Coronal alignment-related mediolateral load distribution and polyethylene wear in a medial-pivot total knee arthroplasty design

While mechanical alignment in total knee arthroplasty aims for a neutral hip-knee-ankle angle, kinematic alignment preserves the native joint line, often allowing residual varus or valgus. Clinically, constitutional variations in alignment affect the coronal joint moments and the mediolateral load distribution, but the impact on polyethylene wear remains unclear.

Wear of a medial pivot total knee arthroplasty insert (MS 5C^®, implantcast GmbH, Germany) was evaluated in a knee wear simulator replicating the walking cycle. Inserts were tested under three conditions representing overall lower-limb coronal alignment and the associated mediolateral load distribution: neutral (60% medial / 40% lateral), varus (70% / 30%), and valgus (50% / 50%), with three (n = 3) dynamically loaded inserts and one load-soak control per condition. Testing followed ISO 14243-1:2009 over 5 million cycles. Gravimetric wear and wear patterns were assessed.

A numerical trend was observed among the groups: The varus-related load distribution demonstrated the lowest overall wear (4.83 ± 1.06 mg/million cycles), whereas the valgus group produced the highest wear (9.43 ± 1.47 mg/million cycles); the neutral group was intermediate (6.81 ± 3.07 mg/million cycles). However, these differences did not reach statistical significance. Visual inspection revealed medial-dominant wear in all groups, with increased lateral wear under valgus-related load distribution.

Overall lower-limb coronal alignment and the associated mediolateral load distribution appear to influence polyethylene wear in total knee arthroplasty. The observed numerical trend suggests that alignment-related changes in mediolateral load distribution may influence polyethylene wear patterns in this medial-pivot TKA design. Further studies are required to determine the clinical relevance of these observations.