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Characterization and Predictive Value of Segmental Curve Flexibility in Adolescent Idiopathic Scoliosis Patients

Yao, Guanfeng, MD, PhD∗,†; Cheung, Jason P.Y., MBBS(HK), MMedSc, FRCS(Edin), FHKCOS, FHKAM(Orth); Shigematsu, Hideki, MD, PhD∗,‡; Ohrt-Nissen, Søren, MD∗,§; Cheung, Kenneth M.C., MBBS, MD, FRCS, FHKCOS, FHKAM; Luk, Keith D.K., MCh (Orth), FRCSE, FRCSG, FRACS, FHKAM (Orth); Samartzis, Dino, DSc

doi: 10.1097/BRS.0000000000002046

Study Design. A prospective radiographic analysis of adolescent idiopathic scoliosis (AIS) patients managed with alternate-level pedicle screw fixation was performed.

Objective. The objective of this study was to characterize segmental curve flexibility and to determine its predictive value in curve correction in AIS patients.

Summary of Background Data. Little is known regarding the distinct segmental curve characteristics and their ability to predict curve correction in patients with AIS.

Methods. The segmental Cobb angle was measured on posteroanterior standing radiographs and on fulcrum bending radiographs. Radiographs were analyzed preoperatively and at 2 years postoperatively and the curve was divided into upper, mid, and lower segments based on predefined criteria. The segmental flexibility and the segmental fulcrum bending correction index (FBCI) were calculated.

Results. Eighty patients were included with mean age of 15 years. Preoperative mean segmental Cobb angles were 18, 31, and 17 degrees in the upper, mid, and lower segments, respectively. Segmental bending Cobb angles were 6, 13, and 4 degrees, respectively, corresponding to segmental flexibilities of 50%, 47%, and 83% in the upper, mid, and lower segments, respectively (P < 0.001). At 2-year follow up, the mean segmental FBCI were 155%, 131%, and 100% in the upper, mid, and lower segments, respectively (P < 0.001), which suggested that the lower segment of the curve was more flexible than the other segments and that higher correction was noted in the upper segments. A significant, positive correlation was noted between the segmental bending Cobb angle and the segmental FBCI (P < 0.05), whereby the strength of the correlation varied based on the curve segment.

Conclusion. This is the first study to demonstrate the segmental variations in curve flexibility using the fulcrum bending radiograph in AIS patients. Curve flexibility is not uniform throughout the curve and different segments exhibit greater flexibility/correctibility than others. Segmental flexibility should be considered in assessing AIS patients and in the clinical decision-making strategy to optimize curve correction outcomes.

Level of Evidence: 03

Department of Orthopedics and Traumatology, University of Hong Kong, Pokfulam, Hong Kong, SAR, China

Department of Orthopedics, Shantou University Medical College, Guangdong, China

Department of Orthopedic Surgery, Nara Medical University, Kashihara, Nara, Japan

§Department of Orthopedics, Rigshospitalet, Denmark.

Address correspondence and reprint requests to Keith D.K. Luk, MCh (Orth), FRCSE, FRCSG, FRACS, FHKAM (Orth), Department of Orthopedics and Traumatology, Queen Mary Hospital, Professorial Block, 5th Floor 102 Pokfulam Road, Pokfulam Hong Kong, SAR, China; E-mail:; Dino Samartzis, DSc, Department of Orthopedics and Traumatology, Queen Mary Hospital, Professorial Block, 5th Floor 102 Pokfulam Road, Pokfulam Hong Kong, SAR, China; E-mail:

Received 10 August, 2016

Revised 11 October, 2016

Accepted 7 November, 2016

G.Y. and J.P.Y.C. are co-first authors and contributed equally in this study.

The device(s)/drug(s) is/are FDA-approved or approved by corresponding national agency for this indication.

No funds were received in support of this work.

Relevant financial activities outside the submitted work: grants.

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