3.1 Surgical treatment of TCS.
The effect of conservative treatment of TCS is not good. Early surgical treatment should be performed after diagnosis, and long-term follow-up should be carried out . Even in order to prevent the occurrence of symptoms, surgical treatment is recommended for asymptomatic patients . The surgical treatment of tethered cord syndrome can be divided into two categories: spinal cord release, terminal filament amputation and spinal shortening. The standard treatment for tethered cord syndrome has long been intradural detethering, and prophylactic detethering has generally been performed before scoliosis correction for patients with both scoliosis and tethered cord . However, it brings great risk and recurrence of the nervous system, as well as limited correction of scoliosis . By separating the spinal cord from the surrounding structure, releasing the tethering of the spinal cord, the lysis of the terminal filament can correct the local distortion and compression, restore the microcirculation of the injured part of the spinal cord, and promote the recovery of neurological function . However, the incidence of retethering after terminal filament release can reach 5–50%, and the rate of nerve injury can reach 40% [11, 18]. Grande et al.  have proved that 15 ~ 25 mm thoracolumbar osteotomy can effectively reduce the tension of spinal cord, lumbosacral nerve root and terminal filum in human cadaveric experiments. Shortening spinal osteotomy is a safe and effective method for the treatment of congenital scoliosis and binding of spinal cord. It has been reported that spinal shortening osteotomy at the apical level of the thoracic spine can not only correct spinal deformity, but also release the tension of the tethered cord, thus improving neurological function . Posterior vertebral osteotomy and spinal shortening can avoid the risk of intradural operation aggravating nerve injury, thus reducing complications such as nerve injury, cerebrospinal fluid leakage and retethering, but it also has some limitations. Because although the tension of spinal cord and nerve root has been alleviated to a certain extent after shortening, it is difficult to achieve the goal of complete release. Therefore, unless combined with severe spinal deformity and vertebral hypoplasia, it is not advisable to destroy the normal vertebral body, HSAD surgery as an improved treatment has been widely reported.
3.2 improvement of bladder function TCS by Surgery
Terminal filament release is not ideal for the improvement of voiding function of TCS. Although Palmer et al.  performed terminal filament lysis and urodynamic examination in 20 patients with TCS, it was found that the detrusor overactivity was relieved in 50% of the patients, the sphincter function was improved in 21% of the patients, and one or more urodynamic indexes were improved in 25% of the patients. However, 8.5% of the patients still experienced deterioration of urodynamic parameters such as deterioration of compliance, increased bladder pressure, sphincter activity and loss of sensation. Most scholars believe that there is no significant improvement in lower urinary tract symptoms in patients with TCS after terminal filament lysis [22, 23]. Kokubun et al.  proposed a method of posterior vertebral osteotomy to shorten the spine and alleviate the longitudinal traction of the spinal cord. Safain et al. In this cadaveric experiment, SPO did not cause a significant decrease in tension, while both PSO and VCR showed a significant response . Repeated untethering surgeries seem to have a positive effect on the patient's weakness and a negative effect on pain. The longer the follow-up, the more likely are improvements in pain, weakness, and paresthesia. Bladder dysfunction is not expected to improve over time . Nakashima  retrospective study found that posterior osteotomy shortening was better than terminal filament release in improving bladder function, especially in difficult cases. Although SSO is a safe and effective technique for patients with TCS, especially in more challenging situations such as complex deformities or revision surgery. However, there is a large heterogeneity in the evaluation of motor function and the improvement rate of urinary and fecal dysfunction . Therefore, the operation of spinal shortening is improved in this paper. the uniform shortening of intervertebral disc can also achieve the purpose of shortening. The last follow-up has obvious effect on the improvement of defecation and defecation function, which can be regarded as an alternative surgical method.
3. 3 Analysis of the reasons for the functional improvement of TCS by HSAD.
HOU et al believe that HSAD operation is a safe and effective surgical method for TCS, which can directly decompress the spinal cord. This operation can restore normal tension on the spinal cord, and improve neurologic and urologic symptoms . Many studies were conducted in pediatric patients who had worsening symptoms many years after previous untethering surgery performed in infancy. In children, there is an imbalance between the growth column of the spine and the spinal cord, resulting in stretching and increasing spinal cord tension. Abnormal extension of the spinal cord wire reduces blood flow, followed by mitochondrial deterioration of oxidative metabolism and electrophysiological injury . Shortening the spinal column seems to represent a safe and effective option for the traditional removal of spinal cord embolism for tethered cord syndrome . The JOA score ranges from preoperative to final follow-up. The recovery rate of the two groups is significantly different. Children with HSAD have significantly improved urodynamic indicators than adults. HSAD is restoring neurological function and defecation function. Whether routine tethering surgery or orthopedic surgery to treat patients with spinal deformities can significantly reduce pain. However, only a small number of patients experienced sensory changes and improvement in sphincter problems . Children are repeatedly tethered, and the symptoms can be attributed to a mismatch between the growth and prolongation of the spine and spinal cord. In adults, although the growth tends to be stable, the intervertebral disc degenerates naturally. Symptoms are thought to result from daily exercise and chronic tension at the distal end of the spinal cord. Activity can lead to neurogenic pain, motor and sensory nervous system defects, and deterioration of bladder function. The author believes that with the growth of children, the spinal cord grows gradually, and the growth of the spine is limited by internal fixation, which leads to the further reduction of the axial tension of the spinal cord. For adults, this operation slows down the traction of the distal active spinal cord after fixation. Removal of a part of the intervertebral disc in each segment and uniform compression restored the lumbar curvature and the natural height of the intervertebral disc corresponding to the lower spinal cord. The scope of the operation was shortened by multi-segmental compression, and each nerve root outlet on both sides was completely decompressed, and some of the nerve roots were also decompressed. Intraoperative electrophysiological monitoring can prevent excessive reduction and injury of spine and nerve root and ensure the safety of operation. An indicator of postoperative shortening: cerebrospinal fluid flow, spinal cord pulsation and relaxation of the dural sac. Postoperative imaging examination showed that the length of the spine was significantly shortened and the tension of the spinal cord decreased. During the last follow-up, urinary function improved . Because the spinal cord and spine of children are in dynamic balance, the operation creates a relaxed environment for the development of spinal cord and nerve roots without traction, the cerebrospinal fluid beats well, the peripheral blood circulates well, and the nerve cells of children are highly constructible. therefore, the defecation function and urodynamic data of children are better than those of adults. However, whether the improvement of its function is natural development, or whether the operation itself brings more advantages, it still needs to be further studied in the future.
The symptoms of tethered syndrome are accompanied by an increase in height and aggravate during growth. It is speculated that various reasons lead to the high tension of the terminal filament of the fixed cauda equina, the untimely rise of the cone, and a series of problems caused by the normal development of the spine. It is well known that Laminoplasty is more effective for lordotic alignment cases than for kyphotic cases of myelopathy . Although the main purpose of cervical laminoplasty is decompression of the spinal cord, the tension of the spinal cord influences recovery. The posterior shift of the spinal cord was observed to be insufficient in the kyphotic aligned spine after posterior decompression . Lumbar lordosis increases when symptoms worsen in children with Lipomyelomeningocele [32–34]. Therefore, there is also a drift in the low cone of the lumbar vertebrae. We believe that the long segment fixation of the operation can restore the normal physiological curvature of the lumbar spine, and the outlet of the nerve root is unobstructed and loosened thoroughly during the operation, and the lumbar spinal cord is uniformly decompressed in the axial direction. MRI showed that the spinal cord and cauda equina tightened in a bowstring state close to the posterior structure of the spine, while the low spinal cord and Conus moved forward and relaxed after operation. Finally, mild to moderate scoliosis can be corrected by excision of intervertebral disc and posterior column structure.
3.4 Analysis of complications of TCS by HSAD.
About half of patients in this study had previous surgery or spina bifida, with more sequelae. Abnormal soft tissue scar coverage of the posterior dura mater of the lumbar spine and congenital spinal deformities can increase the complexity and time of the operation. Lee et al  reported their experience in 60 patients who underwent reoperation, with a wound-related complication rate of 22% (CSF leakage, infection, meningitis) and neurological deterioration in 2 patients. But up to 90% of patients improved. Selcuki et al  reported that the tethered cord of adults has an improvement rate of 95% and 40%. However, for patients with cystic cysts (dermoid, epidermoid or neutral nerve cyst or lipomas), clinical deterioration occurred within 10 years. Therefore, it can be seen that "the benefits of the second operation are limited" and "revision surgery should be performed in patients with complex diseases under abnormal circumstances." HSAD operation only shortens the intervertebral disc to avoid some of the complications of spinal osteotomy, which is effective and safe. The clinical effect of short-term follow-up is satisfactory . It can also significantly improve the neurological function of reoperation patients with tethered cord syndrome . Sofuoglu et al reported 23 cases of tethered cord surgery in adults. The incidence of complications was 26% in surgical wounds (cerebrospinal fluid leakage and infection). Therefore, tethering surgery is complex and has serious complications. In this study, surgery was planned based on the symptoms highlighted by adequate neurological examinations, magnetic resonance imaging, and urodynamic examinations. During the operation, there is no need to open the dura mater and peel off the scar tissue that adheres to the dura mater, but only on both sides, which is a repetitive action of routine operation and is safe in theory. And long-term follow-up found that the incidence of spinal internal fixation failure and pseudoarthrosis was not high. Although long segmental fixation led to a certain loss of spinal motion, it significantly improved the defecation and defecation function of children.
First, there is no statistical difference in the duration of the course of symptoms in patients. In addition, the patients developed dysfunction of urine and feces and affected their lives, and randomly selected the timing of surgical treatment. Finally, the efficacy score and objective data were evaluated by three double-blind neurosurgeons. Therefore, this research is reasonable. However, it was only initially found that the operation has excellent efficacy for TCS patients, and basic mechanism studies are needed to confirm whether children are better than adults. There are still some flaws. The number of cases is too small. Some cases were too old and had a long history, and there were differences in the recovery of sphincter function.