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New mobile-bearing TKA with unique ball and socket post-cam mechanism offers similar function and stability with better prosthesis fit and gap balancing compared to an established fixed-bearing prosthesis



A mobile-bearing (MB) posterior-stabilized total knee arthroplasty (TKA) system with ball and socket post-cam mechanism has been developed with the aims of better prosthesis fit and enhanced stability. However, the data are limited to compare its clinical outcomes with an already established fixed-bearing (FB) implant design.


This is a prospective randomized study comparing 260 patients in the MB group and 133 patients in FB group with a minimum 2 years of follow-up. Intraoperative variables, post-operative functional outcomes and incidence of adverse events were compared.


MB group showed better prosthesis fit as the incidence of over-hang of femoral component at junction (medial: 1% vs. 5% and lateral: 2% vs 4%, p < 0.001) and trochlea (medial: 2% vs 30%, p = 0.042 and lateral: 13% vs 21%, p = 0.015) was less than FB group. MB group also showed better gap balancing as the incidence of medio-lateral gap difference more than 2 mm was less in flexion (2.3% vs. 16%, p < 0.001) and extension (3.1% vs. 9.8%, p = 0.005). Post-operative functional outcomes and incidence of adverse events showed no difference between the two groups at 2 years.


New MB design offers similar functional outcomes and stability along with better intraoperative prosthesis fit and gap balancing compared to an established fixed-bearing design. Hence, this new MB design could be an alternative prosthesis of choice for posterior-stabilized TKA.

Level of evidence


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We thank Jeong Seong Seong, MS, for her contribution in data collection for this study.


This research received grants from the company B.Braun—Aesculap, Tuttlingen, Germany.

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Correspondence to Tae Kyun Kim.

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Tae Kyun Kim has received royalties from B-Braun and Smith and Nephew. The other authors declare that they have no conflict of interest.

Ethical approval

This study was approved by the Institutional Review Board of Seoul National University Bundang Hospital (E-1406/254-001)

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All procedures performed in studies involving human participants were in accordance with the ethical standards of the institutional and/or national research committee, and with the 1964 Helsinki declaration and its later amendments or comparable ethical standards.

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Each author certifies that his or her institution has approved the human protocol for this investigation that all investigations were conducted in conformity with ethical principles of research, and that informed consent was obtained. This work was performed at the Joint Reconstruction Center, Seoul National University Bundang Hospital.

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Tiwari, V., Meshram, P., Park, C.K. et al. New mobile-bearing TKA with unique ball and socket post-cam mechanism offers similar function and stability with better prosthesis fit and gap balancing compared to an established fixed-bearing prosthesis. Knee Surg Sports Traumatol Arthrosc 27, 2145–2154 (2019). https://doi.org/10.1007/s00167-019-05430-5

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  • Total knee arthroplasty
  • Mobile bearing
  • Prosthesis fit
  • Function
  • Outcome