HOW TO AVOID FRACTURE OF THE LOCKING SCREW IN MODULAR REVISION ARTHROPLASTY OF THE HIP USING THE MRP TITAN REVISION...

The use of modular femoral stems in primary and revision arthroplasty of the hip has become popular within the last decade. On the other hand, modularity creates new potential problems like fretting, crevice and galvanic corrosion, component loosening, dissociation, and fracture of modular prostheses. Recently a problem of fracture of a locking screw in revision arthroplasty of the hip using the MRP Titan Stem (Peter Brehm GmbH, Weisendorf, 91085 Germany) appeared. The aim of this study is to evaluate the meaning of surface contamination in respect to fracture mechanism. The titanium nitrid coated locking screw M6 of the MRP Titan system was in vitro tested in several series. After experimental contamination (series 1-4) morse taper junction was fixed by the locking screw with a torque wrench: Series 1: The influence of contamination with dried blood was examined while screw M6 was put into pig's blood. Series 2: The influence of contamination with dried blood and biologic tissue was examined while screw M6 was covered with a pulpous mixture of pig's blood, pig's muscle, and pig's fat tissue. Series 3: The influence of contamination with dried blood and biologic tissue was examined while female thread was covered with a pulpous mixture of pig's blood, pig's muscle, and pig's fat tissue. Series 4: The influence of cleaning of the contaminated female component was examined while female thread contamination (with a pulpous mixture of pig's blood, pig's muscle, and pig's fat tissue) was cleaned with 50 ml saline solution. Comparing series 1 with series 4, series 2 with series 4 and series 3 with series 4 statistical analysis showed a significant reduction of fractures of screw M6 (p-values <0.01). To avoid fracture of the screw M6 of the MRP Titan System we recommend cleaning the inner thread of the morse taper junction with saline solution before junction is fixed with the screw and the torque wrench.