Dynamic knee simulators use muscle analogs to incite motion at the knee joint [1–5]. There is a great variation between simulators in choice of powering of muscle analog systems, what movements are fixed, controlled, or unconstrained, as well as whether or not the system is open or closed kinetic chain. The objective of this work is to develop a portable dynamic knee simulator that allows simulation of knee joint motions when it is maximally flexed during a large range of activities involving the lower limb in both a vertical (e.g. deep squat) as well an horizontal position (e.g. rowing).

As the baby boomer generation ages, knee osteoarthritis (OA) will become increasingly prevalent in our society. Articular cartilage damage in the knee is highly dependent upon subject-specific kinematics and load distribution inside the joint. In particular, researchers have hypothesized that overloading of the medial compartment is a primary contributing factor to the development of the disease [1]. However, since medial compartment load cannot be measured non-invasively in vivo , researchers typically use the external knee adduction moment during stance phase as a surrogate measure. This quantity has been correlated with the medial tibial contact force measured from an instrumented knee implant [2] and with the risk of disease progression over time [3].

The first generation of the knee load application system was developed at the University of California, Davis under the direction of Professor Maury Hull. This apparatus has been described in several abstracts and was published in 1995 [1]. This original system continues to be used by Dr. Hull and associates.

The meniscus plays an important role in many biomechanical functions of the knee, including shock absorption, load distribution, and joint lubrication. The ability to perform these functions is determined by the interactions of the major tissue constituents (water, proteoglycan, and collagen), although these interactions have not been as thoroughly studied in fibrocartilage as those in other soft tissues. In articular cartilage, electrochemical interactions between negatively charged glycosaminoglycan (GAG) side chains of proteoglycans and the interstitial fluid generate an osmotic swelling pressure that contributes to the compressive stiffness [1], and proteoglycan degradation dramatically decreases compressive and shear moduli [2]. Although the concentration of proteoglycan in the meniscus is substantially lower (<1%) than that in articular cartilage, aggrecan degradation also greatly decreases the compressive and shear moduli of meniscal fibrocartilage [3]. The proteoglycan distribution in meniscal fibrocartilage is macroscopically heterogeneous [4] and is concentrated in the secondary matrix surrounding the circumferential collagen bundles, and the extent to which osmotic interactions explain the influence on fibrocartilage material properties is unknown. Altering the osmotic strength of the bathing solution supplies a means to control osmotic interactions between the GAGs and the environment without degrading the tissue matrix. The objective of this study was to examine the effects of an altered osmotic environment on the dynamic shear modulus of meniscal tissue.

Meniscectomy is a well-known risk factor for osteoarthritis (OA) in humans. It has been reported that total meniscectomy increases the risk of developing osteoarthritis radiographically by 14 times after 21 years [1] and that partial meniscectomy increases the risk of developing radiographic evidence of osteoarthritis within 16 years by a factor of four [2]. Two possible functional measures have been suggested as mechanisms for the development and progression of premature knee osteoarthritis: alterations in either kinematics or kinetics. Changes in kinematics, such as a shift in internal-external (IE) rotation after anterior cruciate ligament injury, have been suggested as a basis for an increased rate of cartilage thinning [3]. The other possible reason for the development of premature OA post-meniscectomy is a change in kinetics, the mechanical loading that occurs, particularly in the medial compartment [4]. The knee adduction moment has been associated with the rate of progression of osteoarthritis [5] and it has thus been suggested that the knee adduction moment is a good surrogate measure for in vivo load on the medial compartment osteoarthritis [6].

More than 1 million procedures for the total or partial removal of the meniscus are performed in the United States and Europe each year. However, it has been found that the knee can lose functionality when even small parts of the meniscus are removed, leading to degenerative changes in the joint. Healing of the medial meniscus in particular is problematic since blood vessels are present in only the outer 10–25% of the meniscus, making it desirable to preserve as much of the meniscus as possible.

Verified computational models of total knee replacement serve as the primary design-phase tool for parametric analysis of implant geometry. Previously, dynamic finite element models of the Kansas Knee Simulator (KKS) were developed and tibiofemoral (TF) and patellofemoral (PF) kinematic predictions were verified by comparison with experimental measurements [1,2]. In this prior work, the implants were mounted in metallic fixtures to assess the ability of the model to accurately predict the TF and PF kinematics without the additional complexity of variable cadaver specimens and soft-tissue constraint. The next step in the systematic model verification procedure was to verify kinematic predictions with multiple specimen-specific models. Specifically, the objectives of the present study were: 1) to develop an explicit finite element (FE) model of the KKS capable of recreating experimental loading protocols for a deep knee bend activity and 2) to verify predicted six degree-of-freedom (DOF) TF and PF kinematics of two cruciate retaining (CR) and two posterior stabilized (PS) implanted specimen-specific models with deformable, wrapping soft tissue constraint.

The anterior cruciate ligament (ACL) is critical for knee stability when walking or running. Unfortunately, it does not heal well after significant tearing or rupture and surgery is often necessary to reconstruct the injured ligament. Though ACL ruptures are quite common, the surgical repair of this ligament has inconsistent success rates [1]. The goal of this study was to characterize a biomimetic tissue engineered ACL scaffold using a novel combination braid-twist technique. The braid-twist scaffolds were made using the following procedure: • Nine groups of six 160 mm length PLLA fibers were selected. • Each group of six fibers was twisted in a counter-clockwise manner to form a fiber bundle (a total of nine fiber bundles/scaffold). • Three of these bundles were twisted around one another counter-clockwise to form a yarn (a total of three yarns/scaffold). • These three yarns were braided together to form one scaffold. This technique is based on the structure of ACL tissue and is designed to reduce scaffold fatigue and accurately mimic ACL behavior.

Specimen-specific modeling of the knee can be an effective tool for understanding knee mechanics [1–2]. It can also serve as a design tool for orthopaedic implant design through enhancing understanding of mechanics in the reconstructed knee [3], particularly when used in conjunction with instrumented components that record in vivo joint forces [4]. Techniques for developing specimen-specific computational geometric models of hard tissue and soft tissue are fairly commonplace, using imaging tools such as computed tomography (CT) and magnetic resonance (MR) in conjunction with software tools for image processing. Determination of specimen-specific material properties relies on measuring kinematics of the tissue associated with a defined load, either in vivo or in vitro, selecting an appropriate material model, and estimating values of the parameters of the model that closely match the experimental data. The goal of this work was to utilize inverse finite element (FE) analysis to determine material parameters of ligaments in a specimen-specific model of the knee, using both local and global optimization algorithms.

Abdominal aortic aneurysm stent grafts have been reported to fracture at a rate as high as 8% [1]. Iliac artery deformation induced by cardiac pulsation or musculoskeletal motions has been hypothesized to cause these fractures, but little in vivo data has been available heretofore to test this hypothesis. We have utilized magnetic resonance angiography and image-processing methods to quantify in vivo deformation of the human iliac arteries due to maximal hip flexion.

Osteoarthritis (OA) of the knee affects an estimated 20–40% of individuals over the age of 65 [1], and is nearly 10 times more common in the medial compartment than the lateral compartment [2]. Plain radiography measurements using the Kellgren and Lawrence (KL) scale have been the gold standard for diagnosis of knee osteoarthritis [3]. However, for new treatment interventions for medial compartment knee OA such as load modifying footwear, it would be important to know if the disease-related cartilage loss in the medial compartment occurs initially and predominantly in regions that are weight bearing during walking. Because walking results in highest weight bearing occurring in the anterior and middle regions of the femoral condyle and the anterior region of the tibial plateau, seeing a pattern of thinning in these areas would suggest that walking is an important activity for understanding both the cause and treatment of osteoarthritis.

Many activities of daily living during work, exercise, religious worship, and hobbies require deep knee flexion. Activities such as rising from a low chair or getting into or out of a bath require between 100° and 160° of knee flexion [1]. Other activities such as kneeling or squatting to pick an item off the ground can be difficult with a limited range of motion. Beside deep knee flexion being important for daily living activities, it is essential in non-Western cultures that commonly sit in deep knee-bending positions. In vitro studies looking at knee function often focus solely on the knee joint, ignoring the effect of the muscle, ligament, and tendon constraints of the ankle, and simplifying or neglecting muscle loads. The effects of these assumptions on kinematics are unknown. The purpose of this study was to compare a squatting activity for: 1) whole leg versus knee specimens, and 2) different combinations of quadriceps and hamstrings loading.

Menisci are C-shaped fibrocartilage structures that play an important role in supporting loads in the knee joint. The meniscal attachments anchor to the tibia by means of a ligamentous structure at the anterior and posterior horns. It has been shown that the meniscal attachments are important for restoring functionality to the knee [2].

Many studies have used musculoskeletal models to predict in vivo muscle forces at the knee during gait [1, 2]. Unfortunately, quantitative assessment of the model calculations is often impracticable. Various indirect methods have been used to evaluate the accuracy of model predictions, including comparisons against measurements of muscle activity, joint kinematics, ground reaction forces, and joint moments. In a recent study, an instrumented hip implant was used to validate calculations of hip contact forces directly [3]. The same model was subsequently used to validate model calculations of tibiofemoral loading during gait [4]. Instrumented knee implants have also been used in in vitro and in vivo studies to quantify differences in biomechanical performance between various TKR designs [5, 6]. The main aim of the present study was to evaluate model predictions of knee muscle forces by direct comparison with measurements obtained from an instrumented knee implant. Calculations of muscle and joint-contact loading were performed for level walking at slow, normal, and fast speeds.

Osteoarthritis (OA) is a degenerative disease of articular cartilage that affects millions of people [1]. Local biomechanical factors may severely affect initiation and progression of OA due to changes in loading conditions at the cartilage. The frontal plane tibiofemoral alignment effects the varus/valgus moment which could increase the overall loading at the knee. Biomechanical studies have reported that the varus moment is a key determinant in the load distribution at the knee [2, 3] and has been linked to OA progression [4, 5]. A normal knee will have a tibiofemoral angle approximately 7° valgus [6]. Deviation from this angle leads to a knee joint with a varus or valgus condition. In this investigation, a motion analysis procedure was developed to determine the affect of the frontal plane tibiofemoral angle on the force and moment reactions at the knee. The results of these methods could be utilized in a subject specific finite element model to determine the stress and strain at the knee cartilage and to suggest measures to prevent OA.

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.

Human body movement analysis using stereophotogrammetry has been widely applied in understanding the normal function and pathological conditions of human knee joint. To reconstruct the 3-dimensional (3D) position and orientation of bones from markers placed on body surface, the spatial relationship between anatomical frames and skin marker clusters needs to be identified [1]. Since the determination of anatomical landmark (AL) locations in general lacks accuracy and precision, anatomical frames defined based on ALs are subject to uncertainty. This is a major issue in human movement analysis and its effects on knee rotation kinematics determination have been studied [1]. However, few studies have investigated the effects of uncertainty of anatomical definition on translation measurement of knee join. Although knee translations are secondary motions with only small magnitudes, they are regarded with great clinical significance. On the other hand, translation measurement is more sensitive to definitions of origin positions in addition to axis directions of the anatomical frames. In this work, we studied the effects of three different anatomical frame definitions (neutral standing, prediction method and functional method) on knee joint translation measurement during level walking. The repeatability of translation measurement among three sessions was compared among the three anatomical definition methods.

A stepping response is often used to restore balance following a fall. Using laboratory-induced balance perturbations, various researchers have reported age-related alterations in balance recovery step characteristics including earlier step liftoff time [1; 2], shorter step length [1; 3], and longer step duration [2]. Such age-related changes in the step response may be related to older adults’ reduced strength reserve, which is prominent in the lower extremities [4] and therefore likely plays an important role in balance recovery.

The function of the locking mechanism between the ultra high molecular weight polyethylene (UHMWPE) articular surface and the tibial baseplate is to ensure that the two components remain connected and to minimize the relative motion that may occur between them. This relative motion that can occur between the two components has the potential to generate wear debris, which may eventually lead to bone osteolysis [1–2].

Accurate knowledge of in vivo articular contact kinematics and contact forces is required to quantitatively understand factors limiting life of total knee arthroplasty (TKA) implants, such as polyethylene component wear and implant loosening [1]. Determination of in vivo tibiofemoral contact forces has been a challenging issue in biomechanics. Historically, instrumented tibial implants have been used to measure tibiofemoral forces in vitro [2] and computational models involving inverse dynamic optimization have been used to estimate joint forces in vivo [3]. Recently, D’Lima et al. reported the first in vivo measurement of 6DOF tibiofemoral forces via an instrumented implant in a TKA patient [4]. However this technique does not provide a direct estimation of tibiofemoral contact forces in the medial and lateral compartments. Recently, a dual fluoroscopic imaging system has been used to accurately determine tibiofemoral contact locations on the medial and lateral tibial polyethylene surfaces [5]. The objective of this study was to combine the dual fluoroscope technique and the instrumented TKAs to determine the dynamic 3D articular contact kinematics and contact forces on the medial and lateral tibial polyethylene surfaces during functional activities.