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 Gupta; Justin S Smith; Christopher Shaffrey; Gregory Mundis; Douglas Burton; Christopher Ames; Eric Klineberg; Shay Bess; Richard A Hostin; Frank Schwab; Virginie Lafage; International Spine Study Group, Littleton, CO

doi:10.1097/BSD.0000000000001151

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

Clin Spine Surg. 2021 Jun 1;34(5):E276-E281. doi: 10.1097/BSD.0000000000001151. Epub 2021 Mar 12.

Authors

Nicolas Plais^{1

2}, Hongda Bao^{1

3}, Renaud Lafage¹, Han Jo Kim¹, Munish Gupta⁴, Justin S Smith⁵, Christopher Shaffrey⁵, Gregory Mundis^{6

7}, Douglas Burton⁸, Christopher Ames⁹, Eric Klineberg¹⁰, Shay Bess¹¹, Richard A Hostin¹², Frank Schwab¹, Virginie Lafage¹; International Spine Study Group, Littleton, CO

Affiliations

¹ Department of Orthopaedic Surgery, Hospital for Special Surgery, New York, NY.
² San Cecilio University Hospital in Granada, Granada, Spain.
³ Nanjing Drum Tower Hospital, Nanjing University, Nanjing, Jiangsu Province, China.
⁴ Department of Orthopaedic Surgery, Washington University School of Medicine, St. Louis, MO.
⁵ Department of Neurosurgery, University of Virginia, Charlottesville, VA.
⁶ San Diego Spine Foundation, San Diego.
⁷ Scripps Clinic, La Jolla, CA.
⁸ Department of Orthopaedic Surgery, University of Kansas Medical Center, Kansas City, KS.
⁹ Department of Neurosurgery, University of California San Francisco, San Francisco.
¹⁰ Department of Orthopaedic Surgery, University of California Davis, Sacramento, CA.
¹¹ Presbyterian/St. Luke's Medical Center & Rocky Mountain Hospital for Children, Denver, CO.
¹² Medical City Dallas Spine Hospital, Dallas, TX.

PMID: 38011511
DOI: 10.1097/BSD.0000000000001151

Abstract

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.