Abstract
Objective: We performed total knee arthroplasty (TKA) with a low-contact-stress rotating-platform (LCS RP) mobile-bearing prosthesis (Depuy, Warsaw, IN) in patients with osteoarthritis (OA) of the knee. The purpose of the present study was to measure the potential effects of the posterior condylar offset, the tibial slope, and several other factors on the range of knee flexion.
Methods: A total of 120 patients (148 affected knees) who had undergone LCS RP TKA 6 months or more prior to the start of the study were enrolled [37 men (41 affected knees) and 83 women (107 affected knees) with a mean age of 77.4±5.7 years (range: 65-90 years) ]. We developed a simple index, the posterior condylar offset ratio (PCOR), which is the ratio of the posterior offset to the diameter of the patella on a true lateral view, and we investigated the relationship between PCOR and the postoperative range of knee flexion and the postoperative tibial slope. We also investigated the relationship between the preoperative PCOR and the postoperative range of knee flexion and the condylar twist angle, joint line, patella height, lateral shift ratio, tilting angle, and preoperative flexion. Using The Knee Society total knee arthroplasty roentgenographic evaluation and scoring system, we measured the alignment of these components. The relationships were assessed using Spearman’s correlation coefficient (r).
Results: We found no correlation between postoperative PCOR and the postoperative range of knee flexion or postoperative tibial slope (r = 0.02, r =-0.10), and no correlation between the postoperative range of knee flexion and postoperative tibial slope (r =0.01). In addition, we found no correlation between the postoperative range of knee flexion and the other factors we measured, but we did find a moderate correlation between the postoperative range of knee flexion and the preoperative range of knee flexion (r =0.48).
Conclusion: In this study, when using LCS RP TKA, we found that the only factor correlated to the postoperative range of knee flexion was the preoperative range of knee flexion. This suggested that we need to improve the preoperative range of knee flexion contracture before performing TKA.
