Institutional members access full text with Ovid®

Does Higher Anchor Density Result in Increased Curve Correction and Improved Clinical Outcomes in Adolescent Idiopathic Scoliosis?

Larson, A. Noelle MD*; Polly, David W. Jr. MD; Diamond, Beverly PhD; Ledonio, Charles MD; Richards, B. Stephens III MD§; Emans, John B. MD; Sucato, Daniel J. MD, MS§; Johnston, Charles E. MD§; the Minimize Implants Maximize Outcomes Study Group

doi: 10.1097/BRS.0000000000000204

Study Design. Retrospective review of prospectively collected data.

Objective. To determine whether anchor density is associated with curve correction and patient-reported outcomes.

Summary of Background Data. There is limited information as to whether anchor density affects the results of adolescent idiopathic scoliosis surgery.

Methods. A total of 952 patients with adolescent idiopathic scoliosis met inclusion criteria (Lenke 1, 2, and 5 curves) with predominantly screw constructs (no. of screws/no. of total anchors >75%). Anchor density was defined as the number of screws, hooks, and wires per level fused, with less than 1.54 considered low density. Analysis of covariance was undertaken to determine association of anchor density with percent curve correction, Scoliosis Research Society (SRS), and Spinal Appearance Questionnaire (SAQ) scores, controlling for flexibility, fusion length, demographics, and surgeon.

Results. High- compared with low-anchor density was associated with increased percent curve correction in Lenke 1 curves at 1 year (69% vs. 66% correction, P = 0.0022), controlling for percent preoperative curve flexibility, length of fusion, and sex (model, P < 0.0001). Similar associations held at 2-year follow-up and for Lenke 2 curves. Decreased thoracic kyphosis was found with increased anchor density for Lenke 1 and 2 curve patterns. There were no associations found between anchor density and Lenke 5 curves. For Lenke 1 curve patterns at 2 years postoperatively, in the high- versus low-anchor density cohorts, there were statistically higher SRS Activity (4.3 vs. 4.2, P = 0.019), Appearance (4.3 vs. 4.1, P = 0.0005), Satisfaction (4.5 vs. 4.3, P = 0.028), and Total scores (4.3 vs. 4.2; P = 0.024). Similarly, the SAQ Appearance score at 1 year similarly was improved in the high-anchor density group (high: 14.1 vs. low: 15.0, P = 0.03) for Lenke 1 curve patterns only.

Conclusion. For Lenke 1 and 2 curve patterns, improved percent correction of major coronal curve was noted in the high-screw density cohort. Although statistical significance was reached, it is unclear whether screw density resulted in clinically significant differences in patient-reported outcomes.

Level of Evidence: 3

Higher anchor density was associated with statistically significant increases in percent coronal curve correction for patients with adolescent idiopathic scoliosis and with Lenke 1 and 2 curve types and statistically significant increased patient-reported appearance scores. It is unclear whether these differences are clinically significant.

*Mayo Clinic, Rochester, MN

University of Minnesota, Minneapolis, MN;

PhDx Systems, Inc., Albuquerque, NM;

§Texas Scottish Rite Hospital, Dallas, TX; and

Children's Hospital, Boston, MA. A complete list of the members of the Minimize Implants Maximize Outcomes Study Group is given in the “Acknowledgment” section.

Address correspondence and reprint requests to David W. Polly, Jr., MD, Department of Orthopedic Surgery, University of Minnesota, 2450 Riverside Ave S, R200, Minneapolis, MN 55454; E-mail:

Acknowledgment date: August 6, 2013. First Revision date: October 6, 2013. Second Revision date: December 10, 2013. Acceptance date: December 12, 2013.

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

Scientific Forum/Spine Care grant from Orthopaedic Research and Education Foundation funds were received to support this work.

Relevant financial activities outside the submitted work: grant, consultancy, grants/grants pending, payment for lectures, royalties, and stock/stock options.

© 2014 by Lippincott Williams & Wilkins