Quantitative Characteristics of Consecutive Lengthening Episodes in Early-onset Scoliosis (EOS) Patients With Dual Growth Rods Aakash Agarwal, PhD,  Ankur Goswami, MD, y Govindaraja Perumal Vijayaraghavan, MD, y Abhishek Srivastava, MD, y Pankaj Kandwal, MD, z Upendra Bidre Nagaraja, MD, § Vijay K. Goel, PhD,  Anand K. Agarwal, MD,  and Arvind Jayaswal, MD y Study Design. A prospective single-center study. Objective. The aim of this study was to record the characteris- tic forces and lengths observed during distraction episodes in early-onset scoliosis (EOS), and analyze their interdependencies on the key variability among the patients. Summary of Background Data. The goal of the growing-rod technique is to achieve deformity correction alongside maintain- ing growth of the spine. The deformity correction is achieved during the initial surgery, but follow-up distraction episodes are necessary to maintain the growth. The key variables, under the control of a surgeon, that affect the growth are the applied distraction forces and the distraction lengths. Since the advent of dual growth rod technique, there have been many studies exploring the relationship between these and the actual growth. However, there is sparse evidence on the actual magnitude of distraction forces, and none on its association with patient’s parameters such as sex, age, and deformity. Methods. In a consecutive series of 47 patients implanted with dual growth rods, the distraction forces (in N) and the lengths (in mm) achieved during each distraction episode and compared against the episode-specific demographics. The values obtained from each side, that is, concave and convex sides, were averaged to calculate the mean. Statistical analysis was per- formed using t-distribution because for each normalized time points (distraction episode). Results. In cumulative, the distraction force increased by an amount of 268%, with 120% increase in the early stages (distractions episodes 1–6) and 68% increase in the later stages (distractions episodes 6–11), whereas the cumulative decrease in the length over 11 distractions episodes was 47%, with 34% and 20% in the early and later stages, respectively. The study does not identify any significant trend with respect to sex, age, and deformity. Conclusion. The distraction force and the length increased and decreased respectively with every consecutive distraction epi- sode, with no correlation to sex, age, extent of deformity, or the extent of correction. Key words: autofusion, deformity correction, differential distraction, distraction, distraction forces, distraction-based method, dual growth rods, early onset scoliosis, law of diminishing returns, traditional growth rods. Level of Evidence: 5 Spine 2019;44:397–403 D ual growth rod treatment is the most common surgical philosophy used against progression of scoliosis in growing children. 1–3 The principle behind this type of spine surgery is unique. It requires consecutive distractions, thus creating additional soft-tissue space in-between the vertebrae, for the bone to in. Although it has been practiced for several years now, there still exist many complications that have not been completely eluci- dated. Most of these could be categorized as mechanical (implant breakage, anchor loosening, and/or dislodgement etc.), growth-related (i.e., use of regular distraction in chil- dren who have no growth potential left), and distraction- related (i.e., applying excess of distraction force, law of diminishing return, etc.). 4–7 Furthermore, even though these complications are categorized into different groups, past From the  Engineering Center for Orthopaedic Research Excellence (ECORE), Department of Bioengineering and Orthopaedics Surgery, Col- leges of Engineering and Medicine, University of Toledo, Toledo, OH; y Primus Super Specialty Hospital, New Delhi, New Delhi, India; z Department of Orthopaedics, All India Institute of Medical Sciences (AIIMS), Rishikesh, Uttarakhand, India; and § Department of Orthopaedics, Jain Institute of Spine Care & Research, Bengaluru, Karnataka, India. Acknowledgment date: June 12, 2018. First revision date: July 15, 2018. Acceptance date: July 27, 2018. 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, stocks. Address correspondence and reprint requests to Aakash Agarwal, PhD, Engineering Center for Orthopaedic Research Excellence, University of Toledo, 5051 Nitschke Hall MS 303, 2801 W. Bancroft St., Toledo, OH 43606; E-mail: Aakash.Agarwal@rockets.utoledo.edu DOI: 10.1097/BRS.0000000000002835 Spine www.spinejournal.com 397 SPINE Volume 44, Number 6, pp 397–403 ß 2018 Wolters Kluwer Health, Inc. All rights reserved. DEFORMITY Copyright © 2019 Wolters Kluwer Health, Inc. Unauthorized reproduction of this article is prohibited.