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Biomechanical Evaluation of 4 Different Foundation Constructs Commonly Used in Growing Spine Surgery: Are Rib Anchors Comparable to Spine Anchors?

  • Biomechanics
  • Published:
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Abstract

Study Design

In vitro animal model.

Objective

To compare the strength of 4 different anchor constructs commonly used as foundations in growing spine surgery.

Summary of Background Data

Children with progressive early-onset scoliosis often require surgical intervention to control the deformity and allow continued growth. The foundation sites of growing spine constructs take a significant load and can fail. This study compares the strength of 4 commonly used constructs applying the same load in a porcine model.

Methods

Forty immature porcine specimens including soft tissues (10 per group) were instrumented with 1 of 4 bilateral proximal anchors at T5–T6. The four groups were: screw—screw (SS), lamina hook—hook (HH), rib hook—hook (RR), and transverse process to lamina hook—hook (TPL). The entire specimen was kept intact except for surgical site exposure. A unique fixture was designed to brace the specimen and provide a counterforce. The ultimate load was identified as the greatest load recorded for a construct and analyzed by a set of 1-way analysis of variance using the SPSS 12.0 statistical package.

Results

All specimens eventually failed at the bone—anchor interface. No failures were observed in the instrumentation used. The means and standard deviations of ultimate loads were measured as RR (429 ± 133 N), SS (349 ± 89 N), HH (283 ± 48 N), and TPL (236 ± 60 N). There was no statistically significant difference between the following construct pairs: RR/SS, SS/HH, and HH/TPL. Young’s modulus was calculated for each construct type and no statistically significant difference was determined.

Conclusions

This study showed that RR and SS constructs had the greatest ultimate strength but also the greatest variability among the foundations tested. However, the HH and TPL constructs had lower ultimate strength but were less variable. Rib-based anchors may be considered as an alternative in upper foundation constructs in growing rod techniques.

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Authors and Affiliations

  1. San Diego Center for Spinal Disorders, 4130 La Jolla Village Drive, Suite 300, La Jolla, CA, 92037, USA

    Behrooz A. Akbarnia MD & Nima Kabirian MD

  2. Rady Children Hospital, 3030 Children’s Way, Ste. 410, San Diego, CA, 92123, USA

    Burt Yaszay MD & Diana Glaser PhD

  3. Hacettepe University, Sihhiye Ankara, 06100, Turkey

    Muharrem Yazici MD

  4. Department of Orthopaedics and Rehabilitation, University of Florida College of Medicine, PO Box 112727, Gainesville, FL, 32611-2727, USA

    Laurel C. Blakemore MD

  5. °K2M, lnc K2M, Inc., 751 Miller Drive, SE, Leesburg, Virginia, 20175, USA

    Kevin R. Strauss ME

Authors
  1. Behrooz A. Akbarnia MD
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  2. Burt Yaszay MD
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  3. Muharrem Yazici MD
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  4. Nima Kabirian MD
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  5. Laurel C. Blakemore MD
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  6. Kevin R. Strauss ME
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  7. Diana Glaser PhD
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Consortia

Complex Spine Study Group

Corresponding author

Correspondence to Behrooz A. Akbarnia MD.

Additional information

Author disclosures: BAA (grants from K2M, Inc., during the conduct of the study; grants from DePuy Spine, grants from K2M, Inc., grants from Nuvasive; personal fees from DePuy Spine, personal fees from Ellipse, personal fees from Kspine, personal fees from Nuvasive, personal fees from K2M, outside the submitted work); BY (grants from K2M, during the conduct of the study; grants and personal fees from Depuy Synthes, grants and personal fees from K2M; personal fees from Orthopaediatrics, personal fees from Medtronic; grants from Ellipse, outside the submitted work); MY (other support from DePuy Synthes and Ellipse Technologies, outside the submitted work); NK (none); LCB (Member at large, Scoliosis Research Society Board of Directors; Board of Surgical Advisors for K2M Medical; consulting agreement for reimbursement for faculty participation on instructional courses with K2M Medical, Stryker, and Medtronic); KRS (none); DG (grants from K2M, Inc., during the conduct of the study; other from MAKO, other from Mankind, other from Alphatec, other from NuVasive; grants from EOS Imaging, grants from Scoliosis Research Society, grants from Growing Spine Foundation, grants from KCl, grants from K2M, Inc., grants from Naval Medical Center San Diego, grants from Pediatric Orthopaedic Society of North America, outside the submitted work). The cost of the study and 1 of the implants used were provided by K2M, Inc., Leesburg, VA.

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Akbarnia, B.A., Yaszay, B., Yazici, M. et al. Biomechanical Evaluation of 4 Different Foundation Constructs Commonly Used in Growing Spine Surgery: Are Rib Anchors Comparable to Spine Anchors?. Spine Deform 2, 437–443 (2014). https://doi.org/10.1016/j.jspd.2014.04.001

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  • DOI: https://doi.org/10.1016/j.jspd.2014.04.001

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