512 - When Does Compensation for Lumbar Stenosis Become a Deformity?...

General Session: Lumbar

Presented by: L. Day - View Audio/Video Presentation (Members Only)

Author(s):

A. Buckland(1), S. Vira(1), J. Oren(1), R. Lafage(2), B. Harris(1), M. Spiegel(1), B. Diebo(2), B. Liabaud(2), T. Protopsaltis(1), F. Schwab(2), T. Errico(1), V. Lafage(2), J. Bendo(1)

(1) NYU Hospital for Joint Diseases, Orthopedic Surgery, New York, NY, United States
(2) Hospital for Special Surgery, New York, NY, United States

Abstract

Background Context: Degenerative Lumbar Stenosis (DLS) patients adopt forward bending posture as a compensatory mechanism, increasing spinal canal and foraminal volume. Previous data shows laminectomy ± short segment fusion results in improvement of SVA, pelvic tilt (PT) and PI-LL (pelvic incidence-lumbar lordosis) mismatch by SRS-Schwab classification in < 25% of patients. The magnitude of deformity for which a DLS patient should have realignment remains unknown.

Purpose: To identify differences in compensatory mechanisms between DLS and ASD (Adult Spinal Deformity) patients with increasing SVA, and to identify at what point DLS patients recruit ASD-type compensatory mechanisms.

Outcome Measures: Radiographic spino-pelvic parameters were measured in the DLS and ASD groups, including SVA, PI-LL, T1SPi, TPA and PT.

Methods: Patients were identified using a retrospective single-institution database with sole diagnosis of DLS, >40 years and if they had any of the following: PT>25°, SVA>5cm, Thoracic Kyphosis (TK)>60° or PI-LL >10°. Diagnosis was taken based on correlation between history, examination and available imaging. Matched cohort with sole diagnosis of ASD was identified. Groups stratified by SVA using Schwab-SRS classification: 0(< 4cm), +(4-9.5cm), ++(>9.5cm). Sagittal spino-pelvic parameters were compared between the 2 groups with unpaired t-test.

Results: 239 patients were identified (122 DLS, 117 ASD). There was no difference in age or PI between DLS and ASD with SVA stratifications. DLS patients with SVA '0' had less PT (19.8° vs. 29.2° p< 0.0001), less PI-LL mismatch (3.3° vs. 15.8°, p< 0.001), lower TPA (14.6° vs. 21.8°, p< 0.001) but higher T1SPi (-5.17° vs. -7.44°, p< 0.001) than those with ASD. DLS patients with SVA+ had less PT (22.6° vs. 26.1°, p=0.019) and higher T1SPi (0.64° vs. -0.70°, p=0.008) than ASD patients. DLS patients resembled a decompensated deformity with a higher T1SPi relative to TPA when compared to the ASD cohort in groups 0 and +. No significant differences between ASD and DLS for any parameters in the SVA++ group were identified. No difference was found between DLS or ASD in TK for SVA groups 0, + or ++.

Conclusions: The difference in PI-LL observed in ASD/DLS group '0' underlies the pathogenesis of ASD vs DLS. DLS patients increase SVA for neuronal decompression but without a PI-LL mismatch, they need not increase PT. As PI-LL increases in SVA>9.5cm, recruitment of PT ensues as the need for alignment overtakes desire for decompression. Their compensatory mechanism then resembles ASD. Laminectomy ± fusion may be more appropriate for DLS patients with SVA< 9.5cm. Given < 25% of patients improve in classification after fusion, surgeons should consider realignment surgery in DLS with SVA >9.5cm. Further understanding of HRQOL scores in mal-aligned DLS patients is required to best understand the importance of alignment in DLS.

Stenosis