Maximizing the fixation strength of modular components by impaction without tissue damage.
A Krull1, M M Morlock1, N E Bishop2
1Institute of Biomechanics, TUHH - Hamburg University of Technology, Denickestrasse 15, 21073 Hamburg, Germany.
Bone & Joint Research
|April 24, 2018
Summary
Maximizing hip implant taper junction stability involves using stiffer impaction tools to reduce wear and corrosion without increasing tissue damage. Higher impaction energy enhances stability but also increases forces on surrounding tissues, requiring careful control.
Area of Science:
- Biomedical Engineering
- Orthopedic Surgery
- Materials Science
Background:
- Modular hip arthroplasty components, specifically femoral heads and stems, are susceptible to failure via wear and corrosion.
- Relative motion at the taper junction interface is a primary cause of wear and corrosion.
- Increased assembly force can mitigate these issues but risks damaging surrounding tissues.
Purpose of the Study:
- To investigate the impact of impaction energy and impacter tool stiffness on taper junction stability.
- To evaluate the forces transmitted to surrounding tissues during the assembly of modular hip implant components.
Main Methods:
- A laboratory study modified a commercial impaction tool with varying stiffnesses.
- Simulated patient tissues using springs to measure transmitted forces.
- Assessed taper junction stability via pull-off force and transmitted forces via spring displacement.
Main Results:
- Increased impacter stiffness enhanced head-stem pull-off force without increasing transmitted forces to simulated tissues.
- Higher impaction energy increased pull-off force but also elevated forces transmitted to simulated tissues.
- No damage to the head surface was reported with stiffer impacter tips.
Conclusions:
- Maximize impacter tool stiffness to enhance taper junction stability and minimize wear/corrosion, provided head surface integrity is maintained.
- Impaction energy should be carefully controlled to balance stability gains with acceptable forces on surrounding tissues.
- Current impacter designs may be nearing optimal stiffness for this application.
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