Effects of knee simulator loading and alignment variability on predicted implant mechanics: a probabilistic study

Area of Science:

• Biomechanical Engineering
• Orthopedic Surgery
• Materials Science

Background:

• Inherent variability in total knee arthroplasty (TKA) loading and alignment can affect polyethylene tibial insert wear and implant longevity.
• Understanding how this variability influences implant performance is essential for improving TKA outcomes.

Purpose of the Study:

• To quantify the effect of variability in loading and alignment on the kinematics and contact mechanics of semi-constrained and unconstrained fixed bearing, cruciate retaining TKA implants.
• To evaluate the impact of these variations on the range of motion (ROM) and contact pressures.

Main Methods:

• Utilized a probabilistic finite element model of the Stanmore knee wear simulator to analyze TKA performance under simulated gait loading.
• Varied load inputs (up to 10% SD) and component alignment (0.25 mm, 0.5 degrees SD) to assess their influence on implant kinematics and contact mechanics.
• Compared model predictions with experimental simulator results for semi-constrained implants.

Main Results:

• Model predictions aligned well with experimental data for semi-constrained implants.
• Positional envelopes reached up to 1.8 mm (AP) and 3.4 degrees (IE) for semi-constrained, and 2.6 mm (AP) and 3.7 degrees (IE) for unconstrained implants.
• ROM varied up to 22%, while peak contact pressure variations were below 2 MPa. Loading variability impacted swing phase, while alignment variability affected stance phase kinematics.

Conclusions:

• Loading and alignment variability have distinct effects on TKA kinematics during different gait phases.
• The sensitivity of kinematics and contact characteristics to these variations differs between implant designs.
• Identifying critical parameters influencing TKA performance is key to optimizing implant design and surgical technique.