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 longterm 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.

Numeric simulation of bone remodelling patterns after implantation of a cementless straight stem

“…It has a flat, rectangular shape, lateral fixation fins and a dorsal antirotation wing to give the stem primary stability and proximal force transmission in the intertrochanteric region [5,6]. The ten to 15-year results of Bicontact® uncemented THA show satisfactory pain relief, good functional results and durable implant stability with excellent stem survival.…”

“…Thus, the aim of this study was to establish a numerical model of a cementless straight stem that has provided good, long-term results and been used successfully in its unaltered since 1986/1987 [2][3][4]. We performed a numeric simulation of the cementless Bicontact® straight stem and validated it with bone density data derived from a prospective DEXA investigation [5].…”

Comparison between simulation results and DEXA investigation of the bone remodelling after implanting a cementless long stem hip prosthesis

“…The elements of the upper part of the femur are grouped in seven separated sets as stated in the clinical study in [4] (Fig. 1(b)).…”

“…The hip of every patient individually is virtually divided into seven regions of interest (ROIs) ( Fig. 1 (a)) in order to achieve an accurate measuring of the BMD and its changings during the study period [4]. The FE-model of the periprosthetic femur used at IFUM in [5,6,7] is used in this comparison applying the same conditions and constraints with the same muscle forces and hip contacts but with the following restrictions:…”

“…But a comparison between them is rarely done. Recently a DEXA study on a group of 25 patients with cementless Bicontact long stem system (AESCULAP AG, Tuttlingen, Germany) [4]. This paper represents a comparison between this study and the estimated bone remodelling of a periprosthetic femur with the same kind of prosthesis using the finite element method (FEM) [5, 6, ,7].…”