Three-dimensional Spinal Canal Morphometric Analysis and Relevant Spinal Cord Occupational Ratios in Congenital Cervical Spinal Stenosis: A Classification Algorithm of the Stenosis Phenotypes and Data-driven Decompression Approach.

OBJECTIVES: No standardized magnetic resonance imaging (MRI) parameters have defined the 3-dimensional morphoanatomy and relevant spinal cord occupation ratios (occupation of spinal cord dimensions/similar dimensions within the spinal canal) in congenital cervical stenosis (CCS). METHODS: A retrospective, comparative analysis was conducted on 200 patients >18 years of age with myelopathy and CCS (mean age, 52.4 years) and 200 age-matched controls with no myelopathy or radiculopathy. The variables assessed from high resolution MRI included sagittal and axial spinal canal dimensions (MRI Torg-Pavlov ratios) from C3 to C7. Morphometric dimensions from the sagittal retrodiscal and retrovertebral regions as well as axial MRI dimensions were compared. Sagittal and axial spinal cord occupation ratios were defined and correlated with spinal canal dimensions. RESULTS: Multivariate analyses indicated reduced sagittal and axial anteroposterior (AP) spinal canal dimensions and a large reduction in transverse spinal canal dimensions at all spinal levels. There was a small significant correlation between AP sagittal spinal canal dimensions and axial transverse spinal canal dimensions at C3-C5, but not at C5-C6. Small correlations were noted between AP sagittal spinal canal dimensions and AP axial spinal cord and axial cross-sectional area occupation ratios at C3-C6, but there was no correlation with axial mediolateral spinal cord occupation ratios. CONCLUSIONS: The stenosis effect can involve any dimension, including the transverse spinal canal dimension, independent of other dimensions. Owing to the varied observed morphoanatomies, a classification algorithm that defines CCS specific phenotypes was formulated. Objectivizing the stenosis morphoanatomy may allow for data-driven patient-focused decompression approaches in the future.

Postlaminectomy lumbopelvic sagittal changes in patients with developmental lumbar spinal stenosis grouped into Roussouly lumbopelvic sagittal profiles: 2- to 10-year prospective follow-up.

OBJECTIVE: Roussouly lumbopelvic sagittal profiles are associated with distinct pathologies or distinct natural histories and prognoses. The associations between developmental lumbar spinal stenosis (DLSS) and native lumbopelvic sagittal profiles are unknown. Moreover, the relative effects of multilevel decompression on lumbar sagittal alignment, geometrical parameters of the pelvis, and compensatory mechanisms for each of the Roussouly subtypes are unknown. This study aimed to explore the association between DLSS and native lumbar lordosis (LL) subtypes. It also attempts to understand the natural history of postlaminectomy lumbopelvic sagittal changes and compensatory mechanisms for each of the Roussouly subtypes and to define the critical lumbar segment or specific lordosis arc that is recruited after relief of the stenosis effect. METHODS: A total of 418 patients with multilevel DLSS were grouped into various Roussouly subtypes, and lumbopelvic sagittal parameters were prospectively compared at follow-up intervals of preoperative to < 2 years, 2 to < 5 years, and 5 to ≥ 10 years after laminectomy. The variables analyzed included LL, upper lordosis arc from L1 to L4, lower lordosis arc from L4 to S1, and segmental lordosis from L1 to S1. Pelvic parameters included pelvic incidence, sacral slope, pelvic tilt, and pelvic incidence minus LL values. RESULTS: Of the 329 patients who were followed up throughout this study, 33.7% had Roussouly type 1 native lordosis, whereas the incidence rates of types 2, 3, and 4 were 33.4%, 21.9%, and 10.9%, respectively. LL was not reduced in any of the Roussouly subtypes after multilevel decompressions. Instead, LL increased by 4.5° (SD 11.9°-from 27.3° [SD 11.5°] to 31.8° [SD 9.8°]) in Roussouly type 1 and by 3.1° (SD 11.6°-from 41.3° [SD 9.5°] to 44.4° [SD = 9.7°]) in Roussouly type 2. The other Roussouly types showed no significant changes. Pelvic tilt decreased significantly-by 2.8°, whereas sacral slope increased significantly-by 2.9° in Roussouly type 1 and by 1.7° in Roussouly type 2. The critical lumbar segment that recruits LL differs between Roussouly subtypes. Increments and changes were sustained until the final follow-up. CONCLUSIONS: The study findings are important in predicting patient prognosis, LL evolution, and the need for prophylactic or corrective deformity surgery. Multilevel involvement in DLSS and the high prevalence of Roussouly types 1 and 2 suggest that spinal canal dimensions are closely linked to the developmental evolution of LL.

Anatomic radiological variations in developmental lumbar spinal stenosis: a prospective, control-matched comparative analysis.

BACKGROUND CONTEXT: Developmental lumbar spinal stenosis is a maldevelopment of the dorsal spinal elements involving short pedicles and a trefoil bony spinal canal that increases the likelihood of neural compression at an earlier age. PURPOSE: To identify radiographically the anatomic variations caused by the maldevelopment of the infrequently characterized dorsal spinal elements. STUDY DESIGN: A prospective, control-matched comparative analysis. METHODS: Magnetic resonance imaging (MRI) and anteroposterior (AP) plain radiographs of 66 patients (mean age, 40.7 years) selected and randomized prospectively and compared with images of 45, age- and gender-matched control subjects. Variables assessed included spinal canal cross-sectional area (CSA), thecal sac AP and transverse canal diameters (CSA), and interpedicular distance. All were expressed in ratios with vertebral body diameter (VBD), interlaminar angle, stenosis grade, and MRI evidence of disc degeneration. RESULTS: In the stenosis cohort, global pathology and multilevel involvement with L3, L4, and L5 segments were involved more commonly and severely. Severe stenosis, at L1, L2, and S1 occurs infrequently. Multivariate analysis demonstrated a statistically significant reduction in spinal canal CSA-to-vertebral body CSA ratio, AP spinal canal diameter-to-VBD ratio on axial and sagittal magnetic resonance images, and plain radiograph interpedicular distance-to-VBD ratio at all levels. Interlaminar angle and the transverse spinal canal diameter-to-VBD ratio were reduced significantly in the stenosed cohort at all levels, except L1. No statistically significant difference regarding the incidence of disc degeneration on MRI between the two cohorts, as well as thecal sac CSA-to-spinal canal CSA ratios across all levels were observed, except for L3 and S1 (p<.05). CONCLUSIONS: Three spinal canal morphologies were identified: (1) "flattened" canal with predominantly reduced spinal canal AP diameter, (2) spinal canal with predominantly reduced interlaminar angle, and (3) global reduction of all canal parameters. Early age at presentation and subtle spondylosis, although typical, should not be considered the identifying, differentiating factors.

Pathoanatomic basis for stretch-induced lumbar nerve root injury with a review of the literature.

OBJECTIVE: Persistent pain originating from a dysfunctional lumbar motion segment poses significant challenges in the clinical arena. Although the predominance of the existing spine literature has addressed nerve root compression as the principal cause of pain, it is equally likely that a stretch mechanism may be responsible for all or part of the pathology. METHODS: The literature supporting the role of stretch damage as a primary cause of nerve root injury and pain was systematically reviewed. Pathoanatomic considerations between nerve roots and juxtaposed environment are described and correlated with the available literature. Potential anatomic relationships that may lead to stretch-induced injury are delineated. RESULTS: A dynamic lumbar functional spinal unit that encloses a tethered nerve root can create significant stretch and/or compression. This phenomenon may be present in a variety of pathological conditions. These include anterior, posterior, and rotatory olisthesis as well as degenerative conditions such as the loss of disc interspace height and frank multisegment spinal deformity. Although numerous studies have demonstrated that stretch can result in nerve damage, the pathophysiology that may associate nerve stretch with chronic pain has yet to be determined. CONCLUSION: The current literature concerning stretch-related injury to nerve roots is reviewed, and a conceptual framework for its diagnosis and treatment is proposed and graphically illustrated using cadaveric specimens. The dynamic biomechanical and functional interrelationships between neural structures and adjacent connective tissue elements are particularly important in the face of spinal deformity.