Towards a Standard Clinically Relevant Testing Protocol for the Assessment of Growing Rods

Towards a Standard Clinically Relevant Testing Protocol for the Assessment of Growing Rods

Bibliographic Details
Main Author: Shekouhi, Niloufar
Language:English
Published: University of Toledo / OhioLINK 2020
Subjects:
Biomedical Engineering
Traditional Growing Rods
ASTMF1717
ISO12189
Early Onset Scoliosis
Distraction
Spinal Implants
Online Access:http://rave.ohiolink.edu/etdc/view?acc_num=toledo1596790709273486
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spelling ndltd-OhioLink-oai-etd.ohiolink.edu-toledo15967907092734862021-08-03T07:16:12Z Towards a Standard Clinically Relevant Testing Protocol for the Assessment of Growing Rods Shekouhi, Niloufar Biomedical Engineering Traditional Growing Rods ASTMF1717 ISO12189 Early Onset Scoliosis Distraction Spinal Implants Early Onset Scoliosis (EOS) is the spine's lateral curvature in patients under ten years of age. Emergence of growing rods has reduced the progression of spinal deformity while allowed for its growth. After initial implantation, growing rods undergo repetitive distraction surgeries at consecutive intervals to correct the spinal deformity. Based on the clinical studies, failed implants are associated with more distractions. However, the currently available biomechanical testing protocols do not feature long growing rods, and hence are not able to simulate distraction. Hence, a new Finite Element (FE) distraction-based protocol is presented here to capture the growing rods’ biomechanics in a clinically relevant condition.The vertebrectomy model (VO), based upon the ASTM-F1717 guideline, was modified to accommodate multi-spinal segments (MS) with springs simulated between plastic blocks (with 129 N/mm stiffness). To assess the efficacy of the proposed protocol, the MS models were subjected to 1) compression-bending (MS-CB), and 2) distraction followed by compression-bending (MS-D+CB). In the MS-D+CB models, distraction was applied, stretching the spring-block construct in a scoliosis surgery simulation prior to locking the construct at the connector-rods' interface. Different axial connectors (rods-only (RO), short/long tandem (ST/LT), and side-by-side (SBS) connector positioned in the mid construct, and at proximal site (CR-LT)) were modeled. Different configurations of crosslinks (one-proximal (1PCL), two-proximal (2PCLs) and two-distal-crosslinks (2DCLs)) were modeled. The CR-LT model was distracted at connector's cranial (CR-LT) and caudal interface with rods (CR-LT-D). Models with springs' stiffness of 98 N/mm (SPG-98), 147 N/mm (SPG-147) and 374 N/mm (SPG-374) were modeled and were further modified to simulate follower loads (80N, 100N, and 120N). Finally, modifications of the current guidelines were adapted in the LT model. Stiffness and yield loads were calculated (per ASTM-F1717 guideline) and stresses on the rods were captured.The MS-CB models showed higher stiffness and yield load than the VO models. Distraction produced pre-existing stresses, decreased the stiffness/yield load, shifted the critical stress location, and increased the rods’ stresses. The Inclusion of crosslinks increased the construct’s rigidity and yield load; however, it did not change the location of maximum stress. Positioning connectors at the proximal site (CR-LT) increased constructs’ rigidity, yield load and stresses. In CR-LT model, the distraction position altered the rods’ stresses. Higher load sharing between the anterior column and posterior implant observed as the anterior column’s overall stiffness increased. Simulation of follower loads decreased the stiffness and yield load while increased the rods’ stresses. Shifting the external load fulcrum toward the springs' line of action increased the stiffness, yield load and stresses.To the best of author’s knowledge, this is the first study representing a distraction-based protocol to evaluate the traditional growing rods (TGRs) used for scoliosis patients. Such a protocol is necessary to facilitate the biomechanical evaluation of these devices prior to clinical use. The proposed protocol addresses various clinical parameters that are not feasible in the current guidelines and shows stress patterns consistent with clinical failures. 2020-12-14 English text University of Toledo / OhioLINK http://rave.ohiolink.edu/etdc/view?acc_num=toledo1596790709273486 http://rave.ohiolink.edu/etdc/view?acc_num=toledo1596790709273486 unrestricted This thesis or dissertation is protected by copyright: all rights reserved. It may not be copied or redistributed beyond the terms of applicable copyright laws.
collection NDLTD
language English
sources NDLTD
topic Biomedical Engineering
Traditional Growing Rods
ASTMF1717
ISO12189
Early Onset Scoliosis
Distraction
Spinal Implants
spellingShingle Biomedical Engineering
Traditional Growing Rods
ASTMF1717
ISO12189
Early Onset Scoliosis
Distraction
Spinal Implants
Shekouhi, Niloufar
Towards a Standard Clinically Relevant Testing Protocol for the Assessment of Growing Rods
author Shekouhi, Niloufar
author_facet Shekouhi, Niloufar
author_sort Shekouhi, Niloufar
title Towards a Standard Clinically Relevant Testing Protocol for the Assessment of Growing Rods
title_short Towards a Standard Clinically Relevant Testing Protocol for the Assessment of Growing Rods
title_full Towards a Standard Clinically Relevant Testing Protocol for the Assessment of Growing Rods
title_fullStr Towards a Standard Clinically Relevant Testing Protocol for the Assessment of Growing Rods
title_full_unstemmed Towards a Standard Clinically Relevant Testing Protocol for the Assessment of Growing Rods
title_sort towards a standard clinically relevant testing protocol for the assessment of growing rods
publisher University of Toledo / OhioLINK
publishDate 2020
url http://rave.ohiolink.edu/etdc/view?acc_num=toledo1596790709273486
work_keys_str_mv AT shekouhiniloufar towardsastandardclinicallyrelevanttestingprotocolfortheassessmentofgrowingrods
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