SPINE Volume 39, Number 13, p 1029 ©2014, Lippincott Williams & Wilkins
BlOMECHANICS
Point of View Curtis A. Dickman, MD
D
r. Wade and colleagues provide an interesting, welldesigned in vitro biomechanical and ultrastructural study that examined mechanisms of lumbar disc herniation among sheep during flexion and compression loading. This article is an important contribution to the spinal biomechanics literature. However, a few potential caveats should be considered. Several major structural, mechanical, and biological differences exist between the spines of humans and sheep that may prevent extrapolating these results to humans. Among these are differences in spinal geometry and anatomy''^ and potential differences in mechanical loading between bipeds and quadrupeds. In addition, the authors loaded sheep lumbar specimens exclusively during flexion and compression, but ignored the roles of other loading conditions in contributing to herniation. Other modes of loading, or a combination of different loads applied simultaneously, may play significant roles in causing lumbar disc herniation. Most specimens that developed herniated discs also simultaneously developed facet fractures. This phenomenon rarely
occurs in humans who develop herniated lumbar discs, indicating that the loading conditions and/or the morphological differences may not accurately reflect the actual mechanisms of herniation in humans. In addition, the investigators examined the mechanics and morphology of disc herniation only in normal spines; however, the mechanisms of disc herniation in degenerated discs may differ significantly from that of normal discs. Despite these caveats, this investigation was outstanding, meticulous, and a unique contribution to our knowledge. However, any generalizations to humans should be tempered by the potential differences in the mechanisms of disc failure between sheep and humans. Further studies are needed to investigate these concerns. References 1. Sheng SR, Wang XY, Xu HZ, et al. Anatomy of large animal spines and its comparison to the human spine: a systematic review. Eur Spine j 1O\Q;19A6-S6. 2. Mageed M, Berner D, Julke H, et al. Is sheep lumbar spine a suitable alternative model for human spinal researches.' Morphometrical comparison study. Lab Anim Res 2013;29:183-9.
From the Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ. 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: consultancy, payment for lecture, patents, royalties. Address correspondence and reprint requests to Curtis A. Dickman, MD, do Neuroscience Publications, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, 350 W.Thomas Rd, Phoenix, AZ 85013; E-mail: [email protected] DOI: 10.1097/BRS.0000000000000298 Spine
www.spinejournal.com
1029
Copyright of Spine is the property of Lippincott Williams & Wilkins and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
BlOMECHANICS
Point of View Curtis A. Dickman, MD
D
r. Wade and colleagues provide an interesting, welldesigned in vitro biomechanical and ultrastructural study that examined mechanisms of lumbar disc herniation among sheep during flexion and compression loading. This article is an important contribution to the spinal biomechanics literature. However, a few potential caveats should be considered. Several major structural, mechanical, and biological differences exist between the spines of humans and sheep that may prevent extrapolating these results to humans. Among these are differences in spinal geometry and anatomy''^ and potential differences in mechanical loading between bipeds and quadrupeds. In addition, the authors loaded sheep lumbar specimens exclusively during flexion and compression, but ignored the roles of other loading conditions in contributing to herniation. Other modes of loading, or a combination of different loads applied simultaneously, may play significant roles in causing lumbar disc herniation. Most specimens that developed herniated discs also simultaneously developed facet fractures. This phenomenon rarely
occurs in humans who develop herniated lumbar discs, indicating that the loading conditions and/or the morphological differences may not accurately reflect the actual mechanisms of herniation in humans. In addition, the investigators examined the mechanics and morphology of disc herniation only in normal spines; however, the mechanisms of disc herniation in degenerated discs may differ significantly from that of normal discs. Despite these caveats, this investigation was outstanding, meticulous, and a unique contribution to our knowledge. However, any generalizations to humans should be tempered by the potential differences in the mechanisms of disc failure between sheep and humans. Further studies are needed to investigate these concerns. References 1. Sheng SR, Wang XY, Xu HZ, et al. Anatomy of large animal spines and its comparison to the human spine: a systematic review. Eur Spine j 1O\Q;19A6-S6. 2. Mageed M, Berner D, Julke H, et al. Is sheep lumbar spine a suitable alternative model for human spinal researches.' Morphometrical comparison study. Lab Anim Res 2013;29:183-9.
From the Division of Neurological Surgery, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, Phoenix, AZ. 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: consultancy, payment for lecture, patents, royalties. Address correspondence and reprint requests to Curtis A. Dickman, MD, do Neuroscience Publications, Barrow Neurological Institute, St. Joseph's Hospital and Medical Center, 350 W.Thomas Rd, Phoenix, AZ 85013; E-mail: [email protected] DOI: 10.1097/BRS.0000000000000298 Spine
www.spinejournal.com
1029
Copyright of Spine is the property of Lippincott Williams & Wilkins and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
