The pressure-tension hypothesis is the governing dogma of orthodontic tooth movement. This theory proposes that the application of loads to the crown of a tooth during orthodontic mechano-therapy results in differential site-specific reactionary strains in the para-dental tissues. Briefly, following the application of orthodontic load the bone and periodontal ligament (PDL) on one side of the tooth is placed in compression favoring bone resorption, while on the other side of the tooth they are placed in tension favoring osteogenesis The present in vitro model provides a surrogate for the PDL on the tension side of the tooth during orthodontic tooth movement and aims to identify mechanically induced changes in the expression of osteo-regulatory cytokines in human PDL cell cultures in response to tensile mechanical strain. Materials and Methods: PDL explants were obtained from pathology free bicuspids of two human subjects following extraction of the teeth for orthodontic purposes. Following serial passage, cells were plated on Uniflex� plates and consigned to either the experimental or control groups. Experimental cells were exposed to a cyclic uniaxial tensile mechanical strain for 6,12 or 24 hours using the Flexercell FX 4000 strain unit. Total RNA was extracted using a two-step procedure and samples were analysed using real-time RT-PCR assays for a range of osteo-regulatory cytokines. Results: Human PDL cells expressed mRNA for a range of cytokines of known significance to osteogenesis and osteoclastogenesis in response to mechanical stimulation. Conclusions: The production of osteo-regulatory cytokines by PDL cells in response to mechanical strain suggests that these cells have the potential to contribute to the osseous modeling of orthodontic tooth movement. The presence of osteogenic signalling drive in response to tensile strain tends to support the basic assertions of the pressure-tension hypothesis.

Ill. mounted. Bibliography: 9.1-9.20.

Some mounted ill. Bibliography: leaves 191-226.

Cervical spine injury can range from minor to severe or fatal, where severe injuries can result in incomplete or complete quadriplegia. There are close to 45,000 Canadians currently affected by paralysis due to traumatic spinal cord injury (tSCI) with an estimated 1700 new cases each year. The majority of tSCI occur in automotive collisions, and current methods for injury prediction are limited to predicting the likelihood for occupant injury but lack the detail to predict the specific injury and location at the tissue level. This research focused on major injuries associated with high impact automotive collisions such as rollover type collisions. Although whiplash is an injury commonly associated with automotive collisions, it was not considered for this study based on the low risk of neurological impairment. The goal of this study was to develop a cervical spine segment finite element model capable of predicting severe injuries such as ligament tears, disc failure, and bone fracture. The segment models used in this study were developed from previous cervical spine segment models representative of a 50th percentile male. The segment models included the vertebrae, detailed representations of the disc annulus fibres and nucleus, and the associated ligaments. The original model was previously verified and validated under quasi-static loading conditions for physiological ranges of motion. To accomplish the objectives of this research, the original models were modified to include updated material properties with the ability to represent tissue damage corresponding to injuries. Additional verification of the model was required to verify that the new material properties provided a physically correct response. Progressive failure was introduced in the ligament elements to produce a more biofidelic failure response and a tied contact between the vertebral bony endplates and the disc was used to represent disc avulsion. To represent the onset of bone fracture, a critical plastic strain failure criterion was implemented, and elements exceeding this criterion were eroded. The changes made to the material models were based on experimental studies and were not calibrated to produce a specific result. After verifying the modifications were implemented successfully, the models were validated against experimental segment failure tests. Modes of loading investigated included tension, compression, flexion, extension and axial rotation. In each case, the simulated response of the segment was evaluated against the average failure load, displacement at failure, and the observed injuries reported in the experimental studies. Additionally, qualitative analysis of elevated stress locations in the model were compared to reported fracture sites. Overall, the simulations showed good agreement with the experimental failure values, and produced tissue failure that was representative of the observed tissue damage in the experimental tests. The results of this research have provided a solid basis for cervical spine segment level injury prediction. Some limitations include the current implementation of bone fracture under compressive loads, and failure within the annulus fibrosus fibres of the disc should be investigated for future models. In addition to material model modifications, further investigation into the kinetics and kinematics of the upper cervical spine segment are important to better understand the complex interactions between the bone geometry and ligaments. This would give insight into the initial positioning and expected response in subsequent models. Future research will include integrating the current segment-level failure criteria into a full cervical spine model for the purpose of predicting severe cervical spine injury in simulated crash scenarios, with future applications in sports injury prevention and protective equipment.

Thèse d'exercice : Médecine. Médecine générale : Nantes : 2007. / Bibliogr.

Thesis (M.S.)--University of Alabama at Birmingham, 2008. / Title from PDF title page (viewed on Feb. 3, 2010). Includes bibliographical references (p. 38-42).

Thesis--Auburn University, 2009. / Abstract. Includes bibliographic references (p.115-

Anterior cruciate ligament (ACL) rupture is a major clinical problem in sports medicine. The current mainstay of treatment is arthroscopic-assisted ACL reconstruction with a soft tissue tendon graft. However, the affected patients are required to abstain from any pivoting activity for at least six to nine months after the operation to protect the graft-host bone interface in order to allow the graft to heal. In this study, a method to accelerate the graft healing within the bone tunnel is proposed by using a local application of an osteoconductive bone cement (Strontium enriched calcium phosphate cement, Sr-CPC) at the graft-host bone interface. It is postulated that Sr-CPC can induce earlier new bone formation in the gap between the graft and host bone tunnel and hence can result in an accelerated healing of the graft within the bone tunnel in ACL reconstruction. Preparation of Sr-CPCs using the conventional setting method (a dissolution/precipitation process) leads to a delay in setting. This study adopted a new setting reaction, a chelate reaction, to manufacture a Sr-CPC system. The Sr-CPC system was fast-setting, injectable and cohesive, and it was suitable for use in minimally invasive orthopaedics surgeries (e.g. arthroscopic-assisted ACL reconstruction). In order to investigate the biocompatibility and osteoconductivity of the Sr-CPC, in vitro cell experiments and an in vivo animal study were carried out. The in vitro experiments showed that the Sr-CPC was biocompatible with no local toxicity. In addition, a higher proliferation rate of osteoblastic-like MG-63 cells, accompanying higher alkaline phosphatase activity, was found in the Sr-CPC group. The in vivo study using a rat femur metaphyseal bone defect model showed evidence of earlier endochondral ossification which was noted at 2 weeks post operation. Moreover, a higher peri-cement bone formation rate, accompanied by a higher cement resorption rate, was found in the Sr-CPC group at 32 weeks after the operation compared with the convention calcium phosphate cement group. To study the effect of the Sr-CPC on the graft healing within the bone tunnel, a one-stage bilateral ACL reconstruction using an Achilles tendon allograft was performed in 30 rabbits. One study (15 rabbits) was to investigate the effect of the Sr-CPC on the healing of a soft tissue tendon graft within the bone tunnel, and the other study (15 rabbits) was to study the difference between the Sr-CPC and the conventional CPC in the healing of a soft tissue tendon graft within the bone tunnel. The Sr-CPC treated graft showed an accelerated healing at all of the time points when compared with the non-treated graft; and at time points of 3 to 12 weeks when compared with the CPC treated graft. In conclusion, a strontium enriched calcium phosphate cement, which is suitable for the arthroscopic use, was manufactured. It is biocompatible, osteoconductive and degradable. It accelerates the graft healing within the bone tunnels in a rabbit ACL reconstruction model using an Achilles tendon allograft when compared with both of the non-treated group and the conventional CPC-treated group. / published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

published_or_final_version / Orthopaedic Surgery / Master / Master of Philosophy

Die Ruptur des vorderen Kreuzbandes ist die häufigste Verletzung des Kniegelenkes. Ziel dieser prospektiven klinischen Studie ist es, Kriterien wie Operationsmethode- und zeitpunkt, subjektive Patientenzufriedenheit, Alltagsfähigkeit und betriebene Sportarten nach der Kreuzbandersatzplastik in verschiedenen Abhängigkeiten voneinander zu diskutieren. Um eine möglichst allgemeingültige Aussage treffen zu können, umfasst die Studie ein nicht-selektives Patientenkollektiv, das Männer und Frauen, Sportler und Nicht-Sportler, Schüler, Studenten und Berufstätige beinhaltet. Außerdem handelt es sich um eine Multicenterstudie, bei der Operationen und Untersuchungen von verschiedenen Personen durchgeführt werden und die Studie so eine höhere wissenschaftliche Aussagekraft bekommt. Der standardisierte Fragebogen, mit dem die Untersuchungen an allen drei Zentren durchgeführt wurden, ermöglicht dennoch eine gute Vergleichbarkeit aller Ergebnisse. Es wird ein Patientenkollektiv von 160 Patienten untersucht und nach dem standardisierten Fragebogen befragt. Kriterien der Sportfähigkeit (sportliches Leistungsniveau, Aktivitätsniveau und Zeitpunkt der vollen Sportfähigkeit), prä- und postoperativ betriebene Sportarten und Lysholm-Score, Operationsmethode und –zeitpunkt sowie die subjektive Patientenzufriedenheit werden miteinander in Verbindung gesetzt. Nach einem Zeitraum von durchschnittlich etwa 17 Monaten nehmen 90 Patienten an den Nachuntersuchungen teil. Etwa ein Jahr nach der Operation kann ca. die Hälfte der Patienten von einer komplett wieder erreichten Sportfähigkeit berichten. Auch bei der Befragung nach dem sportlichen Leistungsniveau in Wochenstunden berichtet ca. die Hälfte der nachuntersuchten Patienten von einer unveränderten sportlichen Leistungsfähigkeit im Vergleich zum Leistungsniveau vor der Operation. Hinsichtlich des Bezuges zwischen Sportfähigkeit und Operationsmethode ergibt sich, dass Patienten, die ein Double-Bundle-Transplantat erhielten, ihr sportliches Leistungsniveau am schnellsten und mit den geringsten Einschränkungen wieder erreichen. Patienten aus der Bone-Tendon-Bone-Gruppe erzielen die schlechtesten Ergebnisse hinsichtlich des Zeitpunktes und des Niveaus der Sportfähigkeit. Betrachtet man das gesamte Patientenkollektiv unabhängig von der Operationsmethode in Bezug auf den Lysholm-Score, ist der postoperativ erhobene Wert signifikant höher als der präoperative. Aufgeschlüsselt nach Operationsmethoden zeigt sich diese Signifikanz bei der Bone-Tendon-Bone- sowie bei der Semitendinosusgruppe. Nach der Operation mit einem Double-Bundle-Transplantat findet sich kein signifikant erhöhter Lysholm-Score. Der Operationszeitpunkt in Zusammenhang gesetzt mit dem in dieser Arbeit erhobenen postoperativen Lysholm-Score ergibt keine statistisch signifikante Korrelation. Auch die subjektive Patientenzufriedenheit korreliert nicht mit dem Zeitpunkt der Operation. Unabhängig vom Operationszeitpunkt ist eine große subjektive Patientenzufriedenheit zu finden. Mehr als 80 % der operierten Patienten bewerten ihr behandeltes Kniegelenk gut oder sehr gut. Hier findet sich eine Korrelation zwischen positiver Bewertung und einer möglichst vollständigen und zeitnahen Rückkehr zur ursprünglichen Sportfähigkeit. Durch diese Korrelationen bestätigt sich die These dieser Arbeit, dass die Wiedererlangung der Sportfähigkeit für den Patienten mit einer Ruptur des vorderen Kreuzbandes im Mittelpunkt steht.