Mylène Jansen

170 Chapter 9 The objective of this current study was to evaluate the 1-year results of treatment with the KneeReviver. The primary hypothesis is that KJD using the KneeReviver is clinically effective in the treatment of end-stage knee osteoarthritis below the age of 65 years, based on an increase in both clinical and structural (radiographic JSW) parameters at 1 year as compared to baseline. The secondary hypothesis is that the clinical efficacy and structural repair by KJD using the KneeReviver at 1 year of follow-up is non-inferior to the benefit obtained by using the Dynamic Monotubes in the previously performed RCT studies. Methods Sample size calculation The KneeReviver prospective follow-up study is a registered study with 5 years of follow-up and a sample size calculation based on previous 5-year results (Netherlands Trial Register NL7986). For this interim 1-year analysis, the required sample size was recalculated and based on the 1-year changes over time in the previous RCTs as well as to have the possibility to show non-inferiority. To ensure the primary and secondary hypothesis could be tested reliably, 4 sample size calculations were performed: 1 for both hypotheses and for both the primary clinical and the structural parameter. Primary parameters were the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) for clinical analysis and minimum radiographic joint space width (JSW) for structural analysis. For the changes over time (first hypothesis), G-Power 3.1.9.7 was used with a 2-tailed analysis, an alpha of 0.05, and power of 80%. The input was based on the previous 1-year RCT results for the WOMAC and JSW. For the total WOMAC, this meant a baseline mean of 53.8 points (SD 15.6) and 1-year mean of 80.0 (15.5), with a correlation of 0.397 between the 2 variables. This resulted in a minimal required sample size of 6 patients required to show a change in total WOMAC. For the minimum JSW this number was 22 patients, calculated with a baseline minimum JSW of 0.54 mm (0.95), a 1-year minimum JSW of 1.09 (0.86) and a correlation of 0.556. For the non-inferiority (second hypothesis), the Sealed Envelope online power calculator was used with an alpha of 0.05, power of 80%, and standard deviation (SD) based on the 1-year changes in WOMAC and JSW in the previous RCTs. Based on the WOMAC non-inferiority test, 2/3 of the minimal clinically important difference (MCID) was chosen as non-inferiority limit, viz. 10 points for the WOMAC; the required sample size was 37 patients per group, calculated with a SD of 17.1 for the WOMAC change over time that resulted from the RCT patients. The RCT patients showed a 1-year minimum JSW change of 0.56 mm, which was used as the non-inferiority limit (so at least no worsening of JSW), and a standard deviation of