Is Homogeneous Spinal Cord Shortening and Axial Decompression (HSAD) Superior to Adults in The Treatment of Tethered Syndrome in Children

Objective: Childhood spinal cord syndrome is a refractory and intractable disease, which gradually worsens with developmental symptoms. The purpose of this study was to evaluate the long-term surgical effects of HSAD in the treatment of tethered cord syndrome in children and adults. Methods: 50 Patients receiving HSAD tethered from January 2011 to September 2014 included in this study. At least 5 years after follow-up, imaging and clinical data collection. JOA score, VAS score, waist and leg dysfunction index (ODI) score were used to evaluate the patient's neurological function and pain improvement. ICI-Q-SF score, urodynamics, and residual urine volume (B-ultrasound) are used to assess urinary function. The Rintala score is used to assess stool function. Results: A total of 50 patients were enrolled and the patients were divided into children group (n=26) and adult group(n=24). JOA improvement rate in children group (54.95%±14.14%vs34.95%±11.82%), maximum urine ow rate improvement value (4.87±5.49vs1.40±1.88) and residual urine volume improvement value (118.46±39.11vs62 .83±59.28) was greater than the adult group, and the postoperative ICIQ-SF score (6.21 ± 4.85vs7.75 ±4.23) was lower than that of the adult group (P <0.05). Conclusion: HSAD can achieve good clinical effects in treating children and adults with tether syndrome. In the long run, it may benet urinary function, especially in children. This study was a retrospective study. 50 patients with TCS who received HSAD treatment in spinal surgery of our hospital from January 2011 to September 2014 were divided into children group and adult group according to whether they were older than 18 years old or not. We are studying to explain to patients suitable for TCS diagnosis that HSAD is an unproven but potentially benecial procedure. After discussing the pros and cons with the patient, the patient decides whether to accept surgery. The research protocol has been approved by our ethics committee. The clinical trial followed the relevant guidelines and regulations, and released an identication image obtained from the participants with informed consent. All patient data are users, including demographic characteristics, operating age, urological examination results, urodynamic examination, back or lower limb pain, neurological diseases and recorded orthopedic abnormalities. The termination grade cone, pulp size, the presence of fat in the pulp, and other related spinal cord and spinal cord abnormalities were determined by MRI scans.


Introduction
Tethered cord syndrome (TCS), characterized by longitudinal traction of the spinal cord leading to injury to the lumbosacral spinal cord and cauda equina. Refers to a series of neurological dysfunction syndromes with high incidence. [1]TCS is caused by the thickened lum terminal, lipomyelomeningocele, spina bi da or other congenital abnormalities. [2] Patients with TCS may present various symptoms and signs, including low back pain, gait di culties, sensory or/and motor de cits, sphincter dysfunction. [3][4][5][6]The traditional surgical procedure for treating TCS is untethering surgery, which has been considered to be the golden standard treatment for TCS. [7][8][9]However, 5-50% of patients need revision surgery after untethering surgery due to unsatis ed urologic outcomes. [10][11][12] Moreover. Cerebrospinal uid leakage and retethering, neurological deterioration high risk of suffering postoperative complications remains a problem hard to deal with [5,6]. As an alternative to the treatment of TCS, spine-shortening osteotomy (SSO) reduces the tension of the spinal cord and reduces perioperative complications. On the other hand, homogeneous spinal-shortening axial decompression (HSAD) can also achieve the purpose of uniform shortening of intervertebral disc by means of uniform shortening of intervertebral disc, and good results have been achieved in the treatment of TCS [1]. In this study, although the number of cases is small, but the use of a variety of scores to evaluate the function of patients, urodynamic examination to evaluate the changes of bladder indicators, and divided into adult and child groups, for long-term follow-up, with a certain degree of scienti c, the report is as follows.

Study Design and Participants
This study was a retrospective study. 50 patients with TCS who received HSAD treatment in spinal surgery of our hospital from January 2011 to September 2014 were divided into children group and adult group according to whether they were older than 18 years old or not. We are studying to explain to patients suitable for TCS diagnosis that HSAD is an unproven but potentially bene cial procedure. After discussing the pros and cons with the patient, the patient decides whether to accept surgery. The research protocol has been approved by our ethics committee. The clinical trial followed the relevant guidelines and regulations, and released an identi cation image obtained from the participants with informed consent. All patient data are users, including demographic characteristics, operating age, urological examination results, urodynamic examination, back or lower limb pain, neurological diseases and recorded orthopedic abnormalities. The termination grade cone, pulp size, the presence of fat in the pulp, and other related spinal cord and spinal cord abnormalities were determined by MRI scans.
The diagnostic criteria of TCS were as follows: (1) lumbar MRI showed that the position of the medullary cone was low, and the lower end of the medullary cone was lower than the L2/3 segment; (2) there were symptoms such as low back pain, dysfunction of defecation and defecation, sensorimotor disturbance of the lower extremities;(3) deformities such as meningocele, lipoma, foot deformity and skin abnormalities. The inclusion criteria of this study were as follows: (1) the diagnosis of TCS was clear, and MRI showed that the pulp cone was low and the lower end of the cone was lower than L2/3; (2) voiding dysfunction, with or without other neurological symptoms; (3) complete clinical and follow-up data, including clinical scores and urodynamic results before and after operation. Exclusion criteria: (1) TCS patients with normal cone position; (2) urinary dysfunction caused by non-TCS, such as cauda equina syndrome, urology-related diseases, and (3) incomplete clinical or follow-up data. All patients were fully informed of the expectations and adverse consequences of the surgical trial and obtained their written informed consent. During the study period, HSAD was an unproven but potentially bene cial procedure for patients diagnosed with TCS. After discussing the pros and cons, patients are advised to consider various options and decide whether to undergo surgery or continue conservative treatment. The research scheme has been approved by the ethics committee of the college. Conduct clinical trials in accordance with relevant guidelines and regulations, and obtain the informed consent of the participants.
1.2 Surgical methods and postoperative rehabilitation training (taking L2 ~ S1 as an example) patients were used as prone position, general anesthesia, routine Aner iodine disinfection and towels. After resection, a median incision was made to cut the skin, subcutaneous tissue and fascia in turn to expose the L2 ~ S1 spinous process, lamina and facet joint. Screws were placed into the pedicle of L2 ~ S1 to remove the interspinous ligament and interlaminar ligament of L5/S1. The inferior articular process of L5 was resected by osteotomy and the medial edge of superior articular process of S1 was removed. Enlarge the L5/S1 intervertebral foramen, cut open the brous annulus after the L5/S1 space, and remove the intervertebral disc tissue. The operative segments of L4/5, L3/4 and L2/3 were treated in the same way.
After the treatment of each intervertebral space, connect the connecting rod with bilateral screws, x the nut, press the L2/3 ~ L5/S1 space in turn, and then lock the nut. Exploration showed that the spinous process space and intervertebral space were signi cantly reduced, and the nerve root and dural sac became loose and unobstructed. Saline irrigation, hemostasis, intertransverse bone grafting, layer-bylayer suture dressing and routine drainage. After operation, urination exercises were carried out regularly, urination was carried out regularly, normal micturition re ex was restored, and the recovery of bladder function was promoted.
1.3. The function was evaluated by ICI-Q-SF, JOA, Rintala score, VAS score,and Oswestry Disability Index(ODI)before operation and at the last follow-up. urodynamic examination and urinary ow parameters (including bladder safe volume, detrusor leak point pressure, bladder compliance, maximum urinary ow rate) were measured by MMS solar urodynamic examination system and bladder residual urine volume were measured by Bladder ultrasound (After urination) in our hospital before operation and in the last follow-up. Bladder compliance (ml/cm H2O) = Δ volume (Ml) / Δ pressure (cm/H2O). Improvement rate of residual urine volume = difference / preoperative × 100%. Post-treatment score improvement rate = [(post-treatment score-pre-treatment score) / score (29-pre-treatment score)] × 100%. The highest improvement rate is 100%.

Statistical methods
SPSS21.0 statistical software was used to analyze the data. All scores, bladder compliance, bladder safety capacity, detrusor leak point pressure, bladder residual urine volume and maximum urinary ow rate were expressed in x ± s. Paired t-test was used in preoperative and nal follow-up. Independent sample t-test was used in both groups (P < 0.05). The difference was statistically signi cant.
During the follow-up period, the intertransverse bone graft fusion was good, and no internal xation complications such as broken rod and screw prolapse were found.    (Fig. 1). The difference of residual urine volume in the child group (118.46 ± 39.11vs62.83 ± 59.28) (P = 0.032) (Fig. 2).

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 [13]. Even in order to prevent the occurrence of symptoms, surgical treatment is recommended for asymptomatic patients [14]. The surgical treatment of tethered cord syndrome can be divided into two categories: spinal cord release, terminal lament 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 [15]. However, it brings great risk and recurrence of the nervous system, as well as limited correction of scoliosis [16]. By separating the spinal cord from the surrounding structure, releasing the tethering of the spinal cord, the lysis of the terminal lament 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 [17]. However, the incidence of retethering after terminal lament release can reach 5-50%, and the rate of nerve injury can reach 40% [11,18]. Grande et al. [19] have proved that 15 ~ 25 mm thoracolumbar osteotomy can effectively reduce the tension of spinal cord, lumbosacral nerve root and terminal lum 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 [20]. Posterior vertebral osteotomy and spinal shortening can avoid the risk of intradural operation aggravating nerve injury, thus reducing complications such as nerve injury, cerebrospinal uid 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 di cult 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.

improvement of bladder function TCS by Surgery
Terminal lament release is not ideal for the improvement of voiding function of TCS. Although Palmer et al. [21] performed terminal lament 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 signi cant improvement in lower urinary tract symptoms in patients with TCS after terminal lament lysis [22,23]. Kokubun et al. [24] 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 signi cant decrease in tension, while both PSO and VCR showed a signi cant response [19]. 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 [25]. Nakashima [26] retrospective study found that posterior osteotomy shortening was better than terminal lament release in improving bladder function, especially in di cult 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 [27]. 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 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 [28]. 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 ow, followed by mitochondrial deterioration of oxidative metabolism and electrophysiological injury [29]. Shortening the spinal column seems to represent a safe and effective option for the traditional removal of spinal cord embolism for tethered cord syndrome [4]. The JOA score ranges from preoperative to nal follow-up. The recovery rate of the two groups is signi cantly different. Children with HSAD have signi cantly 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 signi cantly reduce pain. However, only a small number of patients experienced sensory changes and improvement in sphincter problems [30]. 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 xation, 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 xation. 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 uid ow, spinal cord pulsation and relaxation of the dural sac. Postoperative imaging examination showed that the length of the spine was signi cantly shortened and the tension of the spinal cord decreased. During the last follow-up, urinary function improved [19]. 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 uid 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 lament of the xed 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 [31]. Although the main purpose of cervical laminoplasty is decompression of the spinal cord, the tension of the spinal cord in uences recovery. The posterior shift of the spinal cord was observed to be insu cient in the kyphotic aligned spine after posterior decompression [31]. Lumbar lordosis increases when symptoms worsen in children with Lipomyelomeningocele [32][33][34]. Therefore, there is also a drift in the low cone of the lumbar vertebrae. We believe that the long segment xation 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.

Analysis of complications of TCS by HSAD.
About half of patients in this study had previous surgery or spina bi da, 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 [9] 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 [35] 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 bene ts 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 [36]. It can also signi cantly improve the neurological function of reoperation patients with tethered cord syndrome [37]. Sofuoglu [38]et al reported 23 cases of tethered cord surgery in adults. The incidence of complications was 26% in surgical wounds (cerebrospinal uid 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 xation failure and pseudoarthrosis was not high. Although long segmental xation led to a certain loss of spinal motion, it signi cantly improved the defecation and defecation function of children.

Limitations
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 e cacy score and objective data were evaluated by three doubleblind neurosurgeons. Therefore, this research is reasonable. However, it was only initially found that the operation has excellent e cacy for TCS patients, and basic mechanism studies are needed to con rm whether children are better than adults. There are still some aws. 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.

Conclusions
HSAD is an effective surgical method for the treatment of tether syndrome in adults and children. It may bene t urinary function in the long term, especially in children. Availability of data and materials

Abbreviations
The datasets used and/or analyzed during the current study are not publicly available due to feasibility but are available from the corresponding author on reasonable request.

Competing interests
The authors declare that they have no competing interests.

Funding
The study is supported by the National Natural Science Foundation of China, Grant/Award Numbers: No.

81871828, No. 81702141, No.81802218
Authors' contributions Shunmin Wang designed the study, carried out most of the data analysis, and wrote the manuscript; Jian Zhu, Kaiqiang Sun and Rongzi Chen should be considered as co-rst authors. The authors read and approved the nal manuscript.