BackgroundLong-term results of the 'classic’ low contact stress (LCS) total knee replacement (TKR) have been satisfactory; nonetheless, design changes have been made which resulted in the 'complete’ LCS TKR. The aim of this study is to compare the 5-year incidence of revision and midterm clinical performance before and after introduction of the 'complete’.MethodsA retrospective cohort analysis was conducted on 100 primary uncemented TKRs of both designs. At 5-year follow-up, revision and reoperation rates were determined for these 200 TKRs. Knee Society score (KSS), the Oxford Knee score (OKS) and range of motion were determined for 143 TKRs.ResultsIn the 'classic’ cohort, 3% of the TKRs were revised compared with 5% in the 'complete’ cohort (p = 0.72).The mean KSS was 134.1 (SD 38.3) in the 'classic’ cohort compared to 135.0 (SD 42.8) in the 'complete’ cohort (p = 0.89). Of the 'complete’ TKRs, 35.2% scored within the lowest quartile of the KSS knee compared to 16.7% of the 'classic’ TKRs (p = 0.01). The OKS was 23.3 (SD 9.3) in the 'classic’ cohort compared to 22.5 (SD 10.1) in the 'complete’ cohort (p = 0.45). More than 5° flexion contracture was only found in four patients in the 'complete’ cohort (p = 0.04).ConclusionsNo statistical difference in revision rate and average scores for midterm clinical performance was observed between the 'classic’ and the 'complete’. However, the 'complete’ cohort had a higher percentage of KSS Knee in the lowest quartile, which suggests a clinical relevant difference compared with the 'classic’. Further investigation in future studies with new designs is needed.