Does the Global Alignment and Proportion score overestimate mechanical complications after adult spinal deformity correction?

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  • 1 Department of Neurosurgery, Lenox Hill Hospital, Hofstra/Northwell School of Medicine, Manhasset;
  • 2 Department of Orthopedic Surgery Spine, Columbia University, New York;
  • 3 Department of Orthopaedic Surgery, Mount Sinai, New York, New York;
  • 4 Department of Neurosurgery, University of South Alabama, Mobile, Alabama;
  • 5 Department of Neurosurgery, University of California, San Diego, California; and
  • 6 Department of Neurosurgery, Columbia University, New York, New York
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OBJECTIVE

The goal of this study was to validate the Global Alignment and Proportion (GAP) score in a cohort of patients undergoing adult spinal deformity (ASD) surgery. The GAP score is a novel measure that uses sagittal parameters relative to each patient’s lumbosacral anatomy to predict mechanical complications after ASD surgery. External validation is required.

METHODS

Adult ASD patients undergoing > 4 levels of posterior fusion with a minimum 2-year follow-up were included. Six-week postoperative standing radiographs were used to calculate the GAP score, classified into a spinopelvic state as proportioned (P), moderately disproportioned (MD), or severely disproportioned (SD). A chi-square analysis, receiver operating characteristic curve, and Cochran-Armitage analysis were performed to assess the relationship between the GAP score and mechanical complications.

RESULTS

Sixty-seven patients with a mean age of 52.5 years (range 18–75 years) and a mean follow-up of 2.04 years were included. Patients with < 2 years of follow-up were included only if they had an early mechanical complication. Twenty of 67 patients (29.8%) had a mechanical complication. The spinopelvic state breakdown was as follows: P group, 21/67 (31.3%); MD group, 23/67 (34.3%); and SD group, 23/67 (34.3%). Mechanical complication rates were not significantly different among all groups: P group, 19.0%; MD group, 30.3%; and SD group, 39.1% (χ2 = 1.70, p = 0.19). The rates of mechanical complications between the MD and SD groups (30.4% and 39.1%) were less than those observed in the original GAP study (MD group 36.4%–57.1% and SD group 72.7%–100%). Within the P group, the rates in this study were higher than in the original study (19.0% vs 4.0%, respectively).

CONCLUSIONS

The authors found no statistically significant difference in the rate of mechanical complications between the P, MD, and SD groups. The current validation study revealed poor generalizability toward the authors’ patient population.

ABBREVIATIONS ASD = adult spinal deformity; AUC = area under the curve; DJF = distal junctional failure; DJK = distal junctional kyphosis; GAP = Global Alignment and Proportion; GT = global tilt; LIV = lower instrumented vertebra; MD = moderately disproportioned; P = proportioned; PI = pelvic incidence; PJF = proximal junctional failure; PJK = proximal junctional kyphosis; PT = pelvic tilt; SD = severely disproportioned; SRS = Scoliosis Research Society; SS = sacral slope; SVA = sagittal vertical axis; UIV = upper instrumented vertebra; 3CO = 3-column osteotomy.

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Contributor Notes

Correspondence Meghan Cerpa: Columbia University Medical Center, New York, NY. mc4338@cumc.columbia.edu.

INCLUDE WHEN CITING Published online October 2, 2020; DOI: 10.3171/2020.6.SPINE20538.

Disclosures Dr. Baum reports being a consultant for Stryker. Dr. Sardar reports receiving honoraria from Medtronic and Stryker Spine. Dr. Lenke reports being a paid consultant for Medtronic (monies donated to a charitable foundation), EOS Technologies, and Acuity Surgical; receiving royalties from Medtronic and Quality Medical Publishing; receiving reimbursement for airfare/hotel from Broadwater, the Seattle Science Foundation, the Scoliosis Research Society, Stryker Spine, the Spinal Research Foundation, and AO Spine; receiving grant support (monies to institution) from the Scoliosis Research Society, EOS, the Setting Scoliosis Straight Foundation, and AO Spine; being an expert witness in a patent infringement case for Fox Rothschild; receiving philanthropic research funding from a grateful patient/family (Evans Family donation and Fox Family Foundation); and receiving fellowship support to his institution from AO Spine.

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