Contact pressure and three-dimensional tracking of unresurfaced patella in total knee arthroplasty

Ten fresh-frozen cadaver knees were studied to investigate the contact pressure distribution and three dimensional (3-D) tracking of the patella under consecutive three different conditions. They have included (a) an intact knee, (b) the unresurfaced patella in bicompartmental knee arthroplasty (Bi-TKA), and (c) the resurfaced patella in tricompartmental knee arthroplasty (Tri-TKA). A pressure-sensitive conductive rubber (PSR) sensor system was developed to measure the patellar contact pressure dynamically, and two sets of high resolution video cameras with direct linear transformation method was used to measure the 3-D patellar tracking. Total contact area on the patella was decreased in Bi-TKA, and further decreased in Tri-TKA. However, patellar contact area was significantly less in Tri-TKA than in the intact knee in 0 to 100 degrees of knee flexion (P < 0.01), and no statistical difference was seen between Bi-TKA and the intact knee. The mean contact pressure was conversely highest in Tri-TKA, followed by Bi-TKA, and intact knee. The mean contact pressure of Tri-TKA was significantly higher than intact knee in 50 to 100 degrees of knee flexion (P < 0.05), but no statistical difference was seen between Bi-TKA and intact knee. Three-dimensional patellar tracking showed the same tracking pattern in intact knee, Bi-TKA, and Tri-TKA. The results of this study suggest that in this type of TKA system the patellofemoral congruity is not significantly reduced in Bi-TKA, and we could leave the patella unresurfaced during TKA.