Experimental versus computational analysis of micromotions at the implant-bone interface

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Medical device analysis

Background:

• Micromotions at the implant-bone interface are critical for total hip arthroplasty (THA) survival.
• Current methods for measuring micromotions use remote sensors, potentially introducing errors due to the non-rigid nature of the implant-bone system.
• The magnitude of these measurement errors is currently unquantifiable experimentally.

Purpose of the Study:

• To investigate the accuracy of remote micromotion measurements in THA.
• To hypothesize that actual interface micromotions differ from those measured using remote reference points.
• To quantify the error introduced by using remote reference points in micromotion measurement.

Main Methods:

• A case-specific finite element method (FEM) model of the hip implant-bone interface was developed.
• The FEM model was validated against experimental deflection data.
• A simulated 'experimental' method using FEM mimicked remote sensor placement to measure micromotions.

Main Results:

• No correlation was found between micromotions computed at the interface and those measured using remote reference points.
• Remote measurement methods significantly overestimated the magnitude of micromotions.
• Reducing the distance between reference points decreased error but did not improve correlation.

Conclusions:

• Current experimental methods for measuring THA micromotions using distant bony reference points are unreliable.
• FEM analysis reveals significant discrepancies between true interface micromotions and remote measurements.
• Caution is advised when interpreting data from THA micromotion systems employing distant bony reference points.