The cause and best treatment option for mechanical low back pain due to disc degeneration remains unsolved, despite `spinal fusion' being the gold standard of surgical treatment, post conservative care, for a very long time. However, the potential drawbacks of spinal fusion and the ongoing evolution in the understanding of normal and symptomatic spine biomechanics, biology and mechanobiology in conjunction with the advancements in material sciences, and tissue engineering has led to a change in the clinical perspective towards treatment methodologies for spinal disorders. Clinically, a gradual shift in philosophy is being observed from a `one size fits all', i.e. spinal fusion for all patients with symptomatic low back pain to a `customized approach', i.e. patient and indication specific treatment modalities for spine care. This philosophy has laid the ground for concepts of `motion preservation' and `dynamic stabilization', the former being an established treatment modality in orthopedics for a long time. The aim of the current study is to perform a comprehensive scientific investigation to understand, evaluate and establish the in vitro biomechanical characteristics and performance of indication specific treatment modalities incorporating the concept of Posterolateral Disc Arthroplasty and Posterior Dynamic Stabilization for the treatment of symptomatic mechanical back pain. The results of this comprehensive study may help the clinicians to make an informed decision while selecting and designing a treating modality for their patients. To this end, the current thesis was undertaken to study the biomechanics of indication specific treatment modalities like motion preservation and dynamic stabilization with a goal to guide clinical and product development decision making. Through the comprehensive biomechanical investigation conducted in the current thesis we were able to theoretically prove the importance of a customized approach towards the treatment of spine care. Also, the most important conclusion of the biomechanical investigation was the fact that Range of Motion results alone are not sufficient to draw significant conclusions. It is imperative that in depth analysis of the quality of motion through the determination of instantaneous center of rotation is extremely important. Previous studies have shown only a single center of rotation between the extremes of motion which is also insufficient as the end points do not determine the path taken to reach the endpoints. This in depth analysis is also important for biomedical engineers to design and develop physiologically viable implants that will mimic the performance of the physiologic spine. Clinical studies are extremely important as a next step towards validating this customized approach towards spine care.

Light vehicle rollover accidents on soft surfaces can be modeled assuming constant drag with linear motion equations and other engineering principles. The concept of using segment average results to evaluate roll mechanics parameters throughout a roll sequence, and specifically, segment duration to evaluate vehicle trajectory between ground impacts is developed. The trajectory model is presented, explained and compared to values obtained by analyzing digital video of rollover crash tests. Detailed film analysis procedures are developed to obtain data from rollover crash tests that are not otherwise documented. Elevation of the center of gravity of vehicles is obtained where instrumentation does not explicitly yield this data. Instantaneous center of gravity elevation data throughout a roll sequence provides the opportunity to calculate descend distances as a vehicle travels from one ground contact to another. This data is used to quantify severity of ground impacts as a vehicle interact with the ground throughout a roll sequence. Segment average analysis is a reasonable method for determining general roll mechanics parameters. Because of the chaotic nature of rollover accidents, the range of effective drag factors for a given roll surface may be quite large. Choosing an average of typical drag factors is a reasonable approach for a first-order approximation although certain parameters may be predicted less accurately than if actual values were known. The trajectory results demonstrate the influence of drag factor descent height calculations. Typical constant drag factors tend to overestimate descent height early in a roll sequence and underestimate descent height later in the sequence. The trajectory model is a useful tool to aid in understanding rollover mechanics although a rolling vehicle may be in contact with the ground for a significant fraction of a roll segment. The model should not be used at locations in roll sequences where there are extremes in translational center of gravity decelerations. These extremes include the segments immediately following overturn where there are large angular accelerations and large differences between the tangential velocity of the vehicle perimeter and the translational velocity of the center of gravity, as well as segments that include vehicle impacts with irregular topography.