Background:
Radiostereometric analysis (RSA) studies have shown that the continuous migration of tibial components is predictive of aseptic loosening following total knee arthroplasty (TKA). In the present study, we investigated whether accurate sizing and placement of tibial components are related to the degree of implant migration as measured with use of RSA.

Methods:
A total of 111 patients who underwent TKA surgery with a cementless tibial component were followed for a period of 2 years postoperatively, during which implant migration was assessed with use of RSA. RSA was performed within 7 days postoperatively and after 3, 6, 12, and 24 months. Postoperative radiographs were evaluated for component size and placement in the tibia. The evaluations were performed by experienced knee surgeons who were blinded to the migration data and clinical outcomes. A multivariable linear regression analysis was conducted.

Results:
Continuous implant migration (i.e., migration occurring between 12 and 24 months postoperatively) had a negative association with tibial component size (coefficient [B], −0.2; 95% confidence interval [CI], −0.33 to −0.08). Subsidence was associated with the absence of posterior cortical bone support (B, −0.7; 95% CI, −1.09 to −0.28), the absence of lateral cortical bone support (B, 0.8; 95% CI, 0.29 to 1.37), frontal-plane varus malalignment (B, 0.6; 95% CI, 0.12 to 1.16), and component undersizing (B, −0.4; 95% CI, −0.06 to −0.68). Posterior tilt was associated only with undersizing (B, 0.6; 95% CI, 0.27 to 1.11).

Conclusions:
Undersized cementless tibial components are at a higher risk for poor fixation with continuous migration following TKA. Therefore, a higher risk of aseptic loosening should be expected.