The strain distribution in the upper tibia after insertion of two different unicompartmental prostheses

Area of Science:

• Orthopedic biomechanics
• Biomaterials science

Background:

• Understanding proximal tibial strain is crucial for knee arthroplasty outcomes.
• Existing research lacks detailed analysis of strain distribution with different unicompartmental knee prosthesis types.

Purpose of the Study:

• To investigate proximal tibial strain distribution in human autopsy specimens.
• To evaluate the impact of unicompartmental prosthesis insertion and malpositioning on strain patterns.

Main Methods:

• Strain-gauge rosettes were applied to medial proximal tibia in human autopsy specimens.
• Strain measurements were taken before and after implantation of two types of unicompartmental prostheses (constrained and non-constrained).
• Tests were replicated using plastic models to assess prosthesis sensitivity to rotational and positional changes.

Main Results:

• Tensile strain increased significantly (approximately fourfold) anteromedially after prosthesis insertion.
• No significant strain differences were observed between the constrained and non-constrained prostheses in neutral positioning.
• The constrained prosthesis showed altered strain distribution with tibial external rotation; malpositioning of the non-constrained prosthesis also led to significant strain changes.

Conclusions:

• Prosthesis type had minimal impact on strain distribution in neutral alignment.
• Tibial component malpositioning and rotational instability can drastically alter proximal tibial strain patterns.
• These findings highlight the importance of accurate prosthesis placement and alignment in unicompartmental knee arthroplasty to avoid adverse biomechanical effects.