Joint line restoration and alignment after conventional versus robotic unicompartmental knee arthroplasty

Abstract

Introduction: Robotic technique improves accuracy of unicompartmental knee replacement. This study aims to directly compare the CT-based robotic, imagefree robotic and conventional techniques in relation to coronal alignment, joint line restoration and posterior slope. Methodology: This retrospective case control study compared 175 unicompartmental knee arthroplasties performed using conventional spacer block technique (n=52), imagefree robotic system (Navio) (n=57) or CT based robotic system (Mako) (n=66) by a single surgeon between May 2012 and May 2018. Preoperative and postoperative short films were measured for anatomical axis, joint line height and posterior slope. Results and Analysis: There were no significant differences between the groups for age, BMI, laterality, preoperative anatomical axis or slope. The mean post operative posterior slope was highest in the conventional group (5.58˚+/-2.72), followed by Mako (3.59˚ +/- 2.02), with Navio being the smallest (2.45˚+/-2.36). The differences between groups were all statistically significant. If >7˚ was considered an outlier, the percentage of outliers were 25%, 3.5% and 5% for conventional, Navio and Mako respectively. Postoperative mean anatomical axes were 1.49˚+/-2.75 valgus for conventional, 1.25˚+/-2.61 valgus for Navio and 0.27˚+/-2.93 for Mako. Mako produced less overcorrection when compared to conventional (p=0.023) but was not significant compared to Navio(p=0.053). The joint line was significantly lower in conventional (-1.57mm+/-1.62) when compared with Navio (-0.3mm+/-1.06) (p<;0.001) or Mako (-0.26mm+/-0.98)(p<0.001). There were no significant differences between Navio and Mako (p=0.65). Discussion and Conclusion: Both robotic systems produced less outliers in posterior slope, less joint line depression and less overcorrection. All these factors may reduce lateral arthritis progression and improve implant survivorship.