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

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 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.

Αν και η Αυχενική Σπονδυλωτική Μυελοπάθεια (ΑΣΜ) αποτελεί την πιο κοινή αιτία δυσλειτουργίας νωτιαίου μυελού στους ενήλικες άνω των 55 ετών, οι μοριακοί μηχανισμοί παραμένουν άγνωστοι. Μέχρι σήμερα, πολλές προσπάθειες έχουν διενεργηθεί για την ανάπτυξη ενός αξιόπιστου πειραματικού μοντέλου AΣΜ. Ωστόσο, αρκετά μειονεκτήματα εμφανίζονται σε αυτές τις μελέτες. Στη παρούσα μελέτη έχουμε σκοπό τη δημιουργία ενός νέου, πρωτότυπου πειραματικού μοντέλου ΑΣΜ, το οποίο εξομοιώνει τα ιστολογικά και κλινικά χαρακτηριστικά της ανθρωπίνης νόσου. Mεθοδολογία: Μετά από αφαίερεση του πετάλου του έβδομου αυχενικού σπονδύλου, ένα λεπτό τεμάχιο αρωματικού πολυαιθέρα τοποθετήθηκε κάτω από το πέταλο του έκτου αυχενκού σπονδύλου σε κόνικλους Νέας Ζηλανδίας (Ομάδα ΧΠΠ). Σε μία άλλη ομάδα πειραματόζωων ο αρωματικός πολυαιθέρας αφαιρέθηκε 30 δευτερόλεπτα μετά την εμφύτευση (ομάδα ελέγχου). Νευρολογική εκτίμηση πραγματοποιήθηκε χρησιμοποιώντας τη κλίμακα του Tarlov μετά το πέρας της χειρουργικής διαδικασίας και ακολούθως εβδομαδιαίως. Ηλεκτροφυσιολογικές μελέτες πραγματοποιήθηκαν στις 20 εβδομάδες μετά το χειρουργείο και πριν από τη θυσία των πειραματόζωων. Ακολούθησαν ιστολογικές και ανοσοιστοχημικές μελέτες. Αποτελέσματα: Τα πειραματόζωα που άνηκαν στην ομάδα ελέγχου δεν εμφάνισαν νευρολογικά ελλείμματα κατά τη διάρκεια της μελέτης. Αντιθέτως τα πειραματόζωα που άνηκαν στη ΧΠΠ εμφάνισαν νευρολογικά ελλείματα. Στους νωτιαίους μυελούς προερχόμενους από την ΧΠΠ ομάδα ανεδείχθησαν οι χαρακτηριστικές ιστοπαθολογικές αλλοιώσεις της χρόνιας μυελοπάθειας. Ειδικότερα, ανεδείχθη σπογγώδης εκφύλιση της λευκής ουσίας, διάμεσο οίδημα και αποπλάτυνση των πρόσθιων κεράτων της φαιάς ουσίας. Επίσης ανεδείχθη κατακρήμνιση του μυελικού σάκου και διόγκωση του δακτυλίου της μυελίνης. Τέλος, η χρόνια πίεση του νωτιαίου οδήγησε σε ενεργοποίηση της απόπτωσης και διαταραχή της αρχιτεκτονικής του μικροαγγειακού συστήματος του νωτιαίου μυελού Συμπέρασμα: Το πρωτότυπο μοντέλο ΑΣΜ στους κονίκλους ποσομοιώνει το χωρικό και χρονικό προφίλ της ανθρώπινης νόσου στο σημείο της πίεσης του νωτιαίου μυελού. ΜΕΛΕΤΗ B Εισαγωγή: Η φλεγμονή, η δημιουργία ουλώδους ιστού και η διαταραχή του μικροαγγειακού συστήματος του νωτιαίου μυελού είναι ορισμένα από τα κύρια παθοφυσιολογικά φαινόμενα της ΑΣΜ. Ωστόσο οι μοριακοί μηχανισμοί που εμπλέκονται σε αυτά τα φαινόμενα κάτω από τη χρόνια και προοδευτική πίεση του νωτιαίου μυελού παραμένουν ανεξερεύνητα. Mεθοδολογία: Στη συγκεκριμένη μελέτη χρησιμοποιήθηκε το πειραματικό μοντέλο ΑΣΜ που περιγράφεται στη μελέτη Α με σκοπό να διερευνηθεί ο ρόλος του NF-κB και των πρωτεινών της εξωκυττάριας ουσίας στην ΑΣΜ. Εν συντομία, κόνικλοι Νέας Ζηλανδίας (διαφορετικά πειραματόζωα από εκείνα της μελέτης Α) χωρίστηκαν τυχαία σε δύο ομάδες: την ομάδα ΧΠΠ (n=15) και την ομάδα ελέγχου (n=15). Η έκφραση των πρωτεινών των υπομονάδων p50 και p65 του NF-kB, όπως επίσης και των ενζύμων διάσπασης της εξωκυττάριας ουσίας (MMP-2, MMP-9) και του ενεργοποιητή του πλασμινογόνου τύπου ουροκινάσης (urokinase-type plasminogen activator; u-PA) αξιολογήθηκαν σε τομές νωτιαίων μυελών προερχόμενων και από τις δύο ομάδες χρησιμοποιώντας ανοσοιστοχημική τεχνική. Στατιστική ανάλυση πραγματοποιήθηκε χρησιμοποιώντας SPSS για Windows, release 12.0 (SPSS Inc., Chicago, IL). Αποτελέσματα: Σε τομές νωτιαίων μυελών που προέρχονταν από πειραματόζωα που έπασχαν από ΑΣΜ αναδείχθηκε στατιστικά σημαντικά αυξημένη έκφραση των υπομονάδων του NF-κB (p50 & p65), όπως επίσης και των ενζύμων MMP-2, MMP-9, and u-PA σε σύγκριση με εκείνες που προέρχονταν από την ομάδα ελέγχου. Τέλος, σημαντικά θετική συσχέτιση παρατηρήθηκε μεταξύ των επιπέδων έκφρασης του NF-κB και εκείνων των MMP-9, MMP-2, and u-PA. Συμπέρασμα: Τα ευρήματα αυτά αποτελούν ισχυρές ενδείξεις πως η χρόνια και προοδευτική πίεση του αυχενικού νωτιαίου μυελού οδηγεί σε αυξημένη έκφραση των MMP-2, MMP-9 και u-PA πιθανόν μέσω της δράσης του μεταγραφικού παράγοντα NF-κB. Είναι βέβαιο ότι περισσότερες μελέτες απαιτούνται για την εξακρίβωση του ρόλου των πρωτεινών αυτών στην ΑΣΜ. / Although cervical spondylotic myelopathy (CSM) represents the most common cause of spinal cord impairment among individuals over 55 years old, the molecular mechanisms of the disease remain mainly unknown. To date, many experimental studies have been conducted to establish a reliable model of CSM, however most of them appear some limitations. In this study we aim to create a new animal model of CSM, which will reproduce the temporal course of the human disease and the local microenvironment at the site of spinal cord compression. Methods: Following C7 posterior laminectomy, a thin sheet of aromatic polyether was implanted underneath C5–C6 laminae of the New Zealand rabbits. A sham group in which the material was removed 30 sec after the implantation was also included. Motor function evaluation was performed after the material implantation and weekly thereafter using the Tarlov classification. At 20 weeks post-material implantation electrophysiological studies were also conducted. All the animals were sacrificed 20 weeks post-material implantation and histological and immunohistochemical studies were performed. Results: Clinical evaluation of animals after operation reveals no symptoms and signs of acute spinal cord injury. Moreover, no neurological deficits were noticed in the sham group during the course of the study. However, the animals which underwent implantation of compression material exhibited progressive neurological deficits throughout the study. Rabbits of the compression group experienced significant increased axonal swelling and demyelination, interstitial edema and myelin sheet fragmentation. Histological evaluation of C5 and C6 laminae (at the site of implantation) reveals osteophyte formation. Moreover, the chronic and progressive compression of the cervical spinal cord resulted in induction of apoptosis as well as in disruption of the basement membrane of vessels. Conclusion: The proposed rabbit CSM model reproduces the temporal evolution of the disease and creates a local microenvironment at the site of spinal cord compression, which shares similar features with that of human disease. STUDY B Introduction: Inflammation, glial scar formation and disruption of spinal cord microvasculature represent some of the principal neuropathological features of CSM. However, the molecular mechanisms which are implicated in these pathophysiological phenomena under the chronic and progressive compression of the cervical spinal cord remain interestingly unexplored. Methods: In this study (B) in order to evaluate the role of NF-κB and extracellular matrix proteins in cervical myelopathy we used the rabbit CSM model which was extensively characterized in study A. Briefly New Zealand rabbits (different cohort of animals than that of the study A) were randomly and blindly divided into the following two groups: CSM (n=15) and sham group (n=15). The expression pattern of p50 and p65 subunits of NF-kB, as well as that of MMP-2, MMP-9, and u-PA, was evaluated in spinal cord sections coming from both groups using immunohistochemistry technique. Statistical analysis was performed using SPSS for Windows, release 12.0 (SPSS Inc., Chicago, IL). Results: CSM animals exhibited statistically significant increased immuoreactivity in both NF-κB subunits, p50 and p65. Moreover, the levels MMP-2, MMP-9, and u-PA were found to be significantly increased in CSM animals compared to controls. Finally, strong positive correlation between NF-κB subunits immunoreactivity and that of MMP-9, MMP-2, and u-PA was demonstrated. Conclusion: The NF-κB pathway as well as the extracellular matrix proteins (MMP-2 and MMP-9) are involved in CSM. However, more studies are needed to clarify the functional role of these molecules in the pathobiology of CSM.