BJI_Micromotion2022
Evaluating the Efficacy of Measuring Implant-bone Fixation Methods in the Evaluation of Orthopaedic Implants
Presenting Author: David E. Cunningham
Contributing Authors: Dr. G. Athwal, Dr. J. Johnson
Background
Failure of orthopaedic implants due to loss of fixation remains a significant clinical concern. A number of studies have focused on evaluating the loosening of implants, and the ASTM has published evaluation methods in the quantification of implant fixation with focus in the micromotion occurring at the implant/bone interface. However, recent literature has suggested that these industry-accepted evaluation protocols may have some limitations.
Context
The ASTM F2028 standard for the dynamic evaluation of glenoid loosening and disassociation suggests the usage of linear variable differential transducers (LVDTs) to quantify the relative motion of the implant to bone. However, recent studies using combined LVDT and digital tracking (DT) methods have noted that using LVDTs can overreport bone-implant relative motion. The purpose of this work is to directly compare results obtained using DT and LVDT based micromotion measurements.
Methods
A stainless-steel implant surrogate was used in conjunction with a custom loading apparatus to stimulate bone-implant micromotion on a bovine tibial bone bed (n=5). An incrementally increasing eccentric load of 10-160 [N] was applied at one end of the implant surrogate, causing lift-off on the opposite side and hence promoting interface micromotion. Micromotion was quantified synchronously using a LDVT and a previously validated DT technique. Differences in micromotion were recorded and evaluated over five trials at different locations on the bony surface.
Results
Average measurements for LDVT and DT methods were computed at all loading increments (Fig. 1). Over the entire dataset, average micromotion via LVDT was 158% ± 65% higher than average micromotion via DT.
Fig 1: Average micromotion measured using both digital tracking and LDVT methods. This is an interactive plot so feel free to investigate further.
Conclusion
The use of LVDTs is of value when determining the effect of various implant designs and fixation techniques in parametric studies. However, they would appear to not accurately quantify absolute micromotion at the interface. An absolute measurement at the interface is better served using the OT system employed herein.