Are asymmetric designs of tibial components superior to their symmetric counterparts for constrained condylar total knee arthroplasty using metal block augmentation?

Purpose: In total knee arthroplasty (TKA), asymmetric tibial components have been developed alongside symmetric tibial components to enhance bony coverage at the tibia. In primary TKA and revision TKA for patients with significant bone defects, augmentation is employed to fill the bone defect. However, there have been no reports on bony coverage of the tibial component of the revision system in the cases of bone defects. Therefore, we simulated bone defects using CT and compared the bony coverage of asymmetric and symmetric tibial components in the revision TKA system.

Methods: This study included 45 patients (50 knees involved) with medial osteoarthritis. Preoperative CT scans were used to simulate placement using ZedKnee. Three models were evaluated: Persona Revision PCCK (Zimmer) for the asymmetric component, NexGen LCCK (Zimmer) for the symmetric component, and the ATTUNE revision system (Depuy-Synthes). A 130-mm stem extension was utilized. Augmentations of each thickness were placed to simulate bone defects of 5, 10, and 15 mm. The coverage, overhang, and underhang rates were measured for each slice and compared among the models.

Results: In terms of coverage, the rate was greater for PCCK at 0 mm, and only ATTUNE exhibited a significantly lower coverage at 5 and 10 mm. There was no significant difference in coverage at 15 mm. At 0 mm, PCCK demonstrated less posterior underhangs. At 5 and 10 mm, PCCK showed less anterior overhang but more anterior underhang. At 15 mm, PCCK had a less anterior overhang, with an overhang in the posterior region but less underhang. When overhang and underhang were combined and compared, the asymmetric component generally yielded superior results.

Conclusion: In the cases of bone defects, asymmetric components demonstrated reduced anterior overhang and decreased posterior underhang, resulting in greater bone coverage. This may contribute to improved long-term outcomes in the revision TKA system.