We investigated proximal tibial cutting surface in total knee replacement arthroplasty to improve its coverage and get basic data for developing more adequate tibial components for Koreans.

Of cases of total knee replacement arthroplasty performed by one surgeon between September 1995 and October 1996, we chose 100 cases with no bony defect on resected tibial surface. We traced the outline of tibial resection margin manually and then, decided the most adequate size for each tibial tray from 5 companies, AGC (Biomet, Warsaw, USA), Advantim (Wright medical technology, Arlington, USA), AMK (DePuy, Warsaw, USA), MGII (Zimmer, Indiana, USA), and Series 7000 (Osteonics, New Jersey, USA). We divided the tibial cutting surface with 12 quadrants by 30 degree radian. Then, we overlaped both images (traced tibial surface margin and tibial tray) on the computer and fixed the position when we got the largest coverage of area. From this position we calculated the coverage, underhang and overhang ratios by pixel counts. During this process, we discarded 20 cases because of inadequate overlapping.

The overall average ratio of coverage was 82.3%, underhang 17.3%, and overhang 6.0%. The consequence of good coverage and minimal underhang were posterolateral, posteromedial, anterolateral, anteromedial and posterior aspects sequentially. But the posterior side was more overhanged by tibial component than anterior side.

We feel that improving coverage on posterior and anteromedial portion is key to increasing the coverage ratio of proximal tibia in total knee replacement arthroplasty.