Julius M. Böttcher (Hamburg), Kay Sellenschloh (Hamburg), Anna Strube (Hamburg), Dr. Ing. Gerd Huber (Hamburg), Prof. Dr. Michael M. Morlock (Hamburg)
Abstract-Text (inkl. Referenzen und Bildunterschriften)
Introduction In revision surgery, modular implant components allow the surgeon to tailor the characteristics of the implant to the bone situation [Ellman, J ARTHROPLASTY 2013]. Relative motion can occur at the tapered modular junction, causing fretting corrosion and subsequent biological reactions – especially due to insufficient assembly and contamination of the taper junction [Krull, J ARTHROPLASTY 2017].
Aim of the study Aim was to exhibit whether incomplete assembly and unwanted contamination of the modular taper cause a change in junction strength.
Methods Modular taper junctions between neck and stem (n = 48) were divided into seven groups differing in contamination (native, contaminated, cleaned) and assembly conditions (secured, pretensioned&secured). Contamination was achieved using a combination of porcine bone particles together with bovine blood (fig. 1). For each group, the number of rotations of the torque limiter while securing the taper junction was recorded. Implants were subjected to cyclic loading. DIC was used to determine rotation of the neck piece, micromotion and axial subsidence. Loosening torque of the locking screw as well as pull-off forces were measured as an equivalent for the remaining strength of the taper junction.
Results Contamination of the taper junction, especially in combination with improper assembly of the components, significantly increased the rotation (35.3 ± 13.7° vs. 2.4 ± 4.4°; p < 0.001, fig. 2A), micromotion (67.8 ± 16.9 µm vs. 5.1 ± 12.1 µm, p < 0.001, fig. 2B) and axial subsidence (-34.1 ± 16,9 µm vs. 4.3 ± 10.9 µm; p < 0.001) of the neck piece relative to the stem.
Conclusion Intra-operatively, contamination of the taper surface can be identified by the need for multiple rotations when tightening the locking screw. Correct cleaning with the new taper cleaning instrument and complete assembly potentially reduces the risk of early failure and fatigue fracture of the modular taper junction.