General Session: Biomechanics
Presented by: P. Zhou - View Audio/Video Presentation (Members Only)
P. Passias(1), C. Jalai(1), V. Lafage(2), R. Lafage(2), T. Protopsaltis(2), S. Ramachandran(1), S. Horn(1), A. Sure(1), P. Zhou(1), M. Gupta(3), R. Hart(4), V. Deviren(5), A. Soroceanu(1), J. Smith(6), F. Schwab(2), C. Shaffrey(6), C. Ames(5), International Spine Study Group
(1) NYU Hospital for Joint Diseases, Orthopaedic Surgery, New York, NY, United States
(2) Hospital for Special Surgery, New York, NY, United States
(3) Washington University School of Medicine, Spine Surgery, St. Louis, MO, United States
(4) Oregon Health and Science University, Portland, OR, United States
(5) University of California at San Francisco, San Francisco, CA, United States
(6) University of Virginia Neurological Surgery, Charlottesville, VA, United States
Background: Primary drivers (PD) of adult cervical spine deformity (ACD) have not been described in relation to pre-operative alignment or degree of correction in the achievement of cervical deformity operative goals. This study defines the primary drivers of ACD to better understand the impact of driver region on global alignment compensatory mechanisms.
Methods: This is a retrospective review of a multicenter, prospective, consecutive database of ACD patients undergoing surgical correction. The primary cervical deformity driver and vertebral apex level were classified based on spinal region: cervical (CS), cervicothoracic junction (CTJ), thoracic (TH), or lumbo-pelvic (LP). Patients were evaluated if the surgery included the primary driver apex, based on lowest instrumented vertebra. Cervical and thoracolumbar alignment were measured pre-operatively and at 3-months post-operative to assess the effect of PD on acute achievement of operative goals. Considered radiographic parameters included sagittal vertical axis (SVA), thoracic kyphosis (TK), spino-pelvic mismatch (PI-LL), T1 slope minus cervical lordosis (TS-CL), and the chin-brow vertical angle (CBVA). Primary driver groups were compared with ANOVA/Pearson χ2, and paired t-tests.
Results: 84 ACD patients with baseline and 3-month imaging met inclusion criteria. The distribution of PD was as follows: CS = 33 (40.2%), CTJ = 12 (14.6%), TH = 26 (31.7%), LP = 11 (13.4%). Thoracic drivers showed the greatest pre-operative cervical (T1 slope, C2-T3 SVA), spino-pelvic (TK, PI-LL), and upper cervical (C0-C2 angle) malalignment compared against other driver groups (p< 0.05 all cases). Differences in baseline-3-month alignment changes were observed predominantly between patients with thoracic and cervical drivers: TH cases had greater PI-LL mismatch (4.47° vs. -0.87°, p=0.049), TS-CL mismatch (-19.12° vs. -4.30, p=0.050), C2-C7 SVA (-18.12 vs. -4.30 mm, p=0.007), and C2-T3 SVA (-24.76 vs. 8.50 mm, p=0.002) correction. Patients with CTJ drivers also had a trend toward greater lumbar lordosis correction compared to CS driver cases (-6.00° vs. 0.88°, p=0.050). In CS driver patients, there was a difference in the prevalence of 3-month TS-CL modifier grades (0=35.7%, 1=0.0%, 2=13.3%, p=0.030). There was also a significant difference in the 3-month CBVA modifier grade distribution in thoracic driver patients (0=0.0%, 1=35.9%, 2=14.3%, p=0.049).
Conclusions: Characterizing ACD patients by primary driver type reveals differences in pre- and post-operative alignment. Evaluating surgical alignment outcomes based on primary driver inclusion is important in understanding alignment goals for ACD correction. Level of Evidence: IV