Thesis (M.Med.Sc.)--University of Hong Kong, 2004. / Also available in print.

Cervical Spondylotic Myelopathy (CSM) is a common type of spinal cord dysfunction in the elderly. The natural history of CSM is associated with disc degeneration and spondylosis, leading to the static and dynamic compression of the spinal cord, tissue ischemia, tissue damage, and ultimately neurological function deficit. However, the severity of the spinal cord compression does not necessarily correlate with the signs and symptoms of CSM in patients. Until now, the pathomechanism of CSM was not well understood. Establishing an evaluation technique is, therefore, criticalfor the pathophysiological investigation of CSM. Magnetic resonance imaging (MRI) has been widely used for evaluating the spinal cord parenchyma. However, conventional MRI is limited in detecting macroscopic changes, e.g. spinal cord compression, edema or hemorrhage etc. Recently, there has been increasing interest in diffusion tensor imaging (DTI), which permitting detects tissue water molecule diffusion at the microscopic level. The conventional DTI analysis for CSM relies on hand-drawn regions of interest (ROIs), so called ROI-based measurements. The ROIs are drawn on the sagittal image or on the axial image to cover the whole cord, which are insufficient to describe the precise diffusion pattern. In particular, the deformation and degeneration of the myelopathic cord poses a big challenge for the ROI-based analysis. The most commonly used parameter, fractional anisotropy (FA) has difficulty in determining the level diagnosis due to its relatively large variance along the cord. Furthermore, the functional activation following microstructural damage remains underexplored. In this dissertation, several novel methods for region-specific analysis were proposed for the investigation of microstructural changes in the CSM. In Chapter 2, ROI-based analysis was employed to detect the regional diffusion characteristics in CSM. In Chapter 3, an auto-template was developed that segments the cord and measures the DTI parameters automatically. We found that our auto-template outperforms hand-drawn ROI-based methods in terms of efficiency and reproducibility. In Chapter 4, entropy-based analysis was proposed to characterize the loss of complexity of microstructure in the myelopathic cord. It was demonstrated that FA entropy was an objective and quantitative evaluation parameter that was superior to conventional methods for separating CSM patients from healthy subjects. In Chapter 5, orientation entropy was used to detect the disordered orientational distribution of the nerve tracts in CSM, which could be used as a good index for the pathogenic level estimation. In Chapter 6, a diffusion tensor tractography-based method was proposed to overcome the difficulties in column-specific ROI drawing on the deformed and degenerated spinal cords. In Chapter 7, the structure-function relationship in the cervical spinal cord was explored by a combination of DTI and functional MRI. A significant correlation was found between enhanced functional responses and the loss of microstructural integrity in CSM. In this study, several novel post-processing methods were proposed and demonstrated, which were shown to have extraordinary capabilitiesfor the investigation and assessment of CSM. It is expected that these methods can be used as valuable tools for clinical diagnosis and for the selection of the most appropriate treatment strategy for CSM. / published_or_final_version / Orthopaedics and Traumatology / Doctoral / Doctor of Philosophy

Cerebrovascular accidents are a leading cause of morbidity and mortality in the United States. Many conditions exist which may mimic this disease process including seizures, migraines, metabolic derangements, infections, space-occupying lesions, neurodegenerative disorders, peripheral neuropathy, cervical myelopathy, syncope, other vascular disorders, and functional neurologic disorder. Timely diagnosis and treatment are important in order to preserve functional status in these patients. A 48-year-old male presented to the emergency department with a 28-hour history of worsening left sided numbness, tingling, weakness, and feeling off balance. The patient stated that for the past several months he had noticed these symptoms, but they suddenly became worse the day prior. He also described shooting pains down the left arm with certain movements of his neck. The patient denied any difficulty with speaking, understanding words, performing mental tasks, bowel or bladder incontinence, or right sided symptoms. Physical exam showed intact cranial nerves II-XII, 5/5 strength of upper and lower extremities on the right side, 4/5 strength of upper and lower extremities on the left side. Romberg test was normal, heel to shin and finger to nose were intact bilaterally. Foot drop was noted on the left side and placement of the foot on the ground was noted to be clumsy. Initial head CT in the emergency department showed a frontal lobe hypodensity and was without intracranial hemorrhage. Computed tomography angiography of the head and neck showed no large vessel thrombosis or stenosis. Echocardiography revealed normal chamber sizes, normal left ventricular ejection fraction, no patent foramen ovale, and no left atrial or left ventricular thrombus. Telemetry monitoring throughout the stay remained sinus rhythm. Magnetic resonance imaging of brain and cervical spine was performed showing multifocal acute infarcts of the right and left frontal lobes and severe cervical spondylosis at C4-C6 with spinal cord edema in T2 sequences slightly below that level. The patient subsequently underwent a cervical spine decompression for the spinal cord compression during the hospital stay. Due to the multifocal lesions noted on the brain MRI, a vasculitis workup was performed which returned negative for any abnormal test findings. The patient was also diagnosed with diabetes mellitus type 2 during the stay as he was found to have a glycosylated hemoglobin A1C of >12. He was initially hypertensive during hospitalization, but this resolved on its own after day three of the hospitalization so anti-hypertensives were not required. The patient was discharged home on high intensity statin therapy, dual oral hypoglycemic therapy for his diabetes mellitus, home physical therapy, and he was scheduled to start dual antiplatelet therapy seven days after cervical spine surgery. This dual antiplatelet therapy with clopidogrel and aspirin was to be continued for three weeks after which continuation with low dose aspirin was advised. As seen in this case, patients that present with a cerebrovascular accident should always be evaluated for other etiology behind his or her symptoms and having a low threshold for pursing other additional diagnoses is reasonable.

No description available.

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

PURPOSE: The objective was to determine if particular magnetic resonance, clinical and demographic findings were associated with functional status prior to surgery and predictive of functional outcomes at follow-up. RESULTS: The study included 65 consecutive CSM patients. The modified Japanese Orthopaedic Association Scale (mJOA) was used as the primary outcome measure. Higher baseline mJOA scores were associated with younger age, shorter duration of symptoms, fewer compressed segments and less severe cord compression. Better post-operative mJOA scores were associated with younger age, shorter duration of symptoms and higher baseline scores. Using multivariate analysis, baseline and follow-up mJOA scores adjusted for baseline mjOA score were best predicted by age. CONCLUSION: Age and clinical severity scores at admission can both provide valuable information. However, MR imaging features of the spinal cord before surgery cannot accurately predict the functional prognosis for patients with CSM and hence alternative imaging approaches may be required.

PURPOSE: The objective was to determine if particular magnetic resonance, clinical and demographic findings were associated with functional status prior to surgery and predictive of functional outcomes at follow-up. RESULTS: The study included 65 consecutive CSM patients. The modified Japanese Orthopaedic Association Scale (mJOA) was used as the primary outcome measure. Higher baseline mJOA scores were associated with younger age, shorter duration of symptoms, fewer compressed segments and less severe cord compression. Better post-operative mJOA scores were associated with younger age, shorter duration of symptoms and higher baseline scores. Using multivariate analysis, baseline and follow-up mJOA scores adjusted for baseline mjOA score were best predicted by age. CONCLUSION: Age and clinical severity scores at admission can both provide valuable information. However, MR imaging features of the spinal cord before surgery cannot accurately predict the functional prognosis for patients with CSM and hence alternative imaging approaches may be required.

Cervical myelopathy is the most common form of spinal cord injury in North America with roughly 19,000 new cases in the US every year. It results from chronic compression of the spinal cord by osteophytes, intervertebral disc herniation, and ossified ligaments. It commonly affects adults over the age of 50 years and causes upper extremity numbness, loss of hand dexterity, gait disturbances, and decreased proprioception. Recent studies imaging studies have shown this injury is highly dependent on the dynamic motion of the spine, often worsening in extreme flexion and extension. Surgical intervention is the accepted mode of treatment with the aim of decompressing the spinal canal and stabilizing the spine. However, 25% of patients have reoccurrence of symptoms indicating that surgical treatments may not be adequately addressing the injury. A main reason for this is little data has been reported on the spinal cord mechanics during cervical spinal motion in either healthy or cervical myelopathy subjects. To address this, we utilized MR imaging and finite element modeling to investigate spinal cord mechanics. As far as we know, we are the first group to obtain in vivo 3 dimensional spinal cord displacement and strain data from human subjects and the first to develop a C2 to T1 FE model of the healthy and cervical myelopathic spine and spinal cord. Utilizing high resolution 3T MR imaging in neutral, flexion, and extension positions we were able to obtain spinal cord displacement and strain fields from both healthy subjects and cervical myelopathy subjects before and after surgical intervention. In healthy subjects, flexion motion of the spine causes the spinal cord to move superiorly and in extension the spinal cord moves inferiorly. During extension, localizations of high principal strain can be seen in healthy subjects at areas of bony impingement and dural buckling. In both flexion and extension, cervical myelopathy subjects exhibited very little spinal cord displacement due to spinal cord compression. Principal strains during flexion and extension were greater in cervical myelopathy patients than healthy patients, specifically at the C4-6 vertebral levels. Surgical treatments for cervical myelopathy did restore spinal cord motion however, not in the same pattern or direction as healthy subjects. Additionally principal strains of the spinal cord were not reduced after surgical intervention. This indicates that surgical interventions are not adequately addressing the altered mechanics of the spinal cord during cervical myelopathy. To determine the how common surgical techniques for cervical myelopathy affect spinal cord mechanics, a FE model of the cervical spine and spinal cord was developed. The spinal cord motion was validated against MR imaging data obtained from normal subjects. Once validated, the model was used to develop a FE model of cervical myelopathy and surgical interventions. The native FE model predicted spinal cord motion well and replicated bony spinal cord impingement and dural buckling seen in healthy subjects. The FE model of cervical myelopathy also replicated spinal cord motion well as compared to MR imaging data of cervical myelopathy. Principal strains obtained from the healthy and cervical myelopathy FE models were similar in flexion however in extension, principal strains were higher at the C3, C6 and C7 levels. This is different than the patterns exhibited in the MR imaging and is most likely due to the percent of spinal cord compression induced in the FE model. Three, C4 to C7 surgical interventions were introduced to the model: anterior discectomy and fusion, anterior discectomy and fusion with laminectomy, and double door laminoplasty. In flexion, all surgical treatments doubled spinal cord principal strains at the C3 level and minimally reduced tensile strain at C4. The majority of strain reduction occurred at C5-7. In extension, all surgical techniques increased principal strains at the C3 and C4 levels. Little or no reduction in principal strains was seen at the C5 and C7 levels. All surgical techniques reduced principal strains at the C6 level. Of the surgical techniques, ACDF tended to reduce spinal cord principal strains the least in both flexion and extension and tended to induce the highest von Mises stresses. Combining the data obtained from MR imaging and FE modeling we can see that cervical myelopathy alters spinal cord mechanics by limiting spinal cord motion and increasing spinal cord strain. Additionally, current surgical techniques are not addressing the change in spinal cord mechanics effectively. Specifically after surgery, and especially with ACDF, spinal cord displacements and strains are being increased and transferred to different sections of the spinal cord. This indicates not only the need and importance of further research in spinal cord mechanics but also the need to improve treatments for cervical myelopathy which adequately restore the spinal cord mechanics.

Cervical spondylotic myelopathy is the most common spinal cord disorder in persons over 55 years of age in North America and perhaps in the world. Surgical options are broadly classified into two categories namely, anterior and posterior approaches. This study focuses on the posterior based approach (i.e. laminectomy or laminoplasty) which is considered when multiple levels of the spine have to be decompressed or when most of the cord compression results from posterior pathological conditions. The external and internal behavior of the spine after laminoplasty and laminectomy has been evaluated using both experimental and computational methods. Computationally, a validated intact 3D finite element model of the cervical spine (C2-T1) was modified to simulate laminectomy and laminoplasty (open door (ODL) and double door (DDL)) at levels C3-C6. During flexion, after ODL the adjacent levels C2-C3 and C6-C7 showed a 39% and 20% increase in the motion respectively; while no substantial changes were observed at the surgically altered levels. The percent increase in motion after DDL varied from 4.3% to 34.6%. The inclination towards increased motion during flexion after double door laminoplasty explains the role of the lamina-ligamentum flavum complex in the stability of spine. Compared to the intact model, laminectomy at C3-C6 led to a profound increase (37.5% to 79.6%) in motion across the levels C2-C3 to C6-C7. Furthermore, the changes in the von Mises stresses of the intervertebral disc observed after laminoplasty and laminectomy during flexion can be correlated to the changes in the intersegmental motions. An in-vitro biomechanical study was conducted to address the effects of laminoplasty (two-level and four-level) and four-level laminectomy on the flexibility of the cervical spine. Both two-level and four-level laminoplasty resulted in minimal changes in C2-T1 range of motion. For flexion/extension, two-level and multi-level laminoplasty showed an approximate 20% decrease (p>0.05) in the range of motion at C4-C5 and C2-C3 respectively due to the encroachment of the spinous process into the opened lamina. The decrease was mostly observed in older specimens and specimens with adjacent laminae close to each other; thus leading to the encroachment of the spinous process into the opened lamina. Laminectomy resulted in a statistically significant (p<0.05) increase in the range of motion compared to the intact condition during the three loading modes. These results correspond well with the finite element predictions, where a four-level ODL and laminectomy resulted in a minimal 5.4% and a substantial 57.5% increase in C2-T1 motion respectively during flexion. Adaptive bone remodeling theory was applied to the open door laminoplasty model to understand the effect of the surgical procedure on the internal architecture of bone. Bone remodeling was implemented at the C5 vertebra by quantifying the changes in apparent bone density in terms of the mechanical stimulus (i.e. SED/density). After laminoplasty, the increased load distribution through the bony hinge region led to the increased bone density during extension. This increased bone density could eventually lead to bone formation in those regions through external remodeling. The current study proved laminoplasty to be a motion preservation technique wherein the plates and spacer provided additional stability via reconstruction of the laminar arch while laminectomy can cause instability of spine especially during flexion. In the future, patient-specific finite element models that incorporate geometry-related differences could be developed to optimize the number of operated levels and to further explain the effect of surgical procedure on the unaltered levels.

No description available.