title: Dynamic behavior of tripolar hip endoprostheses under physiological conditions and their effect on stability.
abstract: Tripolar systems have been implanted to reduce the risk of recurrent dislocation. However, there is little known about the dynamic behavior of tripolar hip endoprostheses under daily life conditions and achieved joint stability. Hence, the objective of this biomechanical study was to examine the in vivo dynamics and dislocation behavior of two types of tripolar systems compared to a standard total hip replacement (THR) with the same outer head diameter. Several load cases of daily life activities were applied to an eccentric and a concentric tripolar system by an industrial robot. During testing, the motion of the intermediate component was measured using a stereo camera system. Additionally, their behavior under different dislocation scenarios was investigated in comparison to a standard THR. For the eccentric tripolar system, the intermediate component demonstrated the shifting into moderate valgus-positions, regardless of the type of movement. This implant showed the highest resisting torque against dislocation in combination with a large range of motion. In contrast, the concentric tripolar system tended to remain in varus-positions and was primarily moved after stem contact. According to the results, eccentric tripolar systems can work well under in vivo conditions and increase hip joint stability in comparison to standard THRs.
authors.affiliation: Department of Orthopaedics, University Medicine Rostock, Biomechanics and Implant Technology Research Laboratory, 18057 Rostock, Germany. Electronic address: christian.fabry@med.uni-rostock.de.
authors.forename: Christian
authors.initials: C
authors.lastname: Fabry
authors.affiliation: Chair of Technical Dynamics, University Rostock, Faculty of Mechanical Engineering and Marine Technology, 18059 Rostock, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Kaehler
authors.affiliation: Department of Orthopaedics, University Medicine Rostock, Biomechanics and Implant Technology Research Laboratory, 18057 Rostock, Germany.
authors.forename: Sven
authors.initials: S
authors.lastname: Herrmann
authors.affiliation: Chair of Technical Dynamics, University Rostock, Faculty of Mechanical Engineering and Marine Technology, 18059 Rostock, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Woernle
authors.affiliation: Department of Orthopaedics, University Medicine Rostock, Biomechanics and Implant Technology Research Laboratory, 18057 Rostock, Germany.
authors.forename: Rainer
authors.initials: R
authors.lastname: Bader
mesh_terms: D000203:Activities of Daily Living; D019644:Arthroplasty, Replacement, Hip; D006622:Hip Prosthesis; D008422:Materials Testing; D055595:Mechanical Phenomena; D009038:Motion; D011474:Prosthesis Design
keywords: Dislocation; Hip stability; Range of motion; Total hip replacement; Tripolar design