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Biomechanics of Prophylactic Tethering for Proximal Junctional Kyphosis: Characterization of Spinous Process Tether Pretensioning and Pull-Out Force

  • Biomechanics
  • Published:
Spine Deformity Aims and scope Submit manuscript

Abstract

Study Design

Biomechanical evaluation of cadaver functional spinal units (FSUs).

Objectives

Demonstrate the effect of increasing spinous process (SP) tether pretension on FSU flexion range of motion (ROM), intervertebral disc (IVD) pressure, and SP force. Quantify SP tether pull-out forces and relate them to SP forces generated at maximum flexion.

Summary of Background Data

There has been recent interest in the use of SP tethering for prophylactic treatment of proximal junctional kyphosis (PJK). There is currently no consensus on standard tethering technique and no biomechanical data on the effect of tether pretension.

Methods

Nine T11–T12 FSUs were tested to 5 Nm of flexion-extension bending. A strain gauge was applied at the base of the T11 SP to measure force. Two custom pressure sensors were inserted into the anterior and posterior thirds of the IVD. Motion kinematics were measured by a motion capture system. An untethered test was done to describe baseline behavior. A 5-mm polyester tether was looped through holes drilled at the base of each SP and pretensioned to five different pretensions ranging from 0 to 88 N. Following ROM testing, specimens were dissected into individual vertebra and then SP pull-out testing was done at each level.

Results

Increasing pretension significantly reduced flexion ROM, reduced IVD pressures, and increased SP force. All pretensions, including the minimum, significantly reduced flexion ROM. SP pull-out forces were significantly greater than SP forces generated at maximum flexion.

Conclusions

Tether pretension significantly affects segmental FSU biomechanics. Pretension should be considered an integral factor in the overall success of a tethering strategy. Efforts should be made to control and record pretension intraoperatively.

Level of Evidence

Level V, biomechanical study.

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Authors and Affiliations

  1. Department of Orthopedic Surgery, University of Kansas Medical Center, Kansas City, KS, USA

    Damon E. Mar PhD, Steven J. Clary BS, Douglas C. Burton MD & Terence E. McIff PhD, MBA

Authors
  1. Damon E. Mar PhD
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  2. Steven J. Clary BS
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  3. Douglas C. Burton MD
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  4. Terence E. McIff PhD, MBA
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Corresponding author

Correspondence to Damon E. Mar PhD.

Additional information

Author disclosures: DEM (none), SJC (none), DCB (grants, personal fees, and other from DePuy Spine; nonfinancial support from International Spine Study Group, Scoliosis Research Society, and University of Kansas Physicians; and other from Bioventus and Pfizer, outside the submitted work), TEM (none).

IRB Approval: None applicable.

Funding Sources: Marc A. and Elinor J. Asher Orthopedic Research Endowment.

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Mar, D.E., Clary, S.J., Burton, D.C. et al. Biomechanics of Prophylactic Tethering for Proximal Junctional Kyphosis: Characterization of Spinous Process Tether Pretensioning and Pull-Out Force. Spine Deform 7, 191–196 (2019). https://doi.org/10.1016/j.jspd.2018.06.017

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  • DOI: https://doi.org/10.1016/j.jspd.2018.06.017

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