The cementless Bicontact stem in a prospective dual-energy X-ray absorptiometry study

Abstract

Purpose: The cementless Bicontact total hip arthroplasty (THA) system (AESCULAP AG, Tuttlingen, Germany) was introduced in 1986/1987 and has been in successful clinical use in an unaltered form up to today. Although good long-term results with the Bicontact stem have been published, it is questionable whether the implant provides the criteria for a state-of-the-art stem regarding proximal bone stock preservation. The purpose of the study was to monitor the periprosthetic bone mineral density (BMD) in a prospective two-year follow-up dual-energy X-ray absorptiometry (DEXA) study.

Methods: After power analysis, a consecutive series of 25 patients with unilateral Bicontact stem implantation was examined clinically and underwent DEXA examinations. Scans of seven regions of interest were taken preoperatively and at one week, six months, and one and two years.

Results: One patient required stem revision due to a deep infection. The Harris Hip Score increased significantly by 44 points. The most significant bone loss was observed in the calcar region (R7) in the first six months (-19.2 %). It recovered in the following 18 months to -8.5 %. The BMD in the greater trochanter dropped significantly after six months and remained stable at this level. BMD exceeded baseline values in distal regions and even more in the lesser trochanter region after two years.

Conclusions: We conclude that the Bicontact stem provides adequate proximal bone stock preservation. We observed some signs of stress shielding at the tip of the stem, which is inevitable to some degree in THA with cementless straight stems. However, in this prospective DEXA investigation, we showed that proximal off-loading does not occur after THA with the Bicontact system. Thus, we believe that this stem is still a state-of-the-art implant.

Fig. 1

The cementless Bicontact® stem is tapered, with a rough proximal hydroxyapatite coating and a smooth distal portion

Fig. 2

Anteroposterior preoperative (a) and postoperative (b, c, d) radiographs of a right femur over the course of 2 years after implantation of the Biconatct® stem. The region of intertrochanteric force transmission is marked with double arrows. Note the slight decrease in bone density in the proximal calcar and the greater trochanter (grey arrows). A slight bone density increase can be observed in the lesser trochanter region

Fig. 3

The Bicontact® stem with seven regions of interest

Fig. 4

Mean bone mineral density (BMD) changes of the seven regions calculated from the relative changes for each patient after 6 months (a), 1 year (b) and 2 years (c) of follow-up. The immediate postoperative value is set as baseline reference