Principles of a 3D printed mechanical device for total knee balancing.

Area of Science:

• Orthopedic surgery
• Biomechanical engineering
• Medical device design

Background:

• Accurate implant alignment and soft-tissue balancing are critical for successful total knee arthroplasty (TKA).
• Current methods for assessing knee balance during TKA can be subjective and lack precise quantitative feedback.

Purpose of the Study:

• To design and evaluate novel mechanical balancing devices for TKA.
• To provide objective, numerical data to guide ligamentous releases and bone cut modifications for achieving knee balance.

Main Methods:

• Two 3D-printed mechanical balancing devices, 'Pistol Grip' and 'In-line', were designed.
• The Pistol Grip device uses a lever system to indicate differential forces, while the In-line device quantifies absolute forces on each condyle.
• Devices were tested on a rig simulating knee balance and imbalance conditions.

Main Results:

• The Pistol Grip design's deflection correlates to a 2 mm elevation or 3-degree angular change, guiding ligament adjustment or bone cuts.
• The In-line design's deflection indicates up to a 40 N load on the condyle.
• Both devices successfully provided data to guide TKA balancing.

Conclusions:

• The developed mechanical balancers offer a simple, electronic-free method to achieve accurate knee balance in TKA.
• These devices can assist surgeons in making informed decisions regarding ligamentous releases and bone cut adjustments.
• The designs are user-friendly and can be integrated into standard surgical procedures.