Mechanical evaluation of mobile bearing knees

Area of Science:

• Orthopedic biomechanics
• Biomaterials science

Background:

• Mobile bearing knee prostheses (MBK) offer potential advantages in replicating natural knee kinematics.
• Understanding the mechanical behavior of MBK designs is essential for optimizing patient outcomes.

Purpose of the Study:

• To assess the in-vitro mechanical performance of a novel mobile bearing knee prosthesis.
• To evaluate the displacement of the mobile bearing surface during simulated knee flexion.
• To analyze contact pressure distribution on bearing surfaces under varying radii of curvature.

Main Methods:

• Radiographic analysis of 15 cadaveric knees to measure mobile bearing displacement from 0 to 120 degrees flexion.
• Use of pressure-sensitive film to analyze contact pressure distribution on femoral and tibial bearing surfaces.
• Testing with metal cylinders of varying radii of curvature to simulate femoral components.

Main Results:

• Mobile bearing surface displacement increased with flexion, averaging 1.4 mm at 0 degrees and 7 mm at 120 degrees.
• Uniform contact pressure was observed on the femoral bearing surface with 0.1-0.2 mm interference.
• Uniform pressure on the tibial bearing surface was achieved when radii of curvature were equal.

Conclusions:

• The MBK prosthesis, by retaining the posterior cruciate ligament, allows natural ligamentous guidance of motion.
• Uniform pressure distribution is achievable in closely conforming mobile bearing surfaces.
• Minor variations in radii of curvature significantly influence pressure distribution, highlighting the importance of precise manufacturing.