Effects of hip implant modular neck material and assembly method on fatigue life and distraction force

Abstract

Hip implant neck fractures and adverse tissue reactions associated with fretting-corrosion damage at modular interfaces are a major source of concern. Therefore, there is an urgent clinical need to develop accurate in vitro test procedures to better understand, predict and prevent in vivo implant failures. This study aimed to simulate in vivo fatigue fracture and distraction of modular necks in an in vitro setting, and to assess the effects of neck material (Ti6Al4V vs. CoCrMo) and assembly method (hand vs. impact) on the fatigue life and distraction of the necks. Fatigue tests were performed on the cementless PROFEMUR® Total Hip Modular Neck System under two different loads and number of cycles: 2.3 kN for 5 million cycles, and 7.0 kN for 1.3 million cycles. The developed in vitro simulation setup successfully reproduced in vivo modular neck fracture mode and location. Neck failure occurred at the neck-stem taper and the fracture ran from the distal lateral neck surface to the proximal medial entry point of the neck into the stem. None of the necks failed under the 2.3 kN load. However, all hand-assembled Ti6Al4V necks failed under the 7.0 kN load. In contrast, none of the hand-assembled CoCrMo necks and impact-assembled necks (Ti6Al4V or CoCrMo) failed under this higher load. In conclusion, Ti6Al4V necks were more susceptible to fatigue failure than CoCrMo necks. In addition, impact assembly substantially improved the fatigue life of Ti6Al4V necks and also led to overall higher distraction forces for both neck materials. Overall, this study shows that the material and assembly method can affect the fatigue strength of modular necks. Finally, improper implant assembly during surgery may result in diminished modular neck survivability and increased failure rates. © 2016 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 35:2023-2030, 2017.

Finite element study of functionally graded porous femoral stems incorporating body‐centered cubic structure

“…Stems of different geometrical designs have been proposed to overcome the issue of stress shielding. Most of the research work on stem geometry has focused on the optimization aspects of the stem shape and geometry, optimization of hip‐implant cross sections, and hip implant design to reduce stress shielding and enhance stress transfer to the bone.…”

Additively manufactured metallic biomaterials

“…Customized fatigue test setups are required for fatigue testing of the implant with complex external geometries. For instance, based on the ISO 7206-4 standard [ 273 ], the hip implants are required to be oriented in specific angles while the lower portion of the implant is embedded in a cement-based casting material [ 274 ] ( Fig. 12 Ci, ii).…”

Thermal based surface modification techniques for enhancing the corrosion and wear resistance of metallic implants: A review

“…Stress concentrations develop areas that will fail under applied loads of lesser magnitude than the rest of the implant. This creates crack growth, leading to the implants' catastrophic failure due to fatigue [17].…”

“…Joints such as the hip and knee are required to have high fatigue resistance because they are under several repeated load cycles a day, with the average person taking around 9000 steps a day [16]. The cracks that develop due to corrosion mechanisms create stress concentrations at the tip [17]. Stress concentrations create areas that will fail under applied loads of lesser magnitude than the rest of the implant, and this creates crack growth which leads to catastrophic failure of the implants due to fatigue [17].…”

“…The cracks that develop due to corrosion mechanisms create stress concentrations at the tip [17]. Stress concentrations create areas that will fail under applied loads of lesser magnitude than the rest of the implant, and this creates crack growth which leads to catastrophic failure of the implants due to fatigue [17].…”