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Preclinical Bench Testing on a Novel Posterior Dynamic Deformity Correction Device for Scoliosis

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Abstract

Study Design

Biomechanical test.

Objective

To summarize the preclinical tests performed to assess the durability of a novel fusionless dynamic device for the treatment of adolescent idiopathic scoliosis (AIS).

Summary of Background Data

The minimal invasive deformity correction (MID-C) system is a distractible posterior dynamic deformity correction device designed to reduce scoliosis for AIS patients, to maintain curve correction, and to preserve spinal motion. To overcome the challenges of wear and fatigue of this procedure, the system has two unique features: polyaxial joints at the rod-screw interface and a ceramic coating of the moving parts.

Methods

Five biomechanical tests were performed: Static compression to failure, fatigue loading per ASTM F 1717 with 5.5-mm screws for 10 million cycles (MC) at 5 Hz, wear assessment, wear test of the polyaxial joint under 100 N load for 10 MC, and wear particle implantation in rabbits.

Results

The system failed through buckling of the rod with loads over 3000 N (400% of human body weight). Dynamically, the system maintained 700 N for 10 MC with 5.5 mm screws. The maximum total steady-state wear rate was 0.074 mg/MC (0.03 per polyaxial joint and 0.014 mg/MC for the ratchet mechanism). Histologic evaluation of the particle injection sites indicated no difference in the local tissue response between the control and test articles. At 3 and 6 months postinjection, there were neither adverse local effects nor systemic effects observed.

Conclusions

The unique design features of the MID-C system, based on polyaxial joints and ceramic coating, resulted in favorable static, fatigue, and wear resistance properties. Wear properties were superior to those published for artificial spinal discs. Long-term outcomes from clinical use will be required to correlate these bench tests to the in vivo reality of clinical use.

Level of Evidence

Level V.

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Authors and Affiliations

  1. Israel Spine Center, Assuta Hospital, Tel Aviv, Israel

    U. Arnin BSc & Y. Floman MD

  2. IWK Health Centre, Halifax, Nova Scotia, B3K-6R8, Canada

    R. El-Hawary MD

  3. Institute for Spine and Scoliosis Lawrenceville, USA

    R.R. Betz MD

  4. Mount Sinai Hospital, NY, USA

    B.S. Lonner MD

Authors
  1. U. Arnin BSc
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  2. R. El-Hawary MD
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  3. R.R. Betz MD
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  4. B.S. Lonner MD
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  5. Y. Floman MD
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Corresponding author

Correspondence to R. El-Hawary MD.

Additional information

Author disclosures: UA (personal fees from ApiFix Ltd, during the conduct of the study; in addition, UA has a patent PCT/US11/035278 licensed, and a patent PCT/US13/20453 licensed), RE-H (personal fees from Apifix Ltd., during the conduct of the study; grants from DePuy Synthes Spine and Medtronic Spine; personal fees from DePuy Synthes Spine, Medtronic Spine, and Apifix Ltd.; nonfinancial support from Children’s Spine Foundation and Pediatric Orthopaedic Society of North Americal; grants from Canadian Institute of Health Research, Atlantic Canada Opportunities Agency, Scoliosis Research Society, Pediatric Orthopaedic Society of North America, and EOS Imaging; nonfinancial support from Scoliosis Research Society, outside the submitted work), RRB (personal fees and other from ApiFix, during the conduct of the study; personal fees and other from Abyrx, DePuy Synthes Spine, and SpineGuard; other from Advanced Vertebral Solutions, Electrocore, Medovex, MiMedx, Orthobond, and Lifeunit; personal fees from Globus Medical, Medtronic, MacKeith Publishers, and Wishbone, outside the submitted work; and Son Randal Jr. is an employee of DePuy Synthes Spine), BSL (grants from Setting Scoliosis Straight Foundation; personal fees from DePuy Synthes Spine, K2M, Paradigm Spine, Spine Search, and Ethicon; nonfinancial support from Spine Deformity Journal; grants from John and Marcella Fox Fund Grant, OREF; personal fees from Zimmer Biomet, Apifix, and Unyq Align, outside the submitted work), YF (reports personal fees from Apifix, during the conduct of the study).

IRB Approval: Not required as this was a biomechanical testing study.

Funding Sources: This study was funded by Apifix Ltd., Israel.

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Arnin, U., El-Hawary, R., Betz, R. et al. Preclinical Bench Testing on a Novel Posterior Dynamic Deformity Correction Device for Scoliosis. Spine Deform 7, 203–212 (2019). https://doi.org/10.1016/j.jspd.2018.08.010

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  • DOI: https://doi.org/10.1016/j.jspd.2018.08.010

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