# Biomechanical optimization study of posterior tilt extension stems in the repair of tibial plateau bone defects

## TL;DR

This study uses computer models to find the best stem designs for repairing tibial bone defects in knee replacements, aiming to reduce stress and improve implant stability.

## Contribution

The study introduces a biomechanical framework for optimizing posterior tilt angles and stem lengths in tibial plateau defect repairs.

## Key findings

- A posterior tilt of ≤7° with 40mm stems reduced cortical stress in 20% defects.
- 80mm stems with 7°–10° tilt improved stability in 40% and 60% defects but increased cortical stress at 10° tilt.
- Longer stems with moderate tilt angles showed better micromotion reduction in larger defects.

## Abstract

Tibial plateau bone defect represents a pivotal challenge in revision knee arthroplasty, where suboptimal extension stem design predisposes to stress concentration and subsequent prosthesis loosening. Physiological posterior tibial slope (5°–7°) optimizes knee biomechanics, yet bone defects disrupt proximal tibial anatomy, rendering traditional stems biomechanically incompatible. The synergistic optimization of “defect severity-stem length-posterior tilt angle” remains underexplored.

A finite element model was constructed incorporating three defect areas (20%, 40%, 60%), two stem lengths (40mm, 80 mm), and five posterior tilt angles (0°–10°), yielding 30 experimental cohorts. Under 2450N axial loading, stress distribution (cortical/cancellous bone, prosthesis, sleeve) and bone-prosthesis micromotion were quantitatively evaluated.

All micromotion magnitudes remained below the 150 μm osseointegration threshold. In 20% defects, 40 mm stems with ≤7° tilt mitigated cortical stress concentration; 80 mm stems showed lower micromotion but excessive cancellous stress at 10° tilt. In 40%/60% defects, increasing tilt reduced micromotion (37.3%/45.3% reduction), with 80 mm stems exhibiting superior stability. Extreme tilt (10°) in long stems exacerbated cortical stress and prosthesis load.

Based on the finite element analysis results, this study provides a hypothetical reference for the selection of posterior tilt angles of extension stems in the repair of tibial plateau defects: a posterior tilt angle of ≤7° is suggested for 20% defects when using a 40 mm stem; 7°–10° for 40% defects when using an 80 mm stem; and 5°–7° for 60% defects when using an 80 mm stem. This preliminary biomechanical finding offers a basis for exploring personalized implant design, while the realization of precision-based repair and improved prosthesis longevity requires further validation by multi-center clinical data, diverse patient anatomical models (e.g., differences in tibial size and medullary canal morphology), and in vitro experiments.These data need to be verified through multi-center clinical data and in vitro artificial bone experiments.