Patellar Overstuffing in Total Knee Arthroplasty Results in Decreased Extensor Mechanism Efficiency

Area of Science:

• Orthopedic Surgery
• Biomechanical Engineering
• Computational Modeling

Background:

• Patellofemoral offset is a critical factor in total knee arthroplasty (TKA) success.
• Patellar thickness directly influences patellofemoral mechanics, affecting joint function post-TKA.

Purpose of the Study:

• To computationally quantify the effects of altered patellar thickness on key biomechanical parameters in TKA.
• To investigate the impact of patellar
• overstuffing
• and
• understuffing
• on extensor mechanism efficiency (EME), patellar contact moment arm (PCMA), and patellar contact force (PCF).

Main Methods:

• A computational model simulating a cruciate-sacrificing, posterior-stabilized TKA was developed.
• Patellar thickness was modified by ±2mm and ±5mm to simulate
• overstuffing
• and
• understuffing
• across a knee range of motion (ROM) from 0° to 135°.

Main Results:

• Overstuffing
• (2mm and 5mm) decreased EME by up to 12% and 28%, respectively.
• Understuffing
• (2mm and 5mm) increased EME by 8% and 16%, peaking at 25° flexion.
• Increased patellar thickness led to elevated PCMA and PCF, opposing the quadriceps moment arm (QMA).

Conclusions:

• Computational analysis indicates that increased patellofemoral offset (
• overstuffing
• ) in TKA reduces EME and increases PCMA/PCF.
• These biomechanical changes may contribute to abnormal patellofemoral mechanics, potentially causing anterior knee pain and quadriceps weakness after TKA.
• Optimizing patellar thickness is crucial for improving functional outcomes in TKA patients.