Approaching the incorrect site may be prevented by accurate imaging, by exposing and visualizing the anatomical landmarks intraoperatively (e.g., last rib, first transverse process, lumbosacral junction), by preoperative marking (e.g., needle, or methylene blue) of the target vertebra, or by using intraoperative fluoroscopy or radiography (e.g., for intervertebral disc herniations located two or more vertebral segments from the anatomical landmarks mentioned earlier). To mark the correct site, a hypodermic or spinal needle is placed percutaneously next to the appropriate spinous process with radiographic, fluoroscopic, or computed tomography (CT) confirmation. A small volume (0.1 ml) of sterile methylene blue is injected in the subcuteanous tissue overlying the spinous process and the needle withdrawn. Alternatively, the needle is securely placed into the dorsal spinous process and then cut (preferably using a sterilized instrument) so that it no longer protrudes through the skin. This allows the skin to be aseptically prepared, and the surgeon identifies the needle after the skin is incised (see Figure 29.1).

If the incorrect site has been approached, extending the bone removal to the cranial (or caudal) intervertebral disc space generally permits removal of the herniated disc and adequate decompression of the spinal cord. A hemilaminectomy can be extended cranially or caudally without major concerns about spinal stability in the thoracolumbar region. Continuous hemilaminectomy of up to three adjacent vertebrae in the lumbar spine does not significantly decrease spine stiffness during flexion and extension [2]. Multiple continuous hemilaminectomies (up to six consecutive intervertebral disc spaces) in the thoracolumbar spine did not result in secondary postsurgical complications such as subluxations or chronic back pain [3]. Dorsal laminectomy could also be extended over two vertebral bodies without complications [4, 5]. At the cranial or midthoracic level, care should be taken to preserve the stabilizing supraspinous ligament [6]. However, when enlargment of a dorsal laminectomy over more than two vertebrae is performed, potential spinal instability should be taken into consideration since it has been biomechanically demonstrated that standard dorsal laminectomy already results in a marked increase in range of motion in flexion/extension [7].

Wrong side

The diagnostic and surgical errors that can sometimes lead to approaching the wrong side include:

• Incorrect labeling of the images
  
• Difficulty in performing or interpreting myelography
  
• Surgeon error

Incorrect labeling of myelographic images can occur by incorrect manual placement or accidental displacement of the right (or left) marker on the radiographic cassette. Similarly with CT or magnetic resonance imaging (MRI), when the left and right labelings are not modified in accordance with the position of the patient relative to the standard assumption of the computer (e.g., head vs. tail in first or ventral vs. dorsal recumbency), the wrong side might be implicated. Difficulty in performing or interpreting myelography (e.g., poor contrast medium diffusion in the subarachnoid space, mixing of epidurogram and myelogram) is a well-recognized diagnostic problem. For example, when only ventrodorsal and lateral myelographic images are obtained, a 30–40% failure rate in determining the side of lateralization of the extruded disk might be expected. However, combining ventrodorsal and oblique myelographic views results in a 97–99% accurate localization of the side of intervertebral disc herniation [8–10]. Clinical signs may help in the interpretation of the myelography but are unreliable in indicating the side of the lesion [10, 11].

CT and MRI are far superior to myelography in determining the precise location of herniated disc material. Complete agreement between the MR imaging and surgical findings with regard to site and side of intervertebral disc herniation has been reported in the canine thoracolumbar spine [12]. However, despite the increase in diagnostic accuracy provided by CT and MRI, the surgeon can still accidentally approach the wrong side. This mistake is avoided if the surgeon and staff utilize a checklist before the start of surgery.

Stay updated, free articles. Join our Telegram channel

Join