Wrong-level surgery in spine procedures are relatively rare, occurring once in a little over 3,000 procedures, according to a 2008 report of an anonymous survey of the American Academy of Neurologic Surgeons. While rare (0.032%), the survey uncovered some unsettling statistics; foremost, half of respondents reported having performed at least one wrong-level surgery during their career.
The results of the survey were published in Spine, titled “The Prevalence of Wrong Level Surgery Among Spine Surgeons.” The lumbar spine was the most common site of wrong-level surgery, with 71% of reported wrong-level cases being performed there, cervical was next with 21% of cases.
The same survey uncovered only one permanent disability, but 17% of cases resulted in legal action or monetary settlement. Despite the survey being anonymous it seems likely that the number of cases and extreme or punitive outcomes are underreported. Another survey’s results were published the prior year in the Journal of Neurosurgery: Spine, “Wrong-sided and wrong-level neurosurgery: a national survey.” The anonymous survey was sent to a smaller sample of neurosurgeons but found a higher prevalence of wrong-level surgery, with rates of 0.13% and 0.076% of lumbar and cervical discectomies.
A number of precautionary measures have been implemented by various authorities and surgeon groups. For example, the “Sign Your Site” and “Sign, Mark and X-ray” (SMaX) programs from the American Academy of Orthopaedic Surgeons (AAOS) and the North American Spine Society (NASS) encourage surgeons to be extra dutiful when confirming the surgical site before beginning the operation.
A 2012 review of wrong-level spine surgery in the literature, published in The Journal of Bone and Joint Surgery-British Volume, found high costs associated with wrong-level surgery. The article, “Errors of level in spinal surgery: An Evidence-Based Systematic Review,” found that the vast majority of wrong-level spine surgery resulted in indemnity payments (84%), compared with only 30% of all other orthopedic surgeries.
Additionally, nearly all (99%) of the cases in one study resulted in lawsuits with most resulting in settlements that included payments of between $62,000 and $1.5 million. It is estimated that 1 in 4 orthopedic surgeons will be involved in a wrong-level surgery at least once in their career.
The causes of wrong-level surgery in the spine is much more intricate than just gross negligence. The spine is a complex system that’s anatomy can vary greatly from patient to patient. These anatomical variations can make it difficult to enumerate the vertebrae consistently between preoperative and intraoperative assessments. Prior injury, disease, or surgery can also make index-level identification difficult. Minimally invasive techniques, such as percutaneous screw placement can make the process even more complicated, especially for inexperienced surgeons.
A series of articles published in June and July 2020 by a group of surgeons in Detroit provide an overview of pitfalls to consider when planning surgery and how best to avoid wrong-level surgery.
Factors That Involve All Spinal Levels
Some factors can lead to difficulty in enumerating the vertebra successfully either prior to, or during surgery, for cervical, thoracic, and lumbar. In particular, tumors, infection, prior surgery, congenitally deformed vertebra (such as hemivertebrae, or block vertebra), and obesity and osteoporosis can all become obstacles and potentially lead to wrong-level surgery.
Tumors and infection may alter spine anatomy, and the appearance of the vertebra on X-ray imaging. Infection of the intervertebral discs can also lead to spontaneous fusion.
Congenital defects such as block vertebra, also referred to as Klippel-Feil syndrome in the cervical spine occur when segmentation does not occur properly during development, resulting in vertebra with heights equal to two adjacent vertebra. Hemivertebra are vertebra that do not form completely and may or may not lead to spine curvature, depending on whether adjacent vertebra accommodate the partially formed level, additionally the hemivertebra may be fused to an adjacent level, or have its own disc separating it.
Boney defects and scar tissue caused by prior surgery can also hinder visual identification of the correct level. Understanding what surgery was performed previously will assist the surgeon in identifying the correct level for the present surgery.
Finally, obesity and osteoporosis may lead to inadequate x-ray imaging due to greater tissue thickness and lower bone mineral density. The shoulders of obese patients make imaging of the cervical spine, in particular, difficult.
To overcome these challenges surgeons must carefully analyze imaging to identify unusual variations. In many cases the variations can be used as landmarks and actually assist in completing the procedure at the intended level, but without taking time to properly assess the patient they may become a liability. Consultation with interventional radiologists to place fiducial markers should be considered for patients who are expected to have imaging challenges. The use of intraoperative imaging and navigation can also assist in orienting the anatomy during the procedure.
Factors Unique to the Cervical Spine
Craniocervical junction abnormalities, such as atlantooccipital assimilation, caused by failure of the atlas (C1) to segment from the occiput, as well as spontaneous fusion of the axis (C2) and C3 vertebrae, create challenges in enumerating the cervical vertebra. Basilar invagination or impression, seen in 20% of rheumatoid arthritis patients is also associated with several congenital conditions such as Klippel-Feil, Chiari malformation, Paget’s disease, osteogenesis imperfecta, and syringomyelia. The condition can lead to anatomical variations near the base of the skull. Defects of the atlas and odontoid process of the axis can also confuse identification of structures in the area.
Cervical ribs can cause difficulty in identification of the cervical-thoracic junction. Typically forming at C7, but also as high as C4, these complete or incomplete ribs can be identified through proper imaging, and 3D CT imaging is considered the gold standard for identification.
Factors Unique to the Thoracic Spine
Transitional vertebra at the thoracolumbar junction can include features of both thoracic and lumbar segments, such as short ribs, a rib on one side and transverse process or accessory ossification center on the other, various combinations. The studies included in the review found transitional vertebrae at a frequency of 12.6%.
Another thoracic specific issue leading to wrong-level surgery are rib variants. Congenital rib abnormalities may appear in about 1.4% of the population. These abnormalities include bifid type, fusion type, hypoplastic, and rudimentary ribs. Bifid type ribs cleave into two parts at the sternal end, while fusion type ribs result from the fusion of 2 or more adjacent ribs.
Again, appropriate preoperative imaging to provide a clear picture of a patient’s anatomical variations is critical to understanding what will be seen during surgery and to identify the proper surgical level.
Factors Unique to the Lumbar Spine
Lumbar ribs are potential confounders in identifying the top of the lumbar spine. The ribs from lumbar vertebra are typically only up to half as long as adjacent thoracic ribs, and often occur unilaterally. The occurrence of lumbarization and lumbar ribs are correlated.
Similar to the thoracolumbar transitional vertebra, confusion can also arise from the lumbosacral transitional vertebra. Lumbosacral transitional vertebrae may occur in as much as 30% of the population and include a number of morphologies that have been categorized by Castellvi et al. These variants describe either the lumbarization of the S1, or the sacralization of L5. Radiographs of the complete spine may be necessary to facilitate counting of each vertebra to identify L1 correctly.
Another congenital issue is spinal dysraphism. Associated with central nervous system abnormalities, spinal dysraphism is when the neural arch fails to fuse. Spinal bifida occulta is a mild form that usually occurs at the L5-S1 transition. Often, the spinous process remains unattached to the vertebral body, but is held in place by the ligmentum flavum, or fused to adjacent spinous processes. These variations can make imaging difficult to interpret, leading to increased risk of wrong-level surgery.
Conclusions
Due to the relatively frequent occurrence of anatomical variants in the lumbar spine it is clear why more wrong-level surgeries happen there. The authors make it clear that critical analysis of preoperative imaging is an important step in preventing wrong-level surgery in the spine. Coupled with methods to deliberately identify levels during surgery such as intraoperative imaging and navigation, the risk of wrong-level surgery should largely be mitigated.
Most instances of wrong-level surgery occur in misinterpretation of preoperative imaging and not accurately identifying landmarks intraoperatively. Ultimately, consistency in counting vertebra on preoperative, and intraoperative images is critical to operating at the appropriate level.
