The shape of the neural arch as a causative factor in Isthmic spondylolysis: Characterization and biomechanical implications

• Published in: Physical therapy in sport Vol. 7; no. 4; pp. 179 - 180
• Main Authors: Masharawi, Youssef, Dvoral, Alperovitch-Najenson, Dar, Gali, Peleg, Smadar, Nili, Steinberg, Salame, Khalil, Hershkovitz, Israel
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 01-11-2006; Elsevier Limited
• Subjects: Sports medicine
• ISSN: 1466-853X; 1873-1600
• DOI: 10.1016/j.ptsp.2006.09.024

Isthmic spondylolysis (ISP) in the lower lumbar spine is commonly seen in athletes involved in sports with repetitive spinal motions. Some morphometric features in the lumbar spine are considered to be associated with ISP. The exact mechanism responsible for ISP, however, is still obscure. This study aims to test the hypothesis that the shape of the neural arch in the lumbar spine in SP is associated with certain morphometric characteristics.
Using a Microscribe three-dimensional apparatus (Immersion Co. San Jose, CA) the transverse facet angles, articular facet dimensions (length, width and depth) and all interfacet distances in the lumbar spine (L1–L5) were measured. One hundred and twenty male skeletons with normal lumbar spines and 115 with bilateral SP at L5 were selected from the Hamann-Todd Human (HTH) Osteological collection housed at the Cleveland Museum of Natural History (Cleveland, OH). ANOVA was carried out to examine the differences between spondylolytic and normal spines.
From L3 to L5, the transverse angle of the right inferior facets (and left inferior facet of L5) is greater in SP, indicating a more frontally oriented facet. In SP, all lumbar articular facets are flatter than in the norm. L4 in SP is a key vertebra as it's neural arch combines major morphometric characteristics: (a) significantly greater interfacet widths; (b) significantly shorter inter-facet heights; (c) significantly shorter and narrower articular facets; and (d) the inferior inter-facet width is of similar size to the superior interfacet width of the vertebra below (L5).
Individuals with L4 “ISP morphological characteristics” such as smaller, flatter and more frontally oriented facets and increased interfacet width, whose spine is exposed to over-load or involved in repetitive movements such as athletes are at greater risk to develop fatigue fractures in the shape of isthmic lysis at L5.