Radiostereometric measurement of implant migration in robotically assisted vs conventional bi-cruciate stabilized cemented total knee arthroplasty: secondary analysis of a randomized controlled trial.

Background and purpose: Robotically assisted computer navigation (robotic) has been developed to improve the positioning in total knee arthroplasties (TKAs), attempting to achieve better functional results and longevity of the prostheses. However, the benefit of robotics is still controversial. The aim of our study was to compare migration between robotic and conventional techniques in cemented bi-cruciate stabilized TKAs, using radiostereometric analysis (RSA) based on a secondary analysis of a randomized controlled trial (RCT).

Methods:  We enrolled 60 TKA patients from one hospital (2020-2021), with osteoarthritis or arthritic disease. The patients were examined up to 24 months after the surgery, to estimate the mechanical stability of the tibial component. The maximum total point motion (MTPM) representing the magnitude of migration, the largest negative (subsidence) and positive (lift-off) value for y-translation, and prosthetic rotations were measured. The migration in the 2 groups was compared and the precision evaluated.

Results:  51 RSA marked TKAs were available for a comparison of tibial migration between robotically assisted (n = 26) and conventional operations (n = 25). The MTPM in the first year was 0.44 mm and 0.64 mm, and at 24 months 0.46 mm and 0.75 mm, for the conventional and the robotic groups, respectively. The robotic group migrated more than the conventional group at 2 years, 0.21 mm (95% confidence interval [CI] 0.05-0.44; P = 0.01). The overall median MTPM for the investigated implants (both groups) up to 12 months was 0.54 mm (CI 0.44-0.63), and 0.19 mm between 12 and 24 months (CI 0.16-0.22). The magnitude of migration and rotation around the 3 axes was small for both groups, but flexion/extension migration of the tibial component was slightly higher in the robotic group 0.14° (CI 0.00-0.33; P = 0.049).

Conclusion:  MTPM and flexion/extension migrations of the tibial component were higher for the robotic group, up to 24 months. The overall migration pattern for the bi-cruciate stabilized implant was acceptable.