Clinical effect analysis of laminectomy alone and laminectomy with instrumentation in the treatment of TOLF: a multicentre retrospective study

Background To explore the clinical effect of laminectomy alone and laminectomy with instrumentation in the treatment of TOLF. Methods A retrospective study was conducted on the clinical data of 142 patients with TOLF and laminectomy in the Spine surgery of the XXX Medical University from January 2003 to January 2018. According to whether the laminectomy was combined with instrumentation, the patients were divided into two groups: group A (laminectomy alone LA, n = 77) and group B (laminectomy with instrumentation LI, n = 65). Comparison possible inuencing factors of demographic variables and operation-related variables between the two groups. In this study, the clinical effects of laminectomy alone and laminectomy with instrumentation in the treatment of TOLF were discussed. Thus to explore the clinical effect of LA and LI in the treatment of TOLF.

Because most of the disease progresses slowly, the thoracic spinal cord nerves have been compressed for a long time and become attened or even atrophy when obvious symptoms often appear. Therefore, surgical decompression should be performed as soon as possible for patients who are suggested to have thoracic OLF [8]. Early detection, early diagnosis and early treatment are very important to the satisfaction of postoperative e cacy. Traditional open surgery includes posterior laminectomy, laminectomy and laminoplasty, among which laminectomy is widely used and has become one of the classic surgical procedures [9][10]. However, there is no clear standard for the combined application of internal xation after laminectomy. The purpose of this study was to explore the clinical e cacy analysis of LA and LI in the treatment of TOLF.

Inclusion of patients
A retrospective study was conducted on the clinical data of 142 patients with TOLF and laminectomy in the Spine surgery of the XXX Medical University from January 2003 to January 2018. The same group of surgeons performed the operation. The patient was in the prone position under general anesthesia. Monitoring of electromyography and somatosensory evoked potentials during operation was applied. Operation segment con rmed by C-arm uoroscopy.Make a posterior median incision along the spinous process,the skin and subcutaneous tissue were separated layer by layer, and the structures of spinous process, lamina and articular process were exposed.(For patients underwent laminectomy with instrumentation, pedicle screws were screwed rst.)First, the spinous process and the outer layer of the lamina were bited off, and then the lateral lamina were removed by high-speed grinding drill in the longitudinal direction at the inner edge of the facet joints of the bilateral lamina. Then, the interspace of the lamina was enlarged, and the ligaments between the upper and lower spine were removed,and then used a high-speed grinding drill to scan the middle lamina with normal saline ushing, and did not polish each line too deeply until the ossi ed tissues were eggshell-like translucent. The remaining thin layer of bone was lifted with towelet forceps, and the inner vertebral plate, ossi ed ligamentum avum and dural mater were gently probed with nerve exfoliator to see if there was adhesion. If there was no adhesion, the inner vertebral plate and ossi ed ligamentum avum would be removed to achieve full decompression. Continued to nibble on both sides to the outer 1/3of the facet joint, exposed both sides of the dural sac, at this time the dural sac could be completely expanded. In this study, 16 patients (4 cases in group A and 12 cases in group B) were found to have heavy adhesion to the dura mater, which could not be separated.
They were resected together and repaired with local fascia.
After decompression was completed, (The patients who underwent laminectomy and internal xation installed the pre-bent connecting rod on the pedicle screw and tightened and locked it.), rinse the operation eld thoroughly, indwelling negative pressure drainage tube, suture the incision layer by layer, and the operation was nished. All patients were routinely treated with antibiotics within 3 days after operation. 7 days after operation, patients were encouraged to wear braces to move under the ground, and brace protection was maintained for about 3 months.

Satisfaction Evaluation
All patients were followed up by outpatient or telephone at 6 months, 1 year, and 2 years postoperatively.

Statistical analysis
All statistical analyses were carried out by SPSS software version 22.0 (IBM, Armonk, NY, USA), and the test level was α = 0.05.The measurement data between the two groups were compared by independent sample t-test or non-parametric test according to whether they were in line with normal distribution and homogeneity of variance. Analysis of counting data by chi-square test.Signi cance was accepted for a p value < 0.05.

Results
All 142 patients (89 males and 53 females) were successfully operated. According to whether the laminectomy was combined with instrumentation, the patients were divided into two groups: group A (laminectomy alone LA, n = 77) and group B (laminectomy with instrumentation LI, n = 65).
All patients were followed up for 2 years or more.
In terms of demographics, there was a statistically signi cant difference in BMI between group A and Group B (P < 0.05). The differences in Age, Sex, Smoking, Drinking, Heart disease, Hypertension and Diabetes were not statistically signi cant (P 0.05)( Table 2). In terms of preoperative symptoms, there was signi cant difference in Gait disturbance, Pain in LE,Urination disorder between group A and group B (P < 0.05), but there was no signi cant difference in other variables between the two groups (P > 0.05) year,Leakage of cerebrospinal uid between group A and group B (P < 0.05), but there was no signi cant difference in other variables between the two groups (P > 0.05) Table 4).   No neurological deterioration occurred in two groups. One patient in group B had no improvement in postoperative symptoms, and the preoperative JOA score was 1. There was severe spinal cord degeneration before operation. During the operation, the ossi ed ligamentum avum was removed completely, but the spinal cord function was not signi cantly improved. The JOA score reached 2 points at the last follow-up. One patient in group A presented progressive aggravation of lower extremity symptoms 12 hours after surgery. Epidural hematoma was considered. After emergency debridement, hormone and dehydration drugs were administered, muscle strength gradually recovered, and the patient recovered to preoperative level 1 month after surgery. Cerebrospinal uid leakage caused by dural tear in group A (n = 4) and group B (n = 12). The preoperative average JOA score of group A was 6.37, and that of group B was 5.19. In group A, the average JOA score at 6 months, 1 year and 2 years after surgery was 7.87, 8.23 and 8.26, respectively, and the average JOA score improvement rate was 32.79%, 38.32% and 38.53%, respectively. In group B, the average JOA score at 6 months, 1 year and 2 years after surgery was 7.74, 8.15 and 8.29, respectively, and the average JOA score improvement rate was 39.15%, 46.86% and 47.12%, respectively. The preoperative JOA score of group B was signi cantly lower than that of group A, and the preoperative symptom duration of group B was signi cantly higher than that of group A. However, the JOA score improvement rate in group B was higher than that in group A during postoperative follow-up, especially at 1 year of follow-up, and the difference between group A and Group B was statistically signi cant (P < 0.05) (Fig. 2, Fig. 3)

Discussion
TOLF is a disease with relatively low incidence,with the advent of aging society, TOLF has become one of the main causes of chronic thoracic spinal cord injury [13][14].TOLF is often slow [8], with the highest incidence among people aged 50 ~ 59, and increases with age [15]. Nearly half of the patients complained of pain and numbness in one or both lower limbs [16], which was similar to the symptoms of lumbar disease. In our study, a total of 43 patients complained of lower limb pain and 52 patients complained of lower limb numbness. And thoracic spinal stenosis is often associated with lumbar spinal stenosis or cervical spondylosis, resulting in complex symptoms and signs of patients, and early diagnosis is sometimes di cult.The incidence and pathogenesis of TOLF in the population are not clear, mainly in Asia, which is more reported in Japan [6,[17][18].Wang et al. [19] analyzed 142 patients with TOLF and found that TOLF was related to systemic ossi cation disease, spinal load change and aging.The conservative effect of TOLF is poor, its treatment is mainly surgery, and there are many kinds of surgical methods, posterior laminectomy has become the most commonly used classical operation, which can remove the ossi ed ligamentum avum while completing the decompression of compressed spinal cord, prevent the further deterioration of spinal cord function and restore it to varying degrees.
However, due to the low prevalence rate, few studies had been reported so far, and the safety and e cacy of different surgical methods in the treatment of secondary thoracic myelopathy to TOLF remain unclear, especially whether combined instrumentation should be used after laminectomy had not been de nitively concluded. Pedicle screw internal xation was rst used in the surgical treatment of spinal deformity [20]. According to previous literature report, increased spinal mobility after laminectomy alone could cause slight traction or vibration of the injured spinal cord at the level of OLF, which may compromise the recovery of the injured spinal cord. In addition, increased intervertebral range of motion after laminectomy alone could lead to concentration of mechanical stress at the lesion site, which may result in re-extension of OLF, especially at the level of thoracolumbar junction [21][22].
In this study, 65 patients in group B (45.8%), present Gait disturbance, Urination disorder, Preoperative duration of symptoms, Intramedullary signal change on MRI, Dural ossi cation, Residual rate of crosssectional spinal canal area on CT, Shape on the sgittal MRI, Pre-mJOA showed signi cant difference compared with group A, suggested severe thoracic myelosis [10]. High BMI might also lead to severe ossi cation due to increased mechanical stress and repetitive mild trauma of thoracolumbar OLF. In patients with severe ossi ed ligamentum avum, the spinal cord was fragile, and minor traction or vibrations during intraoperative removal of the ligamentum avum might lead to severe paralysis. In addition, intraoperative instability caused by extensive laminectomy and an increase in kyphosis after laminectomy had been considered as potential causes for postoperative neurological deterioration (however, there were no cases of kyphosis during the follow-up period of this study) [23]. Last but not least, it has been reported that application of instrumentation after laminectomy dose good to postoperative recovery of the injured spinal cord due to thoracic myelopathy, and prevents re-extension of OLF [24][25]. In our study, we found that the JOA score improvement rate of group B at 1 year follow-up was signi cantly different from that of group A. This might be because the spinal activity of group B had little interference with postoperative spinal cord recovery. These results showed that laminectomy with instrumentation had a signi cant clinical effect on myelopathy caused by severe ossi cation of ligamentum avum. Especially for TOLF patients with extensive laminectomy.
Laminectomy with instrumentation for TOLF is a major development trend. There were some limitations in this study.First, the maximum time limit of neurological recovery after ossi cation of ligamentum avum in thoracic vertebrae is not clear, and the follow-up period of 2 years in our study may be insu cient.Second,this study is a retrospective study, and it is a single-center and small sample size study, and the sample size is small, so we look forward to a large sample size and multi-center study to further con rm our conclusions. Despite these limitations, we believed that this study had important guidance in clinical work, especially in the implementation of surgical procedures.

Conclusions
Currently, there was no consensus on whether instrumentation is needed after laminectomy for TOLF. We found that for patients with long duration of Gait disturbance, Urination disorder, Preoperative duration of symptoms, Intramedullary signal change on MRI, Dural ossi cation, Residual rate of cross-sectional spinal canal area on CT less than 60%, Shape on the sgittal MRI as Beak and low Pre-mJOA had better clinical effect after LI than that LA, and the incidence of perioperative complications was lower. The written informed consent was obtained from all patients included in this study.