Finding the right fit: studying the biomechanics of under-tapping with varying thread depths and pitches.

Autor: Jazini E; Department of Orthopaedics, University of Maryland, 110 South Paca St, Suite 300, Baltimore, MD 21201, USA., Petraglia C; Department of Orthopaedics, University of Maryland, 110 South Paca St, Suite 300, Baltimore, MD 21201, USA., Moldavsky M; Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., 2560 General Armistead Ave, Audubon, PA 19403, USA., Tannous O; Department of Orthopaedics, University of Maryland, 110 South Paca St, Suite 300, Baltimore, MD 21201, USA., Weir T; Department of Orthopaedics, University of Maryland, 110 South Paca St, Suite 300, Baltimore, MD 21201, USA., Saifi C; New York-Presbyterian/Columbia University Medical Center, 622 West 168 St, New York, NY 10032, USA., Elkassabany O; Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., 2560 General Armistead Ave, Audubon, PA 19403, USA., Cai Y; Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., 2560 General Armistead Ave, Audubon, PA 19403, USA., Bucklen B; Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., 2560 General Armistead Ave, Audubon, PA 19403, USA., O'Brien J; Department of Orthopaedic Surgery, George Washington University, 2150 Pennsylvania Ave NW, Washington, DC 20037, USA., Ludwig SC; Department of Orthopaedics, University of Maryland, 110 South Paca St, Suite 300, Baltimore, MD 21201, USA. Electronic address: sludwig@umoa.umm.edu.
Jazyk: angličtina
Zdroj: The spine journal : official journal of the North American Spine Society [Spine J] 2017 Apr; Vol. 17 (4), pp. 574-578. Date of Electronic Publication: 2016 Dec 01.
DOI: 10.1016/j.spinee.2016.11.019
Abstrakt: Background Context: Compromise of pedicle screw purchase is a concern in maintaining rigid spinal fixation, especially with osteoporosis. Little consistency exists among various tapping techniques. Pedicle screws are often prepared with taps of a smaller diameter, which can further exacerbate inconsistency.
Purpose: The objective of this study was to determine whether a mismatch between tap thread depth (D) and thread pitch (P) and screw D and P affects fixation when under-tapping in osteoporotic bone.
Study Design: This study is a polyurethane foam block biomechanical analysis.
Materials and Methods: A foam block osteoporotic bone model was used to compare pullout strength of pedicle screws with a 5.3 nominal diameter tap of varying D's and P's. Blocks were sorted into seven groups: (1) probe only; (2) 0.5-mm D, 1.5-mm P tap; (3) 0.5-mm D, 2.0-mm P tap; (4) 0.75-mm D, 2.0-mm P tap; (5) 0.75-mm D, 2.5-mm P tap; (6) 0.75-mm D, 3.0-mm P tap; and (7) 1.0-mm D, 2.5-mm P tap. A pedicle screw, 6.5 mm in diameter and 40 mm in length, was inserted to a depth of 40 mm. Axial pullout testing was performed at a rate of 5 mm/min on 10 blocks from each group.
Results: No significant difference was noted between groups under axial pullout testing. The mode of failure in the probe-only group was block fracture, occurring in 50% of cases. Among the other six groups, only one screw failed because of block fracture. The other 59 failed because of screw pullout.
Conclusions: In an osteoporotic bone model, changing the D or P of the tap has no statistically significant effect on axial pullout. Osteoporotic bone might render tap features marginal. Our findings indicate that changing the characteristics of the tap D and P does not help with pullout strength in an osteoporotic model. The high rate of fracture in the probe-only group might imply the potential benefit of tapping to prevent catastrophic failure of bone.
(Copyright © 2016 Elsevier Inc. All rights reserved.)
Databáze: MEDLINE
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