Background The use of school scoliosis screening for early detection of adolescent idiopathic scoliosis (AIS) in order to avoid the need of invasive surgery remains controversial. In an internationally large population-based cohort of students, the Hong Kong scoliosis screening programme has been shown to have low referral rate of students for radiographic diagnosis and high accuracy in identifying AIS patients requiring clinical follow-up. However, before school scoliosis screening is considered worth implementing, its direct effect on the need of surgery should also be assessed as stipulated in the literature. Therefore, we aimed to examine the temporal change of the rate of AIS patients in need of surgery since the inception of the Hong Kong screening programme in 1995, and assess the change of the rate across age and birth year of adolescents. Methods A large scale data collection was made from the Duchess of Kent Children Hospital (DKCH), the Prince of Wales Hospital (PWH) and the Department of Health. We obtained the screening history, spinal curvature, surgical status and demographics of AIS patients aged between 10 and 19 years who visited either of the DKCH or PWH, the only two public specialist hospitals in Hong Kong that managed AIS patients, during 1996 to 2009. The data have been carefully collated and cleaned before data analysis. Age-period-cohort model estimated by the modern intrinsic estimator was used to delineate the effects due to age, period taken as calendar year, and cohort taken as birth year on the rate of reaching an indication for surgery, taken as a Cobb angle ? 45° or operated for AIS. Results During 1996 and 2009, a total of 1,117,182 students participated in the Hong Kong scoliosis screening programme. Of which, 16,780 visited either DKCH or PWH, and had AIS detected. The incidence rate of AIS in Hong Kong adolescents generally increased over years. The proportion of AIS patients who previously participated in screening for scoliosis was 43% in 1996 and increased to over 90% after 2001. A total of 636 AIS patients received spinal fusion surgery. The mean curvature at operation in patients who were previously screened for scoliosis was 2.48 (95% CI = 11.35 to 12.65; p-value = 0.031) smaller than that in those who were not screened. The relative risk of indication for surgery was the maximal at the age of 14-15 years. Since the start of the programme, the risk of reaching indication for surgery generally increased but the rate was reduced by 2004-2005 onwards. However, the risk was fairly stable across birth cohorts. Conclusions This was the largest study that examined the temporal trend of the rate of requiring surgery for AIS in adolescents. The risk of requiring surgery for AIS increased due to changes in the incidence of AIS and exercise pattern. The Hong Kong scoliosis screening programme has provided important information on the annual trends about AIS, a disorder with unfortunately poor knowledge of its aetiology. / published_or_final_version / Nursing Studies / Master / Master of Philosophy

published_or_final_version / abstract / toc / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

published_or_final_version / Orthopaedic Surgery / Master / Master of Philosophy

This thesis presents an experimental study of a bovine vertebra using transmission and pulse-echo methods and a preliminary investigation to guide a screw insertion into a pedicle using TomoScan phased array unit. The results show the cancellous bone has higher attenuation than the cortical bone for 1.0-5.0 MHz. The optimal frequencies for imaging are found to be 3.5 and 5.0 MHz. When the sample is filled with water with the cancellous core removed, all reflections from the layers and screw are visible; however when the core is present, only reflections from the top cortex are identifiable. For the preliminary study, size and placement of the transducer array are important. When the ultrasound beam is normal to the pedicle surface, echoes from the pedicle layers and the steel bit are strong; otherwise, signals are weak and not even identifiable. Larger aperture size will enhance the signal-to-noise ratio but deteriorate lateral resolution.

No description available.

published_or_final_version / Orthopaedic Surgery / Doctoral / Doctor of Philosophy

No description available.

Surgical correction of scoliosis is a complicated mechanical process. Understanding the loads applied to the spine and providing immediate feedback to surgeons during scoliosis surgery will prevent overloading, improve surgical outcome and patient safety. Long-term development of residual forces in the spinal instrument after surgery with the continual curvature changes over time has been unknown. The goal of this research work was to develop a wireless implantable sensor platform to investigate the loads during and after surgery. This thesis describes research leading to the design of a sensor platform that uses both 403 MHz and 2.45 GHz for wireless communication, and reports the resolution and accuracy of the built-in temperature sensor, the A/D accuracy of the sensing platform, the power consumption at different operation modes, the range of the wireless communication and the discharge characteristics of a potential capacitive power module. / Biomedical Engineering

Top screw pullout is a significant problem in anterior scoliosis correction, with rates of 5-15% reported in the literature. The Mater Misericordiae Hospital in Brisbane currently has a series of 125 patients with scoliosis treated by thoracoscopic anterior fusion, instrumentation and correction between April 2000 and August 2007. In this series 11 top screws are known to have pulled out (a rate of 8.8%), with six occurring in the first week, and all within 6 weeks, suggesting that the problem is one of excessive static force rather than fatigue. This thesis describes a biomechanical investigation into the mechanics of vertebral body screw pullout in anterior scoliosis surgical constructs. Previous biomechanical studies of vertebral body screws have evaluated their resistance to either straight pullout or cephalo-caudad compression forces, however the aim of this study was to assess screw resistance to more realistic loading conditions, namely pullout of initially angled screws, and pullout where the motion path is an arc rather than a straight axial pullout, as would be expected in a single rod anterior construct. The first series of experiments involved straight and angled pullout tests using synthetic bone. In the angled tests, both locked and free-to-pivot configurations were tested. The second series of experiments tested the effect of cephalo-caudad pre-compression (the actual deformity correction step performed during surgery) on subsequent axial pullout strength. A third series of experiments performed arc pullouts using synthetic bone, and the final series of experiments tested the pullout resistance of a newly proposed screw position configuration against the standard screw positioning using ovine lumbar vertebrae. Synthetic bone testing revealed that for initially angled pullout, resistance is greatest as the screw angle approaches 0 (ie a direct axial pullout). Cephalo-caudad pre-compression reduced subsequent pullout strength for cases where a staple was not used under the screw head, but if a staple was used the pre-compression did not decrease pullout force significantly. Arc pullout resistance was greatest when the screw was angled at 10 cephalad, and the mean pullout strength for the proposed screw configuration using ovine lumbar vertebrae (1864N) was almost double that of the standard screw positioning (993N). The clinical implication of this study is that top screw pullout resistance can be maximised by placing the top screw as close as possible to the top endplate and the bottom screw as close as possible to the bottom endplate, although this will have detrimental effects on the pullout of the second screw should the top screw pull out. Screw angulation is a less important factor but any angulation should be in a cephalad direction and around 10º in magnitude. The experimental results also suggest that the use of a staple may play a role in preventing cephalo-caudad pre-compression forces from reducing screw resistance to subsequent pullout forces.