When Does the Global Alignment and Proportion (GAP) Score Fail?: Comprehensive Assessment of Failure in Patients Meeting Post-Operative GAP Targets

Saturday, May 4, 2024

3:31 PM – 3:33 PM CT

Location: S403ab

Presenting Author(s)

BJ

Burhan Janjua, MD

Attending Surgeon
Mercy Health
Chicago, Illinois, United States

Co-Author(s)

Peter G. Passias, MD

Assistant Clinical Professor of Orthopedic Surgery
New York University, Langone Medical Center
New Canaan, Connecticut, United States

Co-Author(s)

Ankita Das, BS

Research Fellow
NYU Langone Health
Valhalla, New York, United States
pooja Dave, BS

Research Fellow
NYU Langone Health
glen ellyn, Illinois, United States
D. Kojo Hamilton, MD

Attending Surgeon
University of Pittsburgh School of Medicine
Pittsburgh, Pennsylvania, United States
Jamshaid M. Mir, MD

Research Fellow
NYU Langone Health
Paterson, New Jersey, United States
OO

Oluwatobi O. O. Onafowokan, BMBS, MSc

Research Fellow
NYU Langone Hospital, United States
Peter G. Passias, MD

Assistant Clinical Professor of Orthopedic Surgery
New York University, Langone Medical Center
New Canaan, Connecticut, United States
DS

Daniel Sciubba, M.D., M.B.A.

Senior vice president of Neurosurgery at Northwell Health
Zucker School of Medicine at Hofstra, Long Island Jewish Medical Center and North Shore University Hospital, Northwell Health
Great Neck, New York, United States
pT

peter S. Tretiakov, BS

Research Fellow
NYU Langone Health
petertretiakov@gmail.com, New York, United States

Disclosure(s):

Burhan Janjua, MD: No financial relationships to disclose

Peter G. Passias, MD: No financial relationships to disclose

Jamshaid M. Mir, MD: No financial relationships to disclose

Introduction: Setting surgical goals according to the GAP score may decrease complications. However, addressing these targets does not always prevent high mechanical complication or revision rates.

Methods: Surgical patients with baseline (BL) and 2-year (2Y) data were isolated. Proximal and distal junctional kyphosis and/or failure, rod breakage, and implant-related complications were considered mechanical complications. Patients improved in GAP [Proportioned (GAP-P), Moderately Disproportioned (GAP-MD), Severely Disproportioned (GAP-SD)] by 6W were considered Matched. Failure rates were established for patients meeting Sagittal Age-Adjusted Score and Roussouly targets by 6W. Backstep logistic regression and CIT analysis determined factors associated with failure/optimal outcomes.

Results: 331 patients(59.8±15.1 yrs,78% F,26.8±5.6 kg/m2) were isolated. 47.8% of patients were GAP-P by 6W, 36.1% GAP-MD, and 16.2% GAP-SD by 6W post-op. 50.0% were considered improved by GAP proportionality. 55.2% of GAP-matched patients suffered PJK by 2Y, 8.4% suffered radiographic PJF, 16.0% experienced mechanical failure, 25.0% required reoperation, and 29.0% suffered major complications. Radiographically, GAP-matched patients who required reoperation for mechanical failure demonstrated lessened magnitude of correction between BL and 6W in sacral slope(p=.017), PI-LL(p=.006), and C7-S1 SVA(p <.001), but were comparable in ΔT4-T12 kyphosis(p>.05) versus non-matched patients. For patients with mechanical failure by 2Y, 45.8% met 6W SAAS targets (p=.0550, and 35.0% met Roussouly targets (p=.607) versus non-GAP matched patients. Not matching in GAP was predictive of not meeting Smith et al. Best Clinical Outcomes by last follow-up [.167 (.106-.262), p<.001)]. In patients GAP-matched patients when accounting for osteoporosis and meeting 6W age-adjusted targets, increased BL PI-LL [1.086, p<.001), decreased BL PT [.887, p<.001), and decreased operative correction of T4-T12 TK [1.037, p=.024) was predictive of mechanical failure by 2Y.

Conclusion : Predictive analysis demonstrates that increased baseline PI-LL, decreased pelvic tilt, and TK correction are significantly associated with increased risk of mechanical failure in patients who improved in GAP proportionality post-operatively. Although GAP proportionality is independently predictive of meeting Best Clinical Outcomes, meeting GAP targets alone may not be sufficient to predict post-operative mechanical failure.