Femorotibial alignment measured during robotic assisted knee surgery is reliable: radiologic and gait analysis

Femorotibial alignment is crucial for the outcome of unicompartmental knee arthroplasty (UKA). Robotic-assisted systems are useful to increase the accuracy of alignment in UKA. However, no study has assessed if the femorotibial alignment measured by the image-free robotic system is reliable. The aim of this study was to determine whether measurement of the mechanical femorotibial axis (mFTA) in the coronal plane with handheld robotic assistance during surgery is equivalent to a static measurement on radiographs and to a dynamic measurement during walking. Twenty patients scheduled for robotic-assisted medial UKA using handheld technology were included in this prospective study. Three measurements of the frontal femorotibial axis were compared: intra-operative acquisition by computer assistance (dynamic, non-weightbearing position), radiographic measurements on long leg X-ray (static, weightbearing position), and by gait analysis during walking (dynamic, weightbearing position). There was no significant difference in the mFTA between computer (174.4 ± 3.4°), radiological (173.9 ± 3.3°), and gait analysis (172.9 ± 5.1°) measurements (p = 0.5). There was a strong positive correlation (r = 0.6577355, p = 0.0016) between robotic-assisted measurements and gait analysis. There was no significant difference in the femorotibial axis measured by the image-free robotic assistance, from the preoperative radiographs or by gait analysis. The reliability of intra-operative measurements of the frontal femorotibial axis by these robotic-assisted systems is acceptable.