Insertional Torque and Pullout Strength of Pedicle Screws with or without Repositioning: A Porcine Study. (August 2014)

• Record Type: Journal Article
• Authors: Tan, Chun Ee; Fok, Margaret Woon Man; Luk, Keith Dip Kei; Cheung, Kenneth Man Chee
• Is Part Of: Journal of orthopaedic surgery. Volume 22:Number 2(2014)
• Page Start: 224
• Page End: 227
• Publication Date: 2014-08
• Subjects: bone screws -- spine -- torque; Orthopedic surgery -- Periodicals; Orthopedics; Orthopedic surgery; Periodicals; 617.3
• DOI: 10.1177/230949901402200223
• Languages: English
• ISSNs: 1022-5536

Abstract

Purpose: To evaluate the insertion torque and pullout strength of pedicle screws with or without repositioning. Methods: 20 fresh porcine lumbar vertebrae of similar size were used. The entry point was at the site just lateral and distal to the superior facet joint of the vertebra, and to a depth of 35 mm. A 6.2-mm-diameter, 35-mm-long pedicle screw was inserted parallel to the superior end plate on one side as control. On the other side, an identical screw was first inserted 10° caudal to the superior end plate, and then repositioned parallel to the superior end plate. The insertional torque and pullout strength were measured. Results: Three of the specimens were excluded owing to pedicle fractures during the pullout test. Repositioned pedicle screws were significantly weaker than controls in terms of the maximum insertional torque (3.20±0.28 vs. 2.04±0.28 Nm, 36% difference, p±0.01) and pullout strength (1664±378 vs. 1391±295 N, p±0.01). Conclusion: Repositioning pedicle screws should be avoided, especially when the pedicle wall is breached. If repositioning is deemed necessary, augmentation with polymethyl methacrylate or a screw with a larger diameter should be considered.