Three-dimensional secondary stability of cemented and non-cemented acetabular implants ex-vivo under dynamic load

Abstract

INTRODUCTION: Aseptic loosening is still the most important cause for long-term failure of total hip joint arthroplasty. Therefore, the objective of our investigation is to test the stability of retrieved cemented and noncemented endoprosthetic acetabular cups by measuring the relative motion between the bone and the implant surface at various sites of the interface under physiological dynamic loading conditions. MATERIAL AND hfETHODSz A special device to hold the specimen and to simulate the motion of the hip joint during the stance phase of the gait cycle was constructed (Fig. 1). The gait data, i.e. the angles of flexionextension, abduction-adduction, internal and external rotation and the step frequency, were derived from a gait analysis of a normal person recorded in the gait laboratory. Combined joint movements were carried out between 25” of flexion and 5’ of extension, 5” of abduction and 3” of adduction and 3’ of internal and 5” of external rotation while applying the hip joint force at an angle of 23” to the femoral axis. The force is controlled with reference to telemetric data of Bergmann et al. (1993). Relative motion is measured by a micromechanical 3D-sensor at different locations of the bone-implant-interface. Specimens with a cemented Mueller polyethylene cup and a non-cemented Press-Fit Cup with titanium mesh coating had been tested. The complete set-up is mounted into the load frame of a biaxial material testing machine, where the joint is moved by the rotational actuator and the hip force is produced by the linear actuator. RESULT% In plane relative motions , i.e. transverse movements in the bone-implant interface, were site-dependent for both the cemented and the non-cemented cups. Cemented cups showed higher transverse relative motion up to 90 pm, whereas the maximum transverse movement of the non-cemented cup was 60 pm. Orthogonal motion perpendicular to the implant surface showed compression for all cups at ah sites. Bone and implant approached up to 40 pm when cemented cups were implanted and up to 20 pm for non-cemented cups. The results differed highly from specimen to specimen indicating different degrees of stability. CONCLUSION: Non-cemented acetabular press-fit cups with titanium mesh coating show better secondary stability than cemented polyethylene cups. But more retrieved specimens with comparable history should be tested.