjunction with, or independent of the surface finish of that design of stem.