Neurological complication (NC) is a dreadful event that makes it difficult for surgeons to perform spinal surgeries and is often associated with technical problems. However, if the causes and clinical features are known, then these problems can be prevented and managed more appropriately. According to previous studies, the incidence of myelopathy or cauda equina injury in spinal surgeries was 0%–2.8% and the causes were surgical trauma, compression or distraction, ischemic injury, intradural or epidural hematoma (EH), mechanical compression by ligaments, intervertebral disc, and adjacent vertebral bodies [1-6]. However, it was difficult to extract studies on the influence of causes and treatment methods on the prognosis. Most previous studies have not explained various conditions and the corresponding remedies because these investigated NCs only in a specific disease entity. In addition, the real incidence of NC would be underestimated because they considered only the serious neurological deficit as an NC. In this study, we considered any trivial neurological symptom that did not preoperatively exist as an NC and investigated their treatments, final results, and prognostic factors to raise comprehensive awareness regarding the appropriate management of NCs.

In this retrospective study, the subjects were 65 patients who underwent posterior thoracolumbar surgeries during 19 years (1995–2013) and reported neurological symptoms that did not preoperatively exist before discharge after the index operations. In addition, their medical records and image tests were reviewed. The informed consents were waived. The causes were classified according to the initial and revision operation records, and the causes with no clear reason in the medical records and image tests were classified as “unknown.” Neurological symptoms were evaluated at the initial maximum state and the final follow-up time. The degree of NC was assessed using five numeric scales as follows: G1, increased leg pain or sensory loss; G2, hemiparesis; G3, paraparesis; G4, cauda equina syndrome; and G5, complete paraplegia. Relative, rather than absolute, evaluation was used to assess the degree of improvement. The relative degree of neurological recovery was evaluated using four numeric scales as follows: Gr1, complete recovery; Gr2, almost complete recovery with residual sensory loss or numbness; Gr3, partial recovery with apparent neurological deficit; and Gr4, no recovery. Patients’ age, sex, causes, the degree of NC, the degree of improvement, and whether revision or not and its timing were determined, and the factors influencing the final results were analyzed. In the assessment of prognostic factors, neurological recovery Gr1 and Gr2 were classified as good and Gr3 and Gr4 were classified as poor. Patients who received a revision surgery were assessed as a subgroup to evaluate the prognostic factors among them. In the statistical analysis, the Kruskal–Wallis test was used for neurological recovery according to the causes, and post-hoc analysis was performed using the Mann–Whitney U-test. Multivariable logistic regression analysis was conducted to evaluate prognostic factors and the relationship between the timing of revision and neurological recovery was analyzed using Spearman’s correlation coefficient. The significance level was set at p≤0.05. All statistical analyses were performed using SPSS ver. 16.0 package (SPSS Inc., Chicago, IL, USA).

Demographic data and variables of all patients were presented in Table 1.

The management of NC in spinal surgeries warrants the identification of the causes and early management accordingly. This study showed that the most important prognostic factor was early surgical treatment. However, during the early postoperative period, advanced image tests are usually unavailable. Thus, initial management cannot help depending on surgeons’ knowledge and expertise. In this study, EH was the most common cause and, at the same time, had the best prognosis. A patient who was conservatively managed reported relatively mild symptoms as G2. However, there was no improvement, although EH was completely resorbed in magnetic resonance imaging (MRI), which was performed 1 month postoperatively. In contrast, patients who underwent the surgical removal of EH exhibited better improvement despite severe neurological symptoms. Our results are consistent with those of Lawton et al. [7] reporting that the early removal of EH was the most important factor for neurological improvement. In the early period of this study, diagnosis and surgical removal was delayed because of the lack of awareness and expertise. In this study, three of four patients who underwent surgical removal after 4 days exhibited poor neurological recovery, whereas 14 of 16 patients who underwent surgical removal within 1day exhibited G1 recovery. All patients with EH used suction drains. Unfortunately, several previous studies have already established that EH cannot be prevented using a suction drain [8-10]; however, the reason behind this has not been reported. In our previous study, we presumed that the hypercoagulability of blood hampers the proper functioning of suction drains [11].

Revision surgeries of IDF tended to be delayed. Typically, the neurological symptom was vague during the immediate postoperative period and became distinct as time elapsed, particularly when walking began. It caused frequent delays in the accurate diagnosis and treatment. Conservative treatment was unsuccessful, and it showed poor results in 50%. In case of instrumentation, the dimension of the spinal canal and neural foramen remains fixed. If lordosis increases, then the size of the spinal canal and neural foramen would decrease compared with that observed in the preoperative image tests. It necessitates a more comprehensive decompression. In the case of posterior lumbar interbody fusion, over reduction or an insufficient size of cages resulted in iatrogenic foraminal stenosis; although it was not easy to diagnose it using MRI because the neural foramen was hidden by a metal artifact, suspicion through clinical manifestations was cardinal.

Typically, MI displayed immediate symptom development. A patient injured by an osteotome showed gradual aggravation after 3 days. It was suspected to develop a compartment syndrome due to nerve root edema and partially improved by pedicle screw removal and pedicle excision to reroute the nerve root. Another patient injured by punch complained of neuropathic pain, which did not improve despite further decompression. Patients who were injured by a pedicle screw showed better recovery than those injured by other MIs. In addition, nerve compression by gelatin sponge was classified as an MI because its underlying mechanism was mechanical compression. Several case reports have presented similar experiences [12-15], commonly suggesting that gelatin sponge should be surgically removed, although the prognosis was not very favorable. Our patient showed immediate neurological symptoms, which kept increasing until revision was performed. Despite removal after 3 days, the result was poor. Thus, the mechanical pressure of gelatin sponge should be checked not at the time of insertion but after a while to enable its swelling.

If neurological symptoms were aggravated by ID, then the effect of conservative treatment was unpredictable. One of the three patients did not undergo revision surgery because the patient refused it, and the final result was poor. However, two of the three patients underwent revision surgery after 10 days of ineffective conservative treatment, and their final results were good. Finding similar situations in the published literature was challenging. However, we presumed that though the total volume of extruded nucleus pulposus was reduced by ID, nerve root edema and inflammatory reactions by surgical trauma might increase pain susceptibility. In addition, the average timing of revision surgery in ID was 162 hours. The reason for the delay was not difficulty in diagnosis but the expectation of improvement without revision surgery. In our limited cohort, the conservative treatment was not favorable in ID.

Devising any solution in patients with NCs with an unknown cause was challenging. We classified the cause as “unknown” if no specific cause was observed during the surgery and in the postoperative image tests and revision surgery. We examined five of 11 patients; however, the findings were nonspecific and the results were poor. Cramer et al. [4] have indicated that ischemic damage due to lower blood pressure during the surgery could be a cause. However, in our cohort, we could not determine any clue in the operation and anesthetic medical records supporting such a hypothesis.

There were some limitations in our study. First, we cannot affirm that all surgical conditions were consistent throughout the 19-year study period. During that time, our facility of MRI was changed once, we began using operating microscopes, and only one of five main operators performed surgeries throughout the study period. Second, because it was a retrospective study, we could not consider specific conditions of each case. In addition, because the incidence of NC was very low, the number of patients of each cause was not adequate to obtain statistically significant results. Finally, this was a review of a single hospital. Assumedly, a generalization of the authors’ experiences may include several errors. We only proposed a possibility without any substantial evidence. However, the strength of this study was that no study has analyzed the final results regarding causes and treatment methods as prognostic factors for NC. In the future, we would like to present helpful data for the initial management of the variable causes of NC.

The final results of NC were influenced by causes. EH had the best and unknown had the worst prognosis. Among those who underwent surgical treatments, the earlier they had the revision surgeries, the better their prognosis was, irrespective of the causes. Therefore, performing a revision surgery as soon as possible on the exact diagnosis would be the best method to reduce the neurological deficit in NC of spinal surgeries.