Validation of predicted patellofemoral mechanics in a finite element model of the healthy and cruciate-deficient knee

Abstract

Healthy patellofemoral (PF) joint mechanics are critical to optimal function of the knee joint. Patellar maltracking may lead to large joint reaction loads and high stresses on the articular cartilage, increasing the risk of cartilage wear and the onset of osteoarthritis. While the mechanical sources of PF joint dysfunction are not well understood, links have been established between PF tracking and abnormal kinematics of the tibiofemoral (TF) joint, specifically following cruciate ligament injury and repair. The objective of this study was to create a validated finite element (FE) representation of the PF joint in order to predict PF kinematics and quadriceps force across healthy and pathological specimens. Measurements from a series of dynamic in-vitro cadaveric experiments were used to develop finite element models of the knee for three specimens. Specimens were loaded under intact, ACL-resected, and both ACL and PCL-resected conditions. Finite element models of each specimen were constructed and calibrated to the outputs of the intact knee condition, and subsequently used to predict PF kinematics, contact mechanics, quadriceps force, patellar tendon moment arm, and patellar tendon angle of the cruciate resected conditions. Model results for the intact and cruciate resected trials successfully matched experimental kinematics (avg. RMSE 4.0°, 3.1 mm) and peak quadriceps forces (avg. difference 5.6%). Cruciate resections demonstrated either increased patellar tendon loads or increased joint reaction forces. The current study advances the standard for evaluation of PF mechanics through direct validation of cruciate-resected conditions including specimen-specific representations of PF anatomy.

Combined measurement and modeling of specimen-specific knee mechanics for healthy and ACL-deficient conditions

“…While prior computational studies have evaluated healthy and ACL-deficient knee mechanics, they have not verified predictions in both states during dynamic activity (Guess and Stylianou, 2012; Li et al, 2002; Mesfar and Shirazi-Adl, 2006a; Moglo and Shirazi-Adl, 2003; Shelburne et al, 2004). The current study provided a specimen-specific representation of the TF and PF joints by incorporating material properties and geometric alignment from previous modeling of the same specimens (Ali et al, 2016; Harris et al, 2016). …”

“…In the first step, in-vitro testing replicated a deep knee bend using motor-actuated quadriceps force to calibrate PF mechanics in specimen-specific FE models of the experiment (Ali et al, 2016). In the second step, laxity experiments were performed in the same knees to capture passive constraint of the TF joint (Harris et al, 2016).…”

“…A load cell attached to the proximal end of the tibia recorded 6 DOF loads from each laxity test and provided real-time user feedback via LabView (National Instruments, Austin, TX). Second, PF mechanics were measured by placing the specimens in a test fixture that applied quadriceps force to extend the knee (Ali et al, 2016). Finally, specimens were mounted in the KKS to simulate the stance and swing phase of gait using load-controlled actuators (Figure 1).…”

“…Ligament and tendon material properties and soft-tissue attachments of the patellar mechanism were adopted from our prior computational studies (Ali et al, 2016; Baldwin et al, 2009). KKS actuator loads at the hip and ankle joint were applied to the computational model to simulate dynamic activity performed in the experiment (Figure 1).…”

“…More recently, models have been developed of the natural knee. Calibration of specimen-specific PF mechanics was performed in a muscle-loaded rig (MLR) designed to isolate the quadriceps mechanism during knee flexion (Ali et al 2016). Joint laxity tests were performed on the same specimens to quantify joint constraint and derive optimized TF ligament material properties (Harris et al, 2016).…”