Determination of local micromotion at the stem-neck taper junction of a bi-modular total hip prosthesis design

Publikationstyp
Journal Article
Date Issued
2019-03
Sprache
English
Author(s)
Falkenberg, Adrian  
Drummen, Paul  
Morlock, Michael  
Huber, Gerd  
Institut
Biomechanik M-3  
TORE-URI
http://hdl.handle.net/11420/2268
Journal
Medical engineering & physics  
Volume
65
Start Page
31
End Page
38
Citation
Medical engineering & physics (65): 31-38 (2019-03)
Publisher DOI
10.1016/j.medengphy.2019.01.003
Scopus ID
2-s2.0-85060251869
High rates of clinical complications with bi-modular hip prostheses are attributed to failure of the stem-neck taper junction. Taper wear analyses have shown extensive material loss as a result of corrosion, potentially initiated by micromotion. The purpose of the study was to determine the amount of micromotion at this junction for different loading, assembly and material conditions. Micromotion between the neck adapter (CoCr29Mo6-alloy) and the stem (TiMo12Zr6Fe2-alloy; both Rejuvenate, Stryker) within the taper junction of a bi-modular hip stem were determined by image matching analysis of consecutively recorded images through windows in the stem component. A finite element model was used to determine the micromotion in the taper regions outside the windows and validated with the measured micromotion. With the model, the influence of the load amplitude, assembly force and component materials were then investigated. Determined micromotion (14-79 µm) by far exceeded critical values (5 µm) associated with the onset of fretting corrosion. Increasing assembly forces achieved a significant reduction in micromotion. The numerical model revealed insufficient assembly to cause the neck to perform rocking motions under load, repetitively changing taper contact in combination with gap opening, which facilitates fluid ingress into the junction. Changing the stem material to a stiffer Ti-alloy achieved a reduction of the micromotion of about 30%. This study emphasises the high importance of material selection, assembly force and loading on the susceptibility of bi-modular hip stems to fretting and crevice corrosion. These findings can serve to explain the increased rate of clinically reported problems with this particular prosthesis design.
Subjects
Assembly force
Bi-modular prosthesis
Flexural rigidity
Micromotion
Taper junction