An unplanned revision surgery after a spinal operation is a highly objectionable outcome for a patient and his/her family. Accordingly, the need for revision surgery, in addition to resulting in higher medical care expenditures and higher risks of sequelae, may even jeopardize the patient-doctor relationship. Some previous studies have reported on the causes and risk factors of revision surgery in the long term after lumbar spine surgery [6, 7], while others have focused on the perioperative neurological complications of spinal surgery [8–10]. McCormack et al. took a more general view to evaluate all types of spinal surgeries performed over a three-year period at a single orthopedic specialty hospital in order to analyze the causes of unplanned readmissions within 30 days from last admission [11]. Bernatz et al. took an even more general approach in conducting a meta-analysis of 24 recent studies to determine the present rate of 30-day readmissions in orthopedics in general, as well as in various orthopedic subspecialties [12]. According to the nine spine-related studies included in their analysis, the current 30-day readmission rate for the spine subspecialty is 5.0 %. However, no previous studies have focused specifically on investigating surgical causes of complications requiring revision surgery within only one week after the initial operation.
In the present study, we found that the need for revision spinal surgery was relatively rare, with the overall incidence rate being 1.12 % (116/10,350 patients), which was roughly consistent with the 2.2 % reoperation rate reported by McCormack et al. [11]. In these rare cases requiring revision surgery, we found three surgical causes with relatively high frequencies of occurrence: screw malposition, symptomatic epidural hematoma, and inadequate decompression. In addition, a number of other direct causes for revision surgery were also found; however, each of them occurred far more rarely than the above mentioned three causes, with only a single case for each cause.
The major indication for early reoperation is a deterioration in neurological status [13]. If a patient experiences new-onset motor weakness and sciatica after spinal surgery, several possibilities should be taken into consideration: screw malposition, intraoperative nerve root injury, neuropraxia, and vascular compromise [14]. Spinal instrumentation has previously been reported to increase the risk of neurological injury [8, 15]. The potential risks and complications associated with it include nerve root irritation (0.2–1.1 %), fracture of the pedicle (0.5–1.1 %), and bending of the pedicle screws (0.1 %) [16, 17].
In a systematic review discussing the complications of treating pediatric scoliosis with screw fixation, Hicks et al. [18] stated that the most commonly reported complication of thoracic spine instrumentation was screw malposition, with a rate of 15.7 %. In our series, the malpositioned screws were placed either too inferiorly or too medially. The placement of pedicle screws is technically demanding and time-consuming. As such, patients who undergo spinal instrumentation have a greater chance of requiring revision surgery than patients who do not receive spinal instrumentation.
According to a review by Glotzbecker et al., the incidence rate of symptomatic spinal epidural hematoma ranges from 0 % to 1 % [19], a range that includes the rate of 0.26 % found in our study. The risk factors for spinal epidural hematoma identified in previous studies include multi-level procedures and preoperative coagulopathy [17, 20, 21]. Also, we have previously reported that preoperative diastolic blood pressure, intraoperative use of gelfoam for dura coverage, and postoperative drain output are risk factors with statistical significance for symptomatic epidural hematoma [22]. Other factors such as age, body mass index, durotomy, and the use of drainage tubes do not seem to influence the incidence.
Our data indicated that revision surgeries for symptomatic epidural hematoma are more urgent than those for other complications, having the shortest time interval to reoperation. Preoperative neurological status and time interval to reoperation are correlated with recovery outcomes. Lawton et al. [23] reported that 83 % of Frankel grade D patients recovered completely, compared to only 25 % of Frankel grade A patients. Also, better neurological recovery was achieved for patients who received surgical decompression within 12 h of symptom onset, as compared to patients who had an identical preoperative Frankel grade and for whom revision surgery was delayed beyond 12 h. The findings of Lawton’s study were consistent with the results of our previous study [24], so it would be reasonable to conclude that for those cases in which symptomatic epidural hematoma does occur after operation, rapid diagnosis and urgent surgical evacuation are required to achieve better neurological recovery.
Neural element decompression plays an important role in spinal surgeries by relieving pain and providing an optimal environment for neurological recovery. However, it is not always successful and it may further destabilize the spine. Inadequate decompression, whether resulting from a limited laminectomy or an incomplete discectomy, often leads to undesirable outcomes.
Guigui et al. [25] reported that 56 % of patients who underwent reoperation had inadequate decompression; they thus concluded that preoperative planning of the neural decompression should be carried out to achieve good surgical results and avoid the need for revision surgery.
Spinal decompression involves the release of pressure on the spinal cord and nerve roots, and the removal of osteophytes, hypertrophic ligaments, or protruding discs. However, it is often accompanied by the loss of spinal stability due to the destruction of the aforementioned structures. In our study, inadequate decompression occurred more frequently in patients who did not receive spinal instrumentation. This is most likely because the surgeons tended to ensure sufficiently wide decompression for instrumentation and fusion procedures due to the possibility of spine destabilization, in contrast to instances of relatively narrow decompression that may have occurred when instrumentation and fusion were not performed.
It is notable that while past studies that have investigated the causes of unplanned revision surgery within 30 days have found wound infections to be the most common cause, the current study found no instances in which wound infection was the cause of an unplanned revision surgery within one week of the initial surgery. Naturally, this simply reflects, to a large extent, the different speeds with which different complications cause problems requiring a revision surgery (the symptoms of wound infections, for example, typically do not develop within a week), but we believe that highlighting these differences between causes of reoperation within one week versus the causes within one month will be of practical use and reference to surgeons as they monitor their patients post-operatively. That is, the results of this study, combined with past studies covering longer post-operative timeframes, will give surgeons a better idea of the problems that are most likely to occur within one week, as well as which potential issues may need to be monitored more closely thereafter.
In our clinical practice, we have proposed a post-spinal surgery flow chart to help surgeons determine the possible causes of any revision surgery that may be required (Fig. 4). The most important step is the immediate evaluation of postoperative neurological symptoms and signs. Postoperative exacerbation of neurological symptoms may be caused by screw malposition, spinal cord injury, or neuropraxia, which can be confirmed by radiographic assessment. If motor weakness and sciatica occurs as a result of a screw malposition, it can be clearly seen in plain radiographic imaging, and the misplaced screw(s) should be surgically revised immediately. However, if any screw malposition is radiographically equivocal, then a CT scan is indicated for further confirmation. If the symptoms are caused by spinal cord injury or neuropraxia, then conservative treatment is recommended because the patient would not benefit from revision surgery.
Epidural hematoma plays an important role in patients whose symptoms improve after operation but then experience the progressive onset of neurological deficits. Although there are other possible causes of postoperative neurological symptoms such as cerebral spinal fluid leakage, recurrent herniated nucleus pulposus and cage/implant dislodgement, a surgeon should inform patients the need of an emergent reoperation if they develop urgent symptoms such as motor weakness, decreased anal tone or urine retention, because the possibility of such symptoms resulting from symptomatic epidural hematoma is high and early revision surgery for removing epidural hematoma can result in better neurological outcomes. If the symptoms are less urgent, such as persistent lower limb numbness or saddle anesthesia, MRI with contrast can be used to help decide if revision surgery is needed.
If, after spinal surgery, there are persistent neurological symptoms that are nearly identical to the preoperative symptoms, then one should consider the possibility of inadequate decompression. Although MRI is informative in this regard, it is nonetheless very challenging for a surgeon to determine the presence or absence of inadequate decompression.
There were several limitations in this study, including possible selection bias because the patients were not randomized for retrospective observation. In addition, the cases included in the study all came from a single institution, which can lessen the generalizability of a retrospective analysis of this type. For example, a meta-analysis of 105 spine surgery complication studies conducted by Nasser et al. found that higher rates of complications were reported in prospective case studies versus retrospective cohort studies for cervical and thoracolumbar surgeries [26]. In addition, in some cases, medical chart data elements were missing, so complete data concerning patients’ neurological status was not obtained from all patients. Therefore, the neurological status of each patient was measured via improvements in muscle power, numbness sensation, and pain scale, instead of in the form of a thorough functional score. Furthermore, the choice of surgical procedure can vary greatly among different surgeons; for example, different surgeons may choose different implant systems and fusion levels for posterior instrumentation.
