Investigation on the Effects Induced by Tka Features on Tibio-Femoral Mechanics Part Ii: Tibial Insert Designs

Abstract

Posterior-stabilized (PS) prosthesis have been widely used in total knee arthroplasty (TKA) surgery during the last three decades generally reporting excellent results in long-term studies. Nevertheless, when the patient has nonstable knee envelope, it may require larger degree of restriction in order to manage knee instability. The Semi-constrained version of the PS prosthesis is then introduced, as primary or revision implant, enlarging the size of the post so as to be more restrictive. However, there is a lack of trust from surgeons in this last version based on the intuitive fear that its larger post could lead to higher forces and, therefore, to a premature failure of the post-cam mechanism of the prosthesis. To try to answer this question, the postcam engagement of both designs have been studied under two daily activities, walking and squatting, by means of a finite element analysis (FEA). Kinematics and contact pressures have been evaluated in order to analyze the efforts supported by the prosthesis. The results obtained have shown a change on the kinematics especially along anterior-posterior (AP) direction as well as an increase of contact forces on the post of the semi-constrained design.

Biomechanical analysis of different levels of constraint in TKA during daily activities

“…The constrained condylar knee (CCK) designs are considered as a semi-constrained prosthesis as they rely on a post-cam system like the PS designs, but this design presents a larger post and a deeper femoral box [11,12]. While the post of the conventional PS is slightly rounded, the one of the CCK model is more rectangular with flat lateral and medial surfaces [13]. This design feature is intended to reduce internal-external (IE) rotation compared to the PS design, providing, at the same time, a higher varus and valgus stability from the increased level of constraint [10,13,14].…”

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

“…The tibia is fixed in the region corresponding to the ankle [11,18,24,41]. Loads and kinematics were applied to the femur to dynamically replicate walking and squatting motor [19,22,[34][35][36]. In particular, for the simulated gait task, the boundary conditions were defined by the ISO-14243-1 [22,35] in terms of flexion extension, axial force, anteroposterior translation and internal-external rotation.…”

Sensitivity analysis of the material properties of different soft-tissues: implications for a subjectspecific knee arthroplasty

“…On the other hand, the sensitivity analysis was limited to a maximum flexion of 60° in order to reduce the computational time , but still to get the behaviour of all configuration for the maximum mean flexion reached during gait. External loads and boundary conditions were replicated from experimental tests 54 and from already published numerical studies 5,6,8,9,60 . Details of applied forces are reported in Figure 3.…”

“…Modern finite element models are usually based on medical scans and possess a high accuracy of anatomical realism fundamental for the development of appropriate, reliable and effective tools aimed at supporting clinically-tailored questions 1 . Besides the simulation of the native joints, models are widely used for the prediction of the effects of degenerative pathologies, traumatic events as well as surgical repair and replacement strategie [2][3][4][5][6][7][8] . In particular, they are used for subject-specific analyses and for guiding the surgical pre-planning phase by comparing the effect of different designs of knee prostheses on the same patient [9][10][11][12][13] .…”