published_or_final_version / Mechanical Engineering / Master / Master of Philosophy

<p> Determining natural inner knee mechanics is a longstanding goal for researchers with applications to prevention and treatment of knee trauma and osteoarthritis. Physical testing has only provided limited information of knee mechanics due to technical challenges and cost. Modeling has been used for decades to obtain some of this otherwise inaccessible information, and recently finite element analysis (FEA) has become a popular means to this end. However, FEA requires time intensive mesh-creation and has large computational requirements. Ideally, model creation should be easy and simulations should be fast to allow for sensitivity analysis. Although allowing easier model creation and offering over an order of magnitude more computational efficiency than FEA, current rigid body modeling of the knee is limited by imprecise methodologies for defining material properties. Cartilage and meniscus are particular points of weakness. </p><p> The following thesis develops an improved methodology for cartilage contact which is user-friendly and allows for precise definition of contact via user-supplied material properties while accounting for changes in stiffness due to discretization. Additionally, meniscus modeling is improved by developing and implementing equations which directly define stress-strain relationships to match values reported in literature or those selected by the user. Results from two implemented knee models are compared to experimental results in literature and sensitivity to material properties and driving kinematics is investigated.</p>

<p> Over one&ndash;third of Americans over the age of 65 fall each year, costing more than $19 billion in health care costs in 2000. Many adults 65+ who have not experienced a fall still fear falling, and fear can decrease quality of life and increase the likelihood of falls. Several factors such as muscle strength, power, stiffness and tendon properties change in the human body with age affecting balance, which has been tagged as a fall risk predictor. Additionally, balance recovery strategies also differ between young and older adults, with young adults primarily utilizing their ankle joint and older adults utilizing their hip. The role of passive ankle joint power in balance recovery is unknown. Therefore, we conducted three studies. In Study 1, we investigated the role of passive ankle joint power in balance recovery of young subjects and tested if the contribution of passive power to net ankle joint power changed with perturbation speed. In Study 2, we explored the factor of age in the contribution of passive ankle joint power to net ankle joint power. In Study 3, we searched for a link between the contribution of passive ankle joint power to net ankle joint power and balance recovery strategy. Passive joint torque through the full range of motion was collected for each subject. Each subject performed 5 stepping tasks at two speeds, fast and slow. Joint kinematics and kinetics were collected for each trial. Inverse dynamics were performed and net ankle joint torque and net ankle joint work were computed. Passive ankle joint torque models were optimized for each subject, and passive ankle joint powers were determined. In Study 1, there appeared to be no difference in net or passive joint powers with respect to perturbation speed. In Study 2, age affected net ankle joint powers and passive uniarticular plantar- and dorsiflexor powers. In Study 3, we noted a change in balance recovery strategy between young and older adults. We were unable to predict balance recovery strategy index based off of the percent contribution of passive ankle joint work to net ankle joint work. These studies bring greater clarity to the role of passive ankle joint power with respect to balance recovery. </p>

<p> Advances in medical imaging now provide detailed images of tumors inside the brain and miniaturized energy delivery systems enable tumor destruction through local heating powered by Laser Interstitial Thermal Therapy (LITT). LITT is a thermo-ablative procedure that uses a laser probe to produce a desired thermal profile inside of the tumor and cause heat-injury to the targeted tissue. </p><p> Surgeons can monitor the placement of the probe and the ablation profile using real-time MRI imaging and real-time thermometry data. This real-time imaging and monitoring enable the surgeon to determine how much of the brain tumor has been ablated, while also ensuring that safe boundaries are kept from other critical structures surrounding the tumor. </p><p> Unfortunately, some of these brain tumors are located deep within the sub insular and brain-stem, where access and resection are nearly impossible and the current standard of care is radiation and chemotherapy treatment. Other types of these tumors continually recur and are associated with high morbidity and mortality rates. </p><p> As such, a minimally invasive means of accessing and treating deep, large and complex brain tumors is highly desirable. Thus, a method for steering the laser probe, such that it can follow curved trajectories and target various locations, through a single port, is needed. Many medical procedures involve the use of needles, but targeting accuracy can be limited due to obstacles in the needle's path, shifts in target position caused by tissue deformation, and undesired bending of the needle after insertion. </p><p> In order to address these limitations, we have developed a system that can actively steer a needle in soft tissue. We have designed and built a medical device with a steerable tip that carries an ablation probe to adjacent points within tissue under MRI. We test our steerable guide in a test apparatus using a block of phantom tissue. It is worthy to note that deviation from the path of the model data is never more than 0.41 mm.</p>

<p> The mechanical properties of the extracellular matrix (ECM) have shown to regulate key cellular processes. However, current tools studying cell-ECM biophysical interactions revolve around cell-mediated traction forces, which, as I will show, are not appropriate in natural matrices due to matrix remodeling. I used active microrheology (AMR) to, instead, measure ECM stiffness in order to quantify these interactions in various cell-ECM systems. </p><p> In the first system, I evaluated a commonly used 3D cell-culture method in breast cancer research. I show that this model produces a large physical asymmetry in ECM stiffness, which resulted in altered cellular morphology, adhesion-mediated signaling, and phenotype. Importantly, a hallmark result obtained in this culture method was not repeatable once the asymmetry was removed, highlighting the importance of considering biophysical interactions in cell-culture models. </p><p> In the second system, my work, in collaboration with Dr. Stephen Weiss, led to the discovery that stem cells are not passive recipients of ECM stiffness signals as previously thought. Rather they can deliberately alter local (pericellular) stiffness with matrix metalloproteinases as a control for cellular functions. In particular, we found that skeletal stem cells competent in their ability to degrade collagen, increased pericellular stiffness via matrix remodeling to activate ?1 integrin signaling pathways and thus controlled their own lineage commitment to osteogenic fates. Cells without the ability to degrade their local matrix lost this functionality and were restricted in lineage commitment to adipogenic or chondrogenic fates. </p><p> For the third system, I quantified the contributions of cell contractility and matrix metalloproteinases in matrix remodeling for developing a normal mechanical topography in smooth muscle cells. I also provide evidence that it is the distribution of pericellular stiffness rather than a bulk value that instructs cellular behavior. In order to accomplish this task, I automated the AMR system (aAMR) for a tenfold decrease in measurement time. Importantly, aAMR reduces the complexity of AMR to a few mouse clicks, can create stiffness maps over large distances and provides metrics to assess the distribution of stiffness in the pericellular space within the volume of a natural, fibrous hydrogel.</p>

<p> Injuries from ladder falls are prevalent and severe. Previous research has examined certain elements of ladder falls such as the ladder base slipping, but few studies have examined the factors that contribute to climbers falling from the ladder, particularly for permanent/fixed ladders. In addition, the biomechanical response to a ladder slip/misstep during ladder climbing and the factors that affect a fall from a ladder are not well understood. This thesis is a two part study that simulated ladder slips and missteps in order to find factors 1) associated with ladder slip risk and 2) that decrease fall severity from a ladder. Specifically, 32 participants were recruited for study 1 to investigate restricted toe clearance, hand positioning, age, climbing direction and climbing biomechanics with slip risk. Thirty-five participants were recruited for study 2 to investigate the impacts of gender, climbing direction, gloves, and hand and foot responses on fall severity. Study 1 found restricted toe clearance, younger ladder climbers, and climbing biomechanics with greater variation to be associated with an increased slip risk. Study 2 found that males, ascending climbs, post-perturbation hand placements that extended the arm, and foot responses that hit the top of a ladder rung were associated with decreased fall severity.</p>

Introduction: Claims that foot orthoses can resolve low-back pain are common in the marketing of these devices. The claims are based on the notion that wearing the orthoses will limit excess pronation at the subtalar joint thus reducing excessive internal tibial and femoral rotations. Excess leg rotations increase the anterior tilt of the pelvis and subsequently the degree of lumbar lordosis. Since lumbar lordosis has been suggested as a cause of low-back pain, it is speculated that foot orthoses could be used to treat and prevent pain to the low-back by reducing the forward curvature of the spine. This mechanical link between foot function and the low-back has not been investigated by experimental studies. Purpose: The purpose of this thesis was to investigate whether increased internal rotation of the femur induced an anterior tilt of the pelvis thus increasing the degree of lumbar lordosis and if external rotation induced a posterior pelvic tilt thus decreasing the degree of lumbar lordosis. Methods: In order to internally and externally rotate the femur, participants placed their feet in 18 different foot positions. Seven of these positions ranged from 15 degrees of foot eversion to 15 degrees of foot inversion and 11 positions ranged from 40 degrees of external foot rotation to 40 degrees of internal foot rotation. Six cameras surrounded the motion capture area and angles of pelvic tilt and lumbar lordosis were calculated. Results: Foot eversion and inversion did not have a statistically significant effect on pelvic tilt and lumbar lordosis. In-toeing had a statistically significant linear relationship with anterior pelvic tilt (R2=0.35, F1,131=69.79, p=0.00). Internally and externally rotating the feet had no effect on lumbar lordosis (R2=0.001, F1,153=0.09, p=0.77). Conclusion: Internally rotating the legs caused the pelvis to tilt anteriorly but only at extreme ranges of motion, much greater than what would normally be seen during gait. At which point, lumbar angles remained unaffected. This study does not dispute the effectiveness of foot orthoses to treat low-back pain but the results do not support the mechanical link proposed as the mechanism by which they work.

<p> This thesis consists of four major studies: a study of incipient flight behaviors in young birds over ontogeny (chapter 1); a detailed study of maneuvering using physical models of a likely ancestral bird morphology (chapter 2); a comparative study of maneuvering ability in several stem-group birds, within a phylogenetic context (chapter 3); and development of basic engineering theory to quantify the turbulence sensitivity of shapes to environmental turbulence of given scales and spectral content. The studies have identified: 1) shifts in function from asymmetric to symmetric movements in young birds, contrary to predictions from alternative hypotheses and occurring before wing-assisted incline running; 2) shifts in function, tied to angle of attack, of asymmetric appendage postures in creating yawing and rolling moments; and 3) migration of control effectiveness as tails are shortened and other features change, during the early evolution of birds. The work plugs some considerable gaps in current prevailing theories (e.g. Dial, 2003; Tobalske et al., 2011) and provides a test of hypotheses of flight evolution not based in outdated "trees-down'' or "ground-up'' paradigms from the past, but rather based on the universal need of airborne animals to maneuver (Dudley and Yanoviak, 2011; Maynard-Smith, 1953).</p><p> This work seeks to understand early flight evolution from a maneuvering perspective; every animal in the air must maneuver, and by understanding "powered'' flight as simply a point along a spectrum of <i>maneuvering</i> flight (Dudley and Yanoviak, 2011), unifying breakthroughs are made. It is hoped that the multifaceted approach taken here, with ontogenetic series, aerodynamic studies, and phylogenetic approaches, is robust against the shortcomings of any one approach individually: confounding ontogeny with evolution (as may be the case in others' studies of alternative hypotheses, e.g. Dial, 2003); inferring implausible functions from paleontological material in the absence of proper benchmarking against live animals; or misdiagnosis of how forms work in the absence of functional studies.</p>

Knee osteoarthritis (OA) causes more disability in community dwelling older adults than any other condition. The high costs associated with treating this disability suggest that research needs to focus on ways of preventing the development and progression of knee OA using low cost interventions such as exercise and modifications to certain activities of daily living. One such activity of daily living that has been implicated in the OA disease process is normal level walking or gait. Those with medial compartment knee OA are known to make certain modifications in their gait patterns in an attempt to unload the diseased compartment of their knee. Two of these modifications include the tendency of those with knee OA to walk with an externally rotated foot, and to increase the activity of their lateral hamstrings, while decreasing the activity of their medial hamstring during gait. Therefore, this work attempted to clarify this relationship between foot position, lower extremity loading and hamstring muscle activation patterns during both level walking and lower limb exercise. First, the changes in lower extremity loading with both internal and external rotation of the foot during gait were investigated in a group of young healthy subjects. It was discovered that internal rotation increased the magnitude of both the adduction moment and the medial-lateral shear force at the knee; while external rotation decreased both these measures. This suggests that external foot rotation may be an effective compensation strategy for those with medial knee OA and internal foot rotation may be an effective compensation strategy for those with lateral knee OA. Second, the same study was then repeated in a group of knee OA subjects and age matched healthy normal subjects; but in this work, hamstring EMG was also collected along with the external knee loads. Hamstring EMG data was used to calculate the medial-lateral (M-L) hamstring activation ratio. An increased M-L activation ratio would indicate an internal muscle moment tending to load the medial compartment more than the lateral; while a low M-L activation ratio would tend to unload the medial compartment. Those with knee OA had an increased late stance knee adduction moment and a decreased M-L hamstring activation ratio as compared to the healthy control group. Also, external foot rotation decreased the late stance knee adduction moment, lateral-medial shear force at the knee, and M-L hamstring activation ratio for both groups; but, internal foot rotation did not increase these measures. Lastly, since it is apparent that the hamstring may play a role in unloading the diseased knee compartment, the M-L activation ratio was calculated with changes in foot position during lower limb exercise in young healthy subjects to determine if selective activation of the medial or lateral hamstrings was indeed possible. It was discovered that internal foot rotation increases the M-L hamstring activation ratio and external rotation decreases it. Foot rotation has the ability to shift the external loads on the knee to one side of the joint or the other, and it also has the ability to alter internal knee loads created by hamstring muscular activation. Therefore, foot rotation during gait and lower limb exercise may be an effective intervention that could be used to delay the onset and progression of knee OA, keeping older adults active and healthy much longer. / Thesis (Ph.D, Kinesiology & Health Studies) -- Queen's University, 2007-09-28 14:31:23.908

Knee osteoarthritis is a disease that affects nearly 40% of the global population over the age of seventy. It is believed that the incidence and progression of osteoarthritis can be partially attributed to changes in mechanical joint loading. Consequently, changes in lower-limb joint moments are important outcome measures for its treatment and prevention. The purpose of this study was to investigate the effect of four different anatomic joint models on the detection of changes in lower-limb joint moments due to knee osteoarthritis. Moments during gait were calculated for 44 subjects with moderate osteoarthritis and 44 asymptomatic subjects, then expressed using four joint models: Joint Coordinate System, Plane of Progression, Distal, and Proximal. Discrete peak measures and principal component scores were compared between groups. Hip adduction magnitude, knee adduction magnitude, peak early-stance knee internal rotation, and peak ankle plantarflexion moments were different between groups regardless of joint model. Differences detected using principal component analysis were less sensitive to the choice of joint model. Results support adoption of the Joint Coordinate System as a standard for joint moment expression due to its clinical relevance and ability to detect differences due to moderate knee osteoarthritis. / Thesis (Master, Mechanical and Materials Engineering) -- Queen's University, 2009-07-29 14:08:56.683