title: Design parameters and the material coupling are decisive for the micromotion magnitude at the stem-neck interface of bi-modular hip implants.
abstract: Several bi-modular hip prostheses exhibit an elevated number of fretting-related postoperative complications most probably caused by excessive micromotions at taper connections. This study investigated micromotions at the stem-neck interface of two different designs: one design (Metha, Aesculap AG) has demonstrated a substantial number of in vivo neck fractures for Ti-Ti couplings, but there are no documented fractures for Ti-CoCr couplings. Conversely, for a comparable design (H-Max M, Limacorporate) with a Ti-Ti coupling only one clinical failure has been reported. Prostheses were mechanically tested and the micromotions were recorded using a contactless measurement system. For Ti-Ti couplings, the Metha prosthesis showed a trend towards higher micromotions compared to the H-Max M (6.5 ± 1.6 μm vs. 3.6 ± 1.5 μm, p=0.08). Independent of the design, prostheses with Ti neck adapter caused significantly higher interface micromotions than those with CoCr ones (5.1 ± 2.1 μm vs. 0.8 ± 1.6 μm, p=0.001). No differences in micromotions between the Metha prosthesis with CoCr neck and the H-Max M with Ti neck were observed (2.6 ± 2.0 μm, p=0.25). The material coupling and the design are both crucial for the micromotions magnitude. The extent of micromotions seems to correspond to the number of clinically observed fractures and confirm the relationship between those and the occurrence of fretting corrosion.
authors: Institute of Biomechanics, TUHH Hamburg University of Technology, Hamburg, Germany; Centre for Orthopaedic Biomechanics, University of Bath, Bath, United Kingdom. Electronic address: s.y.jauch@bath.ac.uk.
authors: S Y
authors: SY
authors: Jauch
authors: Institute of Biomechanics, TUHH Hamburg University of Technology, Hamburg, Germany.
authors: G
authors: G
authors: Huber
authors: Institute of Biomechanics, TUHH Hamburg University of Technology, Hamburg, Germany.
authors: H
authors: H
authors: Haschke
authors: Institute of Biomechanics, TUHH Hamburg University of Technology, Hamburg, Germany.
authors: K
authors: K
authors: Sellenschloh
authors: Institute of Biomechanics, TUHH Hamburg University of Technology, Hamburg, Germany.
authors: M M
authors: MM
authors: Morlock
mesh_terms: D004548:Elasticity; D020342:Finite Element Analysis; D006622:Hip Prosthesis; D008422:Materials Testing; D009038:Motion; D011474:Prosthesis Design / Q000379:methods*
keywords: Bi-modular prosthesis; Fretting; Micromotion; Neck fracture; Stem–neck interface