2.5. Spatial Orientation (Clock Face)
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When learning BESS/UBE, spatial orientation often presents difficulties: the endoscopic image differs from the familiar view of the operative field, and an unintentional rotation of the camera changes the position of anatomical landmarks on the screen.
In my practice, I hold the endoscope in my left hand and control image orientation using bony landmarks. For convenience, I use an imaginary “clock face” to help correlate the screen image with the anatomy of the operative segment.
The imaginary “clock face”
The diagram below shows the scheme I use for the lumbar interlaminar approach. The positions of structures relative to the “clock face” correspond to the endoscope orientation shown. When the endoscope is repositioned or the camera rotated, their projection on the screen changes. I therefore always correlate clock-face landmarks with identified anatomical structures.
Surgeon positioned to the patient's left
- The bases of the spinous processes of the cranial and caudal vertebrae project at the 11, 12, and 1 o'clock positions.
- The lamina of the cranial vertebra projects at the 8, 9, and 10 o'clock positions.
- The inferior articular process of the cranial vertebra and, as it is exposed, the superior articular process of the caudal vertebra project at the 8, 7, 6, and 5 o'clock positions.
- The lamina of the caudal vertebra projects at the 2 and 3 o'clock positions.
Surgeon positioned to the patient's right
- The bases of the spinous processes of the cranial and caudal vertebrae project at the 11, 12, and 1 o'clock positions.
- The lamina of the cranial vertebra projects at the 2, 3, and 4 o'clock positions.
- The inferior articular process of the cranial vertebra and, as it is exposed, the superior articular process of the caudal vertebra project at the 6, 5, and 4 o'clock positions.
- The lamina of the caudal vertebra projects at the 9 and 8 o'clock positions.
The moving endoscope lens
The endoscope is held in the nondominant hand, so the image may be unstable. Keeping the hand closer to the trunk reduces image tremor.
During triangulation, the endoscope and instrument move independently, with their tips close to one another. This provides a broad view of the operative field, but using a burr or radiofrequency electrode creates a risk of lens damage. A controlled distance should be maintained between the endoscope and the working end of the instrument.
Even a small movement of the endoscope tip substantially changes the view of the operative field.
Endoscope and instrument movement around a fulcrum
In open surgery, an instrument can be moved directly within the exposed operative field. In biportal endoscopic surgery, the endoscope and instrument pass through separate portals, which act as fulcrums during angular movement.
With this movement, the internal and external portions of the instrument move in opposite directions. To move the working tip to one side, the external portion is moved in the opposite direction.
Mastering these mechanics requires practical training [4].
If I lose orientation, I stop active manipulation. I restore clear visualization, check camera rotation, and identify familiar bony landmarks again. I resume work once I can confidently identify the anatomical structures and the position of the working instrument. Following this sequence is particularly important when learning BESS/UBE.
References
1. Zhang Q, Wei Y, Wen L, et al. An overview of lumbar anatomy with an emphasis on unilateral biportal endoscopic techniques: A review. Medicine (Baltimore). 2022;101(48):e31809. DOI: 10.1097/MD.0000000000031809.
2. Park DK, Weng C, Zakko P, Choi DJ. Unilateral Biportal Endoscopy for Lumbar Spinal Stenosis and Lumbar Disc Herniation. JBJS Essent Surg Tech. 2023;13(2):e22.00020. DOI: 10.2106/JBJS.ST.22.00020.
3. Choi CM, Chung JT, Lee SJ, Choi DJ. How I do it? Biportal endoscopic spinal surgery (BESS) for treatment of lumbar spinal stenosis. Acta Neurochir (Wien). 2016;158(3):459–463. DOI: 10.1007/s00701-015-2670-7.
4. Son S.-K., Kim D.H., Aygün H. The Basics and Concepts of Unilateral Biportal Endoscopy. In: Heo D.H., Park C.W., Son S.K., Eum J.H., editors. Unilateral Biportal Endoscopic Spine Surgery: Basic and Advanced Technique. Singapore: Springer; 2022. P. 9–19. DOI: 10.1007/978-981-16-8201-8_2 (relevant passage: p. 18).
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