Abstract
Introduction
Taper corrosion has been identified to be major problem in total hip replacement during the past years. Patients may suffer from adverse local tissue reactions (ALTR) due to corrosion products that are released from modular taper connection. So far, the mechanism that leads to taper corrosion in taper connections is not fully understood. Some retrieval studies tried to correlate implant related design parameters to the incidence and the severeness of taper corrosion. For example Kocagöz et al.[1] have not seen an influence of the taper clearance to taper corrosion. Hothi et al.[2] showed that shorter and rougher tapers increase taper corrosion. One limitation of retrieval studies may be that the analysed tapers are used and may have been altered during in vivo service. Beside the effect of taper corrosion many surgeons are not aware that the tapers may vary among different manufactors. With our study we want to provide taper related data that may be used for comparison and correlation (e.g. retrieval studies). Therefore we aimed to assess and compare geometric and topographic design parameters of currently available hip stem tapers from different manufacturers.
Material
For comparison well established cementless hip stems made of titanium alloy were choosen. All of them have a 12/14-taper. The analysed implants are shown in Fig. 1. As geometrical parameters the taper angle, the opening taper diameter and the taper length were measured using a coordinate measuring machine (CMM) (MarVision MS 222, Mahr, Göttingen, Germany; accuracy: ±2.3 µm). Several topographical parameters (e.g. Ra, Rz, etc.) were determined using a tactil roughness measurement instrument (Perthometer M2, Mahr, Göttingen, Germany; accuracy: 12 nm). Three independent samples of each taper were measured five times.
Results
In Fig. 2 the geometrical parameters like taper angle and opening diameter are given. As roughness parameters the average roughness (Ra) and the average maximum height of the profile (Rz) are presented in Fig. 3.
Discussion and conclusion
As expected, this study shows that the tapers differ among the manufactures. Regarding the geometry, high variations in taper length were seen whereas the taper angle and opening taper diameter vary only to a small extent. However, if the combination of taper angle and opening diameter are considered these small differences may become relevant regarding the contact situation in the taper junction. Clearly, the tapers differed in topography. The surface roughness parameters vary to a large extent from smooth to very rough values. In combination all these parameters will influence the crevice of the taper junction. Considering that taper corrosion is mostly initiated within the crevice, further studies may help to understand the influence of taper variations to the corrosion mechanism.
