Modular Polyethylene Inserts for Total Knee Arthroplasty: Can Surgeons Detect 1-mm Thickness Increments?

Some manufacturers have introduced polyethylene (PE) inserts in 1-mm increment thickness options to allow for finer adjustments in total knee arthroplasty kinematics.

Two surgeons with extensive experience performed 88 total knee arthroplasties using implants with 1-mm PE inserts. After trial components were inserted and the optimal PE thickness was selected, the insert was removed and a trial insert size was randomly chosen from opaque envelopes (1-mm smaller, same size, and 1-mm larger). The knee was re-examined and the surgeon determined which size PE had been placed.

Surgeons reliably determined insert thicknesses in 62.5% (55 of 88; P = .050) of trials. Surgeons were not able to accurately detect 1-mm incremental changes of trial PE implants on a consistent basis.

The potential clinical usefulness of this concept should be further evaluated.