Modularity in total knee arthroplasty, particularly in revisions, is a common method to fit the implants to a patient's anatomy when additional stability or fixation is needed. In such cases, it may be necessary to employ multiple points of modularity to better match the anatomy. Taper junction strength at each of these levels is critical to maintain the mechanical stability of the implant and minimize micromotion. This effect of distributed assembly loads through multiple tapers and the resulting strength of the construct have not been previously evaluated on this revision tibial implant. The purpose of this study was to evaluate the possible dissipation of impaction force through multiple taper connections as compared to a single connection. Two different constructs representative of modular implants were studied: a construct with a single axial taper connection (Group A; representing implant-stem) was compared to a construct with an adaptor that included two, offset, modular taper connections (Group B; representing implant-adapter-stem). For Group A, the stem taper was assembled and impacted through the stem. For Group B, the two tapers of the adapter and stem were hand assembled with the mating components and impacted simultaneously through the stem. Assembly load for each construct was recorded. As shown in Figure 1, the constructs were then fixed in a mechanical test frame and an axial distraction force was applied to the end of the stem at a constant displacement rate of 0.075 mm/sec until taper separation or mechanical failure occurred. Force and displacement data were recorded at 50 Hz. Disassembly force was normalized to assembly force for each component. Minitab software was used to analyze the data using a t-test.Objectives
Methods
Quadriceps performance following total knee arthroplasty (TKA) is a critical factor in patient satisfaction that can be significantly affected by implant design (Greene, 2008). The objective of this study was to compare quadriceps efficiency (QE) following TKA with a medial-pivot system (EVOLUTION®, MicroPort Orthopedics Inc., Arlington, TN, USA) to non-implanted control measurements. Five cadaveric leg specimens with no prior surgeries, deformities, or disease were obtained. Each was placed in a custom closed chain device and loaded to simulate a heel-up squat from full-extension to deep flexion (approximately 115°) and back to full extension. Quadriceps force (FQ) and ground reaction force (FZ) were measured, and the ratio of the two was calculated as the quadriceps load factor (QLF). QFLs are inversely related to QE, with higher QFLs representing reduced efficiency. Each specimen was then implanted with a medial-pivot implant by a board certified orthopedic surgeon and force measurements were repeated. Mean pre- (represents control values) and post-implantation QFLs were compared to determine any differences in QE throughout the range of motion.Introduction
Methods
Modular necks allow intra-operative adjustment of neck length, offset, and version, enabling the surgeon to better match leg length and accommodate anatomical differences. However, there have been recent reports of early fatigue failures of the neck initiating from the neck/stem taper, and some retrieved components exhibit severe fretting corrosion.1 Fatigue testing according to ISO 7206-6 (10/9 orientation) has been shown to replicate the clinical fatigue failures, but results in relatively minor fretting and corrosion. The purpose of this pilot study was to evaluate techniques for accelerating fretting corrosion with the goal of replicating the most severely corroded clinical retrieval cases. Constructs tested in this study consisted of a single stem and neck design (PROFEMUR modular, Wright Medical Technology). The worst case long varus neck design was evaluated in two materials: Ti6Al4V and wrought CoCr. Introduction:
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