Lightning Podiums: Adult Spinal Deformity - Room 801A

Presented by: T. Pannu

Author(s):

T. Pannu(1), R. Lafage(1), J. Smith(2), C. Shaffrey(2), G. Mundis(3), R. Hostin(4), C. Ames(5), L. Lenke(6), M. Gupta(7), H.J. Kim(1), S. Bess(8), J. Gum(9), F. Schwab(1), V. Lafage(1), International Spine Study Group (ISSG)

(1) Hospital for Special Surgery, New York, NY, United States
(2) University of Virginia, Charlottesville, VA, United States
(3) San Diego Center for Spinal Disorders, La Jolla, CA, United States
(4) Baylor Scoliosis Center, Plano, TX, United States
(5) University of California, San Francisco, San Francisco, CA, United States
(6) Columbia University Medical Center, New York, NY, United States
(7) Washington University, Saint Louis, MO, United States
(8) Denver International Spine Center, Denver, CO, United States
(9) Norton Leatherman Spine Center, Louisville, KY, United States

Abstract

Background: The abrupt transition from fused to unfused spine following long-segment instrumented fusion for ASD results in mechanical loading at the proximal junction and risk of PJK. Our objective was to establish the expected mechanical loading at different vertebral levels in a normal population and to explore the contribution of loading at the proximal junction to PJK after ASD surgery.

Purpose: To determine how much mechanical loading occurs at different vertebral levels in a normal population and how it plays role, if any, in the development of PJK after ASD surgery. Design: Retrospective review of 2 prospective cohorts

Methods: This study included two cohorts, normative (n=116, asymptomatic volunteers) and ASD (n=289, age >18 yrs, treated surgically with complete fusion of the lumbar spine and UIV below T7). Spinopelvic parameters and bending moments at each vertebral level were assessed for both cohorts. Patients in the ASD cohort were grouped into PJK and No-PJK groups based on standard definitions, and the mechanical loading at the UIV for these ASD subgroups were compared with each other and the normative cohort.

Results: In the normative cohort, the thoracic spine was subject to bending moments in flexion (max at T8), and the lumbar spine was subject to bending moments in extension (max at L4), with an inflexion point corresponding to the thoracolumbar area. Bending moments significantly correlated with SVA (r>.4 from T4 to T10, and r>.7 from T11 to S1, Figure). The lumbar spine of normative patients with negative SVA was loaded in extension, while the entire spine of patients with a positive SVA (>15mm) was subject to bending moments in flexion. Among the ASD cohort, 278 of 289 patients had complete data (64yo, 71% women). The pre- to post-op sagittal alignment improved: PT=25° to 21°, PI-LL=22° to 2°, SVA=79mm to 33mm (p< .05). The most common UIVs were T10 (60%), T11 (21%) and T9 (10%) and the PJK incidence was 35% at 6 wks. Analysis of bending moments at T10 demonstrated that PJK patients had a significantly larger bending moment than non-PJK patients (13.7±3.8Nm vs. 10.6±4.6Nm, p< .001) and normative patients for the same level (13.7±3.8Nm vs 8.4±3.8Nm, p=.037).

Conclusion: This study establishes important references of magnitude and direction (flex/ext) of bending moments for each vertebral level in an asymptomatic population. Positive SVA was associated with increased flexion moments. ASD patients who developed radiographic PJK exhibited larger bending moments than the normative population. Further analysis should investigate the relationship between mechanical loading and PJK progression.

Bending moment by vertebra