Introduction: The aim of this study was to compare the clinical, radiological and functional outcome results of the Scorpio PS TKA prosthesis with either a mobile (MB) or fixed bearing (FB) Pe insert. We hypothesized that the MB group would perform better over time in clinical and functional outcome as well as showing a reduction in anterior knee pain occurrence.

Methods: In a prospective, randomised, single centre, multi surgeon clinical study, a total of 100 patients were enrolled equally divided between MB and FB groups. A standard surgical protocol was used for implanting the Scorpio knee prosthesis with either an MB or FB insert. Post-op rehabilitation was standardized and unrelated to insert type. Patients were assessed pre-op and after 3–6-12–24 months post-op. RAND-36 and Knee Society Score (KSS), were assessed as well as pain measurement during functional testing (chair rise and stair climb) using Visual Analogue Scale (VAS) scale. X-rays were assessed for implant positioning, migration, radiolucent lines and patella tilt (using a Skyline view in 30–60 and 90 degrees).

Results: Both tests groups showed a statistical significant decrease of VAS pain score over time (p < 0.01). No significant differences were seen between both groups at any time point. results did show the MB group to have less pain the first postoperative year in both chair rise test and stair climb test tests. No statistically significant differences were found in total range of motion between the two groups. Repeated measures tests showed a significant improvement over time for both groups for KSS and most RAND 35 subscores. There were no significant differences between groups at any given follow up moment. Within 8 out of 9 RAND 36 subdivisions showed the MB group to score non significantly better the first postoperative year. After one year the differences disappeared. Radiology showed stable implants with no progressive radiolucent lines in all patients. No significant differences in patellar tilting were found.

Discussion: Our hypothesis, that the MB prostheses would provide a better ROM and less anterior knee pain, was not confirmed by the results. In our study the MB group showed less decrease in ROM immediately postop. This phenomenon was also seen by Harrington et al. The MB prosthesis regained its ROM after surgery earlier than the FB implants. This difference could potentially be attributed to the implant design and its kinematics. This advantage did not persist and the FB group slowly leveled. In conclusion, our study does not show any clear advantages in terms of function, pain, ROM, general health, radiological evaluation, KSS and RAND 36 of MB compared with FB TKA at a follow-up of 2 years.