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  • Flexible Sagittal Imbalance: A Compensatory Mechanism for Lumbar Stenosis

    Final Number:

    Akshay Sharma BA; Sina Pourtaheri MD; Jason Savage MD; Iain H. Kalfas MD; Thomas Mroz; Edward C. Benzel MD; Michael P. Steinmetz MD

    Study Design:

    Subject Category:

    Meeting: Congress of Neurological Surgeons 2016 Annual Meeting

    Introduction: The flexed posture of the lumbar spine increases the diameter of the spinal canal and neuroforamina and can relieve neurogenic claudication symptoms. No study has determined if sagittal imbalance may be secondary to a postural flexion to alleviate lumbar stenosis.

    Methods: 138 patients with sagittal imbalance, undergoing a total of 148 fusion procedures of the thoracolumbar spine were identified. Patient reported outcomes (PROs) were evaluated using the EQ-5D, Pain Disability Questionnaire, and Patient Health Questionnaire, preoperatively and at 12 months follow-up. Demographic, clinical, and radiographic parameters, including pelvic incidence, lumbar lordosis, pelvic tilt, and sagittal vertical axis were obtained from images preoperatively and at 6 and 24 months follow-up. Twenty-four patients with flexible sagittal imbalance were identified and individually matched with a control cohort with fixed deformities.

    Results: Sixty-eight percent of the patients in the flexible cohort were diagnosed preoperatively with lumbar stenosis as compared to only 22% in the fixed cohort (p=0.0032). At 12 months, the flexible cohort exhibited pre- to postoperative improvement that was significant for the EQ-5D (p = 0.0026), PDQ (p = 0.0048), and PHQ-9 (p= 0.018). The fixed cohort showed no statistically significant change in pre- to postoperative PROs at 12 months. There was no statistical difference between the flexible and fixed cohorts with regard to the C2 (p=0.95) or C7 (p=0.43) SVA. The ratio of pelvic tilt to pelvic incidence was found to be significantly greater in the patients with stenosis (p= 0.019).

    Conclusions: Surgical treatment of lumbar stenosis in tandem with the treatment of sagittal imbalance was associated with favorable clinical outcomes. A portion of pelvic retroversion was found to be compensatory for lumbar stenosis for the flexible deformities.

    Patient Care: Significant preoperative attention should be given to the root cause of sagittal malalignment, since the malalignment could be compensatory and not structural. Furthermore, a portion of pelvic retroversion was found to be compensatory for lumbar stenosis for the flexible deformities, which provides a new method for clinical insight into the generation of lumbar stenosis.

    Learning Objectives: 1) Understand the underlying physiologic implications of pelvic retroversion in sagittal imbalance 2) Understand the utility of Pelvic Tilt in assessing for lumbar stenosis in sagittal imbalance


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