Management of aggressive recurrent thoracic spine aneurysmal bone cyst in a 7-year-old male: A case report and review of the literature.

Background: Spinal aneurysmal bone cysts (ABCs) are rare, histologically benign tumors with aggressive behavior, which may cause bone and soft-tissue destruction, particularly affecting neural elements. Management of these tumors, including treatment modalities and follow-up protocols, remains challenging. Case Description: A 7-year-old boy presented with chest wall pain persisting for two months before admission, accompanied by progressive mono paresis lasting ten days before admission. Myelopathy signs were evident during the examination. Imaging confirmed a multicystic lesion at the T6 level involving the posterior elements of the vertebra, with significant cord compression. Due to deteriorating neurological function, he underwent urgent laminectomy and neural decompression, followed by subtotal tumor resection. Postoperative histopathological examination confirmed the diagnosis of an ABC, and the patient experienced significant neurological recovery. However, after 21 days, the patient was readmitted to the emergency department with severe paraparesis. Magnetic resonance imaging revealed rapid growth of the residual tumor, leading to cord compression. He underwent aggressive total tumor resection, T6 vertebral body corpectomy, and fixation with pedicle screws and cage insertion. Following the second surgery, prompt neurological recovery occurred. Conclusion: This rare case report emphasizes the importance of a close follow-up protocol for spinal ABCs in the pediatric population. It highlights the challenges in managing these tumors and the need for vigilant monitoring to detect and address rapid recurrences.

The Advantages of 4-rod Construct over the 2-rod Techniques in Adult Spinal Deformity Patients who Underwent Pedicle Subtraction Osteotomy: A Multicenter Retrospective Comparative Study.

OBJECTIVE: In this retrospective study we compared clinicoradiologic outcomes and complication profiles of the traditional 2-rod construct versus the 4-rod construct in patients with adult spinal deformity (ASD) who underwent pedicle subtraction osteotomy (PSO). METHODS: We performed a retrospective review of 208 ASD patients at 2 referral centers who underwent lumbar PSO and long fusion from thoracic to the pelvis. Two different techniques, including the 4-rod construct and the traditional 2-rod technique, were used at the PSO level. Clinicoradiologic outcomes and complication profiles of the patients were documented and compared statistically between the groups. RESULTS: The 4-rod construct was associated with statistically lower rates of rod fracture (44.8% vs. 26.4%, P < 0.01), pedicular screw loosening at the PSO level (25.3% vs. 14.0%, P = 0.04), and reoperation (49.4% vs. 33.9%, P = 0.02). Radiologically, the 4-rod construct was associated with higher degree of lumbar lordosis (LL) (-37.4°vs. -26.8°; P < 0.01) and improved pelvic tilt (PT) (-17.2° vs. -9.9°; P < 0.01) and sacral vertical axis (SVA) corrections (-211.5° vs. -192.2°; P = 0.04). Overall, the 4-rod construct was associated with improved quality of life (P = 0.04) and statistically lower Oswestry Disability Index score at 12 months postoperatively (P < 0.01). CONCLUSIONS: Our results showed that the 4-rod construct was associated with statistically lower rates of rod fracture and pedicular screw loosening at the osteotomy level, higher degree of LL correction and improved PT and SVA than the 2-rod technique. The 4-rod construct was also associated with improved quality of life and Oswestry Disability Index and lower complication profiles.

The quality of care index for low back pain: a systematic analysis of the global burden of disease study 1990-2017.

BACKGROUND: . Low back pain is one of the major causes of morbidity worldwide. Studies on low back pain quality of care are limited. This study aimed to evaluate the quality of care of low back pain worldwide and compare gender, age, and socioeconomic groups. METHODS: . This study used GBD data from 1990 to 2017 from the Institute for Health Metrics and Evaluation (IHME) website. Extracted data included low back pain incidence, prevalence, disability-adjusted life years (DALYs), and years lived with disability (YLDs). DALYs to prevalence ratio and prevalence to incidence ratio were calculated and used in the principal component analysis (PCA) to make a proxy of the quality-of-care index (QCI). Age groups, genders, and countries with different socioeconomic statuses regarding low back pain care quality from 1990 to 2017 were compared. RESULTS: The proxy of QCI showed a slight decrease from 36.44 in 1990 to 35.20 in 2017. High- and upper-middle-income countries showed a decrease in the quality of care from 43.17 to 41.57 and from 36.37 to 36.00, respectively, from 1990 to 2017. On the other hand, low and low-middle-income countries improved, from a proxy of QCI of 20.99 to 27.89 and 27.74 to 29.36, respectively. CONCLUSION: . Despite improvements in the quality of care for low back pain in low and lower-middle-income countries between 1990 and 2017, there is still a large gap between these countries and higher-income countries. Continued steps must be taken to reduce healthcare barriers in these countries.

Clinicoradiological Outcomes and Complication Profiles of Bilateral Dual Sacral-Alar-Iliac Screws versus Bilateral Single Sacral-Alar-Iliac Screws in Patients with Spinal Deformity Who Underwent Grade 3 or 4 Spinal Osteotomies: A Retrospective Comparative Study.

OBJECTIVE: To compare short-term clinical and radiological outcomes and complication profiles between bilateral dual sacral-2-alar-iliac (S2AI) screw and bilateral single S2AI screw fixation techniques in patients who underwent grade 3 or 4 spinal osteotomies. METHODS: A retrospective review of 83 patients treated with bilateral dual S2AI screws and 32 patients treated with bilateral single S2AI screws was conducted between 2018 and 2020 with a minimum 1-year follow-up. Clinical and radiological outcomes of patients and incidence of perioperative complications, including rod breakage, screw dislodgment, proximal junctional kyphosis, proximal junctional failure, need for reoperation, and systemic adverse effects, were collected and statistically compared between the groups. RESULTS: With a mean follow-up of 18.2 months, rod fracture (6.0% vs. 18.7%, P = 0.03), screw dislodgment (0 vs. 12.5%, P < 0.01), and S2AI screw loosening (1.2% vs. 18.7%, P < 0.01) were significantly lower in the dual S2AI screws group than in the single S2AI screws group. However, the reoperation rate was similar between the 2 groups (24.1% vs. 34.3%, P = 0.26). No significant differences in clinical and radiological outcomes as well as proximal junctional kyphosis (10.8% vs. 18.7%, P = 0.25) and proximal junctional failure (9.6% vs. 18.7%, P = 0.18) were identified between the 2 groups. CONCLUSIONS: The dual S2AI screw fixation technique showed more advantages over the single S2AI screw fixation technique with reduced incidence of screw dislodgment, rod fractures, and sacral-alar-iliac screw loosening.

Targeted drug delivery in pulmonary therapy based on adhesion and transmission of nanocarriers designed with a metal-organic framework.

With the recent increase in lung diseases, especially with the onset of the coronavirus pandemic, the design of a highly efficient and optimal targeted drug delivery system for the lungs is crucial in inhaler-based delivery systems. This study aimed to design a magnetic field-assisted targeted drug delivery system to the lungs using three types of metal-organic frameworks (MOFs) and nanoliposomes. The optimization of the system was based on three main parameters: the surface density of the nanocarriers' (NCs) adherence to each of the lung branches, the amount of drug transferred to each branch, and the toxicity based on the rate of nanocarrier delivery to the branches. The study investigated the effect of increasing the diameter of the drug carriers and the amount of drug loaded onto the NCs in improving drug delivery to targeted areas of the lung. Results showed that the presence of a magnetic field significantly increased the adhesion of NCs to the targeted branches. The application of a magnetic field and the type of drug carrier had a significant effect on drug delivery downstream of the lung and reduced drug toxicity. The study found that Fe3O4@UiO-66 (iron-oxide nanoparticle attached to the surface of UiO-66, a type of MOF) and Fe3O4@PAA/AuNCs/ZIF-8 carriers, (iron-oxide nanoparticle attached to a hybrid structure composed of three different materials: poly (acrylic acid) (PAA), gold nanoclusters (AuNCs), and zeolitic imidazolate framework-8 (ZIF-8)), had the greatest drug delivery rate in diameters above 200 nm and less than 200 nm, respectively.

Translation, cross-cultural adaptation and validation of the Persian version of selected PROMIS measures for use in lumbar canal stenosis patients.

BACKGROUND: The National Institutes of Health (NIH) developed a new measurement system called the Patient-Reported Outcomes Measurement Information System (PROMIS) which can be used for multiple health conditions. The 29-item short form (PROMIS-29) with seven domains was more often used by clinical researchers to measure the physical function, mood and sleeping status of patients with low back pain (LBP). Translation of the PROMIS into multiple languages and adaptation of its application in different cultural diversities can help to further standardize clinical research studies and make them comparable to each other. This study aimed to cross-culturally adapt the PROMIS-29 into Persian (P-PROMIS-29) and evaluate the construct validity and reliability of the translated questionnaire among patients with lumbar canal stenosis. MATERIALS AND METHODS: The translation was conducted by using the multilingual translation methodology guideline. Construct validity, internal consistency, and test-retest reliability at a two-week interval for the P-PROMIS-29 were calculated. Construct validity was assessed by calculating correlations between the P-PROMIS-29 with Oswestry Disability Index (ODI) and Roland-Morris results. RESULTS: The study sample included 70 participants with lumbar canal stenosis. Internal consistencies were moderate to good with Cronbach's alpha ranging from 0.2 to 0.94. The test-retest reliability evaluation was excellent with intraclass correlation coefficients (ICCs) ranging from 0.885 to 0.986. Construct validity of different domains of P-PROMIS-29 were moderate to good, with Pearson's correlation coefficient results ranging from 0.223 to 0.749. CONCLUSION: Our results showed that P-PROMIS-29 is a valid and reliable measurement tool for evaluation of patients with lumbar canal stenosis.

The Impact of Rigid Cervical Collars on Outcome of Patients Who Underwent Posterior Cervical Laminectomy and Fusion: A Retrospective Comparative Study.

STUDY DESIGN: Retrospective cohort study. PURPOSE: This study aimed to investigate the cervical collar impact on the functional outcomes of patients after posterior cervical laminectomy and lateral mass screw fixation (PCLF) surgery. OVERVIEW OF LITERATURE: The safety and possible benefits of implementing rigid cervical collars subsequent to PCLF are insufficiently investigated. METHODS: Patients who underwent PCLF and received postoperative cervical collars from 2018 to 2020 were included in this retrospective cohort study. Their data were compared with an age- and sex-matched group of subjects who did not receive collars after PCLF during the same period. Pain intensity (using the Visual Analog Scale), Neck Disability Index, and quality of life (using 36-item Short Form Health Survey) of the patients were compared at baseline, 1, 3, 6, and 12 months postoperatively. RESULTS: A total of 36 patients who received cervical collars after surgery and 40 controls were included. At baseline and 1-month follow-up, there were no differences in pain intensity, functional status, and quality of life between the groups. However, at 3 months postoperatively, the quality of life of the subjects with no orthosis was higher than those who received cervical collars (p =0.01). At 6- and 12-month follow-up, there were no differences between the groups in pain intensity, functional status, and quality of life. CONCLUSIONS: No difference in the pain intensity and functional status of patients who used cervical collars and controls was shown in our study. Patients who did not wear cervical collars had a higher quality of life during the 3-month postoperative evaluation. Future prospective, well-controlled studies with longer follow-ups are needed to further investigate the effects of cervical orthosis on the clinical outcome of patients after PCLF.

Effect of Topical Administration of Tranexamic Acid on Intraoperative and Postoperative Blood Loss during Posterior Cervical Laminectomy and Fusion Surgery: A Retrospective Study.

AIM: To assess the role of topical administration of tranexamic acid (TXA) on intraoperative and postoperative blood loss of patients undergoing posterior cervical laminectomy and lateral mass screw ?xation (PCLF) compared to a control group. MATERIAL AND METHODS: The data of 88 patients that underwent PCLF surgery, including 41 females and 47 males, were included in this retrospective study. Data elements including intraoperative blood loss (IBL), postoperative blood loss (PBL), amount of blood transfusion, surgical time, use of hemostatic agents, length of hospital stay, and time to return to work were extracted from medical records and compared between those who received topical TXA during surgery (irrigation of the surgical field with a solution of 3 g TXA in 100 ml normal saline) and an age- and sex-matched control group. RESULTS: There were 48 patients in the TXA group and 40 patients in the control group. There were no significant differences in the baseline measurements and the level of operation between the two groups. The results showed that IBL and PBL were significantly lower in the TXA group compared to the control group (p=0.03 and p < 0.01, respectively). There were no significant differences in the need for blood transfusion, surgical time, and hospital stay between the two groups (p > 0.05). Moreover, the use of hemostatic materials during surgery and the time to return to work were significantly lower in the topical TXA group (p=0.04 and p < 0.01, respectively). CONCLUSION: Topical TXA efficiently reduces intraoperative and postoperative bleeding in patients undergoing posterior cervical laminectomy and PCLF surgery. These results need further investigation in future studies to draw a definite conclusion.

Percutaneous iliosacral screw insertion with only outlet and inlet fluoroscopic view for unstable pelvic ring injuries: Clinical and radiological outcomes.

Background: Percutaneous iliosacral screw fixation in posterior pelvic ring fractures is challenging and commonly performed under fluoroscopy or navigation techniques. This study aimed to assess the safety and efficacy of percutaneous iliosacral screw implantation under fluoroscopy guidance with only inlet and outlet views. Methods: This retrospective study included 58 consecutive unstable posterior pelvic injury patients (36 sacral fractures and 22 sacroiliac joint disruptions) treated with percutaneous iliosacral screws between January 2015 and November 2019. Acceptable inlet radiographs show the anterior cortex of the S1 body superimposed on the S2 body. Acceptable outlet radiographs show the superior pubic symphysis at the level of the S2 foramen and visualize the S1 and S2 sacral foramina. In our technique, the screw was inserted at the inferior half of the outlet view and the posterior half of the inlet view. The time needed for screw insertion and the radiation exposure time was recorded. Intra and postoperative complications were documented. Postoperative computed tomography (CT) scans assessed screw position. Results: In total, 69 iliosacral screws were inserted in 58 patients. In postoperative CT scans, the screw position was assessed, 89.8% were in a secure position, and 10.2% had malposition. The mean operation time per screw was 21.18 min and the mean fluoroscopy time per screw was 112 s. There was no evidence of wound infection or iatrogenic neurovascular injury. No reoperation was performed. Conclusion: Percutaneous iliosacral screws can be placed using the only outlet and inlet fluoroscopic views with comparable radiological and clinical outcomes to the conventional method.

The Impact of Single-Level Anterior Cervical Discectomy and Fusion on Cervical Sagittal Parameters and Its Correlation With Pain and Functional Outcome of Patients With Neck Pain.

BACKGROUND: This study examines the changes in segmental and global cervical sagittal parameters after single-level anterior cervical discectomy and fusion (ACDF) in patients with cervical radiculopathy or myelopathy. We also investigate whether these changes have any relation with postoperative pain and functional outcome of the patients. METHODS: Sixty patients (37 females and 23 males) with a mean age of 45.9 ± 9.5 years who were candidates of single-level ACDF due to cervical myelopathy or radiculopathy participated in the study. At baseline, 1 month, and 6 months after ACDF, outcomes of the study including sagittal balance parameters, pain intensity, and Neck Disability Index (NDI) were measured among the patients. Intensity of pain and neck disability were measured using the visual analog scale (VAS) and validated version of NDI, respectively. Using a standard lateral cervical radiography, the Cobb angle for occiput-C2, C1-C2, and C2-C7 as well as operation-level angle (OA; Cobb's angle at the level of discopathy), the thoracic inlet angle, and C7 and T1 slope angles were measured. RESULTS: The intensity of pain and neck disability of patients improved significantly during the follow up of the study comparing with baseline measurements (P < .001). There was a significant correlation between the increase of C2-C7 angle, C1-C2 angle, and OA and improvement in neck pain and NDI at 1- and 6-month follow ups. CONCLUSIONS: We found that changes at C2-C7 angle, C1-C2 angle, and OA have positive significant correlation with clinical outcome including pain improvement and decrease of disability in patients who undergo ACDF. LEVEL OF EVIDENCE: 3. CLINICAL RELEVANCE: The results of this study might be beneficial in selection of cervical cages with appropriate size during ACDF surgery, as our findinds showed that larger cages could lead to better functional outcome in patients.

The Management and Outcomes of Coronavirus Disease 2019 Infection in a Series of Neurosurgical Patients.

BACKGROUND: The coronavirus disease 2019 (COVID-19) pandemic has impacted neurosurgical practice worldwide. In Iran, hospitals have halted their routine activities, and most hospital beds have been assigned to COVID-19 patients. Here, we share our experience with 10 neurosurgical cases with confirmed COVID-19. MATERIALS AND METHODS: From February 24, 2020 to April 20, 2020, we were able to obtain clinical data on ten neurosurgical patients with COVID-19 through a predefined electronic form. RESULTS: Of the 10 patients with COVID-19 on neurosurgical units, eight underwent surgical interventions. The age of the patients ranged from 21 to 75 years and 70% were males. The diagnosis of COVID-19 was based on chest imaging findings and reverse transcriptase-polymerase chain reaction for coronavirus and an infectious disease specialist and a pulmonologist confirmed the diagnoses. In two cases, there was a significant decrease in O2 saturation intraoperatively. Three patients in this series died during the assessment period. One death was due to respiratory failure induced by the coronavirus infection. The cause of death in other two patients was cardiovascular failure not related to COVID-19. CONCLUSIONS: We hope we can provide a reference for future studies and help develop a clearer understanding of neurosurgical practice and outcomes in patients with COVID-19. In the time of COVID-19 pandemic when dealing with neurosurgical emergencies, a conservative approach is recommended. Using committed personal protective equipment, short-time operating procedures or minimally invasive surgery must be considered in the management of emergent patients. Resuming elective surgeries need defining measures needed to ensure patients and health-care providers' safety. Reorganizing the health-care system for telemonitoring released patients can lessen hospital visits.

Surgical Management of Pediatric Cervical Angular Kyphosis with 540° Approach and Metacarpal Plate: A Case Report and Introduction of a Novel Technique.

Surgical decompression, deformity correction, and instrumentation of the upper cervical spine are challenging problems in cervical kyphosis, especially in infants and pediatrics. According to patients' age, surgical exposure is difficult and selecting the appropriate instrument for rigid fixation is crucial. In this article, we present a case of 2 years old with cervical angular kyphosis, which was approached posteriorly at first. Through posterior approach, C3-C5 laminectomy with complete excision of spinous process was performed. Then, the patient's position was changed to supine and C3-C5 corpectomies were performed anteriorly with a longitudinal incision, and the thecal sac was decompressed. A titanium cage with appropriate size and graft was placed after possible deformity correction conducted with head traction and neck extension. Anterior fixation was performed with two, 2-mm T-shaped metacarpal plates with two screws in C2 and four screws in C6. The patient's position was changed to prone again, and posterior fixation was done with two metacarpal plates located on lateral masses. We showed that a novel technique in correction and fixation of cervical kyphosis in pediatric is using metacarpal plates while they are fixed to lateral masses.

Surgical management of a thoracic extradural arachnoid cyst with communication to subarachnoid space through nerve root: a case report.

Spinal extradural cysts are uncommon and may cause cord and nerve root compression. The cysts usually appear in thoracic spine. We report a 29-year-old man with an extradural arachnoid cyst from T4 to T6. The cyst was communicated to the subarachnoid space through a fistula at the left T6 nerve root. To access the fistula, we had to unroof the foramen of left T6 nerve root which could lead to spinal instability. We decided to save the bony and soft tissue elements of the foramen at the mentioned thoracic spine level. Therefore, the cyst walls were excised and then the ostia of the cyst at the cystic side of the fistula was tightly closed.

Outcome of Posterior-Only Approach for Severe Rigid Scoliosis: A Retrospective Report.

BACKGROUND: The management of severe scoliosis may lead to significant complications, and adequate mobilization is a key step to achieve maximal correction, usually requiring extensive approaches. There is still no consensus on the management of these severe and rigid curves. In this study we evaluated the clinical and radiologic outcome of a posterior-only approach with multilevel asymmetric Ponte osteotomy with a minimum of 2 years' follow-up. METHODS: In this retrospective study, 23 patients with severe and rigid adolescent idiopathic scoliosis who underwent surgery with a single-staged posterior-only approach were included. The surgical procedures in these patients were excision of posterior ligaments and spinous process, partial laminectomy in caudal part of lamina, excision of the ligamentum flavum, facetectomies, and multilevel asymmetric posterior column osteotomies (Ponte) followed by instrumented fusion. Clinical records-including demographic data; operating time; hospitalization time; blood loss; number of segments instrumented, fused, and osteotomized; functional improvement; follow-up duration; and complications-were recorded. RESULTS: The mean preoperative Cobb angle of major curve in coronal plan was 97.5° (range, 82°-131°) with the mean flexibility of 21.4° (range, 10°-25°) on bending radiography. The mean immediate postoperative Cobb angle of major curve was 34.8° (range, 17°-61°), showing a 64.2% correction. The mean preoperative coronal and sagittal imbalances of 3.8 and 4.2 cm were improved to 1.0 and 1.3 cm at postoperative measurements, respectively. A mean of 6.1 (range, 5-9) vertebral segments were osteotomized. We experienced no major complications. CONCLUSIONS: We found that a posterior-only procedure in patients with severe and rigid adolescent idiopathic scoliosis could provide correction rate, coronal and sagittal balance, and clinical outcomes comparable with other procedures. Using this technique can eliminate the need for the anterior release, with the associated complications related to anterior surgery, in the treatment of severe rigid scoliosis.

Delayed Infection of Occipitocervical Fixation in a Patient with Achondroplasia: A Case Report and Review of Literature.

BACKGROUND: Infections are a major concern in fixation surgeries. Most of the infections could occur in the first three months after the operation. CASE REPORT: We present a 45-year-old man who known case of achondroplasia who underwent craniospinal fixation and was presented to our clinic with surgical site infection after six years. His instruments were removed, and a halo vest was fixed for the patients. Accordingly, he received intravenous antibiotics, and during nine months' follow-up, no any significant problems were found. CONCLUSION: Infection of instruments in spinal surgeries might be presented years after the surgery. Hence, it needs to be considered by surgeons in patients' follow-ups.

Dysphonia, Stridor, and Dysphagia Caused By Diffuse Idiopathic Skeletal Hyperostosis: Case Report and Review of Literature.

Diffuse idiopathic skeletal hyperostosis (DISH) also known as Forestier disease is a noninflammatory, systemic skeletal disease of unknown etiology. DISH is usually asymptomatic but may compress the posterior wall of the aero digestive tract and lead to dysphagia, globus, hoarseness, stridor, dyspnea, and neurological problems. Although dysphagia is not uncommon among the presenting symptoms of DISH but dysphonia and stridor are rarely reported. We report a 68-year-old man who presented with a history of progressive dysphagia over 1 year and recent dysphonia and stridor secondary to cervical osteophytes. We discuss the symptoms, radiological features, and management of this uncommon case of DISH in conjunction with review of literature.

Correction to: Comparison of cervical sagittal parameters among patients with neck pain and healthy controls: a comparative cross-sectional study.

Unfortunately, the affiliation of the second author (Jean Charles Le Huec) was incorrectly published in the original publication.

Comparison of cervical sagittal parameters among patients with neck pain and healthy controls: a comparative cross-sectional study.

INTRODUCTION: Previous studies have shown poor health-related outcomes among patients with spinal sagittal malalignment of the thoracolumbar or spinopelvic region, and less interest has been paid to the relationship between cervical sagittal balance and functional outcome of the patients. This study aims to compare the cervical sagittal parameters between patients with non-specific neck pain and asymptomatic controls. METHOD: Twenty-five patients (21 females/4 males) with non-specific neck pain and 25 age-, sex- and BMI-matched controls (18 females/7 males) participated in the study. Using a standard lateral cervical radiography, the Cobb angle between occiput-C2, C1-C2, C1-C7 and C2-C7 as well as the thoracic inlet angle (TIA) and C7 and T1 slope angles was measured. Also the spine cranial angle (SCA) and the C2-SVA (sacral vertical axis) and C1-SVA were measured. The primary outcome measure of the study was comparison of the sagittal balance variables between the patients and the healthy controls. Secondary outcome measures were correlation between pain intensity of the patients in neck pain group and their demographic and radiographic findings. Data analysis was performed using independent sample T test and Pearson's correlation for primary and secondary outcome measurements, respectively. RESULTS: There was no difference in cervical lordosis curvature (measured by C2-C7 and C1-C7 lordosis angle) between patients with non-specific NP and healthy controls (P value = 0.45 and 0.37, respectively). We found that T1 slope angle was significantly (P value = 0.02) lower in patients with neck pain. CONCLUSION: Our findings showed that the slope of the upper endplate of T1 vertebrae body (T1 slope) is significantly lower among patients with non-specific neck pain compared to controls. A compensatory mechanism to bring the center of head gravity back to the spinal axis might be the possible explanation for this difference. These slides can be retrieved under Electronic Supplementary Material.