• John S Albietz, Patricia Rosasarellano, Jennifer C Fleming, Kevin R Gurr, Stewart I Bailey, and Christopher S Bailey.
• Division of Orthopaedics, Department of Surgery, Orthopaedic Spine Program, London Health Science Centre, University of Western Ontario, E4-120 Victoria Hospital. 800 Commissioners Road East, London, ON, N6A-5W9, Canada.
• Eur Spine J. 2012 Jan 1;21(1):145-8.

PurposeThe purpose of this study is to quantify the interspinous anatomy at the L4/5 and L5/S1 levels.MethodsOne hundred reconstructed computer tomography scans of the lumbosacral spine were reviewed by two separate surgeons. Data were collected from the midline sagittal reconstructed image at the L4-5 and L5-S1 levels. Measurements obtained included the disc angle, anterior and posterior disc height, and maximum interspinous space in both the anterior-posterior and cephalad-caudal directions. The disc height and disc angle were correlated with the interspinous height.ResultsThe mean age of the patients reviewed was 47 years (range: 16-91; standard deviation: 20). According to our data population, the average length of the interspinous space was larger at the L4-5 level (13 mm) than the L5-S1 level (9 mm). The interspinous height was similar between the two levels. A poor correlation existed between the disc height or disc angle and the interspinous height. There was no correlation between measurements and age.ConclusionsThe interspinous space available, as defined by computer tomography, at the L5/S1 level, is less able to accommodate current interspinous devices compared to the adjacent L4/5 level. The limiting factor is the length of the sacral part of the L5-S1 interspinous space.

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