The incidence of CSFL
According to the literature reports, the incidence of CSFL is ~ 2–20% [2,3,4]. The incidence of CSFL in primary lumbar surgery ranges from 5.5 to 9.0%, while that in revision surgery ranges from 13.2 to 21.0% [9]. Koji et al. [3] retrospectively analysed 2146 patients who underwent lumbar posterior surgery in 8 hospitals, and the overall incidence of CSFL was approximately 7.7% (166/2146), among which the incidence of CSFL was 7.5% (123/1644) for LSS, 38.9% (7/18) for OPLL/OYL, 5.5% (23/422) for LDH, and 21.0% (13/62) for LDS. In this study, the overall incidence of CSFL was 3.6% (115/3179): 0.7% (6/807) for LDH, 2.5% (29/1143) for LSS, 3.3% (37/1122) for LS, 33.3% (31/93) for LDS, and 85.7% (12/14) for LST. The incidence of CSFL in initial surgery was approximately 1.7% (42/2515) and that in revision surgery was ~ 11.0% (73/664), which was slightly lower than that reported in the domestic and foreign literature. This finding might be related to the status of our hospital as a specialized orthopaedic institution. Lumbar surgery is now a routine operation in our hospital, and doctors at all levels have mastered the various operations and formed our own characteristic procedures.
Possible reasons for CSFL
Possible reasons for CSFL mainly include the following: (1) Trauma: CSFL caused by lumbar burst fracture tearing dura, and CSFL caused by bone fragments protruding towards the spinal canal puncturing the dura [10]. (2) Patients' own factors: long course of disease, severe spinal stenosis, herniated disc tissue, hyperplastic bone block or ligament adhesion to the dural sac [11]. After multiple operations, the dural sac adheres to the surrounding tissues. The wall of a spinal canal tumour is a part of the dural sac, and the partial dural sac is removed when the tumour is completely removed [12]. (3) Iatrogenic factors: Iatrogenic injuries are the main cause of most CSFLs [13] and involve insufficient preoperative preparation, insufficient estimation of intraoperative difficulties, residual sharp bone edge injury of the dura mater, intraoperative injury of the dural sac [14], inexperience of the operator, careless operation, etc. (4) Unexplained CSFL: spontaneous CSFL, which may be related to dural dysplasia and degeneration. In such cases, there is no obvious CSFL in preoperative fracture films or intraoperative dural lesions, but hidden CSFL appears after the operation.
Risk factors for CSFL
Multivariate regression analysis showed that the risk factors for CSFL were type of disease, preoperative intraspinal hormone injection, number of surgical levels and revision surgery (P < 0. 05). Intradural tumours, degenerative scoliosis and severe LSS have been previously reported as high-risk factors for CSFL [3, 13]. In our study, the OR of the type of disease was 3.9, with a 95% confidence interval of 3.0–5.2, P < 0.01, indicating that the type of disease had a significant effect on patients with CSFL. The incidence of CSFL was 85.7%, that of degenerative scoliosis was 33.3%, that of spondylolisthesis was 3.3%, that of LSS was 2.5%, and that of lumbar disc herniation was 0.7%.
Studies [15] have shown that a long course of disease and long-term dural pressure lead to a reduction in epidural fat, thinning of the dural thickness, and expansion of the dura after laminectomy and that DTs are prone to occur during decompression. However, in our multivariate study, the OR of disease duration was 1.0, and the 95% confidence interval was 0.7–1.4, P > 0.05, indicating that duration of disease was not a risk factor for CSFL.
In our study, the OR of preoperative epidural steroid injection was 2.0, with a 95% confidence interval of 1.2–3.3, P < 0.01, indicating that preoperative epidural steroid injection was also one of the risk factors for CSFL. We considered that the hormones injected into the spinal canal (triamcinolone acetonide, etc.) were mostly macromolecules, which could not be completely absorbed by the body. They accumulated around the lesions in the spinal canal and formed adhesions between the dural sac. In the process of decompression, dural rupture easily formed, leading to CSFL.
The number of surgical levels was also one of the risk factors for CSFL. In our study, the incidence of CSFL was 1.7% (18/1046) in patients with 1 level of decompression, 3.8% (42/101) in patients with 2–3 levels of decompression, and 5.3% (55/1032) in patients with more than 4 levels of decompression. With the increase in the number of surgical levels, the risk of CSFL also increased, which was basically consistent with the results of foreign studies [16]. A possible reason may be that with the increase in the number of surgical levels, more extensive treatment is needed. The incidence of CSFL was expected to be higher when the dural sac was exposed for a longer time. Meanwhile, the operative time was longer, the energy consumption of the operator was greater, and the operation was not meticulous, which increased the chance of iatrogenic dural injury.
The incidence of CSFL in revision surgery was 11.0%, which was 2.9 times higher than that in primary surgery, suggesting that this factor had a greater impact on the occurrence of CSFL. In revision surgery, the vertebral lamina and other bone structures in the surgical area had been removed, the anatomical structure was different from normal, the dura mater was widely adhered to the surrounding scar tissue, and dura mater injury easily occurred in the process of surgical operation to release the nerve root and dura mater [16, 17].
Management of CSFL
Combining our experience and the related literature, we summarize the following management methods:
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(1)
Intraoperative management
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(1)
Once CSFL occurred, according to the degree of dural injury, the dura was immediately, patiently and carefully repaired. Early and timely detection of CSFL and tight suturing of the dura mater were the main methods to prevent postoperative CSFL [18]. In our study, 93 cases of dural sac rupture were found during the operation, of which 79 underwent suture repair.
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Artificial spinal patch repair, subcutaneous fascia or deep muscle fascia coverage, and fibrin glue sealing can be considered the choice of dural rupture repair during surgery [5]. In our study, all patients with CSF were covered with an artificial dura mater or deep fascia layer.
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(3)
Close suturing of muscle, fascia and skin, especially the deep fascia layer, plays a beneficial role in preventing postoperative CSFL [19]. Tight suturing of deep fascia was the key to ensuring good wound healing in patients with CSFL.
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Postoperative management
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(1)
Bed rest. Keeping a reasonable position and using head low and feet high (raising the bed tail approximately 10-15 cm) could prevent symptoms of low intracranial pressure and reduce the pressure of CSF on dural breaks, which was conducive to their healing.
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Choosing antibiotics that can pass through the blood–brain barrier to prevent the occurrence of intracranial infection and appropriately prolong the use time of antibiotics.
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(3)
Frequently changing dressings, keeping the wound dry, strengthening nursing, hydrating the intestines and promoting defecation, and reducing cough can promote an increase in CSF pressure caused by abdominal pressure, which is conducive to the healing of the dura.
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(4)
Strengthening fluid supplementation, maintaining the balance of water and electrolytes, and properly supplementing protein can promote dural healing.
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(5)
Prolonging the time of drainage tube placement. In our study, the drainage tube time of the CSFL patients was 7-11 days (average: 7.1 ± 0.5 days). The drainage tube was clamped for approximately 7 days to observe the wound and muscle strength of both lower limbs for 24 hours. If the wound was dry and there was no obvious motor sensory disturbance of either lower limb, the drainage tube could be removed. If there was exudation on the wound surface and obvious motor sensory disturbance of both lower limbs, the drainage tube was opened in time to continue drainage for 1–2 days. The time of extubation was judged by the above steps again. In our study, the drainage tube was removed from 3 patients for 11 days. If the drainage tube could not be removed, another operation should be performed to repair the dura. In our study, 1 patient underwent surgery again, and a dural break was found during the operation. No CSFL occurred after dural repair.
Complications of CSFL
CSFL causes the loss of CSF, which reduces intracranial pressure and leads to postural headache, dizziness, nausea, vomiting and other symptoms of low intracranial pressure [20]. In our study, 29 patients with low intracranial pressure symptoms were gradually relieved after raising of the bed and full fluid supplementation. If CSF accumulates in the incision and compresses the related nerves, this leads to lower limb pain, numbness and even paralysis [21]. In our study, 6 patients with lower limb pain and numbness symptoms were treated with local physical therapy, dehydration and detumescence, and local suction, and the symptoms were gradually relieved without causing serious nerve injury. CSFL could lead to an incision that is directly exposed to the outside environment, which easily causes incisional infection. If pathogenic microorganisms are retrograded with CSF, they can cause spinal canal and intracranial infection, endangering the life of patients [22]. In the present study, there were no complications, such as intraspinal infection, intracranial haemorrhage or delayed healing of the incision. At the end of the follow-up period, there were no long-term complications, such as dural pseudocysts.