SYMPOSIA PAPER Published: 01 January 2003

Clinical Relevance of Pull-out Strength Testing of Pedicle Screws


Pull-out strength testing is described in many published manuscripts and is specially treated in ASTM F1692-96, “Standard Test Method for Determining Axial Pull-Out Strength of Medical Bone Screws.” Extensive biomechanics are reported on the importance of variables like hole preparation and cement augmentation. In this study, the pull-out strengths of variously-shaped, titanium pedicle screws were tested and the literature was searched for cited incidences of pull-out. The screws were extracted from polyurethane foam that modeled weak, moderate, and strong cancellous bone. Testing revealed significantly different pull-out strengths depending upon screw design and substrate strength. However, the literature search yielded few citations of screw pull-out. Screw loosening and hardware failure are sometimes mentioned in clinical reports but rarely is pull-out documented as a failure mechanism. Standardized testing is useful in comparing various designs but may have little relationship to in vivo performance.

Author Information

Dawson, JM
Centerpulse Spine Tech Inc., Minneapolis, MN
Boschert, P
Centerpulse Spine Tech Inc., Minneapolis, MN
Macenski, MM
Centerpulse Spine Tech Inc., Minneapolis, MN
Rand, N
Vanderbilt University, Nashville, TN, ISRAEL
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Developed by Committee: F04
Pages: 68–77
DOI: 10.1520/STP11134S
ISBN-EB: 978-0-8031-5480-3
ISBN-13: 978-0-8031-3463-8