Limited Predictive Performance of the Global Alignment and Proportion (GAP) Score for Mechanical Complications in Older Asian Patients With Adult Spinal Deformity: A Multicentre Validation Study
Global Spine Journal · 30 Jul 2026
† Impact is the editorial-priority score. All scores are out of 100. Clinical is a stored clinical-importance score from the earlier method; it has not been recalculated.
Why it matters
Spine surgeons using the GAP score to counsel older Asian patients about mechanical complication risk should know it performs poorly, essentially no better than a coin flip, in this population.
The evidence
This retrospective multicentre Japanese study tested whether the Global Alignment and Proportion (GAP) score, designed to predict mechanical complications after adult spinal deformity surgery, works as well in older Asian patients as it does in the Western populations it was developed from. Among 274 patients followed at least 2 years, 34% developed a mechanical complication, and the GAP score failed to distinguish complication from non-complication patients overall; in patients 70 and older, those who developed complications actually had lower (more 'proportioned') GAP scores (6.6 vs 7.9, p=0.039) after matching, the opposite of what the score predicts, though the age-by-GAP interaction itself was not statistically significant. The ROC area under the curve for GAP score alone predicting complications was 0.466, essentially no better than chance.
Mechanical complication (MC) occurrence vs GAP score: Mean difference -1.3 (95% CI unavailable; GAP score). Interpret in the study's stated comparison; this alone does not establish a treatment's causal effect.
Why this rigour score?
Retrospective cohort
Methods at a glance
Recorded assessment- Confounding adjustmentPropensity scores
- Covariate balance confirmedMet
- Outcome assessors blindedNot reported
- Comparable start of follow-upNot applicable
- Adequate statistical powerCalculation absent
- Prospective registrationNot met
Not reported does not mean not done. Checks have different weights; this is not a count of boxes ticked.
How to read this assessment
The recorded methods are shown alongside the published score. A verified point-by-point calculation is not available for this version of the appraisal.
Checklist from the stored appraisal. “Not met” describes the recorded criterion; it does not always produce a deduction. This overview supports reading the full study.
For journal club
1.If GAP score alignment targets don't predict mechanical complications in older Asian patients, should surgeons weight bone quality (e.g., Hounsfield units) or muscle mass more heavily than radiographic alignment when planning correction goals in this population?
2.Given that well-aligned older patients still developed complications while some malaligned patients did not, should surgeons reconsider how aggressively they pursue GAP-defined 'proportioned' alignment in frail elderly patients if it doesn't reduce mechanical complication risk?
Original publication title
Limited Predictive Performance of the Global Alignment and Proportion (GAP) Score for Mechanical Complications in Older Asian Patients With Adult Spinal Deformity: A Multicenter Validation Study