Biomechanical analysis of the post-cam mechanism in a TKA: comparison between conventional and semi-constrained insert designs

Abstract

Posterior-stabilized (PS) total knee arthroplasty (TKA) designs were introduced to compensate for the resected or deficient posterior cruciate ligament and to avoid paradoxical anterior sliding of the femur. Knee joint stability may differ among patients and, therefore, orthopaedic companies developed several solutions to compensate for these differences. In particular, conventional PS designs are used for conventional TKA and semi-constrained PS designs are mainly applied in revision surgery or in conventional surgery when there is a compromised soft tissue envelope. However, despite good functional long-term results, a better understanding of forces acting on the post of the polyethylene insert is needed to find an eventual correlation with the risk of post-cam failure or loosening of the tibial baseplate for the two PS solutions. To the authors' best knowledge, no literature data is currently available to compare the two solutions. In this paper, a validated numerical model was developed to analyse and compare the posterior of the post-cam mechanism of the same TKA design with conventional and semi-constrained inserts during several motor tasks. For each solution, different motor tasks show different values of maximum post-cam force. Comparing the two solutions, a general slightly higher force (range between 3 and 5%) is observed in the semi-constrained solution. The results concerning the conventional solution are in agreement with the literature. After this analysis, we can report that a semi-constrained design shows only slightly higher posterior post-cam contact force, and thus would not be expected to significantly increase the risk of failure of the post-cam mechanism, as compared to a conventional PS design.

Analysis of Biomechanical Differences Between Condylar Constrained Knee and Rotating Hinged Implants: A Numerical Study

“…Even if a validated model was adopted in the present work, several assumptions were made during the implementation of the FE models: first, the different structures are based on only one geometry so no variation in the anatomy of the specimen was taken in consideration; however, this approach has already been used in literature studies for similar knee biomechanical analyses [28,36,39,40]. Only one implant design was chosen to represent each level of constraint, but it is to be noted that the aim of the study was to compare 2 different constrain levels and not 2 specific designs.…”

“…As revision TKA solutions, the Legion Revision Condylar Constrain Knee (Smith & Nephew, Memphis, TN) and the RT-PLUS Rotating Hinged prostheses (Smith & Nephew, Memphis, TN) were taken respectively as CCK and RTH implants. The CCK implant used constrains, as reported by previous study [28], varus-valgus, and internal-external rotations together with mediolateral translation.…”

“…To ream the intramedullary canal, numerical models of the surgical rasps were virtually created, to exactly reproduce all the steps of the actual implantation procedure. To define the position of the stem in the numerical models, the cortex engagement of 3 edges of the stem was recognized [28].…”

“…CCK systems have been introduced more recently and are generally assumed to be less constrained than RTH designs, so their use has become increasingly popular as the alternative to the hinged prostheses in cases of intermediate severity [5]. This design is characterized by a wide and long tibial post engaging the large and deep intercondylar cam of the femoral component, thus ensuring mediolateral and rotational stability without constraining the anteroposterior direction [27,28]. They can be preferable to hinged TKA in case of medial and/or lateral collateral ligament insufficiency and limited bone loss [29e31].…”

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

“…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] .…”