Rotating Platform versus Fixed-bearing Total Knees: An In Vitro Study of Wear

Abstract

One of the assumed benefits of mobile bearings is the reduction of UHMWPE wear. However, to date, such benefit has not been categorically proven. To test the hypothesis that rotating platform total knee arthroplasty would have less wear than a fixed-bearing of the same design, this in vitro study compared the wear and kinematics (which influence wear) of one type of mobile with fixed-bearing tibial components of otherwise identical design. We tested four fixed bearing (FB) and four rotating platforms (RP) on force control knee simulators using identical ISO standard force inputs and simulated soft tissue restraint for 6 million walking cycles. The internal/external rotations peaked just before toe off, reaching an average maximum of 7°internal (tibial rotation) in the RP, 1.5 times that of the FB, which peaked at approximately 4.5°inter-nally. Two of the RP specimens showed infrequent and mostly temporary dislocations of the UHMWPE insert. The wear rate for the FB averaged 8.14 ± 2.63 mg/million cycles and the RP averaged 6.78 ± 1.74 mg/million cycles. Both were very low wear rates compared with most other implants tested similarly in the same laboratory. We concluded polyethylene wear was similar for both designs.

Survival rates and causes of revision in cemented primary total knee replacement

“…23 Similar polyethylene wear was found for a mobile-bearing rotating platform and a fixed modular bearing in an in vitro study. 28 Another in vitro study, however, concluded that the wear rate of the fixed bearing was four times higher than for the rotating platform, 29 but in two meta-analyses no differences in the incidence of radiolucent lines or clinical outcome were found. 21,30 Recent reports from the NAR did not show differences in pain, function or survival for the LCS Classic, or survival for the LCS Complete, compared to the AGC Universal TKR.…”

Effect of joint laxity on polyethylene wear in total knee replacement

“…crosslinked vs. conventional) (Muratoglu et al, 2007), the conformity of the inlay and the loading conditions (Galvin et al, 2009), as well as the implant concept (e.g. fixed vs. mobile) (Haider et al, 2008) have an effect on PE wear. Additionally implant kinematics are important.…”

“…Additionally, the stiffness of these springs is often too high to represent a sectioned ligament, which commonly exists when implanting a TKR (Benson et al, 2001, Schwenke et al, 2005. Haider et al (2008Haider et al ( , 2002 proposed a triphasic spring model to simulate the knee laxity. They recommended a gap in the AP direction to remove stiffness around the neutral position.…”

Mobile Bearing Concept in Knee Arthroplasty

“…The cautious approach for the efficiency of mobile bearing prostheses is even supported by the results of their biomechanical testing. It has been shown by a simulator based experiment, utilizing six million cycles of repetitive testing of prosthesis movement of mobile bearing designs with rotating platform and one fixed bearing implant, that there was no difference in the amount of in vitro wear (23).…”