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Dimensions of the Subaxial Lateral Mass

A Systematic Review of Anatomic (Morphometric) Measurement Studies

Schroeder, Gregory D. MD*; Kepler, Christopher K. MBA, MD*; McKenzie, James C. MD*; Casper, David S. MD*; Sutton, Ryan BS*; Hecht, Andrew C. MD; O’Shaughnessy, Brian A. MD; Skelly, Andrea C. PhD, MPH§; Brodt, Erika D. BS§; Vaccaro, Alexander R. MBA, MD, PhD*

doi: 10.1097/BSD.0000000000000772

Study Design: This was a systematic review.

Objective: To review and synthesize information on subaxial lateral mass dimensions in order to determine the ideal starting point, trajectory, and size of a lateral mass screw.

Summary of Background Data: The use of lateral mass instrumentation for posterior cervical decompression and fusion has become routine as these constructs have increased rigidity and fusion rates.

Methods: A systematic search of Medline and EMBASE was conducted. Studies that provided subaxial cervical lateral mass measurements, distance to the facet, vertebral artery and neuroforamen and facet angle made either directly (eg, cadaver specimen) or from patient imaging were considered for inclusion. Pooled estimates of mean dimensions were reported with corresponding 95% confidence intervals. Stratified analysis based on level, sex, imaging plane, source (cadaver or imaging), and measurement method was done.

Results: Of the 194 citations identified, 12 cadaver and 10 imaging studies were included. Pooled estimates for C3–C6 were generally consistent for lateral mass height (12.1 mm), width (12.0 mm), depth (10.8 mm), distance to the transverse foramen (11.8 mm), and distance to the nerve. C7 dimensions were most variable. Small sex-based differences in dimensions were noted for height (1.2 mm), width (1.3 mm), depth (0.43 mm), transverse foramen distance (0.9 mm), and nerve distance (0.3–0.8 mm). No firm conclusions regarding differences between measurements made on cadavers and those based on patient computed tomographic images are possible; findings were not consistent across dimensions. The overall strength of evidence is considered very low for all findings.

Conclusions: Although estimates of height, width, and depth were generally consistent for C3–C6, C7 dimensions were variable. Small sex differences in dimensions may suggest that surgeons should use a slightly smaller screw in female patients. Firm conclusions regarding facet angulation, source of measurement, and method of measurement were not possible.

*Rothman Institute at Thomas Jefferson University Hospital, Philadelphia, PA

Icahn School of Medicine at Mount Sinai, New York, NY

St. Thomas Midtown Hospital, Nashville, TN

§University of Washington, Seattle, WA

There was no funding of any kind from the following sources: National Institutes of Health (NIH); Wellcome Trust; Howard Hughes Medical Institute (HHMI).

Dr Schroeder has received funds to travel from AOSpine and Medtronic. Dr Vaccaro has consulted or has done independent contracting for DePuy, Medtronic, Stryker Spine, Globus, Stout Medical, Gerson Lehrman Group, Guidepoint Global, Medacorp, Innovative Surgical Design, Orthobullets, Ellipse, and Vertex. He has also served on the scientific advisory board/board of directors/committees for Flagship Surgical, AO Spine, Innovative Surgical Design, and Association of Collaborative Spine Research. Dr Vaccaro has received royalty payments from Medtronic, Stryker Spine, Globus, Aesculap, Thieme, Jaypee, Elsevier, and Taylor Francis/Hodder and Stoughton. He has stock/stock option ownership interests in Replication Medica, Globus, Paradigm Spine, Stout Medical, Progressive Spinal Technologies, Advanced Spinal Intellectual Properties, Spine Medica, Computational Biodynamics, Spinology, In Vivo, Flagship Surgical, Cytonics, Bonovo Orthopaedics, Electrocore, Gamma Spine, Location Based Intelligence, FlowPharma, R.S.I., Rothman Institute and Related Properties, Innovative Surgical Design, and Avaz Surgical. He has also served as deputy editor/editor of Spine. In addition, Dr Vaccaro has also provided expert testimony. The remaining authors declare no conflict of interest.

Reprints: James C. McKenzie, MD, Department of Orthopaedic Surgery, 1025 Walnut Street, Room 516 College, Philadelphia, PA 19107 (e-mail:

Received March 27, 2018

Accepted October 24, 2018

© 2019 by Lippincott Williams & Wilkins, Inc.