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A kinematic comparison of fixed- and mobile-bearing knee replacements

¹ 60 Regentiestraat, B-9100 Sint, Niklaas, Belgium.
² Department of Mechanical & Aerospace Engineering, University of Florida, Gainesville, Florida 32611-6250, USA.
³ University Hospital Kuleuvem, U. Z. Pellenberg, Weligerveldt 1, B-3212 Lubbeek, Belgium.

Correspondence should be sent to Dr H. P. Delport; e-mail: hendrik.delport{at}pandora.be

Mobile-bearing posterior-stabilised knee replacements have been developed as an alternative to the standard fixed- and mobile-bearing designs. However, little is known about the in vivo kinematics of this new group of implants. We investigated 31 patients who had undergone a total knee replacement with a similar prosthetic design but with three different options: fixed-bearing posterior cruciate ligament-retaining, fixed-bearing posterior-stabilised and mobile-bearing posterior-stabilised. To do this we used a three-dimensional to two-dimensional model registration technique. Both the fixed- and mobile-bearing posterior-stabilised configurations used the same femoral component. We found that fixed-bearing posterior stabilised and mobile-bearing posterior-stabilised knee replacements demonstrated similar kinematic patterns, with consistent femoral roll-back during flexion. Mobile-bearing posterior-stabilised knee replacements demonstrated greater and more natural internal rotation of the tibia during flexion than fixed-bearing posterior-stabilised designs. Such rotation occurred at the interface between the insert and tibial tray for mobile-bearing posterior-stabilised designs. However, for fixed-bearing posterior-stabilised designs, rotation occurred at the proximal surface of the bearing. Posterior cruciate ligament-retaining knee replacements demonstrated paradoxical sliding forward of the femur.

We conclude that mobile-bearing posterior-stabilised knee replacements reproduce internal rotation of the tibia more closely during flexion than fixed-bearing posterior-stabilised designs. Furthermore, mobile-bearing posterior-stabilised knee replacements demonstrate a unidirectional movement which occurs at the upper and lower sides of the mobile insert. The femur moves in an anteroposterior direction on the upper surface of the insert, whereas the movement at the lower surface is pure rotation. Such unidirectional movement may lead to less wear when compared with the multidirectional movement seen in fixed-bearing posterior-stabilised knee replacements, and should be associated with more evenly applied cam-post stresses.

This article has been cited by other articles:

				S. Hamai, H. Miura, H. Higaki, T. Shimoto, S. Matsuda, and Y. Iwamoto Evaluation of impingement of the anterior tibial post during gait in a posteriorly-stabilised total knee replacement J Bone Joint Surg Br, September 1, 2008; 90-B(9): 1180 - 1185. [Abstract] [Full Text] [PDF]

				Y.-H. Kim, S.-H. Yoon, and J.-S. Kim The long-term results of simultaneous fixed-bearing and mobile-bearing total knee replacements performed in the same patient J Bone Joint Surg Br, October 1, 2007; 89-B(10): 1317 - 1323. [Abstract] [Full Text] [PDF]

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