Safety and feasibility of lumbar spine for intralaminar screw fixation: a computed tomography-based morphometric study.

OBJECTIVE: The use of intralaminar screws (ILS) in spinal surgery has experienced a recent increase in popularity. The aim of this study is to define the morphological parameters of the lumbar laminas so that guidance may be defined for ILS placement. METHODS: The study involved the evaluation of lumbar computed tomography (CT) images of patients. Two hundred thirty-five patients (127 male, 108 female) were included in the study. The mean patient age was 44.2 years (19-78 years). The measured parameters of the lamina were the transverse inner diameter, transverse outer diameter (lamina width), lamina length, subdural space (safe zone), and spinolaminar angle for each lumbar level (L1-L5). RESULTS: The mean transverse outer diameter (L1-L5) ranged from 7.2-7.8 mm, and mean transverse inner diameter ranged from 2.5-3.0 mm. The lamina of L3 had the largest width and the lamina of L1 and L5 the smallest. The mean lamina length was 26.6 mm, ranging from 21.0-34.0 mm, and the mean spinolaminar angle was 124.7°, ranging from 111-135°. The L1 level had the shortest mean lamina length and L4 the lowest spinolaminar angle. Mean subdural space (safe zone), which was narrowest at the L5 level, was 2.4 mm, ranging from 1.3-3.6 mm. CONCLUSION: ILS of the appropriate size (3.5-4.5 mm) and length (20 and 25 mm) can be used safely in the lumbar spine. However, further biomechanical studies should be performed to measure strength of the fixation.