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Effects of Misalignment on Static Torsional Strength of Anterior Cervical Plate Systems

Scientific Paper

Chin KR1, Cumming VBHenson MMurrell BChan FW.

Interested medical professionals can read through the full paper, as published in the Spine Journal, here.


There is little understanding of cervical plate misalignment as a risk factor for plate failure at the plate-screw-bone interface.


To assess the torsional strength and mode of failure of cervical plates misaligned relative to the midsagittal vertical axis.


Plastic and foam model spine segments were tested using static compression and torsion to assess effects of misaligned and various lengths anterior cervical plate (ACPs).


Different length ACPs and cancellous fixed angle screws underwent axial torsional testing on a servo-hydraulic test frame at a rate of 0.5°/s. A construct consisted of one ACP, four screws, one ultrahigh-molecular weight polyethylene inferior block, and one polyurethane foam superior block. Group 1 had ACPs aligned in the midsagittal vertical axis, group 2 plates were positioned 20° offset from the midline, and group 3 had the ACP shifted 5 mm away and 20° offset from midline. Torques versus angle data were recorded. The failure criterion was the first sign of pullout determined visually and graphically.


Group 1 had a more direct screw pullout during failure. For the misaligned plates, failure was a combination of the screws elongating the holes and shear forces acting between the plate and block. The misaligned plates needed more torque to failure. The failure torque was 50% reduced for the longer versus the shorter plates in the neutral position. Graphically shown initial screw slippage inside the block preceded visual identification of slippage in some cases.


We observed different failure mechanisms for neutral versus misaligned plates. Clinically, misalignment may have the benefit of needing more torque to fail. Misalignment was a risk factor for failure of the screw-bone interface, especially in longer plate constructs. These comparisons of angulations may be a solid platform for expansion toward a more applicable in vivo model.

Copyright © 2013 Elsevier Inc. All rights reserved.


Dr. Kingsley R. Chin, Founder of philosophy and practice of The LES Society and The LESS Institute

Dr. Kingsley R. Chin is a board-certified Harvard-trained Orthopedic Spine Surgeon and Professor with copious business and information technology exposure. He sees a niche opportunity where medicine, business and info. tech meet – and is uniquely educated at the intersection of these three professions. He has experience as Professor of Clinical Biomedical Sciences & Admissions Committee Member at the Charles E. Schmidt College of Medicine at Florida Atlantic University, Professor of Clinical Orthopedic Surgery at the Herbert Wertheim College of Medicine at Florida International University, Assistant Professor of Orthopaedics at the University of Pennsylvania Medical School, Visiting Spine Surgeon & Professor at the University of the West Indies, Mona, and Adjunct Professor of Clinical Biomedical Sciences at the University of Technology, Jamaica.

Learn more about Dr. Chin here and connect via LinkedIn.


Less Exposure Surgery (LES) is based on a new philosophy of performing surgery, leading the charge to prove through bench and clinical outcomes research that LES treatment options are the best solutions – to lowering the cost of healthcare, improving outcomes and increasing patient satisfaction. Learn more at LESSociety.org.

The LES Society philosophy: “Tailor treatment to the individual aiding in the quickest recovery and return to a pain-free lifestyle, using LES® techniques that lessen exposure, preserve unoffending anatomy and utilize new technologies which are safe, easy to adopt and reproducible. These LES®techniques lessen blood loss, surgical time and exposure to radiation and can be safely performed in an outpatient center. Less is more.” – Kingsley R. Chin, MD


The LESS Institute is the world leader center of excellence in Less Exposure Surgery. Our safe, effective outpatient treatments help patients recover quickly, avoid expensive hospital stays and return home to their family the same day. Watch our patient stories, follow us on Facebook and visit TheLESSInstitute.com to learn more.


The above study utilized LES Technology from SpineFrontier – leading provider of LES Technologies and instruments – offering surgeons and patients superior technology and services.



Chin KR1, Cumming VBHenson MMurrell BChan FW.

Author information

  1. Institute for Modern and Innovative Surgery, 1100 W. Oakland Park Blvd, Suite #3, Fort Lauderdale, FL 33311, USA. Electronic address: [email protected]

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