Asymmetric polyethylene inserts promote favorable kinematics and better clinical outcome compared to symmetric inserts in a mobile bearing total knee arthroplasty

Abstract

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

“…The decrease in stress will then bring to better performance of the tibial component, in terms of cement stability and lift-off: the lesser the stress coming from the femoral component, the less stress at the tibial component-bone interface. This outcome is thus in agreement with the findings of the previous study, 15 and it can be a reason for many patients implanted with the AD to feel less pain rather than the ones with the SD.…”

“…The biomechanical study showed that the ranges for the rotation between tibia and insert are in agreement with the clinical-numerical study previously carried out and published 15,33 ; the AD insert design is furthermore able to internally/externally rotate in agreement with the femur, thus limiting the relative motion between the two. This factor is in agreement with the findings of the previous study [ 15], which stated that the stresses found in case of AD design were lower if compared to the ones in SD: indeed, the higher compliance of the insert with femoral internal-external rotation enables contact areas between the two components to be broader and to maintain this situation along the whole motion, resulting then in the lower stresses.…”

“…The biomechanical study showed that the ranges for the rotation between tibia and insert are in agreement with the clinical-numerical study previously carried out and published 15,33 ; the AD insert design is furthermore able to internally/externally rotate in agreement with the femur, thus limiting the relative motion between the two. This factor is in agreement with the findings of the previous study [ 15], which stated that the stresses found in case of AD design were lower if compared to the ones in SD: indeed, the higher compliance of the insert with femoral internal-external rotation enables contact areas between the two components to be broader and to maintain this situation along the whole motion, resulting then in the lower stresses. This result is due to the design of the AD insert which, while maintaining high congruence in the medial sector, allows the lateral condyle to slide on its plateau; this peculiarity allows the prosthesis to follow the variation of the physiological internal-external rotation axis (which occurs during the flexion extension movement analyzed), consequently leading to the minimization of rotation between the AD insert and the femoral component.…”

“…The PCL was preserved in all patients, and ligaments release was avoided whenever possible by the use of a Minimally Invasive alignment device (EMAS, Extra-Medullary Alignment system) offered by the manufacturer. [15][16][17] In detail, the EMAS device allows for femoral component positioning and joint balancing without requiring the use of intramedullary rods, avoiding violation of the intramedullary canal, which can potentially enable the incidence of fat embolism and perioperative blood loss or femoral fractures risk in the case of osteoporotic bone. 2,15,18,19 Particular care was taken to minimize the tibial bone cut, in order to preserve bone integrity.…”

“…[15][16][17] In detail, the EMAS device allows for femoral component positioning and joint balancing without requiring the use of intramedullary rods, avoiding violation of the intramedullary canal, which can potentially enable the incidence of fat embolism and perioperative blood loss or femoral fractures risk in the case of osteoporotic bone. 2,15,18,19 Particular care was taken to minimize the tibial bone cut, in order to preserve bone integrity. In detail, the 10 mm insert (the smallest thickness provided by the manufacturer) was used in 88% of the cases: as SD insert, the 10 mm insert was used on 127 patients, the 12 mm on 20 patients and the 14 mm for the remaining 4 patients; for the AD group, 135 patients received the 10 mm insert and the remaining 17 patients received the 12 mm insert; no patient received the 14 mm insert.…”