Measure sagittal spinal alignment rigorously, without the friction.
SpineCalc automates the GAP score, the T4–L1–hip axis, the Roussouly classification, the SRS–Schwab modifiers and more, directly on digital lateral radiographs. Free, in the browser.
A calculation and educational support tool. It is not a medical device.
Why alignment matters
A mismatch between pelvic morphology and spinal alignment is a known predictor of mechanical complications after adult spinal deformity surgery: screw loosening, proximal junctional kyphosis and nonunion, among others.
The GAP score (Yilgor et al., 2017) was developed precisely to capture that global proportion and predict the risk. It has been externally validated (Kwan et al., 2021) and reanalysed in recent meta-analyses (Cho et al., 2024; Ferraz et al., 2025).
Measuring well — and fast — makes it possible to plan surgery against an evidence-based alignment target, and to compare the preoperative and postoperative states by the same criterion.
What SpineCalc computes
A single radiograph upload and a single set of landmarks feed several published frameworks at once. No transcribing between calculators.
GAP score
Global alignment and proportion (Yilgor 2017), with its five subcomponents.
T4–L1–hip axis
Normal ideal sagittal alignment (Hills 2022), with vertebral tilts.
Roussouly
Current and target morphotype, and their agreement with pelvic incidence.
SRS–Schwab
Standard sagittal modifiers: PI−LL, PT and SVA.
GAP-B
GAP variant with BMI and bone mineral density (Noh 2020).
Basic parameters
PI, SS, PT, L1–S1 and L4–S1 lordosis, global tilt and SVA.
Grounded in published evidence
SpineCalc proposes no new parameters or thresholds: it automates the arithmetic of methods published by third parties, whose scientific merit belongs to their authors. The bibliography runs from Legaye 1998 to Haddad 2025.
See the referencesWho builds it
Spine surgeons at Centro Médico ABC in Mexico City, together with Virtual Medical Learning (VML).
Meet the teamStart measuring
Upload a lateral radiograph and get the full analysis in minutes.