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Measurement Techniques and Utility of Hounsfield Unit Values for Assessment of Bone Quality Prior to Spinal Instrumentation

A Review of Current Literature

Zaidi, Qasim, MD; Danisa, Olumide A., MD; Cheng, Wayne, MD

doi: 10.1097/BRS.0000000000002813
LITERATURE REVIEW

Study Design. A systematic review.

Objective. The aim of this study was to evaluate the clinical utility of assessing bone quality using computed tomography (CT) attenuation in Hounsfield units (HU).

Summary of Background Data. Assessing bone quality before spine instrumentation is an essential step of preoperative planning. Dual energy x-ray absorptiometry (DEXA) has been the gold standard for assessing bone mineral density (BMD); however, DEXA can result in spuriously elevated BMD measurements in patients with degenerative disease, compression fractures, and/or vascular calcifications. Measuring vertebral HU values has been proposed as an alternate method of assessing BMD and bone quality.

Methods. We searched MEDLINE, Cochrane Library, and EMBASE for studies correlating HU to BMD and to spine surgery outcomes.

Results. HU measurements correlate with success of lumbar interbody fusion (133.7 vs. 107.3 HU) and posterolateral fusion (167 vs. 139.8 HU), cage subsidence (112.4 vs. 140.2 HU), adjacent segment fractures (145.6 vs. 199.4 HU), pedicle screw loosening (116.4 vs. 132.7 HU) and (99.1 vs. 141.2 HU), and risk of incidental durotomy (149.2 vs. 177.0 HU). Intra and inter-rater reliability coefficients are 0.964 and 0.975. The correlation between HU values and BMD in nondegenerative patients is r 2 = 0.52 compared with HU versus BMD in degenerative patients r 2 = 0.18.

Conclusion. HU value measurement is a simple and rapid technique to assess bone quality that should be performed in all patients with pre-existing CT scans. HU measurement has excellent inter and intra-rater reliability and can be performed on axial or sagittal images. L1 HU threshold values of 110 HU for detecting osteoporosis, and 135 HU for detecting osteopenia are 90% specific. In patients with significant degenerative disease, HU values should be given more credence. Additional high-quality prospective studies comparing HU and DEXA values to patient outcomes are necessary to validate the role of CT measurements in preoperative evaluation.

Level of Evidence: 4

Hounsfield unit value measurement is a rapid and reproducible technique that correlates well with bone mineral density measured by DEXA, and to several spine surgery complications. Preoperative evaluation of surgical patients with HU measurement provides an alternate means of detecting osteoporotic and osteopenic patients and allows surgeons to plan accordingly.

Department of Orthopedic Surgery, Loma Linda University Health Center, Loma Linda, CA

Departments of Orthopedic Surgery and Neurological Surgery, Loma Linda University Health Center, Loma Linda, CA

Department of Orthopedic Surgery, VA Loma Linda Medical Center, Bones and Spine Surgery, Loma Linda, CA.

Address correspondence and reprint requests to Qasim Zaidi, MD, 24550 Lawton Avenue, 11234 Anderson Street, Loma Linda, CA 92354; E-mail: Qasimhasanzaidi@gmail.com

Received 14 December, 2017

Revised 9 June, 2018

Accepted 11 July, 2018

The manuscript submitted does not contain information about medical device(s)/drug(s).

No funds were received in support of this work.

Relevant financial activities outside the submitted work: grants.

Copyright © 2018 Wolters Kluwer Health, Inc. All rights reserved.