UMD Theses and Dissertations
Permanent URI for this collectionhttp://hdl.handle.net/1903/3
New submissions to the thesis/dissertation collections are added automatically as they are received from the Graduate School. Currently, the Graduate School deposits all theses and dissertations from a given semester after the official graduation date. This means that there may be up to a 4 month delay in the appearance of a given thesis/dissertation in DRUM.
More information is available at Theses and Dissertations at University of Maryland Libraries.
Browse
5 results
Search Results
Item Effect of Load History on Ovine Intervertebral Disc Biomechanics(2014) Goodley, Addison; Hsieh, Adam H; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Loading of the intervertebral disc (IVD) alters biomechanical properties by modifying fluid distribution in the nucleus pulposus -changing hydrostatic pressure and tissue response- during force transmission along the spine. This study combines pressure, vertical displacement, and radial bulge measurements to assess biomechanical function during healthy and adverse loading of ovine lumbar motion segments. High compressive loads and simultaneous transient exertions, representative of obesity or other high-load lifestyles, are expected to limit fluid recovery and inhibit IVD biomechanical function compared to low compressive load controls with similar transient exertions. Specifically, the adverse group will (1) lose the ability to generate intradiscal pressures equivalent to control discs at equal loads and (2) exhibit a greater degree of deformation and bulge during comparable loading. This study contributes a greater understanding of the effects of load on IVD health. Findings may inform future efforts to preserve disc biomechanics and reverse IVD loss of function.Item Physical properties of lamprey spinal cord regeneration: adaptive vs. maladaptive recovery(2014) Luna Lopez, Carlos; Aranda-Espinoza, Helim J.; Bioengineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Spinal cord injury (SCI) is a physical trauma that can result in paralysis and even death; to date no treatment exists that can successfully promote functional or adaptive recovery. Although humans are unable to regenerate after complete SCI, there are animal models that have been studied for their ability to regrow and reconnect their nerve fibers. From the group of animals that are capable of spinal cord regeneration, in the best studied is the lamprey (Petromyzon Marinus) it has been noted that recovery can be maladaptive. When left to recover at warm temperature (23 ⁰C) most lampreys had adaptive behavior, but at cold temperature (10 ⁰C) most lampreys showed maladaptive behavior. In this thesis we studied the physical factors that influence adaptive and maladaptive recovery in lampreys. In the first part, we analyzed axonal regeneration and blood clot formation at early time points after injury (1-2 weeks). We found that lampreys in cold temperature have a blood clot that could be blocking spinal cord regeneration. In the second part of this work, we analyzed the biomechanical and structural differences between lampreys in warm and cold temperature. We used in vivo X-ray imaging and tensile loading testing of the spinal cord and notochord structures, before and after injury. We found that lampreys at warm temperature are more favorable to create a permissive mechanical and structural environment for regeneration. Lastly, we used those lessons learned previously to enhance regeneration of maladaptive animals. We removed the blood clot at the injury site and created a time frequency analysis to measure the recovery of coordination. We found that lampreys in cold temperature with clot removal had a more adaptive recovery after injury than those without removal. In summary, by using the lamprey we were able to compare the differences between regeneration in warm and cold temperature and found the physical factors that influence maladaptive recovery. Removing one of these factors, in this case the blood clot, successfully enhanced the recovery of coordination. These results have the potential to be translated to higher animals and aid in the creation of successful treatments for SCI.Item Kinetics in Individuals with Unilateral Transtibial Amputations Using Running-Specific Prostheses(2012) Baum, Brian Svercauski; Shim, Jae Kun; Kinesiology; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Improvements in rehabilitation and prosthetic design are needed to help promote activities such as running that increase physical activity levels of individuals with lower extremity amputation (ILEA). However, effectively developing these improvements requires a detailed understanding of prosthetic and ILEA running biomechanics. Running-specific prostheses (RSPs) have been developed to improve running performance for ILEA runners, but altered running kinetics may still be necessary to accommodate for the loss of musculoskeletal function caused by lower extremity amputation. The few studies investigating ILEA running with RSPs focus on maximal performance, but our understanding of how ILEA using RSPs modulate kinetics to run at submaximal velocities remains limited. The purpose of this study was to characterize changes in kinetics and mechanical energy across a range of running velocities in ILEA wearing RSPs. This dissertation investigated six specific aims through six corresponding experiments that improve our knowledge of mechanical and anthropometric properties of RSPs and the kinetic profiles of ILEA running at submaximal velocities. Four common RSP designs were tested for mechanical and anthropometric properties. ILEA with unilateral transtibial amputations who wear RSPs and an able-bodied control group participated in the running experiments. Mechanical and anthropometric results indicated that RSP marker placement had little effect on joint kinetic estimations proximal to the prostheses, and trifilar pendulums can measure moments of inertia with <1% error. The running experiments provided the first 3D kinetic descriptions of ILEA running. The prosthetic limb typically generated lower peak kinetic parameters and 50% lower total mechanical work than the intact and control limbs, indicating a greater reliance on the intact limb. To counter the prosthetic limb deficiencies, ILEA increased stride frequencies compared to control subjects. Additionally, the prosthetic limb demonstrated prolonged periods of anterior ground reaction force to increase propulsive impulse and prolonged hip stance phase extension moments that generated increased hip concentric work. The data indicated that ILEA wearing RSPs run differently than able-bodied runners and use several adaptive mechanisms to run at the same velocity and to increase running velocity. These mechanisms are discussed and future directions of research are suggested.Item MODELING CRUTCH COMPENSATION OF HIP ABDUCTOR WEAKNESS AND PARALYSIS(2011) Borrelli, James Rocco; Balachandran, Balakumar; Haslach Jr, Henry W; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Hip abductor weakness or paralysis is prevalent in the half a million cases of low level spinal injuries in the United States alone. Crutches are often used as an ambulatory aid by individuals with this type of permanent disability. This study investigates whether using a crutch with a wide stance, as opposed to a conventional vertical stance, returns the hip rotation and pelvic obliquity to a more normal range of motion for individuals with weak or paralyzed hip abductors. An inverse dynamics six link model of the body with ten degrees of freedom and a forward dynamics six link model with six degrees of freedom were used to simulate the swing and stance phases of gait with hip abductor weakness/paralysis while using either compensatory motions (hip hiking or lateral displacement of the torso) or crutches. The forward dynamics model characterizes the effect of hip abductor weakness on the gait kinematics hip rotation and pelvic obliquity. The model also characterizes the effect of compensatory motions and crutch use on gait with paralyzed hip abductors. The inverse dynamics model calculates the time varying body weight that must be supported on a contralateral crutch to achieve normal gait kinematics even with paralyzed hip abductors. The forward dynamics model predicts that hip abductor paralysis reduces the range of pelvic obliquity and increases the range of hip rotation. The model also predicts that compensatory motions and crutch use restore the range of motion of hip rotation and pelvic obliquity in gait with paralyzed hip abductors to more normal. The inverse dynamics model predicts that the portion of body weight that must be supported on a crutch for normal gait kinematics with paralyzed hip abductors is lowered by using a wide crutch stance. This study suggests that contralateral crutch use replaces the need for the compensatory motions hip hiking and lateral displacement of the torso while restoring the range of hip rotation and pelvic obliquity to more normal ranges in an individual with weak or paralyzed hip abductors. Furthermore, angling the crutch side-to-side restores the range while supporting less body weight on a contralateral crutch.Item Humeral Fracture Fixation Techniques: A FEA comparison of locing and compression techniques with cadaveric pullout comparison of cortical compression and internal locking screws.(2007-08-13) Johnson, Aaron; Barker, Donald; Mechanical Engineering; Digital Repository at the University of Maryland; University of Maryland (College Park, Md.)Locking and non-locking humeral repair techniques provide different mechanical constructs for securing fractures, and consequently could generate different strain fields at the callus. The purpose of this study was to investigate the strain field callus, and to compare to determine if one construct offers a healing advantage over another. An FEA analysis was conducted using ABAQUS, with all contact surfaces modeled as friction interfaces; additionally, a pretension was applied to the non-locking construct to simulate the effect of installation. The models were subjected to axial tension loads, and results were compared with existing cadaveric and synthetic experimental loading. Additional validation involved screw pullout testing conducted on cadaveric humeri. Results showed that the strain fields at the fracture site showed no significant variation in distribution, shape, or magnitude, therefore concluding that the locking plate offered no biomechanical healing advantage.