Abstract
INTRODUCTION
Mobile-bearing knee prostheses have been designed in order to provide less constrained knee kinematics compared to fixed-bearing prosthesis. Currently, there is no evidence to confirm the superiority of either of the two implants with regard to walking performances. It has been shown that subjective outcome scores correlate poorly with real walking performance and it has been recommended to obtain an additional assessment of walking ability with objective gait analysis.
OBJECTIVES
We assessed recovery after total knee arthroplasty (TKA) with mobile- and fixed-bearing between patients during the first postoperative year, and at 5 years follow-up, using a new objective method to measure gait parameters in real life conditions.
METHODS
56 patients with mobile- and fixed-bearing of the same design were included in this randomised controlled double-blinded study and evaluated pre- and post-operatively at 6 weeks, 3 months, 6 months 1 year and 5 years. At each visit a WOMAC and Knee Society Score were calculated and each participant completed an EQ-5D questionnaire. To assess the patients' gait five miniature angular rate sensors mounted respectively on the sacrum and each shank and thigh measured lower limb movement and rotation. The patients walked 30 metres on a flat surface and gait parameters were recorded with a small ambulatory device in order to carry out an objective gait analysis.
RESULTS
Objective recovery was strongly correlated with patients' age. When the whole population was considered, there was no significant difference between groups at any time in objective gait parameters. After separating the population according to their age (less than 71 years old, compared to those of more than 71 years old) a secondary analysis showed that the bearing type can lead to opposite results in different age groups. At five years follow-up, most of the recorded gait parameters (stride length, knee max rotation speed, shank and thigh range of motion, and limp) showed better results for mobile bearing in younger patients, while better gait performances were found systematically with fixed-bearing TKA in older patients.
CONCLUSION
To our knowledge, this is the first study where similarly designed posterior-stabilised knee replacements with fixed- and mobile-bearing have been compared with gait analysis in real-life conditions. We observed systematically differences between mobile and fixed bearing groups, which are confirmed by multivariate analysis. Our results suggest that older patients might not benefit from a mobile bearing TKA and that extended age controlled study should be performed to identify an age, above which fixed bearing should not be the recommended choice. Before choosing the bearing type, surgeons should take into account the age of the patient.
