Fixation of the shorter cementless GTS™ stem: biomechanical comparison between a conventional and an innovative implant design

Introduction

Conventional cementless total hip arthroplasty already shows very good clinical results. Nevertheless, implant revision is often accompanied by massive bone loss. The new shorter GTS™ stem has been introduced to conserve femoral bone stock. However, no long-term clinical results were available for this implant. A biomechanical comparison of the GTS™ stem with the clinically well-established CLS^® stem was therefore preformed to investigate the targeted stem philosophy.

Materials and methods

Four GTS™ stems and four CLS^® stems were implanted in a standardized manner in eight synthetic femurs. A high-precision measuring device was used to determine micromotions of the stem and bone during different load applications. Calculation of relative micromotions at the bone–implant interface allowed the rotational implant stability and the bending behavior of the stem to be determined.

Results

Lowest relative micromotions were detected near the lesser trochanter within the proximal part of both stems. Maximum relative micromotions were measured near the distal tip of the stems, indicating a proximal fixation of both stems. For the varus–valgus–torque application, a comparable stem bending behavior was shown for both stems.

Conclusion

Both stems seem to provide a comparable and adequate primary stability. The shortened GTS™ design has a comparable rotational stability and bone–implant flexibility compared to a conventional stem. This study demonstrates that the CLS^® stem and the GTS™ stem exhibit similar biomechanical behavior. However, a clinical confirmation of these experimental results is still required.