Experimental and clinical analysis of the use of asymmetric vs symmetric polyethylene inserts in a mobile bearing total knee arthroplasty

Abstract

This study compared the effects of symmetric and asymmetric designs for mobile bearing polyethylene insert for total knee arthroplasty (TKA), both clinically and biomechanically through experimental cadaver tests. Methods: 303 patients implanted with a mobile bearing TKA were retrospectively analyzed up to 2-year follow-up with relative scores. The same femoral and tibial components were used for all the patients; 151 patients received a Symmetric Design (SD) insert and 152 an Asymmetric Design (AD). A biomechanical experimental test was performed to improve the comprehension of the clinical results, analyzing passive squat on 5 cadaveric knee specimens: internal-external rotations of femur and tibial insert respect to the tibia tray were analyzed in native and implanted configurations (with both symmetrical and asymmetrical inserts for each specimen). Results: After surgery, patients' average flexion improved from 105 • (with preoperative extension deficit of 5 • ), to 115 • (SD-group) and 120 • (AD-group) at the 2-year follow-up. There was no postoperative extension deficit. AD-group presented better ability to perform certain routines and wasn't affected by any pain, while anterolateral pain was reported in some SD-group patients. The experimental tests returned no statistically relevant difference in tibio-femoral flexion-extension and internal-external rotations among all the three configurations tested; a statistically significant difference is found for insert-tray internal-external rotations between SD and AD configurations; in details, the AD insert showed insert-tray angles comparable to the ones found for femoral component-tibial tray, while the SD insert returned lower angular values. Conclusion: Clinically and biomechanically, an asymmetric mobile bearing insert could represent a valid alternative to symmetric mobile bearing insert.

Application strategy of finite element analysis in artificial knee arthroplasty

“…Under the condition of the same tibial and femoral components, symmetric and asymmetric polyethylene inserts were used in 151 and 152 patients, respectively. During standing and squatting, the contact stress in the tibial component was lower in those with asymmetric inserts (Figure 1B), at the 2-year follow-up, the asymmetric polyethylene insert group was able to perform certain routine movements better and without any pain, while patients in the symmetrically designed polyethylene group reported pain, validating the FEA results (Castellarin et al, 2021).…”

No difference between mobile and fixed bearing in primary total knee arthroplasty: a meta-analysis

“…The polyethylene inlay of FB implants is secured on the tibial plateau. On the other hand, MB implants allow rotation of the polyethylene inlay around its longitudinal axis, miming the physiological kinematics of the knee and promoting a wider range of motion [ 22 , 34 , 93 ]. Previous evidence suggested that MB may promote greater outcomes in functional scores and complications [ 40 , 44 , 45 , 75 , 95 ].…”

Mobile medial pivot (lateral slide) type total knee arthroplasty exhibits a medial pivot pattern: three-dimensional motion analysis using cadaveric knees

“…2 Department of Orthopaedic Surgery, Niigata Medical Center, Niigata, Japan. 3 Department of Health and Sports, Faculty of Health Sciences, Niigata University of Health and Welfare, Niigata, Japan.…”

“…In recent years, TKA, which has both a medial pivot mechanism with high medial constraint and a mobile mechanism of insert, has been developed and clinically used. However, previous studies have only described kinematics of up to less than 90° of the knee joint [3, 4] and the dynamic kinematics of this mobile medial pivot‐type TKA (MMPTKA) in the deep flexion phase remains unclear. Whether MMPTKA, which employs both MBTKA and MPTKA mechanisms, can demonstrate both advantages at the same time also remains unclear.…”