The morse taper junction in modular revision hip replacement - A biomechanical and retrieval analysis

All biomaterials used for total joint surgery are subjected to wear mechani sms. Morse taper junctions of modular hip revision implants are predilectio n sites for both fretting and crevice corrosion, dissociation and breakage of the components. The aim of this study is to quantify wear and study meta llurgical changes of morse taper junctions of in-vitro and in-vivo loaded m odular revision stems. Three modular revision stems (MRP-Titan, Peter Brehm GmbH, Germany) were lo aded by a servohydraulic testing machine. The loads and conditions used exc eeded by far the values required by ISO-standard 7206. The tests were perfo rmed with maximum axial loads of 3 500 N to 4 000 N over 10-12 x 10(6) cycl es at 2 Hz. Additionally, the female part of the taper junctions were coate d with blood and bone debris. The free length of the implant was set to 200 mm. One other MRP stem was investigated after retrieval following 5.5 year s of in-vivo use. All contact surfaces of the modular elements were assesse d by visual inspection, optical microscopy and scanning electron microscopy (SEM). The degree of plastic deformation of the male part of the morse tap er junction was determined by contouroscopy. None of the morse taper junctions broke or failed mechanically. Corrosion a nd wear affected all tapers, especially at the medial side, The retrieved i mplant showed no cracks and the amount of debris measured only one third of that for the stems tested in-vitro. The present retrieval and laboratory investigations have proven, that the m orse taper junctions of the MRP-titanium stem are stable and resistant to r elevant wear mechanisms. The longevity of the junctions for clinical use is given. If an optimal taper design is selected, the advantages of modular f emoral components in total hip revision arthroplasty will outweigh the poss ible risks.