For patients with unrelenting patellofemoral pain, tibial tuberosity realignment procedures are commonly performed to improve patellofemoral alignment and decrease the pressure applied to patellofemoral cartilage. Because malalignment is typically attributed to an excessive lateral force applied to the patella by the quadriceps muscles and the patella tendon, the tibial tuberosity is commonly osteotomized and transferred medially to decrease the lateral force applied by the patella tendon. The tibial tuberosity can also be anteriorized to increase the extensor moment arm of the patella tendon, which decreases the forces applied by the quadriceps muscles during function and subsequently decreases joint compression. Anteriorization and medialization of the tibial tuberosity can also be combined in a single procedure. The goal of the current study was to characterize how medialization, anteriorization and anteromedialization of the tibial tuberosity influence the patellofemoral force and pressure distributions within symptomatic knees. The authors hypothesize that all three realignment techniques decrease the pressure applied to patellofemoral cartilage, but that anteromedialization produces the largest pressure decrease.

Gender differences have been identified in a variety of spine-related disorders including rates of thoracic sagittal plane scoliosis and rates of whiplash associated disorder following automotive rear impacts. For example, female gender was identified as a main risk factor for thoracic curve progression in adolescent idiopathic scoliosis [1]. Clinical and epidemiological studies have identified females to be more susceptible to whiplash injury [2]. However, biomechanical evidence for these discrepancies has been limited. Experimental investigations using human volunteers and post mortem human head-neck specimens have identified dynamic gender differences in overall head kinematics relative to T1 [3] and segmental and localized spinal kinematics [4, 5] following simulated automotive rear impacts. However, it remains unclear whether dynamic gender differences resulted from anthropometry, or geometrical or structural differences in the head-neck complex and/or cervical spine. Structural gender differences identified in anterior cruciate ligaments of the knee [6] and histological differences identified in the ligamentum flavum of the lumbar spine may indicate possible structural or material gender differences in spinal ligaments [7]. Therefore, the present investigation was conducted to experimentally identify soft tissue structural differences in spinal biomechanics.

Changes in load transmission through facet and facet orientation have been considered as an important factor in intervertebral disc degeneration and osteoarthritic changes of the facet joint. (1)(2)(3) Facet joint surface area and orientation of the facets play key roles in load transmission. Their information is important for designing implants of the spine. They have been 2-dimentionally measured using CT and MRI. (4)(5) The purpose of the current study was to establish a three-dimensional (3D) technique for measuring lumbar facet joint area and orientation in vivo.

Anterior cruciate ligament (ACL) injuries are very common, causing pain, loss of function, and medical expense. Women sustain ACL injuries more often than men. Most of these injuries (70%) are non-contact for women [1], occurring during pivoting or sudden deceleration [2]. Training programs have been developed to try to prevent these injuries in women. These programs are designed to improve strength, muscle balance, and knee control. Evaluating the effectiveness of training programs is difficult. To date, these evaluations have only assessed factors such as muscle activation and joint angles that are not directly related to ACL strain and ACL injury risk.

Joint instability may lead to modified and excessive mechanical stresses on the articular surfaces. This repetitive, chronic mechanical overload is one possible source behind the initiation and progression of osteoarthritis (OA). However, the mechanisms by which excessive mechanical force may lead to OA remain unknown. It has been proposed that a change in the location of load bearing regions following joint instability may initiate OA, while the progression of OA is driven by increased tangential shear loading [1]. In addition to changing the load location, joint instability may modify bone kinematics, and in turn articulating surface interactions (e.g. sliding, pivoting and rolling contacts). These altered surface interactions may result in novel and damaging loading applied to the articular cartilage.

Approximately 15,000 Americans suffer complications associated with inadequate sternal fixation after open-heart surgery each year [1]. Although alternative fixation methods exist, limitations of current device evaluation systems have led to uncertainty about the relative increase in stability that these novel devices provide, thereby diminishing their widespread clinical use. Sternal closure techniques are typically evaluated in situ where estimated sternal forces (180–400N) are applied to an intact chest [2] or in vitro on isolated sternal models [3]. The mechanical stability afforded by each technique is quantified as the resultant separation along the bisected sternal midline. This displacement is assumed to reflect micro-motion that would occur at the wound site under physiological loading, a critical factor during bony healing [4]. However, the loading in these studies is hardly physiological; it is generally simplified to a single direction and applied quasistatically to only a few discrete locations along the sternum without regard for the in vivo distribution of forces. It is also unclear whether the transfer of loads from sternum to fixation device during in situ tests [5](cadavers) accurately reflects loading in vivo due to the potential effects of rigor mortis and/or embalming. To improve the accuracy of current in situ and in vitro sternal fixation test methods it is essential to advance our knowledge of in vivo dynamic multi-directional sternal loading.

Kneeling, deep squatting, crouching, and gardening represent activities that require flexing the knee maximally. Yet, the present-state-of-the-art of knee mechanics does not provide an accurate understanding of how this joint functions in deep flexion in normal individuals as indicated by Kurosaka, et al. [1]. This limited understanding of the complex 3-D dynamic tibio-femoral and patello-femoral motions past 130° of knee flexion hinders the development of a prosthesis that would provide for full flexion of the knee. One of the questions that is being presently debated is whether lift-off occurs during deep squat or not [2, 3]. The purpose of this paper is to provide an answer to this question by determining the kinematics of the knee while it is maximally flexed, past 155 degrees of flexion.

Robotic technology has been adopted for studying the biomechanics of the knee joint by our research center and others since 1993 to gain a fundamental understanding of the knee, as well as to provide orthopedic surgeons with scientific data on the efficacy of various reconstructive techniques [1–4]. A robotic testing system generally consists of a six degree-of-freedom (DOF) robotic manipulator with a universal force-moment sensor (UFS) attached to the end effector [5]. This testing system offers a wide range of motion with precision path and position repeatability.

Knee joint laxity can result from soft tissue injury, such as an anterior cruciate ligament (ACL) tear, or genetic factors such as joint hypermobility syndrome (JHS). The degree of a subject’s knee laxity along a continuous spectrum depends on the mechanical properties of the structures, and increased motion that typically follows joint injury. At some threshold along the continuum, instability becomes pathologic and the risk of further joint injury increases.

Patellofemoral Pain (PFP) syndrome is a very common knee disorder. A possible cause may be excessive lateral force applied by the quadriceps and the patellar tendon producing an abnormal distribution of force and pressure within the patellofemoral joint [1]. EMG and in-vivo studies have been conducted to understand the function of the quadriceps and its relationship with PFP [2,3]. These studies suggest a strong relationship between muscle forces and PFP which originates from high lateral retropatellar contact forces. A dynamic computational model of the knee was developed which includes the quadriceps muscles Rectus Femoris (RF), Vastus Intermedius (VI), Vastus Lateralis (VL), and Vastus Medialis (VM) represented as force vectors. The model can predict retro-patellar contact pressures and the action of the individual quadriceps muscles based on the predicted pressures. The objective of this study was to develop a control system which could optimize the distribution of quadriceps muscle forces to minimize contact pressure between the patella and the femur of the knee during a squat.

Intervertebral disc tissue consists of a fluid-filled extra-cellular matrix, in which living cells are sparsely dispersed. The mechanical function is highly dependent on the composition of the extra-cellular matrix, which primary consists of collagen fibrils and negatively charged proteoglycans. Due to the fixed charges of the proteoglycans (PG’s), the cation concentration inside the tissue is higher than physiological. This excess of ion particles leads to an osmotic pressure difference, which causes swelling of the tissue [1]. Because the intervertebral disc is gripped between two vertebrae, the swelling is constrained in vivo , resulting in a intradiscal pressure of 0.1 to 0.2 MPa in supine position. It has been shown that the osmotic pressure inside cartilaginous tissues is much higher than would be expected based on its FCD [2]. This is because part of the water in the tissue is absorbed by the collagen fibers. The proteoglycan molecules, because of their large size, are excluded from this intra-fibrillar space. This means that their effective concentrations are much higher in the extra-fibrillar space than if they were distributed uniformly throughout the entire matrix. Hence, the effective fixed charge density is higher than if computed from total tissue water content. A recent study demonstrates that intrafibrillar water increases osmolarity within the annulus fibrosus substantially [3]. On the other hand, Wognum et al. [4] showed by means of a physical and a numerical model of the disc that high osmolarity within the disc has a protective effect against crack propagation within the disc. Hence, the decrease in osmolarity associated with degeneration may be an explanation of (1) the growing number of cracks observed in the degenerating disc as well as (2) the poor correlation between external loading and crack propagation [5]. The purpose of the present study is to test the hypothesis of Wognum et al. [4] through direct observation of the deformation of annulus fibrosus tissue around discontinuities within its collagen network.

Musculoskeletal computational modeling can be a powerful and useful tool to study joint behavior, examine muscle and ligament function, measure joint contact pressures, simulate injury, and analyze the biomechanical results of reconstructive procedures. Commonly, biomechanical models are based on either finite element analysis (FEA) or three-dimensional rigid body dynamics. While each approach has advantages for specific applications, rigid body dynamics algorithms are highly efficient [1], thus significantly reducing solution time. Many musculoskeletal models of the elbow have been developed [2, 3], but all have constrained the articulations to have particular degrees of freedom and ignored the effects of ligaments. An accurate and robust model without these limitations has potential as a clinical tool to predict the outcome of injuries and/or surgical procedures. This work develops and validates an accurate computational model of the elbow joint whereby joint kinematics are dictated by three-dimensional bony geometry contact, ligamentous constraints, and muscle loading.

In search of a complete understanding of a joint’s function, one must understand both the anatomic parameters and how the brain controls the joint’s actuation. Accurate measurements of anatomical parameters are critical to non-linear biomechanical modeling and control and also to a clinical understanding of orthopaedic reconstruction. Likewise, new frontiers in the study of neuromuscular control contribute to our understanding of joint structure and function. One approach to study joint function is to use a joint simulator to actuate cadaver limbs. Towards the goals of understanding and improving human elbow joint control, a physiologic elbow joint simulator was previously constructed in our laboratory. It is the first elbow simulator to operate completely under closed-loop control. The closed-loop force control used to study joint mechanics permits measurement of moment arms in cadaveric elbow specimens. We hypothesized that the approach yields comparable results to previously-reported moment arm values.[1]

Orofacial pain associated with osteoarthritis (OA) in the temporomandibular joint (TMJ) is a significant clinical problem [1]. The pathophysiologic and cellular mediators that underlie the development of such chronic orofacial pain are not well understood, nor has a relationship to mechanical loading been defined. Several experimental models have been developed to examine causative factors in TMJ OA progression and joint pathology. Such models often involve intra-articular injections or surgical manipulation of tissue structures in order to alter joint kinematics and stability [2–6]. For example, severing of the discal attachments followed by anterior displacement of the disc has been employed in a rabbit model, while disc perforation and scraping of the condylar surface have been used in sheep models to induce OA symptoms [2,3]. A limitation of the above approaches is that they introduce artificial damage to the joint structures and do not approximate the clinical disorder of mechanically-induced TMJ OA. Therefore, the goal of this pilot study was to develop a novel model of TMJ OA via non-invasive and mechanically relevant methods that could produce behavioral hypersensitivity (mechanical allodynia) suggestive of pain symptoms and histological changes in the TMJ consistent with osteoarthritic pathology.

Studies of muscle moment arms have classically followed a method of superposition whereby the measurement or derivation of moment arm magnitudes at any given joint assume independence of the position of joints proximal to the joint under study. This is particularly important for muscles crossing multiple joints. However, because of the nature of the soft tissue anatomy that defines the paths of the intrinsic muscles of the hand inserting into the extensor hood (also known as the dorsal expansion), this assumption may not be true for the intrinsic muscle moment arms at the Proximal Interphalangeal (PIP) Joint. These are muscles that insert into the “hood” of the dorsal expansion at the metacarpophalangeal (MCP) joint of the fingers acting as flexors at the MCP joint and extensors at the PIP joint. The gliding and flexible nature of these tissues bring into question the validity of the assumption that the extension moment arm of the intrinsic muscles at the PIP joint are independent of the position of the MCP joint. Indeed the fact that some of the intrinsic muscles exhibit an increasing (bowstringing) moment arm at the MCP joint with increased flexion infers that the paths of muscles acting through the dorsal expansion do change with respect to phalanx rotation. Does this changing path then affect the extension moment arm of the intrinsics acting at the PIP joint? This project investigates this question with the hypothesis that the extension moment arms of the second lumbrical (2Lum), the second and third dorsal interosseous (2DI and 3DI) at the middle finger PIP joint are significantly different with the middle MCP joint flexed, neutral (at extension) and hyperextended.

Modeling and testing of the patello-femoral joint (PFJ) presents challenges in simulating the appropriate loading and kinematics. Walking is an activity of lower demand for patella performance. Higher demands occur during higher flexion activities such as stair ascending/descending, chair rising, and squatting. High patellofemoral joint reaction forces (PFJR) have been shown to begin around 60° of tibiofemoral flexion and remain high (2.5 × BW to 3.35 × BW) until approximately 110° of tibiofemoral (TF) flexion, at which point contact with soft tissue will tend to off-load the knee joint. Therefore, the flexion range of highest load for the patella is considered to be between 60° and 110° of TF flexion.

The knee is a complex joint comprised of two main bones (femur and tibia) that articulate in a stable manner through the support of surrounding meniscus, musculature, and ligaments. The anterior cruciate ligament (ACL) is one of the main ligaments connecting the femur to the tibia. The ACL restricts anterior translation of the tibia with respect to the femur and aids in preventing internal and external rotation. The ACL is the most commonly injured ligament in the knee [1] and has been shown to increase the risk of cartilage degeneration leading to osteoarthritis (OA) [2]. The mechanics of the joint are altered following an ACL rupture, but the relations between the resulting joint instability and OA are not well understood.

Deep knee flexion is required for many activities of daily living during work, exercise, religious worship, and hobbies. Walker et al . [1] found that activities such as rising from a low chair or getting into or out of bath require between 100° and 160° of knee flexion. 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.

Polyethylene wear is a leading cause of failure in total knee arthroplasty (TKA). Knowing the stresses experienced by the polyethylene would be pivotal information for efforts to improve polyethylene longevity. Previous investigations into the stress and wear of the polyethylene have required estimates of in-vivo conditions [1]. This work investigates the feasibility of using actual in-vivo kinematics obtained using dual fluoroscopy as boundary conditions for finite element analysis of the polyethylene.

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.