A Best-Fit of an Anatomic Tibial Baseplate Closely Parallels the Flexion-Extension Plane and Covers a High Percentage of the Proximal Tibia.

There are no reports of in vivo internal-external (I-E) rotational alignment and coverage of the proximal tibia after performing a best-fit method of an anatomically designed and asymmetrically shaped tibial baseplate during calipered kinematically aligned (KA) total knee arthroplasty (TKA). We hypothesized that a best-fit plane sets the anterior-posterior (A-P) axis of the anatomic baseplate closely parallel to the flexion-extension (F-E) plane of the knee and covers a high percentage of the proximal tibia. A total of 145 consecutive primary TKAs were prospectively collected. The calipered KA method and verification checks set the positions and orientations of the components without ligament release in all knees without restrictions on the preoperative deformities. A best-fit method selected one of six trials of anatomic baseplates that maximized coverage and set I-E rotation parallel to and within the cortical edge of the proximal tibia. The angle between the transverse axes of the components (i.e., the deviation of the A-P axis of the anatomic baseplate from the F-E plane of the native knee) and the cross-sectional area (CSA) of the proximal tibia were measured on postoperative computerized tomographic scans. The mean deviation of the anatomic baseplate from the F-E plane was 2-degree external ± 5 degrees. The mean coverage of the proximal tibia was 87 ± 6% (CSA of baseplate from the manufacturer/CSA of proximal tibia × 100). The anatomic baseplate and best-fit method adequately set I-E rotation of the baseplate closely parallel to the F-E plane of the knee and cover a high percentage of the proximal tibia.