'The Stegosaurus Appearance' on ultrasound to assist in identifying the correct spinal level for primary lumbar spinal surgery

Abstract

Lumbar spinal surgery relies on palpation of anatomical landmarks and X-ray imaging confirmation to identify the correct spinal level, therefore exposing patients and staff to radiation, and increasing intraoperative time and cost. Ultrasound (US) assistance is being used to visualise spinal anatomy by many specialities, such as neurology and anaesthetics, and can be used intraoperatively in selected spinal surgery cases. However, its potential use to check spinal levels prior to surgery remains understudied. This prospective, pilot study screened all patients requiring a primary elective or emergency lumbar discectomy, under the supervision of a single consultant neurosurgeon, over an 8-month period at a single neurosurgical unit. US assistance was used to identify and mark the proposed spinal level prior to skin incision. The resemblance of the parasagittal lumbar US images to the back of the dinosaur Stegosaurus aided users in identifying the relevant anatomical structures necessary to mark the desired spinal level, (e.g., lumbar laminae, intervertebral spaces, sacrum). This inspired our description of the US images of the lumbar spine as 'The Stegosaurus Appearance'. The spinal level marked by US was then confirmed in the standard fashion using intraoperative X-ray imaging. In 100% of cases (12/12), the desired spinal level was correctly identified using US, confirmed by the subsequent intraoperative X-ray images. US assistance appears to be a safe, quick, and accurate tool for identifying the correct lumbar spinal level prior to skin incision, and could therefore represent a useful adjunct to supplement level checking in lumbar spinal surgery.

Keywords: Ultrasound (US); check; discectomy; level; spinal.

Figure 1

‘The Stegosaurus Appearance’ of the lumbar spine on US. (A) An US scan of the lumbar spine in the parasagittal plane. The sacrum is readily identifiable (asterisk), above which the acoustic shadows caused by the L3–L5 laminae are clearly visible. From these landmarks, the lumbar intervertebral spaces can be easily discerned and marked on the skin, and/or with insertion of a fiducial under direct US visualisation. (B) The position to place the curvilinear probe (blue line) to obtain the view in (A). (C) There is a similarity in the appearances of the lumbar laminae and sacrum on US with the plates (laminae) and tail (sacrum) of the dinosaur Stegosaurus. This inspired our description of these features as ‘The Stegosaurus Appearance’ of the lumbar spine on US. Figure (C) was redrawn under an open access Creative Commons CC BY License. Proietti A., Stegosaurus Species, Wikimedia Commons, 2023. Available online: https://commons.wikimedia.org/wiki/File:Stegosaurus_species.jpg. US, ultrasound.

Figure 2

Identification of lumbar spinal level using ‘The Stegosaurus Appearance’ on US. (A) Example US image of the lumbar spine of a patient prior to an L5/S1 discectomy. The desired spinal level, (vertical red line) can be calculated using ‘The Stegosaurus Appearance’ of the L4 and L5 laminae and the hyperechoic sacrum (asterisk). (B) Following skin marking and needle fiducial placement using US guidance, an X-ray-based image intensifier snapshot of the lumbar spine confirmed that the spinal level for this patient was indeed L5/S1. US, ultrasound.

Figure 3

Comparison of the desired spinal level with the level marked via palpation, US, and the level confirmed via X-ray image intensifier. Half of the patients had the incorrect level marked when palpation alone was used (n=6/12). In all twelve operations, the level identified by US correlated exactly with the desired level on X-ray imaging confirmation. US, ultrasound.