Posterior-stabilized total knee arthroplasty kinematics and joint laxity: A hybrid biomechanical study

Abstract

Background Posterior-stabilized (PS)-total knee arthroplasty (TKA) arose as an alternative to cruciate-retaining (CR)-TKA in the 1970s. Since then, it has become a popularly utilized TKA design with outcomes comparable to CR-TKA. The post-cam mechanism is unique to PS-TKA as it substitutes the function of the posterior cruciate ligament (PCL). The study aimed to understand the kinematic and laxity changes in PS-TKA with under- and overstuffing of the tibiofemoral joint space with the polyethylene (PE) insert. Methods This study employed a hybrid computational-experimental joint motion simulation on a VIVO 6 degrees of freedom (6-DoF) joint motion simulator (AMTI, Watertown, MA, USA). Physical prototypes of a virtually-performed TKA in mechanical alignment (MA) and kinematic alignment (KA) based on cadaveric CT scans and a virtual ligament model were utilized. The reference, understuffed (down 2 mm) and overstuffed (up 2 mm) joint spaces were simulated, neutral flexion and laxity testing loads and motions were performed for each configuration. Results The PE insert thickness influenced post-cam engagement, which occurred after 60º in the overstuffed configurations, after 60º–75º in the reference configurations and after 75º in the understuffed configurations. The understuffed configurations, compared to the reference configurations, resulted in a mean 2.0º (28%) and 2.0º (31%) increase in the coronal laxity in MA and KA respectively. The overstuffed configurations, compared to the reference configuration, resulted in an increase in the mean joint compressive forces (JCFs) by 73 N (61%) and 77 N (62%) in MA and KA models, respectively. Conclusions The under- and overstuffing in PS-TKA alter the kinematics with variable effects. Understuffing decreases the stability, JCFs and inverse with overstuffing. Subtle changes in the PE insert thickness alter the post-cam mechanics.

Exploration of the Advanced VIVOTM Joint Simulator: An In-Depth Analysis of Opportunities and Limitations Demonstrated by the Artificial Knee Joint

“…The VIVO TM joint simulator can be used to analyse a broad range of joints, for example the elbow [16,17], patellofemoral joint [18,19], tibiofemoral joint [19][20][21][22][23], and mandible [24] joint. The VIVO TM joint simulator disposes of two different control modes-the "Cartesian" mode, which interprets the kinematics according to the actuator axes (Figure 1), and the "Grood & Suntay (GS) mode".…”

“…Furthermore, it has the possibility to consider up to 100 virtual ligaments during the examinations by virtually applying forces and moments during the movement, depending on the joint pose [15]. These features provide the possibility to use the VIVO TM joint simulator for a variety of joints, for example the elbow [16,17], patellofemoral joint [18,19], tibiofemoral joint [19][20][21][22][23], and mandible joint [24].…”

“…Additionally, some of the test-setup conditions are relevant for general experimental testing. These include, for example, lubrication, for which many different approaches are known in the literature [3,4,14,21,[25][26][27][28][29][30]. In experimental investigations of joint endoprostheses, additional lubrication is neglected due to the selflubricating properties of polyethylene, e.g., studies with test rigs [25], robots [14], and wear simulators [26].…”

“…In experimental investigations of joint endoprostheses, additional lubrication is neglected due to the selflubricating properties of polyethylene, e.g., studies with test rigs [25], robots [14], and wear simulators [26]. Other studies used silicone oil to enforce ideal lubrication behaviour [21].…”

Virtual Joint Motion Simulator Accurately Predicts Effects of Femoral Component Malalignment during TKA

“…These virtual multifiber ligament models calculate and incorporate forces that are collinear with the ligament fibers, which are resolved to equivalent forces and moments acting across the knee [13]. This simulator and its virtual ligament system have been successfully employed in previous studies to examine knee laxity and investigate knee implant effectiveness [14][15][16]. Ligament wrapping can be enabled, which determines if a point along the length of a virtual ligament is penetrating through a wrapping surface (bone or prosthesis component).…”