Dissertations / Theses on the topic 'Knee – Mechanical properties'

Separating the study of kinematic geometry of the human knee from the study of its behaviour under load provides insight into the complex relationship between form and function at the joint. The development of a three-dimensional mathematical model which examines the mobility and stability of the joint in sequence is described in this thesis. A previously proposed model of knee mobility, in which the ligaments and ar- ticular surfaces act as rigid constraints between the bones in a single degree-of- freedom spatial mechanism, was re-examined and its limitations addressed. A new geometric-numerical approach to solving the model kinematics, capable of handling both idealised and more anatomical representations of the articular surfaces, was developed. A database of specimen-specific motion and geometry was established, based on cadaver studies. Articular contact kinematics and ligament length patterns were also quantified. In experiment, all components of passive knee movement were found to be coupled to the flexion angle, providing justification for the underlying concept of the model of knee mobility. Specimen-specific models of mobility were successful in predicting the main fea- tures of passive knee motion through a full range of flexion. Incorporation of second order tibial articular surfaces permitted the prediction of physiological motion com- patible with more realistic contact point movement. Through incorporation of continuous three-dimensional arrays of extensible lig- ament fibres, a preliminary model of knee stability was formulated. Although in need of further refinement, sample predictions of joint behaviour during a/p drawer and axial rotation have demonstrated the potential of the model in highlighting the subtleties of ligament mechanics. It was concluded that the sequential approach is appropriate for the study of joint behaviour in three dimensions and that, based on the success of the analogous two-dimensional theory, it provides an invaluable tool in the study of joint mechanics in activity and in the design and assessment of surgical procedures for treating knee injury and disease.

Considerable evidence indicates that damage, to or removal of, the menisci can have detrimental effects upon primary knee joint function and cause degeneration by predisposing the knee to the effects of osteoarticular disease. To understand fully how the menisci function, their intrinsic material properties and essential features of their behavioural response to loading conditions and how these properties vary throughout the tissue must be precisely defined. This provides the ability to understand the normal function of the knee meniscus, quantify pathologies, detect injurious mechanisms and evaluate the effects of injury and repair. Load-deformation studies, obtained through precisely prepared material samples and standardised loading conditions were used to obtain the relationship between stress and strain of the meniscus when subject to uniaxial compressive, tensile and shear loading in different orthogonal planes and regions. The fundamental understanding of the relationships between the structural organisation and biomechanical properties of fresh, human meniscal tissue has been reported. Failure mechanisms within the highly anisotropic and inhomogeneous material are presented. Material coefficients and mathematical equations modelling stress-strain response are defined and the effects of pathology, location and age effects have been determined. This primary information provides us with a better understanding of the functional behaviour of the meniscus under physiological loading conditions and an insight into possible failure mechanisms. The precise materials and mechanical property data presented will enable accurate computer simulations to be constructed and provide a reference by which future developments in the fields of meniscal repair and tissue engineering can be realistically assessed for performance in vivo.

The tribology of a wide range of designs of compliant layer acetabular cups has been evaluated using a simulator. The simulator applied a dynamic load of 2 kN and a sinusoidal motion of ±25 , and measured the frictional resistance directly. In general the friction developed in these joints was extremely low, with friction factors typically below 0.01. When the experimental results were compared with theoretical estimates of friction a poor correlation was found. Further analysis suggested that the design of compliant layer acetabular cups was insensitive to many of the parameters suggested by theory. In particular, the radial clearance and femoral head size were not found to be critical. In addition, methods were proposed and their effectiveness demonstrated to measure friction at the on-set of motion (start-up friction), and the steady state friction in realistic compliant layer knees. The adhesion between compliant layers and a rigid backing have been investigated, with the aim of developing a good bond between them. The peel test was used to demonstrate an excellent diffusion bond between a low modulus medical grade polyurethane, and a similar high modulus grade of polyurethane. The processing conditions used to manufacture the test piece were optimised to maximise the bond strength. The bond was found to be stable after immersion in Ringers solution at 37 C for 52 weeks, and after acetabular cups were subjected to 14 million 4 kN loading cycles. A six station knee wear simulator was designed and commissioned. The simulator applied a dynamic load and an anterior-posterior translation individually to each station, as well as a flexion-extension motion common to all six stations. The simulator was computer controlled entirely using servo hydraulics. Wear rates were obtained from tests lasting up to 8 million cycles conducted on UHMWPE joints.

Ground reaction force (GRF) data collected and synchronized with film data to determine peak GRF and calculate moments about ankle and knee during rope skipping. Two, five minute conditions were analyzed for 10 subjects. Condition 1 was set rate and style. Condition 2 was subjects' own rate and style. Means and standard deviations were reported for peak GRF, ankle and knee moments. One way ANOVAs reported no significant difference between conditions for variables measured. Efficiency and nature of well phased impacts during rope skipping may be determined by combination of GRF, similarities in magnitude and direction of joint moments, and sequencing of segmental movements. Technique and even distribution of force across articulations appear more important than magnitudes of force produced by given styles.

The aim of the work presented in this thesis was to examine the associations between the kinematics of the knee characterised by the tibiofemoral contact pattern, and degenerative change, in the context of anterior cruciate ligament (ACL) injury. While the natural history of degenerative change following knee injury is well understood, the role of kinematics in these changes is unclear. Kinematics of the knee has been described in a variety of ways, most commonly by describing motion according to the six degrees of freedom of the knee. The advantage of mapping the tibiofemoral contact pattern is that it describes events at the articular surface, important to degenerative change. It was hypothesised that the tibiofemoral contact pattern would be affected by injury to the knee. A model of ACL injury was chosen because the kinematics of the knee have been shown to be affected by ACL injury, and because the majority of chronic ACL-deficient knees develop osteoarthritis, the associations between kinematics and degenerative change could be explored. A technique of tibiofemoral contact pattern mapping was established using MRI, as a quantifiable measure of knee kinematics. The tibiofemoral contact pattern was recorded from 0º to 90º knee flexion while subjects performed a leg-press against a 150N load, using sagittal magnetic resonance imaging (MRI) scans. The technique was tested and found to be reliable, allowing a description of the tibiofemoral contact pattern in 12 healthy subjects. The tibiofemoral contact patterns of knee pathology were then examined in a series of studies of subjects at a variety of stages of chronicity of ligament injury and osteoarthritis. Twenty subjects with recent ACL injury, 23 subjects with chronic ACL deficiency of at least 10 years standing, and 14 subjects with established osteoarthritis of the knee were recruited. The 20 subjects with recent ACL injury were examined again at 12 weeks and 2 years following knee reconstruction. The tibiofemoral contact patterns were examined for each group of subjects and the associations between changes in the contact patterns and evidence of joint damage explored. Evidence of joint damage and severity of osteoarthritis were recorded from xrays, diagnostic MRI, operation reports and bone densitometry at the tibial and femoral condyles of the knee. Each of the three groups with knee pathology exhibited different characteristics in the tibiofemoral contact pattern, and these differences were associated with severity of joint damage and osteoarthritis. The recently ACL-injured knees demonstrated a tibiofemoral contact pattern that was posterior on the tibial plateau, particularly in the lateral compartment. Those with chronic ACL deficiency demonstrated differences in the contact pattern in the medial compartment, associated with severity of damage to the knee joint. Osteoarthritic knees showed reduced femoral roll back and longitudinal rotation that normally occur during knee flexion. Two years following knee reconstruction there was no difference between the contact pattern of the reconstructed and healthy contralateral knees. This technique of tibiofemoral contact pattern mapping is sensitive to the abnormal characteristics of kinematics in ligament injury and osteoarthritis. This is the first time the tibiofemoral contact characteristics of chronic ACL-deficient and osteoarthritis knees have been described and links examined between tibiofemoral contact patterns and degenerative change.

Doctor of Philosophy
The aim of the work presented in this thesis was to examine the associations between the kinematics of the knee characterised by the tibiofemoral contact pattern, and degenerative change, in the context of anterior cruciate ligament (ACL) injury. While the natural history of degenerative change following knee injury is well understood, the role of kinematics in these changes is unclear. Kinematics of the knee has been described in a variety of ways, most commonly by describing motion according to the six degrees of freedom of the knee. The advantage of mapping the tibiofemoral contact pattern is that it describes events at the articular surface, important to degenerative change. It was hypothesised that the tibiofemoral contact pattern would be affected by injury to the knee. A model of ACL injury was chosen because the kinematics of the knee have been shown to be affected by ACL injury, and because the majority of chronic ACL-deficient knees develop osteoarthritis, the associations between kinematics and degenerative change could be explored. A technique of tibiofemoral contact pattern mapping was established using MRI, as a quantifiable measure of knee kinematics. The tibiofemoral contact pattern was recorded from 0º to 90º knee flexion while subjects performed a leg-press against a 150N load, using sagittal magnetic resonance imaging (MRI) scans. The technique was tested and found to be reliable, allowing a description of the tibiofemoral contact pattern in 12 healthy subjects. The tibiofemoral contact patterns of knee pathology were then examined in a series of studies of subjects at a variety of stages of chronicity of ligament injury and osteoarthritis. Twenty subjects with recent ACL injury, 23 subjects with chronic ACL deficiency of at least 10 years standing, and 14 subjects with established osteoarthritis of the knee were recruited. The 20 subjects with recent ACL injury were examined again at 12 weeks and 2 years following knee reconstruction. The tibiofemoral contact patterns were examined for each group of subjects and the associations between changes in the contact patterns and evidence of joint damage explored. Evidence of joint damage and severity of osteoarthritis were recorded from xrays, diagnostic MRI, operation reports and bone densitometry at the tibial and femoral condyles of the knee. Each of the three groups with knee pathology exhibited different characteristics in the tibiofemoral contact pattern, and these differences were associated with severity of joint damage and osteoarthritis. The recently ACL-injured knees demonstrated a tibiofemoral contact pattern that was posterior on the tibial plateau, particularly in the lateral compartment. Those with chronic ACL deficiency demonstrated differences in the contact pattern in the medial compartment, associated with severity of damage to the knee joint. Osteoarthritic knees showed reduced femoral roll back and longitudinal rotation that normally occur during knee flexion. Two years following knee reconstruction there was no difference between the contact pattern of the reconstructed and healthy contralateral knees. This technique of tibiofemoral contact pattern mapping is sensitive to the abnormal characteristics of kinematics in ligament injury and osteoarthritis. This is the first time the tibiofemoral contact characteristics of chronic ACL-deficient and osteoarthritis knees have been described and links examined between tibiofemoral contact patterns and degenerative change.

Conventional anterior cruciate ligament (ACL) reconstruction grafts have not been able to replicate the mechanical behaviour of the native ACL, reproduce normal knee mechanics and kinematics, or prevent degenerative disease progression of the knee. The aim of this thesis was to investigate a novel ACL design to more closely mimic the normal mechanical behaviour of the ACL, reconstruct the isometric ACL fibre and potentially reproduce the normal kinematics and mechanics of the knee. The designed artificial ACL reconstruction (ACLR) system could be used as a stand-alone device or in conjunction with a total knee replacement (TKR). The nominated design option for the ACLR system consisted of a connecting cord made of ultra-high molecular weight polyethylene (UHMWPE) fibres and an elastic system made of cobalt-chrome-molybdenum (CoCrMo) alloy with similar load-elongation characteristics to the native ACL. The design requirements were defined based on the mechanical properties of the native ACL, size constraints from the bony geometry and TKR components, and the location of the isometric fibres of the native ACL. The in vitro mechanical tests performed in this project on the designed cord showed a 2-3 times greater ultimate tensile load compared to the ACL in young human cadavers. The decreasing creep modulus of the UHMWPE cord under fatigue loading in simulated body conditions (3118 MPa at 6.5×10⁶ cycle) indicated nominal creep and stabilised mechanical properties by the 3000^th loading cycle. To replicate the non-linear stiffness of the ACL with ~38 N mm^-1 toe and ~100 N mm^-1 linear regions, the artificial ACLR device consisted of a femoral spring (~60 N mm^-1) in series with a tibial spring (~100 N mm^-1) and a connecting cord (~2000 N mm^-1). Two helical springs in series were used for the stand-alone ACLR, whereas a helical spring in series with a spiral spring was designed for the ACLR-TKR. As both the helical and spiral springs had a constant stiffness, stop mechanisms were added to the springs to create a non-linear stiffness and control the maximum safe deformation limit of each spring. To understand the mechanical behaviour of the reconstructed isometric fibre of the ACL, passive and loaded motions were simulated in 18 sets of segmented MRI models of healthy human knees. Constant load and elongation was observed throughout flexion during the passive movements, whereas maximal load and elongation in the reconstructed ACL was identified at 50 º of flexion during loaded motion. An ACL attachment placement sensitivity study, conducted in this project to assess the effect of surgical implantation error on the behaviour of the reconstructed ACL, revealed that misplacement of the femoral attachment would significantly influence the load-elongation of the reconstructed ACL. Finite element (FE) models of the designed ACLR devices enabled their behaviour under simulated axial loading, squatting and the Lachman test to be assessed. Both ACLR devices successfully reproduced stiffness of the native ACL with a multi-linear stiffness curve, however, elongation greater than 3.1 mm could not be achieved. It can be concluded that the designed artificial ACLR devices were able to mimic the mechanical behaviour of the ACL provided it was positioned at the isometric attachment points; potentially enabling achievement of more natural kinematics and mechanics of the reconstructed knee. However, ACL placement was shown to have a significant impact on the behaviour of the reconstructed ACL, therefore, placement error may over-constrain the joint. For this reason, a more forgiving design with a lower stiffness and a larger deformation limit would be advised.

The purpose of the present investigation was to determine the net passive elastic joint moment and the angular damping coefficient of the human knee joint in full range flexion-extension. A secondary purpose was to develop regression equations to predict the measured passive properties from anthropometric data. The passive elastic moments increased exponentially as the limits of either flexion or extension were approached. The midrange of joint motion was a low moment (5 N$\cdot$m), low stiffness region. Considerable variability in the magnitudes of the passive elastic moments existed across subjects. At 140$\sp\circ$ of flexion, between about 5 N$\cdot$m and 86 N$\cdot$m was measured while the range at full extension (0$\sp\circ$) was about 6 N$\cdot$m to 22 N$\cdot$m. The angular damping coefficient was a nonlinear function (approximately quadratic) of the knee joint angle. The variability was not quite as high compared to the elastic component. Application of the data to the late swing phase of walking indicated that, for some subjects, the passive moments may contribute (or oppose) significantly to the net joint moment. (Abstract shortened by UMI.)

Focal chondral defects of the knee develop in hyaline cartilage when subjected to repetitive overloading or impact trauma. The degeneration of the articular surface results in joint pain and stiffness during daily activities such as walking. In most cases palliative non-invasive treatments can be used to alleviate pain; however, more severe lesions require restorative or replacement surgical interventions to repair the damaged cartilage. The use of a novel pyrolytic carbon knee trochlear implant aims to eliminate the aforementioned orthopedic pain by providing a focal replacement of lesions in the patellar sulcus. Pyrolytic carbon was the selected material due to its superior wear properties, mechanical strength, and biocompatibility. The purpose of this study was to develop a verified computational simulation in Abaqus to evaluate the experienced tensile stress of six different pyrolytic carbon trochlear implants undergoing two different physiologically relevant load conditions. This data was compared to an experimental conjugate study to provide insight into the implants strength. Regions of peak maximum principal stress were observed to be at the medial fillet and sulcus groove when undergoing a single- or two-point loading condition, respectively. The magnitude of tensile stress in the medial fillet was 2-3 times of that experienced at the sulcus groove. These findings reflected experimental data in which trochlear implants failed at either the medial fillet or sulcus groove during their respective loading conditions. Verified simulations allowed for computational testing of a modified implant and calculations of expected critical fracture loads.
acase@tulane.edu

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School of Physical Education, Sport, and Exercise Science

Passive knee motion is guided by the interaction of the articular surfaces and the restraining role of the soft-tissue structures. It is defined by characteristic kinematics within an envelope of motion. The main goal of this thesis was to simulate this characteristic motion by developing a subject-specific anatomically based finite element model. CT and MR image stacks were used to develop the geometry model and experimental (mechanical) test data was used as model input. Passive knee flexion was simulated and translational and rotational motion described using the Joint Coordinate System (JCS). The model was validated using clinical flexion and AP drawer tests. An ACL reconstruction model was also developed. Highest AP laxity was found at 30?? of flexion when the graft was positioned in the original native ACL insertion point. ACL tunnel positions were simulated according to surgical techniques. For this case, the highest AP laxity was displayed at 0?? of flexion. Four different graft materials were examined, with the quadriceps tendon graft exhibiting highest laxity, followed by the patellar tendon, braided hamstring and finally unbraided hamstring graft. The effect of malpositioning the graft's femoral attachment point from its central location was also investigated. The proximal femoral attachment point most closely mimicked the central attachment point in terms of AP laxity in the native ACL insertion group. In the ACL tunnel group, the posterior femoral attachment point most closely mimicked the intact knee. In this thesis it was found that changing the femoral insertion point of the graft can highly influence the AP laxity behaviour. Also using the surgical technique to create ACL tunnels may not necessarily produce the same kinematic behaviour as the intact knee. Lastly, this thesis has shown the importance of explicitly defining the local reference coordinate system when describing knee kinematics. Changing the coordinate system markedly alters the calculated kinematics. Ideally, a standardisation of local coordinate systems, similar to the JCS, would be proposed within the biomechanics community.

Access to abstract permanently restricted to Ball State community only.
Access to thesis permanently restricted to Ball State community only.
School of Physical Education, Sport, and Exercise Science

The purpose of this study was to examine the relationship between leg dominance and knee mechanics to provide further information about the etiology of ACL injury. Sixteen healthy females between the ages of 18 and 22 who were NCAA Division I varsity soccer players participated in this study. Subjects were instructed to perform a cutting maneuver; where they sprinted full speed and then performed an evasive maneuver (planting on one leg and pushing off to the other leg in a new direction) at a 45° angle with their dominate leg (DL) and non-dominate leg (NDL). Subjects were required to perform five successful cuts on each side given in a random order. Bilateral kinematic and kinetic data were collected during the cutting trials. After the cutting trials, subjects performed bilateral isometric and isokinetic testing using a Cybex Norm dynamometer at a speed of 60°/sec to evaluate knee muscle strength. During the braking phase the NDL showed greater (P=0.003) power absorption, greater (P=0.01) peak internal rotation angle and greater (P=0.005) peak flexion velocity. During the propulsive phase the DL showed greater (P=0.01) power production, greater (P=0.038) peak internal adductor moment and greater (P=0.02) peak extension velocity. In addition, no differences (P>0.05) in knee extensor and flexor isometric and isokinetic torques between the two limbs were shown. The results of this study show that a difference in knee mechanics during cutting does exist between the DL and NDL. The findings of this study will increase the knowledge base of ACL injury in females and aid in the design of more appropriate neuromuscular, plyometric and strength training protocols for injury prevention.
School of Physical Education, Sport, and Exercise Science