New neurological deficits (NNDs) following surgical correction of complex spinal disorders are rare. Bridwell et al.[10] reported a large series of 1090 patients with complex spinal disorders undergoing surgery, in which only 4 patients (0.36%) developed NNDs. The possible causes for NNDs were classified as spinal ischemia in 3 of the 4 cases as well as vascular and mechanical problems in 1 case. After conservative treatment, all patients showed marked improvement. MacEwen et al.[11] reviewed 7885 scoliosis patients who underwent surgery, and they reported that 57 patients (0.72%) developed NNDs for complete and incomplete paraplegia. Among these patients, only 36% achieved a complete recovery, while 32% achieved partial recovery. Other similar studies have reported a rate of NNDs ranging from 0.3–0.6%. More recently, Hamilton et al.[5] reported data from the Scoliosis Research Society Morbidity and Mortality Committee (SRS M&M) on NNDs in 2010. According to the report, the NND rate in patients with a primary diagnosis of scoliosis or kyphosis ranges from 0.99–3.54%, and the complete recovery rate is between 37.5% and 55.6%. The inconsistency in the incidence and recovery rate of NNDs in each study may be related to the inclusion and exclusion criteria as well as the skill of surgeons and the overall medical level. Although the incidence is low, NNDs remain one of the most feared complications of spinal surgery. To prevent NNDs or select an appropriate treatment for NNDs, an in-depth understanding of their etiology and risk factors is needed.
Risk factors for NNDs in complex spine disorders
Complex spinal diseases are generally related to a complex surgical procedure, increased surgical fusion segment, osteotomy, orthopedics, and stripping of the adherent tissue, such as a tumor or postoperative scar on the spinal cord. At the same time, the increase in operation complexity also indicates extension of operation time, increase in blood loss, decrease in MAP, and low O2 saturation, which may also increase the incidence of NNDs[12–16]. In the present study, a longer operation time (488 ± 264 min), an increase in blood loss of 1920 ± 1413 ml, and a lower MAP at surgery (66.2 ± 7.6 mmHg) were observed. In addition, anatomical features result in a higher incidence rate of cervical and thoracic segments (especially T2-T4), and intraspinal abnormalities, such as vascular malformation, syringomyelia, and intraspinal space-occupying lesion, also have a potential risk of NNDs[15, 17–22]. In the present study, 3 cases underwent orthopedic and osteotomy surgery, and 1 case with a history of cervical and thoracolumbar surgery underwent orthopedic surgery, osteotomy surgery, and stripping of the postoperative scar from the spinal cord. Moreover, 1 case underwent stripping of the tumor tissue from the spinal cord. All 5 cases were located at the cervical to thoracic level. All patients underwent fusion and implant surgery with a mean fusion level of 7.8 ± 3.48. Similar to our study, the survey based on 108,419 spine surgeries in the SRS M&M database reported that features likely reflective of increased case complexity, such as primary diagnosis of spondylolisthesis scoliosis or kyphosis, and procedures, such as revision, fusion, and use of implants, have increased rates of NNDs[5].
Etiologies of NNDs in complex spine disorders
The exact etiology of NNDs remains unknown but is likely multifactorial. There are 3 major potential causes of NND as follows: spinal cord compression, spinal cord overdistraction, and spinal cord ischemia. In the present, 2 patients had spinal cord compression with spinal cord ischemia, 2 patients had spinal cord distraction with spinal cord ischemia, and 1 patient had spinal cord ischemia.
Requirement of reoperation with the occurrence of NNDs
When NND occurs during or after surgery, it is necessary to exclude mechanical obstruction in the spinal canal caused by internal implants, hematoma, and bony tissue. In addition, excessive traction and shrinkage of the spinal cord also need to be ruled out. If mechanical obstruction is found, emergency revision surgery is needed. With physical compression eliminated, no progressive aggravation of NNDs is presented, and the possibility of spinal cord ischemia, postoperative hypotension, and/or anemia should be considered[23, 24]. The options include induced hypertension, prednisone pulse therapy, and nutritional nerve therapy. Revision surgery for partial correction release is also recommended when conservative treatment provides no sign of recovery. In the present study when conservative treatment showed no sign of improvement, 2 patients had partial correction release during surgery, and 1 patient had partial correction release 1 week after surgery. Two patients underwent conservative treatment because there was no sign of mechanical obstruction.
Reduction of the incidence of NNDs
The measures can be taken to minimize NNDs: 1) accurate screw placement, firm fixation, moderate orthopedic angle, and no excessive pursuit of orthopedic angle; 2) for severe rigid scoliosis and/or spinal cord deformity, preoperative traction can reduce the incidence of NNDs [25, 26]; 3) during the operation, the vertebral venous plexus should be destroyed as little as possible to stop bleeding thoroughly and prevent the formation of hematoma; 4) IONM and intraoperative wake-up test should be used during operation; 5) aggressive perioperative volume repletion should be performed to maintain mean arterial pressure with the mean arterial pressure maintained above 65 mm Hg during operation and approximately 100 mmHg postoperation [14]; 6) conservative treatment should include high-dose methylprednisolone (30 mg/kg bolus followed by 5.4 mg/kg/hr for 23 hours), neurotrophic therapy, blood vessel dilation treatment, and HPOT.