Original Research
Pullout Strength Variance Among Self-Tapping Screws Inserted to Different Depths
Am J Orthop. 2008 September;37(9):466-469
Author and Disclosure Information
Andrew Schoenfeld, MD, Gregory Vrabec, MD, FRCS(C), Suneel Battula, PhD, Ann Salvator, MS, and Glen Njus, PhD
Dr. Schoenfeld is Clinical Fellow at Harvard Medical School/ Brigham and Women's Hospital, Boston, Massachusetts. At the time of this submission, he was a resident in orthopaedic surgery at Akron General Medical Center and Northeastern Ohio Universities College of Medicine, Akron, Ohio.
Dr. Vrabec is Associate Professor of Orthopaedic Surgery, Department of Orthopaedic Surgery, Akron General Medical Center and Northeastern Ohio Universities College of Medicine, Akron, Ohio.
Dr. Battula is Senior Research Associate, Zimmer Dental, San Diego, CA.
Ms. Salvator is Research Coordinator, Department of Neurology, Children's Hospital Medical Center of Akron, Akron, Ohio.
Dr. Njus is Professor, Department of Biomechanical Engineering, University of Akron, Akron, Ohio.
The cortical self-tapping screw (STS) has replaced the non-STS as an aid in fracture fixation. In a recent biomechanical investigation, Berkowitz and colleagues found that STS pullout strength increased with insertion depth up to 1 mm past the far cortex only. In the present study, we wanted to apply a standardized protocol of assessing pullout strength to STSs of different compositions and manufacturers while eliminating the sample-size and block-variance issues that affected the previous investigation. Ninety STSs were randomly divided into 5 groups, each representing a different insertion depth. Peak force was determined with trials ending in screw pullout or failure. A statistically significant difference in pullout strength was identified with insertion depths up to 1 mm past the far cortex. No block variance was detected. These results support the recommendation that STSs be inserted only 1 mm past the far cortex in healthy cortical bone.