Fallon Fitzwater

Mapping of Contributions From Collateral Ligaments to Overall Knee Joint Constraint: An Experimental Cadaveric Study

Understanding the contribution of the soft-tissues to total joint constraint (TJC) is important for predicting joint kinematics, developing surgical procedures, and increasing accuracy of computational models. Previous studies on the collateral ligaments have focused on quantifying strain and tension properties under discrete loads or kinematic paths; however, there has been little work to quantify collateral ligament contribution over a broad range of applied loads and range of motion (ROM) in passive constraint. To accomplish this, passive envelopes were collected from nine cadaveric knees instrumented with implantable pressure transducers (IPT) in the collateral ligaments. The contributions from medial and lateral collateral ligaments (LCL) were quantified by the relative contribution of each structure at various flexion angles (0-120 deg) and compound external loads (±10 N m valgus, ±8 N m external, and ±40 N anterior). Average medial collateral ligament (MCL) contributions were highest under external and valgus torques from 60 deg to 120 deg flexion. The MCL showed significant contributions to TJC under external torques throughout the flexion range. Average LCL contributions were highest from 0 deg to 60 deg flexion under external and varus torques, as well as internal torques from 60 deg to 110 deg flexion. Similarly, these regions were found to have statistically significant LCL contributions. Anterior and posterior loads generally reduced collateral contribution to TJC; however, posterior loads further reduced MCL contribution, while anterior loads further reduced LCL contribution. These results provide insight to the functional role of the collaterals over a broad range of passive constraint. Developing a map of collateral ligament contribution to TJC may be used to identify the effects of injury or surgical intervention on soft-tissue, and how collateral ligament contributions to constraint correlate with activities of daily living.

In Vitro Experimental Testing of the Human Knee: A Concise Review.

In vitro testing of the human knee provides valuable insight that contributes to further understanding knee biomechanics. Cadaveric testing correlates well with clinical trials because the tissue has similar properties to that of live subjects. In addition, in vitro testing allows studies to be performed that would otherwise be unethical to evaluate in vivo. Due to their many advantages, cadaveric testing has been utilized to evaluate many of medical devices and surgical techniques that have been developed in recent decades. This article aims to review the current technologies and methodologies utilized in experimental in vitro testing of the human knee. The article provides a summary of the different rigs and machines that are currently used to examine the biomechanics of the knee. It also highlights the variable experimental techniques and measurement systems that are used to collect the kinematics and kinetics of the knee joint. As technologies advance so do the measurement systems and equipment in the experimental biomechanics field. The influence of improvements to these testing equipment and measurement devices on in vitro testing of the knee will also be discussed in this review.

Variations in medial-lateral hamstring force and force ratio influence tibiofemoral kinematics.

A change in hamstring strength and activation is typically seen after injuries or invasive surgeries such as anterior cruciate reconstruction or total knee replacement. While many studies have investigated the influence of isometric increases in hamstring load on knee joint kinematics, few have quantified the change in kinematics due to a variation in medial to lateral hamstring force ratio. This study examined the changes in knee joint kinematics on eight cadaveric knees during an open‐chain deep knee bend for six different loading configurations: five loaded hamstring configurations that varied the ratio of a total load of 175 N between the semimembranosus and biceps femoris and one with no loads on the hamstring. The anterior–posterior translation of the medial and lateral femoral condyles’ lowest points along proximal‐distal axis of the tibia, the axial rotation of the tibia, and the quadriceps load were measured at each flexion angle. Unloading the hamstring shifted the medial and lateral lowest points posteriorly and increased tibial internal rotation. The influence of unloading hamstrings on quadriceps load was small in early flexion and increased with knee flexion. The loading configuration with the highest lateral hamstrings force resulted in the most posterior translation of the medial lowest point, most anterior translation of the lateral lowest point, and the highest tibial external rotation of the five loading configurations. As the medial hamstring force ratio increased, the medial lowest point shifted anteriorly, the lateral lowest point shifted posteriorly, and the tibia rotated more internally. The results of this study, demonstrate that variation in medial‐lateral hamstrings force and force ratio influence tibiofemoral transverse kinematics and quadriceps loads required to extend the knee.

A novel unembalmed human cadaveric limb model for assessing conformational changes in self-expanding nitinol stents in the popliteal artery

To develop an unembalmed human cadaveric lower limb model as a more realistic environment for testing self‐expanding nitinol stents. We studied conformational changes and strain induced by knee flexion in nitinol stents deployed in the popliteal artery (PA).

Joint Loading Effect on Kinematics of the Natural Knee During a Range of Simulated Walking Profiles

The physiological ratio of compression to anterior-posterior (A-P) knee joint loads has substantial effects on the loading of soft tissue structures, patellofemoral loads, and knee kinematics [1, 2]. There is also a direct relationship between resultant kinematics and joint forces. D’lima et al. was also able to compute A-P kinematics at a given flexion angle with minimal error using measured A-P and compressive load acquired from the instrumented tibia [3]. The direction of A-P load measured at the tibia is associated with the direction of translations of the femur relative to the tibia.Copyright

Modeling of a Dynamic Knee Simulator With Advanced PID Controller to Evaluate Joint Loading Conditions

In-vitro dynamic knee simulators allow researchers to investigate changes in natural knee biomechanics due to pathologies, injuries or total joint replacement. The advent of the instrumented tibia, which directly measures knee loads in-vivo, has provided a wealth data for various activities that in-vitro studies now aim to replicate [1, 2]. Dynamic knee simulators, such as the Kansas Knee Simulator (KKS), achieve these physiological loads at the joint by applying external loads to either bone ends or musculature. Determining the external loading conditions necessary to replicate activity specific joint loads, obtained from instrumented tibia data, during dynamic simulations are calculated using computational models.Copyright

Cadaveric Evaluation of Knee Joint Kinematics Using the Kansas Knee Simulator

Computational models of the knee are useful for evaluating changes in kinematics, soft tissue loadings, new prosthetic geometries, and surgical techniques [1, 2]. These models are advantageous in their ability to quickly and efficiently evaluate the effect of changes in these parameters on knee joint function. The limitation of modeling is that the results are greatly influenced by the constraints and parameters used to create the model.Copyright

Assessing Rotary Stability of the Knee In Vitro Using Principal Component Analysis

Clinicians typically assess the functional status of the knee subjectively through manipulations to the knee’s passive connective tissue restraint under minimal load. The resulting translation or rotation at a given flexion angle is defined as the laxity of the knee which is used to suggest (in)stability. However, recent studies have shown that instability is not necessarily determined by knee laxity1. Dynamic stability at the knee is achieved through a complex interaction between soft tissue structures, neuromuscular control and articular geometry. It is during dynamic functional movements, such as walking, that patients suffer from buckling or giving way sometimes resulting in falls 2.Copyright