Postoperative Flexion Analysis of 3 Rotating-platform Knee Designs

Abstract

Rotating-platform knee implants have successively undergone modifications to improve postoperative flexion. The cruciate-sacrificing Low Contact Stress (LCS) implant (DePuy Orthopaedics, Inc, Warsaw, Indiana) was modified into the cruciate-substituting PFC Sigma RP (ΣRP) implant and further into the PFC Sigma RPF (ΣRPF) implant (DePuy Orthopaedics, Inc). The goal of this study was to determine whether these modifications improved postoperative flexion. Postoperative flexion at 2 years was compared against preoperative flexion with regard to the general demographics of each group.Statistical analysis showed that the pre- to postoperative flexion changes achieved by the ΣRP (14.6°) and the ΣRPF (2.9°) were better (P<.001) than that achieved by the LCS (-10.3°); however, between the ΣRP (14.6°) and the ΣRPF (2.9°), the change was statistically insignificant (P=.045). In subgroups with preoperative flexion less than 125°, postoperative flexion achieved was 100.1° with the LCS, 119.8° with the ΣRP, and 121.3° with the ΣRPF. The difference between the ΣRP and ΣRPF and the LCS was statistically significant (P<.001), but between the ΣRP and the ΣRPF was statistically insignificant (P=.621). In subgroups with preoperative flexion 125° or more, postoperative flexion was 125° with the LCS, 132° with the ΣRP, and 130° with the ΣRPF, with no significant difference between groups (P=.416). Both cruciate-substituting designs produced better postoperative flexion than the cruciate-sacrificing design. The ΣRP, despite less preoperative flexion (P=.004), achieved statistically better postoperative flexion than the LCS (P<.001). In subgroups with comparable preoperative flexion, no statistical difference in postoperative flexion was achieved by the ΣRP and the ΣRPF.

No difference in anterior knee pain between a fixed and a mobile posterior stabilized total knee arthroplasty after 7.9 years

“…Matsuda et al [33] noted that the Nex Gen LPS knee is not fully conformed in the tibio‐femoral articular surface, allowing up to 12 degrees of rotational freedom in full extension. This could be part of the reason why different studies did not find a clinically relevant difference between a mobile‐ and a fixed‐bearing knee [2, 7, 9, 10, 16, 24, 28, 30, 31, 34, 38].…”

Posterior Shift of Contact Point between Femoral Component and Polyethylene in the LCS Rotating Platform Implant under Weight Bearing Condition

“…However, deeper flexion and femoral rollback have been reported after fixed bearing TKA 9 10 11 12 13 14) . Greater range of motion and femoral rollback have been reported in TKA using a Sigma RP-F (DePuy), which is a mobile bearing can and post design 15) . However, these studies all evaluated flexion in a nonweight bearing condition.…”

Mid-term Results of Total Knee Arthroplasty Using PFC Sigma RP-F

“…In the current study, patients with degenerative osteoarthritis obtained excellent results (the mean maximal flexion angle, 135°) at 5 years after TKA using the PFC Sigma RP-F model. There are many short-term follow-up studies showing that the flexion angle and the maximal flexion angle are 27° greater after TKA using the Sigma RP-F model than TKA using the conventional implants4,15-18). Gupta et al4) reported that the mean increase in flexion angle was 10° greater in the PFC Sigma RP-F group than the PFC Sigma RP group.…”