An Unusual Chordoma of the Odontoid Process: A Case Report and Literature Review.

The aim of this study is to present a rare case of chordoma in the odontoid process in which the tumor involved the odontoid process and compressed the spinal cord at the craniocervical junction. We report on the effectiveness and successful outcome of anterior microscopic tumor resection combined with posterior occipitocervical fixation and review the current standard treatment. A 39-year-old man presented with sudden dyspnea and quadriparesis caused by an unknown tumor compression at C2. Radiographic examination revealed a large destructive mass at C2 and heterogeneous enhancement. The patient received urgent surgical intervention by microscopic-assisted anterior tumor resection and posterior spinal fixation from the occiput to the C5 level. The pathohistologic reports for cytokeratins, epithelial membrane antigen, and S-100 protein were positive. The final diagnosis was chordoma of the odontoid process. At the 2-year follow-up, the patient's condition had improved, and a postoperative MRI showed no indication of tumor regrowth. Chordoma of the odontoid process or C2 body is very rare. The current standard management is wide tumor resection to prevent recurrence. The combined approach of anterior tumor resection with microscopic assistance and posterior stabilization of the occiput to C5 is the optimal treatment for this condition.

An unusual presentation of thoracic diffuse idiopathic skeletal hyperostosis (DISH) and video-assisted thoracoscopic surgery (VATS).

INTRODUCTION AND IMPORTANCE: Diffuse idiopathic skeletal hyperostosis (DISH), also known as Forestier's disease and Forestier and Rotes-Querol disease, is a systemic condition characterized by calcification and ossification of ligaments and entheses which often mainly affects the thoracic spine. Anterior osteophyte compression of the esophagus resulting in dysphagia and dyspepsia is extremely rare in symptomatic thoracic DISH. CASE PRESENTATION: A 72-year-old male presented with dyspepsia and dysphagia for 10 months. A large beak-like anterior osteophyte, detected by a radiographic study and by a Barium esophagogram test at the T9-T10 level of the thoracic spine, was established by gastrointestinal medicine specialists to be the cause of the symptoms. The large anterior osteophyte was removed using video-assisted thoracoscopic surgery (VATS). At the one-year follow-up, the patient's symptoms had significantly improved and there was no recurrence of the osteophyte or the dyspepsia and dysphagia. CLINICAL DISCUSSION: Thoracic DISH rarely presents with dysphagia and dyspepsia due to the greater mobility of the esophagus in the area of the thoracic spine than in the area of the cervical spine. This is the first reported case of symptomatic thoracic DISH treated by anterior thoracic osteophytectomy with VATS. The treatment was effective with no post-operative complications. CONCLUSION: Anterior thoracic osteophytectomy with VATS is an effective surgical treatment option for this condition.

Surgeons' Perspective, Learning Curve, Motivation, and Obstacles of Full-Endoscopic Spine Surgery in Thailand: Results From A Nationwide Survey.

Objective: To report a nationwide survey of the endoscopic spine surgeons across Thailand. Furthermore, the survey will be focused on the perspective of experience, learning curve, motivations, and obstacles at the beginning of their practices. Materials and Methods: The online survey consisting of 16 items was distributed to spine surgeons who are performing endoscopic spine surgery in Thailand via the Google forms web-based questionnaire to investigate participants' demographics, backgrounds, experience in endoscopic spine surgery, motivations, obstacles, and future perspectives. The data was recorded from January 7, 2020 to January 21, 2022. Descriptive statistics were used for analysis. Results: A total of 42 surveys were submitted by 6 neurosurgeons (14.3%) and 36 orthopedic surgeons (85.7%). From the surgeons' perspective, the average number of cases that should be performed until one feels confident, consistently good outcomes, and has minimal complications was 27.44 ± 32.46 cases. For surgeons who starting the endoscopic spine practice, at least 3 workshop participation is needed. Personal interest (39 selected responses) and trending marketing or business purpose (25 selected responses) were the primary motivators for endoscopic spine surgery implementation. Lack of support (18 selected responses) and afraid of complications (16 selected responses) were pertinent obstacles to endoscopic spine surgery implementation. Conclusions: The trend of endoscopic spine surgery has continued to grow in Thailand, shown by the rate of implementation of endoscopic spine surgery reported by Thai spine surgeons. The number of appropriate cases until one feels confident was around 28 cases. The primary motivator and obstacles were personal interest and lack of support.

Anterior screw fixation for type II odontoid process fractures: A single-center experience with the double Herbert screw fixation technique (Retrospective cohort study).

BACKGROUND: In type II odontoid fractures with intact transverse ligament as classified by the Anderson and D'Alonzo system, anterior screw fixation offers the best anatomical and functional results. The goal of this study is to review the results of the double screw technique in anterior odontoid surgery using a headless 3.0-mm.-diameter cannulated Herbert screw on patients with odontoid process fractures. METHODS: From January 2015 through March 2019, 12 cases of acute traumatic type II odontoid fractures were treated with double anterior screw fixation using 3.0-mm Herbert screws, slightly smaller than the standard size for Caucasian populations. The data collected included radiographic measurements, postoperative complications, union rate and clinical outcomes in follow-up examinations over an average of 24-months. RESULTS: The age of the 12 patients, 8 males and 4 females, ranged from 17 to 68 years (mean, 38.42 ± 20.14). The fracture type was type IIa in 4 patients (33.33%) and type IIb in 8 patients (66.67%). The period of follow-up was 15-64 months (mean, 31.42 ± 17.37). All the patients had good clinical results after surgery with no postoperative complications. Eleven cases (92%) had achieved bone union with 1 case (8%) of nonunion. In the nonunion case, the patient was a chronic smoker who continued smoking both during treatment and follow-up. CONCLUSIONS: This series of satisfactory clinical results demonstrates that double anterior screw fixation of type II odontoid process fractures using 3.0-mm screws is highly effective in the Thai population. Headless cannulated cancellous screws provide significant biomechanical strength which is not inferior to the traditional screws.

Symptomatic retro-odontoid pseudotumor causing calcium pyrophosphate dihydrate deposition combined with multilevel cervical spondylotic myelopathy.

INTRODUCTION: Symptomatic retro-odontoid pseudotumor (ROP) caused by cervical compression and myelopathy is rare. Pathological diagnosis is recommended for differential diagnosis including the following: inflammatory disease, primary bone tumor, metastatic disease and calcium pyrophosphate dihydrate deposition (CPPD) also known as "crowned dens syndrome". The authors report a rare case of ROP caused by CPPD deposition combined with multilevel cervical spondylotic myelopathy (MCSM) which was treated by tumor resectioning using a transoral approach combined with posterior decompression and fusion. CASE PRESENTATION: A 66-year-old male presented with progressive neck pain and spastic gait with no history of trauma. Radiographic imaging revealed degenerative change involving the atlanto-axial and atlanto-occipital joints with calcified enhancing soft tissue around the odontoid process causing cord compression and cervical instability at the C1-C2 level combined with MCSM and spinal cord compression at C3 to C7. Microscopic assisted transoral tumor resection combined with posterior decompression and fusion was performed at the occiput to T2. The pathology report describes a rhomboid-shaped crystal caused by calcium pyrophosphate dihydrate deposition (CPPD) disease. At the 6-month follow-up following the operation, the patient's neck pain and spastic gait were improved compared to the preoperative examination. DISCUSSION: Cervical compression and myelopathy from ROP causing CPPD combined with MCSM is rare. Pathology diagnosis and surgical management are highly recommended. CONCLUSION: In this case, a combined surgical approach: tumor resection using a transoral approach and a posterior approach for decompression and fusion at occiput to T2 was an effective option for this condition.

A multilevel noncontiguous spinal fracture with cervical and thoracic spinal cord injury.

INTRODUCTION AND IMPORTANCE: A multi-level non-contiguous spinal fracture (MNSF) caused by a high-energy impact is a type of complex traumatic injury that is been frequently initially missed, and resulting in delayed diagnosis which adversely affects can result in spinal deformity and neurological deficit. This report describes the operative management of a patient with MNSF with spinal cord injury involving the cervical and thoracic vertebrae by cervical orthosis and posterior thoracic decompression and fusion. CASE PRESENTATION: An 18-year-old male presented with extensive neck pain and paraplegia (ASIA A), following a motor vehicle accident. Radiographic imaging revealed MNSF: a non-displaced spinous process fracture of C5 (AO Spine subaxial cervical injury classification A0) with spinal cord injury combined with fracture-dislocation of T5 to T9 (AO Spine thoracolumbar injury classification C3). Posterior thoracic decompression and fusion was performed at T3 to T8. After the patient underwent the thoracic spine and cervical orthosis treatment, He received rehabilitation program and training transfer with wheelchair without caregiver. His sitting and balance were significantly improved at the 6 months follow-up. Although the lower extremity functions (ASIA A) may not improve due to the severe spinal cord injury. CLINICAL DISCUSSION: MNSF with spinal cord injury following a high-velocity accident is an unstable and complex injury. Important of the clinical assessment and according to the injuries the treatment may vary. CONCLUSIONS: Cervical orthosis was alternative treatment to preserve cervical motion treatment and posterior thoracic decompression with fixation is an effective option for patients in this MNSF with spinal cord injury.

Preoperative halo-gravity traction for treatment of severe adult kyphosis and scoliosis.

STUDY DESIGN: Retrospective case series. OBJECTIVE: To assess the efficacy of preoperative halo-gravity traction (HGT) in the treatment for severe adult kyphosis and scoliosis. Preoperative HGT improves severe curve magnitude and clinical condition in pediatric spinal deformity. However, the efficacy of HGT on severe adult spinal deformity has rarely been studied. MATERIALS AND METHODS: This study included 18 patients with severe adult kyphosis and scoliosis (age ≥ 18) who underwent a preoperative HGT (mean 4 weeks), and subsequent definitive posterior-alone corrective fusion. Etiologies were neurofibromatosis (n = 5), adult idiopathic (n = 3), multiple vertebral fractures due to osteoporosis (n = 1) and multiple myeloma (n = 1), degenerative failed back syndrome (n = 1), Scheuermann kyphosis (n = 1), Marfan syndrome (n = 1), and other genetic and connective tissue disorders (n = 5). We reviewed baseline demographics, including coronal and sagittal radiographic profiles. The changes in major curve magnitude, pulmonary function tests (PFTs), and nutritional status were assessed between pre- and post-traction and immediate post-definitive corrective surgery. RESULTS: There were 11 male and 7 female patients, aged 18-69 years with their major coronal and sagittal curves being 92.0° ± 25.2° and 111.6° ± 40.1°, respectively. The major coronal and sagittal curves were reduced by 18.4% and 16.8% after halo-traction, and 54.7% and 44.2% after definitive fusion, respectively. PFTs showed significant increase in %FEV1 and %FVC when comparing pre- and post-traction [43.0% ± 17.4% vs. 49.6% ± 18.7%, and 44.8%. ± 16.7% vs. 54.3% ± 20.7%, respectively, p < 0.01 (n = 11)]. Effective weight gain was observed after traction (46.8 ± 14.5 vs. 49.3 ± 13.5 kg, p < 0.01). CONCLUSION: Halo-gravity traction (HGT) for severe coronal and sagittal plane spinal deformity in adult patients significantly reduced Cobb angles, improved PFTs, and allowed for effective weight gain in the preoperative period. The use of preoperative HGT is extremely beneficial to optimize the alignment and overall health of severe adult spinal deformity patients before their spinal reconstruction. LEVEL OF EVIDENCE: Level IV.

Reciprocal change of sagittal profile in unfused spinal segments and lower extremities after complex adult spinal deformity surgery including spinopelvic fixation: a full-body X-ray analysis.

BACKGROUND CONTEXT: Few studies have described reciprocal changes of pathologic compensatory mechanisms in the setting of spinopelvic fixation using full-body radiograph. PURPOSE: To elucidate how sagittal alignment of unfused spinal segments and lower extremities change reciprocally following complex thoracolumbar realignment surgery including fusion to the sacrum in adult spinal deformity. STUDY DESIGN: Retrospective cohort. PATIENT SAMPLE: Thirty-four patients who underwent fusion from lower thoracic to the sacrum/pelvis and 49 patients with fusion from upper thoracic to the sacrum/pelvis. OUTCOME MEASURES: The postoperative sagittal alignment change, and the correlation between the instrumented spinopelvic alignment change and reciprocal changes in unfused spinal segments/lower extremities. MATERIALS/METHODS: This study included 34 patients who underwent fusion from lower thoracic to the sacrum/pelvis (LT-P group) and 49 patients with fusion from upper thoracic to the sacrum/pelvis (UT-P group). The postoperative sagittal alignment changes were evaluated after subdividing the two groups according to T1 pelvic angle (TPA) (aligned group: TPA<20 and malaligned group: TPA>20). The correlation between the instrumented spinopelvic alignment change (ΔTPA and ΔLL), reciprocal changes in unfused spinal segments and lower extremities, and the cranial sagittal vertical axis-hip/ankle change (ΔCrSVA-Hip/Ankle) were also analyzed. RESULTS: At the baseline in both LT-P and UT-P groups, the patients in the malaligned subgroups showed greater C2-7 lordosis (C2-7L), sacrofemoral angle (SFA), and knee flexion angle (KA) than those in the aligned subgroups. At average 7.1 months postoperatively, these compensatory mechanisms were restored in accordance with instrumented TPA/LL change, especially in the UT-P group. The mid-thoracic alignment changed significantly kyphotic in the LT-P group. ΔTPA and ΔLL linearly correlated with ΔC2-7L, ΔKA, and ΔAA in the malaligned patients. The multivariate regression analysis revealed that change in lower extremity parameters (ΔSFA, ΔKA, and ΔAA) independently impacted ΔCrSVA-Hip/Ankle. CONCLUSION: Adequate thoracolumbar realignment surgery results in restoration of the pathologic compensatory mechanisms in the unfused spinal segments and lower extremities, especially in patients fused from upper thoracic spine. A preoperative clinical evaluation of the lower limb joints, as well as a full-body radiographic evaluation, is paramount to achieve optimal global sagittal balance in thoracolumbar realignment surgery.

Reciprocal Change in Sagittal Profiles After Adolescent Idiopathic Scoliosis Surgery With Segmental Pedicle Screw Construct: A Full-body X-ray Analysis.

STUDY DESIGN: Retrospective cohort. OBJECTIVE: This radiographic analysis using a full-body x-ray evaluated the ways in which the sagittal profiles of the unfused spinal segments, pelvic, and lower extremities spontaneously change after adolescent idiopathic scoliosis (AIS) surgery with segmental pedicle screw constructs. SUMMARY OF BACKGROUND DATA: Reciprocal lordotic changes in unfused spinal segments after corrective surgery for AIS have been reported. However, a full-body analysis has not been studied. METHODS: The sagittal profiles of 51 (age ≤18) patients with AIS undergoing corrective surgery with segmental pedicle screw constructs were investigated. Patients were divided into two groups: group T; selective thoracic fusion and group L; fusion to the low lumbar spine. They were further subcategorized according to preoperative thoracic kyphosis (TK: T5-12): hypokyphotic (TK <20°) and normohyperkyphotic (TK >20°) groups. The postoperative change in the sagittal parameters and the correlation between the instrumented thoracic alignment change (ΔT2-12) and reciprocal changes of unfused segments were analyzed. RESULTS: At baseline, the entire cohort had a relatively hypokyphotic thoracic spine (TK: 25.5°â€Š±â€Š13.7°), low T1 slope (13.6°â€Š±â€Š7.7°), and kyphotic cervical spine (C2-7 lordosis: 7.7°â€Š±â€Š13.1°). The lower extremities were in neutral alignment overall. Postoperatively, the cervical alignment changed significantly lordotic (average -13.4° increased lordosis) after the adequate preservation of TK (average 17.8° increased kyphosis) in the hypokyphotic group T. Linear correlations were observed between ΔT2-12 and spontaneous reciprocal changes in C2-7 lordosis, lumbar lordosis, and knee flexion angle in group T. CONCLUSION: The sagittal profiles of patients with AIS can significantly change after adequate restoration of TK which averaged 17.8°, particularly in the cervical spine. Lordotic reciprocal change in the cervical spine as well as increase in lumbar lordosis can occur in a linear correlation after adequate restoration of TK. There were no significant changes that occurred in the pelvis or lower extremities after AIS corrective surgery. LEVEL OF EVIDENCE: 4.

The Amount of Relative Curve Correction Is More Important Than Upper Instrumented Vertebra Selection for Ensuring Postoperative Shoulder Balance in Lenke Type 1 and Type 2 Adolescent Idiopathic Scoliosis.

STUDY DESIGN: Retrospective review of a prospectively collected multicenter database. OBJECTIVE: To assess how "overcorrection" of the main thoracic curve without control of the proximal curve increases the risk for shoulder imbalance in Lenke type 1 Adolescent Idiopathic Scoliosis (AIS). SUMMARY OF BACKGROUND DATA: Postop shoulder imbalance is a common complication following AIS surgery. It is thought that a more cephalad upper-instrumented vertebra (UIV) decreases the risk of shoulder imbalance in Lenke type 1 and 2 curves; however, this has not been proven. METHODS: Thirteen surgeons reviewed preop and 5-year postop clinical photos and PA radiographs of patients from a large multicenter database with Lenke type 1 and 2 AIS curves who were corrected with pedicle screw/rod constructs. Predictors of postop shoulder imbalance were identified by univariate analysis; multivariate analysis was done using the classification and regression tree method to identify independent drivers of shoulder imbalance. RESULTS: One hundred forty-five patients were reviewed. The UIV was T3-T5 in 87% of patients, with 8.9% instrumented up to T1 or T2. Fifty-two (36%) had shoulder imbalance at 5 years. On classification and regression tree analysis when the proximal thoracic (PT) Cobb angle was corrected more than 52%, 80% of the patients had balanced shoulders. Similarly, when the PT curve was corrected less than 52% and the main thoracic (MT) curve was corrected less than 54%, 87% were balanced. However, when the PT curve was corrected less than 52%, and the MT curve was corrected more than 54%, only 41% of patients had balanced shoulders (P = 0.05). This relationship was maintained regardless of the UIV level. CONCLUSION: In Lenke type 1 and 2 AIS curves, significant correction of the main thoracic curve (>54%) with simultaneous "under-correction" (<52%) of the upper thoracic curve resulted in shoulder height imbalance in 59% of patients, regardless of the UIV. This suggests the PT curve must be carefully scrutinized in order to optimize shoulder balance, especially when larger correction of the MT curve is performed. LEVEL OF EVIDENCE: 2.

Prevalence and Predictive Factors of Concurrent Cervical Spinal Cord Compression in Adult Spinal Deformity.

STUDY DESIGN: Retrospective cross-sectional cohort. OBJECTIVE: To investigate the prevalence and predictive factors of concurrent cervical spinal cord compression (CSCC) in patients with adult spinal deformity (ASD). SUMMARY OF BACKGROUND DATA: In patients with ASD undergoing major thoracolumbar realignment surgery, concurrent CSCC potentially increases the risk of progression of myelopathy or cervical cord injury due to various perioperative factors including poor intraoperative neck positioning and hypotension. However, the prevalence of CSCC in ASD patients has not been previously studied. METHODS: This study included ASD patients who were indicated for major thoracolumbar corrective surgery (>5 levels). The presence of CSCC was determined using the modified Cord Compression Index (Grades 0-3) based on the cervical magnetic resonance imaging (MRI). Significant CSCC was defined as Grade>2, and the distribution of compression level as well as the number of Grade>2 segments were investigated in each patient. A multivariate regression analysis was performed to identify the predictors of CSCC with variables being the patients' characteristics including radiographic sagittal alignment parameters. RESULTS: Of 121 patients with ASD, 41 patients (33.8%) demonstrated significant CSCC on MRI. Intramedullary T2 hyper-intensity (myelomalacia) was present in eight patients (6.6%). Thirty-five of 41 patients were asymptomatic or with myelopathy that is difficult to detect. Significant CSCC was most commonly observed at C4/5 level. Four patients (3.3%) underwent cervical decompression and fusion prior to thoracolumbar reconstruction. Multivariate regression analysis revealed old age, increased body mass index (BMI), and PI-LL mismatch independently predicted the CSCC grade. CONCLUSION: The prevalence of concurrent significant cervical cord compression in patients with ASD is relatively high at 33.8%. Preoperative evaluation of cervical MRI and examinations for signs/symptoms of myelopathy are essential for patients with (1) older age, (2) increased BMI, and (3) high PI-LL mismatch to avoid progressive myelopathy or cord injury during ASD surgery. LEVEL OF EVIDENCE: 4.

Inter-spinous process distance: a novel parameter predicting segmental lordosis during posterior cervical spine deformity surgery.

PURPOSE: To investigate the normative value of distance between the spinous processes (inter-spinous process distance, ISPD), correlations between patients' demographics and ISPD, and determine cutoff ISPD values that result in segmental lordosis in posterior cervical-thoracic arthrodesis with instrumentation. METHODS: We reviewed patients with visible lower cervical and cervicothoracic spinous processes (C5-T2) on dynamic X-rays. Radiographic measurements included segmental Cobb angles (S-Cobb) and ISPD, defined as the distance between midpoints of the spinous processes. Correlations between patient demographics and ISPD were evaluated. In addition, the cutoff ISPD values that predict segmental lordosis (S-Cobb < 0°) were determined using the receiver operating characteristics (ROC) curve and linear regression model. RESULTS: We evaluated a total of 153 films on 51 patients. The mean ISPDs in neutral position were 16.0, 20.7, 23.2, and 26.0 mm at C5/6, C6/7, C7/T1, and T1/T2, respectively There were no or only weak correlations between ISPD and age, race, height, body weight, and BMI. We observed significant difference between male and female ISPDs at C7/T1 and T1/T2 (P < 0.05). The ISPDs had moderate/strong correlations with S-Cobb at each segment (- 0.450 ≤ r ≤ - 0.705). Based on the ROC curves, the following cutoff values of ISPD provided 100% positive predictive value for segmental lordosis: < 10 mm at C5-6; < 15 mm at each level from C6 to T2. CONCLUSION: ISPD is a simple and useful parameter that correlates with the segmental Cobb angle. During posterior cervical deformity surgery, surgeons can intraoperatively predict adequate segmental lordosis by utilizing the vertebral level specific cutoff values of ISPD. These slides can be retrieved under Electronic Supplementary Material.

Natural History and Prognostic Factors of Cholangiocarcinoma With Spinal Metastasis: A 10-Year Single Center Study.

STUDY DESIGN: This is a retrospective analysis. OBJECTIVE: The aim of this study was to determine the epidemiology, survival, and prognostic factors for cholangiocarcinoma (CCA) with spinal metastasis. SUMMARY OF BACKGROUND DATA: CCA is an epithelial cell malignancy of the bile duct, and a frequent site for its metastasis is the spine. Many areas of Asia are endemic for CCAs. To date, there is limited data on the epidemiology, natural history, and prognostic factors of CCA with spinal metastasis, which is crucial for better management and treatment of the disease. MATERIALS AND METHODS: Patients diagnosed with CCA were recruited to our study, in order to identify cases with spinal metastasis. The survival rate was estimated by the Kaplan-Meier method. The univariate and multivariate analyses of tumor-specific and spinal metastatic factors were performed to identify the independent factors that affect survival. RESULTS: From 2006 to 2015, 4585 CCA patients were identified and 182 of these patients had spinal metastasis. The overall median survival of patients with spinal metastasis was 88 days. Serum carcinoembryonic antigen <5 ng/mL, carbohydrate antigen 19-9 <39 U/mL, albumin ≥3.5 g/L, and Frankel score D-E were found to be independent factors that resulted in better survival in a multivariate Cox regression analysis. CCA resection or spinal surgery did not prolong the survival of patients with spinal metastasis. CONCLUSION: Spinal surgery should be considered for CCA patients with spinal metastasis, who have a favorable prognosis, and are likely to live long enough to benefit from surgery. The aim is to palliate the symptoms and not as much to improve the survival.

Safety entry point, size and direction for placement of thoracic pedicle screw--a cadaveric study.

BACKGROUND: Understanding of the pedicle anatomy is necessary for pedicle screw placement; however, there have been few Thai studies reporting on thoracic pedicle morphometry. OBJECTIVE: To determine important anatomical measurements for thoracic pedicle screw fixation. MATERIAL AND METHOD: T1-T12 vertebral pedicles were evaluated in 27 cadavers. The diameter angle, length and entry point of the pedicle were measured. RESULTS: The transverse diameter was smaller than the sagittal diameter at all levels. The narrowest transverse diameter was at the T5 level in males and T4 level in females. The pedicle diameter in males was statistically significantly greater than in females at all levels except at the T12 level. Most pedicles with a transverse diameter of 5.0 mm or less were found at the T4, T5, T6 and T7 levels. The transverse angle was widest at the T1 level; it faced medially at all levels. The sagittal angle was widest at the T12 level andfaced cephaladly at all levels. The axis length was shortest at the T1 level. Most entry points were at the inferolateral zone. CONCLUSION: A 4-mm diameter screw should be used carefully at the mid-thoracic levels for Thai people, especially females. Screw lengths of less than 30 mm are safe for placement at all levels. The safe zone for the pedicle entry point is in the inferolateral zone.