SPINE Volume 33, Number 8, pp 898 –902 ©2008, Lippincott Williams & Wilkins Facet Asymmetry in Normal Vertebral Growth Characterization and Etiologic Theory of Scoliosis Youssef M. Masharawi, PhD,* Smadar Peleg, PhD,† Hanne B. Albert, PhD,‡ Gali Dar, MSc,†§ Nili Steingberg, MSc,†¶ Bahaa Medlej, MD,† Janan Abbas, BPT,† Khalil Salame, MD, Yigal Mirovski, MD,** Nathan Peled, MD,†† and Israel Hershkovitz, PhD† Study Design. The shape and orientation of the tho- racic and lumbar zygapophyseal facets at the T1–L5 level in children were measured and analyzed. Objective. To detect the pattern of zygapophyseal facet asymmetry in the thoracic and lumbar spines in children. Summary of Background Data. Whereas many studies have defined the pattern of zygapophyseal facet asymme- try in adults, there is insufficient data in children. Methods. A 3-dimensional digitizer was used to mea- sure zygapophyseal facet size, topography (length, width, concavity, convexity, and lateral interfacet height), and ori- entation (transverse and sagittal facet angles) at the T1–L5 level. Thirty-two complete, nonpathologic skeletons of chil- dren (age range from 4 to 17 years), housed at the Hamman- Todd Human Osteological Collection (Cleveland Museum of Natural History, Cleveland, OH) were assessed. Statistical anal- ysis included paired t tests and analysis of variance. Results. In general, zygapophyseal facet asymmetry in children exists only in the superior facets of the thoracic spine and is independent of age: The right superior facet is significantly shorter than the left in all thoracic vertebrae T1–T12 (up to -2.91 mm at T1), and significantly wider than the left in thoracic vertebrae T1–T9 (T8 excluded) (P  0.003). The right superior transverse and sagittal facet an- gles are significantly greater than the left in thoracic verte- brae T1–T11, indicating a lesser inclination (in the sagittal plane) and more frontally positioned facet (in the transverse plane) (P  0.003). Facet asymmetry was not evident in the superior or inferior facets of the lumbar vertebrae. Conclusion. Facet asymmetry in thoracic vertebrae ap- pears in early childhood. The pattern of this asymmetry differs from that reported for adults and may be consid- ered as a possible contributing etiological factor in the development of different types of idiopathic scoliosis. Key words: zygoapophyseal facet asymmetry, verte- bral growth, scoliosis. Spine 2008;33:898 –902 The shape, orientation, and asymmetry of the zyg- apophyseal facets are well recognized in the adult human spine 1–9 yet poorly examined during growth. An asym- metrical shape in the lumbar zygapophyseal facets in young individuals (aged 12–20 years) was linked with pathologic condition of lumbar intervertebral disc herni- ation yet with no comparison to the normal state. 10 Asymmetrical vertebral growth is usually related with common spinal disorders in children (e.g., adolescent posttraumatic and congenital scoliosis), altered spinal load distribution, and left-right skeletal length asymme- tries. 11–16 The developmental aspect of zygapophyseal facet asymmetry and its possible link with daily activities in children has never been examined. The central question raised in the current study is whether normal asymmetry in the shape and orientation of the zygapophyseal facets exists in children? If so, is the pattern of facet asymmetry similar to that observed in the adult population? Answering these questions may shed light on a possible etiology of scoliosis. The aim of the current study is to detect the pattern of zygapophyseal facet asymmetry in nonpathologic tho- racic and lumbar spines of children. Materials and Methods The thoracic and lumbar spines of 87 young individuals (under the age of 18) from the Hamann-Todd Human osteological collection housed at the Cleveland Museum of Natural His- tory, OH, were initially examined for the present study. Exclu- sion criteria were: (a) individuals whose medical reports indi- cated the presence of a disease which could affect the vertebrae/ spine; (b) damaged vertebrae-visual inspection of all vertebrae was carried out by 3 experienced spinal researchers in order to identify pathologic vertebrae, this includes among others, the presence of isthmic spondylolysis, idiopathic scoliosis (using the method of Parent et al 17 for identification), Scheuermann’s kyphosis vertebrae with anterior extension, as elucidated by Scoles et al, 18 and traumatic fractures; (c) missing vertebrae (only individuals with all vertebrae from T1 to L5 were in- cluded); and (d) vertebrae with incomplete fusion. The residual final number examined was 32 children (10 boys and 22 girls) with 544 thoracic and lumbar complete vertebrae (T1–L5). From the *Spinal Research Laboratory, Department of Physical Ther- apy, The Stanley Steyer School of Health Professions, Sackler Faculty of Medicine, Tel-Aviv University, Ramat Aviv, Israel; †Department of Anatomy and Anthropology, Sackler Faculty of Medicine, Tel-Aviv University, Ramat Aviv, Israel; ‡The Back Research Center, Part of Clinical Locomotion Science, University of Southern Denmark, Linde- vej, Ringe, Denmark; §Department of Physical Therapy, Faculty of Social Welfare and Health Studies, Haifa University, Mount Carmel, Haifa, Israel; ¶Zinman College of Physical Education and Sports Sci- ences, Wingate Institute, Netanya, Israel; Department of Neurosur- gery, Tel Aviv Sourasky Medical Center, Tel Aviv, Israel; **Spine Unit, Assaf Harofe Medical Center, Israel; and ††Department of Radiology, Hacarmel Medical Center, Haifa, Israel. Acknowledgment date: July 2, 2007. Revision date: October 21, 2007. Acceptance date: November 19, 2007. The manuscript submitted does not contain information about medical device(s)/drug(s). No funds were received in support of this work. No benefits in any form have been or will be received from a commercial party related directly or indirectly to the subject of this manuscript. Address correspondence and reprint requests to Dr. Youssef Masharawi, Spinal Research Laboratory, Department of Physical Therapy, The Stanley Steyer School of Health Professions, Sackler Faculty of Medi- cine, Tel-Aviv University, University Campus, P.O.B. 39040, Ramat- Aviv 69978 Israel; E-mail: yossefm@post.tau.ac.il 898