[Abstract] Objective To investigate the effect of cervical laminectomy on the stability of the cervical spine and related factors. Methods Retrospective analysis of 62 cases of intracervical spinal canal tumors from 1997 ~ 2009. The clinical and medical images before and after surgery were reviewed, and the changes in spinal biomechanics of patients were evaluated by postoperative follow-up. Results The 62 laminectomies were divided into group A: <3 and group B: ≥3 according to the number of laminectomies; and group C: intramedullary and group D: extramedullary according to the lesion site. The patients had satisfactory clinical results in the near term and satisfactory clinical results in the long term. From 3 months to 12 years of follow-up, the incidence of cervical instability was 3,1% in group A and 16,7% in group B, with group B higher than group A (P < 0,1); 36,4% in group C and 4,3% in group D, with group C higher than group D (P < 0,1); the incidence of deterioration of cervical curvature was 3,1% in group A and 23,3% in group B, with group B higher than group A (P < 0,1); 45,5% in group C and 6,4% in group D Group C was higher than group D. Conclusion The laminectomy style can lead to changes in the biomechanics of the cervical spine. The occurrence of postoperative instability or deformity should be noted when the number of laminectomy is ≥3, intramedullary occupancy or both cervical 2 and cervical 7 are involved. [Keywords] Intravertebral tumor, laminectomy, microsurgery, spinal stability Laminectomy is a routine procedure for resection of intravertebral lesions [1], including removal of the lamina, spinous process and the corresponding posterior binding tension bands such as the interspinous ligament, supraspinous ligament and ligamentum flavum. Due to the destruction of posterior structures, which causes bone and ligament defects and neuromuscular imbalance, it may cause biomechanical changes in the cervical spine with changes in curvature and movement, and even cervical instability and deformity [2-4]. And with the development of surgical equipment and techniques, the efficacy of surgery for intravertebral lesions is increasingly improved, and the function of the spine after surgery is increasingly of concern to both physicians and patients. However, the extent to which laminectomy leads to cervical instability or deformity is controversial. The author retrospectively analyzed 62 cases of cervical intradural tumors from May 1997 to September 2009 to investigate the effect of different degrees of laminectomy on cervical spine stability. Data and methods 1. General data: 338 cases of cervical intracanalicular tumors treated by surgery. Inclusion criteria of this trial: (1) those who underwent posterior laminectomy for cervical intradural lesions; (2) complete clinical and pathological data; (3) received at least 3 months of clinical and medical imaging follow-up. Exclusion criteria: (1) hemilartebral laminectomy patients; (2) patients with small joint destruction; (3) patients with laminectomy repositioning; (4) patients with malignant tumors in the spinal canal; (5) patients with preoperative cervical instability or deformity. Of the 62 patients in this group, 32 (51,6%) were male and 30 (48,4%) were female. The age ranged from 14 to 79 years, with an average of (45,65±11,67) years. 2. Surgical method: 62 patients underwent laminectomy, and the number and location of the operated segments were decided according to the lesion. Preoperative positioning of the lamina corresponding to the lesion was performed 1 day before surgery. Patients were positioned prone or laterally to simulate the position at the time of surgery, and localization marks were made on the spine corresponding to the lesion segment with a varicose needle, while the body surface was marked with nail violet. Frontal and lateral cervical radiographs were taken to determine the surgical incision by the relative position of the markers to the bony structures. The operation was performed using general anesthesia with endotracheal intubation in the prone position with an invasive head frame to immobilize the head and the neck in a neutral forward flexion position. The skin is incised along the preoperative incision, and the supraspinous ligament is separated along the midline after the muscles of the collar reach the supraspinous ligament, and the supraspinous and interspinous ligaments are protected. Care is taken to protect the small joint capsule bilaterally, generally not exceeding the medial edge of the articular eminence to avoid damage to the small joint capsule. After revealing the vertebral plates of the lesion, the number of plates removed was decided according to the size of the tumor (2 cases of 1 plate removed, 30 cases of 2 plates removed, 19 cases of 3 plates removed, 8 cases of 4 plates removed, 1 case of 5 plates removed, and 2 cases of 6 plates removed in this group), and the spinous process of the lesioned segment was removed with spinous scissors, and the supraspinous and interspinous ligaments belonging to it reached the root of the spinous process, and the plates were gradually removed from the midline to the sides with a bone biting forceps. The laminae were gradually removed from the midline to the sides, and the laminae were removed bilaterally to the medial aspect of the lesser articular eminence, preserving the lesser articular eminence. The dural layer was cut longitudinally along the midline or at the highest point of the spinal membrane expansion, and the dura was cut near the tumor as far as possible, paying attention to the protection of the adjacent spinal cord or nerve roots, and the tumor envelope was cut first for intracapsular resection, and then the adhesions between the tumor envelope and the spinal cord or nerve roots were separated after decompression, and the tumor and envelope were removed piece by piece. The blood supply artery of the tumor is cut off by electrocoagulation, but attention is paid to avoid damaging the larger vessels supplying the spinal cord and to stop the bleeding completely. After the tumor is removed, the dural layer is closed with interrupted sutures with 1 gauge, which should be carefully sutured to prevent cerebrospinal fluid leakage. The epidural cavity around the window was filled with gelatin sponge and the wound was closed layer by layer. 3. Evaluation of clinical results: (1) After surgery, the neurological function of the patient was evaluated and compared with that before surgery, and the patient was classified as improved, unchanged and deteriorated according to the symptoms and signs. (2) After discharge from the hospital, the patient's long-term functional status was evaluated according to the McCormick classification. (Note: McCormick classification: Grade I, mild neurological dysfunction, but does not affect the function of the affected limb, mild ankylosis or abnormal reflexes, normal gait; Grade II, sensorimotor impairment, affecting the function of the affected limb, mild to moderate gait difficulties, pain seriously affects the patient's quality of life, but the patient can still live independently and walk independently; Grade III, severe neurological dysfunction, walking requires crutches or (Grade IV, severe neurological dysfunction, requiring wheelchair, crutches or brace, impaired function of both upper limbs, life can be self-care or not; Grade V, paraplegia or quadriplegia) 4. Measurement of biomechanical changes of cervical spine: analyzed by frontal and lateral cervical spine and lateral X-ray of hyperextension and hyperflexion before and after surgery. (1) cervical instability, defined as adjacent segmental angle >11°, or dynamic slip of vertebral body ≥3,5mm.(2) cervical curvature before and after surgery, the overall curvature was evaluated by the change in angle formed by the tangent line parallel to the posterior edge of C2 and C7 vertebrae on the lateral cervical radiographs, which was gradually classified from normal to deterioration: physiological anterior curvature, upright shape, S shape and posterior protrusion shape. The cervical spine curvature was classified into: no change; deterioration of curvature, i.e., evolution from one type to another deterioration type, according to the comparative changes before and after surgery. (3) Cervical mobility was calculated as the change in angle formed by the tangent line parallel to the posterior edge of C2 and C7 vertebrae during hyperextension and hyperflexion, and the total cervical mobility (ROM) was the sum of the maximum hyperflexion angle and the maximum hyperextension angle of the cervical spine. 5, Statistical analysis:SPSS 17 statistical software package was used to establish a database for each variable, and the measurement data were expressed as ±s (mean ± standard deviation), and statistical analysis was performed by variance and t-test, and P<0, 1 was considered statistically significant difference. Results 1. Surgical tumor resection: 58 of the 62 cases in this group were intradural occupying lesions and 4 cases were spinal cavities. 52 of the 58 cases of occupying lesions achieved complete resection of the lesions, and 6 cases had only subtotal resection of the lesions with unclear boundaries with the surrounding structures. Among the 47 cases of extramedullary occupations in this group, 25 were nerve sheath tumors, 5 were neurofibromas, 12 were spinal meningiomas, 3 were ganglioneuroma, 1 was a cavernous hemangioma, and 1 was a prolapsed disc. Among them, 44 cases accounted for 93.6% of total resection and 3 cases accounted for 6.4% of subtotal resection. There were 11 cases of intramedullary tumors, 6 cases of benign ventricular meningioma, 3 cases of grade I astrocytoma, and 2 cases of vascular reticulocytoma. The total resection of intramedullary tumors accounted for 72.7% in 8 cases and the secondary resection accounted for 27.3% in 3 cases. The operation time was 2 to 3 hours, with an average of 2.5 hours. The total hospital stay ranged from 9 to 12 days, with an average of 10 days. Bed activities started 3 days after surgery, and bed activities started 5 days after surgery. After surgery, the patient wore a neck brace for 1 to 3 months and exercised the neck muscles. 2. Recent clinical efficacy: (1) Of the 32 cases of preoperative radicular pain, 30 cases (93,8%) had pain relief or disappearance, and 2 cases (6,3%) had no change. (2) Among 48 cases of motor disorders, 41 cases (85,4%) improved to varying degrees after surgery, 5 cases (10,4%) had no change and 2 cases (4,2%) had aggravation. (3) Among 50 patients with sensory disorders, 45 cases (90%) showed varying degrees of improvement after surgery, 4 cases (8%) showed no change and 1 case (2%) showed aggravation. (4) Eleven cases (91.7%) of 12 patients with chest banding sensation were reduced, and one case (8.3%) had no change. (5) Among the 4 patients with sphincter dysfunction, 28 cases improved (76%), 6 cases had no change (16%), and 3 cases worsened (8%). 3. Investigation of spinal stability: (1) Incidence of cervical instability: 62 patients were followed up from 3 months to 12 years (mean 4,36 years). During the follow-up period, 6 cases (9, 7%) developed cervical instability. Two of them occurred in patients with cervical 2-7 laminectomy. (2) Changes in cervical curvature: 8 cases (12, 9%) deteriorated during the follow-up period, and 2 of them had significant cervical retrognathism undergoing spinal orthopedic surgery. (3) Changes in cervical spine motion: The range of motion was reduced by 16% after surgery. (4) Long-term clinical outcome: During the follow-up period, 55 cases (72%) were graded by McCormick as Grade 0, 5 cases (18%) as Grade I, 2 cases (5%) as Grade II, and 0 cases as Grade III or above. 3 cases (1 case of ganglioneuroma, 1 case of ventricular meningioma, and 1 case of astrocytoma) were found to have recurrence after surgery, and no recurrence has been found since the follow-up after reoperation. The incidence of postoperative instability and deterioration of cervical spine curvature was significantly higher in group B than in group A. The incidence of postoperative instability and deterioration of cervical spine curvature was significantly higher in group B than in group A. The incidence of cervical instability and curvature deterioration in group B was significantly higher than that in group A. Grouped according to whether cervical 2 and 7 were involved, 22 cases involving cervical 2 had cervical instability in 2 cases (9,1%) and cervical curvature deterioration in 3 cases (13,6%); 40 cases not involving cervical 2 had cervical instability in 4 cases (10%) and cervical curvature deterioration in 5 cases (12,5%), with no significant difference between the two groups. In 18 cases involving cervical 7, 3 cases (16,7%) showed cervical instability and 4 cases (22,2%) showed deterioration of cervical curvature; in 44 cases not involving cervical 7, 3 cases (6,8%) showed cervical instability and 4 cases (9,1%) showed deterioration of cervical curvature, and there was no significant difference between the two groups. In 38 cases involving cervical 2 or 7, 3 cases (7, 9%) showed cervical instability and 5 cases (13, 2%) showed deterioration of cervical curvature; in 24 cases not involving cervical 2 or 7, 3 cases (12, 5%) showed cervical instability and 3 cases (12, 5%) showed deterioration of cervical curvature, with no significant difference between the two groups. Two cases involving cervical 2 and cervical 7 showed cervical instability and deterioration of curvature, but the sample size was too small to allow statistical analysis. The incidence of cervical instability and deterioration of curvature was significantly higher in group C than in group C. In group D, there were 47 cases, with 2 cases (4 or 3%) showing cervical instability and 3 cases (6 or 4%) showing deterioration of curvature. Discussion Cervical laminectomy is often required to perform extensive extended laminectomy in order to obtain adequate decompression in decompression surgery for spinal cord-type cervical spondylosis, ossification of the posterior longitudinal ligament, and developmental spinal stenosis [5]. Postoperatively, it often causes cervical deformity, resulting in a poor prognosis [6]. When used for intradural tumor resection, the dural sac is revealed from the posterior side, which is necessary to remove the intradural tumor, and the extent and location of resection is related to the size and location of the tumor, which is often a limited laminectomy, with hemi-laminectomy feasible in some patients and long segmental laminectomy required in only some patients due to the large tumor. Nevertheless, postoperative cervical instability or deformity has been reported, with an incidence of 20% in adults and up to 45% in children [2-4]. This can lead to varying degrees of clinical symptoms and/or cosmetic defects and, in severe cases, to spinal cord dysfunction. In our group, two cases required cervical spine orthopedic surgery due to significant posterior protrusion deformity after surgery. How to maintain the biomechanical stability of the spine is of increasing concern to physicians [7]. According to the "three-column" theory, the posterior column of the spine contains the posterior joint capsule, the ligamentum flavum, the attachments of the spine, the articular processes and the supraspinous and interspinous ligaments. The center of gravity of the head is slightly in front of the cervical spine and gravity has the effect of causing the cervical spine to flex forward, while the posterior ligaments and other structures resist their action and are important in maintaining the stability of the cervical spine. Any alteration of the posterior bone or ligamentous structures may cause displacement of the weight-bearing axis [8] and disrupt the biomechanical stability of the spine [9]. Cervical laminectomy shifts the weight-bearing axis ventrally to the anterior part of the vertebral body so that most of the weight is carried by the anterior vertebral body and intervertebral discs; when the load increases, the anterior column of the spine tends to be deformed in compression and the posterior column is in tension; because the posterior tension band has weakened, its force against changing the alignment of the cervical spine is reduced, which causes the loss of anterior cervical convexity and straightens or changes its alignment to posterior convexity. Risk factors for instability or deformity after cervical laminectomy include (1) age is probably the greatest risk factor, with children at greatest risk for deformity [4, 9, 10], which may be related to laxity of the ligaments, more horizontal orientation of the small joints, skeletal immaturity, and growing vertebrae in children than in adults [9]. (2) The extent of laminectomy (length and width) is associated with postoperative cervical stability [4, 9]. sciubba et al. found a significant increase in postoperative instability in cervical subdural tumors with laminectomy beyond 3 segments [11], similar to the results in this group. simon et al. found that laminectomy beyond 4 segments in children with intramedullary tumors was associated with postoperative spinal deformity [12]. (3) The site of laminectomy is also an important factor in postoperative cervical stability [9]. Asazuma et al. found that cervical curvature and mobility were more altered with surgical involvement of C2 [13]. Inoue et al. found that involvement of either C2 or C7 affected postoperative cervical curvature [14]. McGirt et al. suggested that involvement of both C1-2 and C7-T1 was associated with postoperative deformity, while involvement of C1-2 or C7-T1 alone was associated with postoperative deformity [15]. involvement of C1-2 or C7-T1 alone was not associated with deformity [10]. This may be related to the fact that surgery impairs the ability of the spine to resist stresses associated with cervical motion at these high stress sites [9]. (4) Intramedullary tumors affecting the anterior horn of the spinal cord and causing neuromuscular imbalance may also be associated with the development of deformity [9]. The significantly higher rate of postoperative cervical instability or curvature deterioration of intramedullary tumors than extramedullary occupations in our group of cases may be related to this. The risk of postoperative cervical instability should be considered in all patients, especially in high-risk patients such as those with laminectomy ≥3, intramedullary lesions or simultaneous involvement of cervical 2 and cervical 7, and should be closely followed up postoperatively [9]. Intraoperatively, efforts should be made to limit the extent of laminectomy. Posterior ligaments such as the supraspinous and interspinous ligaments should be preserved as much as possible. the C2 spinous process, which is the main attachment point for the cervical extensors, should be preserved to prevent the development of flexion deformity [14]. Although there is a risk of postoperative instability, there is still controversy regarding prophylactic fusion fixation. Prophylactic fusion or internal fixation may be considered in cases of multisegmental decompression, and Sciubba et al. suggested that cervical fusion should be performed in the presence of spinal motor symptoms in laminectomies of ≥3 segments [11], and Simon found that prophylactic fusion significantly reduced postoperative deformity after laminectomy for intramedullary tumors in children [12]. Some authors have also concluded that fusion is not necessary in pediatric patients even if most deformities are present, and that prophylactic fusion is not recommended because immature spinal fusion is prone to failure and affects the use of MRI [9]. Moreover, fusion can cause decreased mobility, increased stress in adjacent segments, and increased degeneration. To reduce the occurrence of postoperative instability, many authors have proposed improvements to the surgical approach. Compared to laminectomy, laminoplasty may slow down or reduce the occurrence of deformities, especially in pediatric patients [4, 14]. However, laminoplasty, whether single- or double-opening, has limited exposure of the spinal canal. Laminotomy repositioning (or laminoplasty) provides sufficient exposure of the spinal canal to facilitate smooth surgery, while anatomically repositioning and fixing the lamina, spinous process, and corresponding ligaments after resection of the lesion has less biomechanical impact on the spine [15]. In contrast, for intradural extramedullary subdural and epidural lesions that are biased to one side, hemilaminectomy and its modified methods can minimize damage to the posterior structures and maintain the normal curvature and range of motion of the cervical spine [13]. Domestic scholars concluded clinically that hemilaminectomy has less impact on cervical spine stability, cervical curvature and mobility compared to conventional laminectomy [7]. The laminectomy procedure can lead to changes in the biomechanics of the cervical spine. The occurrence of postoperative instability or deformity should be noted in cases of ≥3 laminectomies, intramedullary occupancy or simultaneous involvement of cervical 2 and cervical 7. The maintenance of cervical stability with prophylactic fusion fixation and laminectomy repositioning needs further study.