Understanding the behavior of the natural knee in deep flexion can offer insight into the necessary design characteristics of a total knee implant. Andriacchi et al. [1] measured the in vivo characteristics of knee motion down to ∼150° knee flexion during a weight bearing squat. Likewise, Li et al. [2] investigated deep knee flexion in vitro using robotic technology during passive knee flexion. Both of these studies offer insight into the behavior of the knee in deep knee flexion; however, they have some limitations with regards to assessing physiological activities in a controlled manner. The purpose of this study was to measure the kinematics of the knee during a simulated in vitro deep knee squat so that in the future a dynamic, load-bearing, simulated deep knee squat could be used as a tool in the design of total knee prostheses.

Many researchers have studied the tibial passive motion, the boundaries of which are defined by various knee ligamentious and bony constraints [1, 2, 3]. The technique has been used in clinical practices and experimental research to assess injury and predict likely surgical outcomes [1, 2]. After total knee replacement surgery (TKR), the implants’ design features and altered ligamentious tension provide the joint constraint and stability. Therefore, the change in passive envelope of motion from the natural condition could be used to observe the altered constraints and stability achieved in TKR knees. The objective of this study was to assess the change in passive envelope of motion after TKR with two implant designs: cruciate retaining and posterior stabilized.

Experimental testing with cadaveric tissue allows the application of controlled loads and/or motions while still maintaining the inherent variability in the anatomy and soft tissue of the specimens. Multi-axial dynamic loading of tissue allows for experiments to be conducted that simulate conditions approaching physiological. Knee simulators have been used to generate physiological loading on the human knee to study kinematics, soft tissue loading, and joint contact pressure. These machines have been used to investigate injury, surgical outcomes, and prosthetic design. While there are a number of different geometries for knee loading devices, most are based on the Oxford rig design [1] with a vertical orientation of the leg where the hip is able to translate up and down while allowing flexion at the hip, knee, and ankle. The foot or ankle can have a variety of constraints and degrees of freedom. One of the recent areas of interest in knee biomechanics is the role different structures of the knee play during deep knee flexion activities. This is of particular interest to the orthopedic industry because of the common complaint regarding a feeling of a loss of stability during high flexion activities for post-TKR patients and the prevalence of high-flexion activities in emerging worldwide markets. The objective of this abstract is to describe two knee loading devices that have been used to study knee biomechanics, and most recently high flexion motion, and present some representative data from these tools.

During knee flexion and extension the ACL and PCL help to coordinate the movement and rotation of the knee by constraining the sliding and rolling motions at the joint. In the natural knee the femur pivots about the medial condyle and the femur tends to roll back on the tibia with increasing flexion [1]. The purpose of this study was to observe if and how rollback occurs in the natural knee using the lowest point (LP) method, and to understand how anterior-posterior (AP) motion is related to flexion angle in the natural knee. A better understanding of natural knee femoral rollback will influence future design of total knee arthroplasties.

The motion patterns of the human knee joint depend on its passive motion characteristics, which are described by the ligamentious and articular constraints. Since active motions, like walking and squatting are believed to fall within a passive envelope, the basis for the understanding of the knee joint kinematics lies in the description of its passive constraint characteristics [1]. Although several authors studied passive envelope characteristics of a knee, it is not clear from the literature which anatomical structures guide the knee in passive or active motion and how their geometric arrangement produces the unique path of passive knee motion [1–3]. A few mathematical models have been developed to study the structures that guide the passive knee motion [1, 2]. However, their hypotheses were not supported by a sufficiently detailed ligament bundle model, soft tissue properties, ligament insertion-origin sites and their intra-subject variability. To explain the relationship between knee anatomy and its variability with three-dimensional knee motion completely, new methodology must be developed. The objective of the present study was to estimate the effects of variation in knee anatomical factors on the tibiofemoral passive envelope using a multivariate analysis technique, principal component (PC) analysis.