Definition of safe zone in vertebral body in relation to anterior instrumentation.
Egea-Gámez RM., Wilson-MacDonald J., Murray D., González-Díaz R.
OBJECTIVES: We set out to determine the "safe zone" for anterior instrumentation in scoliosis surgery assessing the relationship of the great vessels to the spine. METHODS: A total of 34 children undergoing posterior idiopathic scoliosis surgery were included in the study between 2010 and 2016. The preoperative scans were assessed to identify the position of the great vessels relative to the spine from T4 to L4. A coordinate system was specifically designed to determine safe zones for device locations. The safe zone right (SZR) was defined as the angle formed between X-axis (0°) and a line connecting the origin and the edge of the aorta and the safe zone left (SZL), the angle between the edge of the aorta to 180°. RESULTS: The average age was 14 years, with 30 females (88.2%). Lenke classification, the most common curve was 1BN (20.6%), followed by 1AN, 3C- and 6CN (8.8% each). The Apex was T8 and T9 (29.4 and 23.5% respectively). 58% of the curves were right sided. The mean SZL was from 155.7° to 180° at the T4 level to 104.3°-180° at L4. The mean SZR was from 0 to 110.7° at T4 to 0-76.18° at L4. The side of the curves was correlated at p level with the SZL and SZR. There was a significant correlation in the following levels: from T4 to L2 in the SZL, and from T7 to L2 in the SZR. CONCLUSIONS: Between T4 and T11, the right side of the vertebrae is safe, and from T12 to L4 the safe zones are more lateral and smaller. In a right-sided scoliosis, the danger zone moves more posterolateral at every level. In a left-sided curve, the danger zone is more anteromedial. Knowledge of these safe zones should allow safer placement of anterior devices. LEVEL OF EVIDENCE: Level III.