A Novel Concept for the Best Coronal Alignment of Pedicle Screws in Multilevel Lumbar Posterior Instrumentation - A Technical Note.
10.4184/jkss.2008.15.2.96
- Author:
Suk Jung KANG
1
;
Changju HWANG
;
Sung Woo LEE
;
Young Joon AHN
;
Yung Tae KIM
;
Dong Ho LEE
;
Choon Sung LEE
Author Information
1. Department of Orthopaedic Surgery, Asan Medical Center College of Medicine, University of Ulsan, Seoul, Korea. cslee@amc.seoul.kr
- Publication Type:Original Article
- Keywords:
Pedicle screw;
Coronal alignment;
Entry point;
Multilevel posterior lumbar instrumentation
- MeSH:
Head
- From:Journal of Korean Society of Spine Surgery
2008;15(2):96-101
- CountryRepublic of Korea
- Language:Korean
-
Abstract:
Correct alignment of pedicle screws is imperative in multilevel instrumentation. However, there has been no report addressing the technical aspects of this subject. If the head diameter of a pedicle screw is D, the head height is H, and the convergence angle of the screw being inserted is alpha, then the distance between the extension line of the medial borders of the inserted screw heads and the insertion point of the adjacent screw (A) is described by the following formula: A = 1/2Dcos alpha- Hsin alpha If an L3 pedicle screw (D=13 mm, H=15 mm) is to be inserted with a convergence angle of 14 degrees after the insertion of L4 and L5 screws, its insertion point should be 3.6 mm medial to the extension line of the centers of the L4 and L5 screws and 2.7 mm lateral to the extension line of their medial borders for all screw heads, so it can be aligned in the coronal plane. In order to achieve the best alignment, a pedicle screw is inserted between the extended line of the centers and that of the medial borders of the inserted adjacent screw heads. For the routine range of convergence angles, it is essential to move the entry point medially toward the extended line connecting the medial borders of the inserted adjacent screw heads.
