Fractional Curve in Adult Spinal Deformity: Is it a Driver of or a Compensation for Coronal Malalignment?

Nicolas Plais, Hongda Bao, Renaud Lafage, Han Jo Kim, Munish C Gupta, Justin S. Smith, Christopher Shaffrey, Gregory Mundis, Douglas Burton, Christopher Ames, Eric Klineberg, Shay Bess, Richard A. Hostin, Frank Schwab, Virginie Lafage

Research output: Contribution to journalArticlepeer-review


Study Design: This was a retrospective review of the multicenter adult spine deformity database. Objective: The objective of this study was to investigate the role of the fractional curve (FC) on global coronal malalignment. Summary of Background Data: Despite being very common, the role of the coronal FC as either a driver or compensation for global coronal malalignment is not well documented Materials and Methods: Patients with the following characteristics were extracted from a prospective multicenter database: lumbar/thoracolumbar (TL) major coronal curve >15 degrees, apex at T11-L3, lower end vertebra at L3 or L4, above 45 years old, and FC >5 degrees. In addition to the classic radiographic parameters, baseline analysis included Cobb angle, pelvic obliquity (PO), fractional ratio (fractional Cobb/main Cobb), the sum of PO and FC, as well as the coronal Qiu classification. Curves distribution (TL vs. FC) were compared across the 3 Qui types, and the role of the FC was investigated. Results: A total of 404 patients (63 y old, 83.3% female) were included: 43 patients were classified as type B, 120 as type C, and 241 were coronally balanced (type A). Compared with the balanced patients, type C patients had similar major TL Cobb angles but significantly larger fractional Cobb angles (17.5 vs. 22.3 degrees, P<0.001). By opposition, type B patients had significantly larger major TL Cobb angles (49 vs. 41 degrees, P=0.001) but smaller fractional Cobb angles (P<0.001). PO>5 degrees in the same direction as FC was more common in type B patients (20%) than in type C patients (7.5%), which suggests the preferential role of pelvic compensation. Conclusions: Our findings challenge the idea that FC is only a compensatory curve below a main lumbar or TL curve. In type B patients, FC acts as a compensation mechanism but fails to maintain coronal alignment despite the presence of PO. In type C patients, however, the lumbosacral FC acts as a primary driver of coronal malalignment. Level of Evidence: Level III.

Original languageEnglish (US)
Pages (from-to)E276-E281
JournalClinical Spine Surgery
Issue number5
StatePublished - Jun 2021


  • adult spine deformity
  • coronal malalignment
  • coronal Qiu classification
  • global coronal alignment
  • pelvic compensation
  • pelvic obliquity
  • primary patients
  • scoliosis

ASJC Scopus subject areas

  • Surgery
  • Orthopedics and Sports Medicine
  • Clinical Neurology


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