Short-Form New Knee Society Score: What Is Its Responsiveness and Convergent Validity with Other Scores?

The short-form version of New Knee Society Score (SF-NKSS) was designed with a purpose to reduce respondent burden. Literature review revealed only one report by Scuderi et al on responsiveness of derived SF-NKSS, but it was evaluated in two separate patient cohorts pre- and postsurgery. Our study had evaluated responsiveness and convergent validity of derived SF-NKSS in a single, large patient cohort followed longitudinally from preoperative status to over 1 year. Our database of 148 knee arthroplasty patients operated by the same surgeon, whose NKSS, Western Ontario and McMaster Universities Arthritis Index (WOMAC), and 12-item Short-Form Survey (SF-12) scores were prospectively collected preoperatively and postoperatively at 3 and 12 months for a study published earlier, was analyzed for derived SF-NKSS. Responsiveness was evaluated by determining the effect size, standardized response mean (SRM), and ceiling and floor effects. For convergent validity, Pearson's correlation coefficient was used. SF-NKSS was found to be most responsive with the largest effect size and SRM at 3 months (3.02 and 2.50, respectively) and at 12 months (3.58 and 2.92, respectively) with no ceiling or floor effect. SF-NKSS was followed in responsiveness by original NKSS, WOMAC, and SF-12 in a descending order. Convergent validity showed a strong correlation (r = 0.8-1.0; p < 0.001) of SF-NKSS with NKSS and a moderate to strong correlation (r = 0.5-0.6; p < 0.001) with WOMAC and SF-12. We concluded that SF-NKSS is a reliable, highly responsive tool for post-total knee replacement evaluation. It also has the ability to register improvement in the patient's recovery, which can continue even after 1 year. We found that the SF-NKSS can be used interchangeably with the original NKSS.

Postoperative flexion analysis of 3 rotating-platform knee designs.

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.