Background New bone formation around cement less stem after total hip arthroplasty is dependent on implant design, material, and mode of porous coating. These osteogenesis patterns are classified as follows, proximal endosteal bone bridging spot welds, increased cortical thickness (cortical hypertrophy) and thin radiodense lines surrounding the tip of the implant (halo pedestal). However, no reports showed the comparison of bone remodelling patterns surrounding stem among diseases: such as osteoarthritis (OA), rheumatoid arthritis (RA), avascular necrosis and neck fracture.

Objectives The purpose of this study is to clarify whether there are differences of the postoperative bone remodelling pattern around the femoral stem between RA and OA patients.

Methods Total hip arthroplasty with the Mallory-Head cement less titanium prosthesis has been performed since 1992 in our institute. This tapered stem has plasma spray coating in proximal one third of it. RA group included 18 hips (mean age at operation was fifty-five years old and mean duration of follow-up was 4.6 years). OA group included 70 hips (mean age at operation was fifty-eight years old and mean duration of follow-up was 5.2 years). Anteroposterior radiographs of the hip were made at 6 weeks, 3 months, 6 months, one year and every year after the operation. We evaluated the frequency and time of new bone remodelling appearance around the stem such as spot welds, cortical hypertrophy, and pedestal. We defined that the radiographic signs of instability were progressive subsidence or the presence of radiolucent lines around the porous coating.¹ To evaluate the differences in both groups, the Mann-Whitney’s U test and chi-square test were used. P values of less than 0.01?@were considered significant.

Results In both groups, there was no case, which has radiographic sign of instability. Age and intramedurally canal fill of the stem at the operation and follow-up period were not significantly different between RA and OA groups. In endosteal spot welds, the time of its appearance in RA group (2.7 months after operation) was significantly shorter than that in OA group (5.2 months) and the frequency of it did not differ between both groups. However, in halo pedestal, the frequency in RA group (50%) was significantly lower than that in OA group (87%) and the time of its appearance did not differ between both groups. On the other hand, concerning about cortical hypertrophy, time and frequency showed no significant differences between two groups.

Conclusion We revealed that in RA patients, endosteal spot welds appeared significantly earlier than that in OA patients, and the frequency of halo pedestal was significantly lower than that in OA patients.

Reference

1. Mulliken BD, Bourne RB, Rorabeck CH, et al. A tapered titanium femoral stem inserted without cement in a total hip arthroplasty. J Bone Joint Surg Am. 1996;78:1214