The role of clivus and atlanto-occipital lateral mass height in basilar invagination with or without atlas occipitalization.

Basilar invagination (BI) is a common deformity. This study aimed to quantitatively evaluate the height of clivus and atlanto-occipital lateral mass (LM) in patients with BI with or without atlas occipitalization (AOZ). We evaluated 166 images of patients with BI and of controls. Seventy-one participants were control subjects (group A), 68 had BI with AOZ (group B), and 27 had BI without AOZ (group C). Parameters were defined and measured for comparisons across the groups. Multiple linear regression analysis was used to test the relationship between Chamberlain's line violation (CLV) and the clivus height ratio or atlanto-occipital LM height. Based on the degree of AOZ, the lateral masses in group B were classified as follows: segmentation, incomplete AOZ, complete AOZ. From groups A to C, there was a decreasing trend in the clivus height and clivus height ratio. There was a linear negative correlation between the clivus height ratio and CLV in the three groups. Generally, the atlanto-occipital LM height followed the order of group B < group C < group A. The atlanto-occipital LM height was included only in the equations of groups B. There were no cases of atlantoaxial dislocation (AAD) in group C. There was a decreasing trend in LM height from the segmentation type to the complete AOZ type in group B. BI can be divided into three categories: AOZ causes LM height loss; Clivus height loss; Both clivus and LM height loss. The clivus height ratio was found to play a decisive role in both controls and BI group, while the atlanto-occipital LM height loss caused by AOZ could be a secondary factor in patients with BI and AOZ. AOZ may be a necessary factor for AAD in patients with congenital BI. The degree of AOZ is associated with LM height in group B.

A screw algorithm for congenital C2-3 fusion with high-riding vertebral arteries: feasibilities and clinical outcomes of five different fixation techniques.

OBJECTIVE: To propose a screw algorithm and investigate the anatomical feasibilities and clinical outcomes of five distinct fixation methods for C2-3 fused vertebra with high-ridding vertebral arteries (VA) (HRVA) when the C2 pedicle screw placement is unfeasible. METHODS: Thirty surgical patients with congenital C2-3 fusion, HRVA, and atlantoaxial dislocation (AAD) were included. We designed a algorithm for alternative screw implantation into C2-3 fused vertebrae, including C2 pedicle screw with in-out-in (passing VA groove) technique (in-out-in screw), subfacetal screw, translaminar screw, lateral mass screw, C3 pedicle screw. VA diameter and position, C2 and C3 pedicles, superior facets, fused lamina, and fused lateral mass dimensions were evaluated for screw implantation indication. Implant failure, reduction loss, implant placement accuracy were investigated by computed tomography. RESULTS: A total of 5 VAs were identified as distant VAs; a total of 2 VAs were categorized as occlusive VAs. Sufficient dimension of lateral mass and lamina provided the broadest indications for screw implantation, while the distant or occlusive VA provided the most limited indications for in-out-in screw. The indications of five alternative methods ranged from narrowest to widest as follows: in-out-in screw, C3 pedicle screw, subfacetal screw, translaminar screw, lateral mass screw. The translaminar screws and the lateral mass screws increased the probability of implant failure. All patients who received in-out-in screws, C3 pedicle screws, and subfacetal screws achieved fusion. The accuracy ranged from lowest to highest as follows: C3 pedicle screw, lateral mass screw, in-out-in screw, subfacetal screw, translaminar screw. No translaminar screws deviated. CONCLUSIONS: The algorithm proved to be a valuable tool for screw selection in cases of C2-3 fused vertebrae with HRVAs. The subfacetal screw, boasting broad indications, a high fusion rate, and exceptional accuracy, stood as the primary preferred alternative.

Comparison of radiological and clinical outcomes of cervical laminoplasty versus lateral mass screw fixation in patients with ossification of the posterior longitudinal ligament.

PURPOSE: This study aimed to compare cervical sagittal parameters and clinical outcomes between patients undergoing cervical laminoplasty(CL) and those undergoing lateral mass screw fixation(LMS). METHODS: We retrospectively studied 67 patients with multilevel ossification of the posterior longitudinal ligament (OPLL) of the cervical spine who underwent lateral mass screw fixation (LMS = 36) and cervical laminoplasty (CL = 31). We analyzed cervical sagittal parameters (C2-7 sagittal vertical axis (C2-7 SVA), C0-2 Cobb angle, C2-7 Cobb angle, C7 slope (C7s), T1 slope (T1s), and spino-cranial angle (SCA)) and clinical outcomes (visual analog scale [VAS], neck disability index [NDI], Japanese Orthopaedic Association [JOA] scores, recovery rate (RR), and minimum clinically significant difference [MCID]). The cervical sagittal parameters at the last follow-up were analyzed by binary logistic regression. Finally, we analyzed the correlation between the cervical sagittal parameters and each clinical outcome at the last follow-up after surgery in both groups. RESULTS: At the follow-up after posterior decompression in both groups, the mean values of C2-C7 SVA, C7s, and T1s in the LMS group were more significant than those in the CL group (P ≤ 0.05). Compared with the preoperative period, C2-C7 SVA, T1s, and SCA gradually increased, and the C2-C7 Cobb angle gradually decreased after surgery (P < 0.05). The improvement in the JOA score and the recovery rate was similar between the two groups, while the improvement in the VAS-N score and NDI score was more significant in the CL group (P = 0.001; P = 0.043). More patients reached MCID in the CL group than in the LMS group (P = 0.036). Binary logistic regression analysis showed that SCA was independently associated with whether patients reached MCID at NDI postoperatively. SCA was positively correlated with cervical NDI and negatively correlated with cervical JOA score at postoperative follow-up in both groups (P < 0.05); C2-7 Cobb angle was negatively correlated with cervical JOA score at postoperative follow-up (P < 0.05). CONCLUSION: CL may be superior to LMS in treating cervical spondylotic myelopathy caused by OPLL. In addition, smaller cervical SCA after posterior decompression may suggest better postoperative outcomes.

Biportal endoscopy-assisted lateral mass screw fixation using a third portal.

BACKGROUND: The technique of spinal decompression under endoscopy has been widely applied, but reports on endoscopic cervical fixation are rare. The unilateral biportal endoscopic (UBE) technique stands out for its lesser muscle intrusion and more flexible surgical approach. METHOD: We applied the UBE approach for cervical fixation and laminectomy. We achieved bilateral lateral mass screw fixation by making an auxiliary UBE portal combined with the Roy-Camille and Magerl techniques. CONCLUSIONS: Our successful implementation of cervical fixation using the UBE technique at the C3/4 level suggests its efficacy. This approach is a valuable and minimally invasive option for cervical fixation.

Complications associated with subaxial placement of pedicle screws versus lateral mass screws in the cervical spine (C2-T1): systematic review and meta-analysis comprising 4,165 patients and 16,669 screws.

Lateral mass screw (LMS) and cervical pedicle screw (CPS) fixation are among the most popular techniques for posterior fusion of the cervical spine. Early research prioritized the LMS approach as the trajectory resulted in fewer neurovascular complications; however, with the incorporation of navigation assistance, the CPS approach should be re-evaluated. Our objective was to report the findings of a meta-analysis focused on comparing the LMS and CPS techniques in terms of rate of various complications with inclusion of all levels from C2 to T1. We conducted a systematic review of PubMed and EMBASE databases with final inclusion criteria focused on identifying studies that reported outcomes and complications for either the CPS or LMS technique. These studies were then pooled, and statistical analyses were performed from the cumulative data. A total of 60 studies comprising 4165 participants and 16,669 screws placed within the C2-T1 levels were identified. Within these studies, the LMS group had a significantly increased odds for lateral mass fractures (odds ratio [OR] = 43.2, 95% confidence interval [CI] = 2.62-711.42), additional cervical surgeries (OR = 5.56, 95%CI = 2.95-10.48), and surgical site infections (SSI) (OR = 5.47, 95%CI = 1.65-18.16). No other significant differences between groups in terms of complications were identified. Within the subgroup analysis of navigation versus non-navigation-guided CPS placement, no significant differences were identified for individual complications, although collectively significantly fewer complications occurred with navigation (OR = 5.29, 95%CI = 2.03-13.78). The CPS group had significantly fewer lateral mass fractures, cervical revision surgeries, and SSIs. Furthermore, navigation-assisted CPS placement was associated with a significant reduction in complications overall.

Minimally Invasive Posterior Cervical Fusion: A Handsome Option.

Cervical spondylosis is the leading cause of cervical myelopathy. When surgery is indicated, it is commonly addressed through an anterior or posterior cervical approach, such as cervical discectomy and fusion (ACDF) or laminectomy and fusion (LMF). Besides their own merits, each one has specific approach- or device-related complications, such as dysphagia, significant postoperative pain, wound infection, adjacent segment degeneration (ASD), and pseudoarthrosis. Through a tissue-sparing minimally invasive technique, posterior cervical fusion (PCF) has shown unfolding compelling evidence of biomechanical stability, good clinical outcomes, and high fusion rates, with fewer complications and better econometrics. On the basis of our own experience, we discuss here the indications, advantages, and drawbacks of minimally invasive PCF.

Nuance in Craniovertebral Junction Surgical Approach for Posterior C1-C2 Harms Stabilization: "Window Transposition" of the External Vertebral Venous Plexus for Bloodless C1 Lateral Mass Screw Insertion: Anatomical Aspects and Technical Notes.

Atlas and axis instrumentation may be necessary in cases of several craniocervical junction pathologies. According to the Harms technique, C1-C2 polyaxial screws are inserted respectively in the C1 lateral masses and in C2 pedicles. C1 lateral mass screw insertion requires the careful subperiosteal dissection of the posterior elements of C1, the identification of the screw entry point by the downward distraction of C2 nerve root, and the cautious sparing of the overlying posterior external vertebral venous plexus (peVVP), whose bleeding, obstructing the surgical field, is sometimes barely controlled by hemostatic agents and swabbing. The authors describe in detail the anatomical aspects of an alternative surgical technique developed for the microsurgical transposition of the C1-C2 interposed external vertebral venous plexus in the case of Harms C1-C2 screw stabilization. The longitudinal median incision of the atlantoaxial membrane, followed by bilateral subperiosteal dissection and microsurgical section respectively at the inferior borders of the C1 laminae and at the superior borders of the C2 laminae, allows, as a "window opening," the symmetrical mediolateral transposition of the peVVP. This procedure provides a faster and cleaner anatomical exposition of the posterior surface of the C1 lateral mass and the C2 isthmus, preventing troublesome intraoperative venous bleeding that hinders C1 lateral mass screw insertion.

Strategies to avoid internal carotid artery injury in "sandwich" atlantoaxial dislocation patients during surgery.

PURPOSE: To elucidate the anatomic relationship between the internal carotid artery (ICA) and the bony structures of the craniovertebral junction among "sandwich" atlantoaxial dislocation (AAD) patients, and to analyze the risks of injury during surgical procedures. METHODS: The distance from the medial wall of ICA to the midsagittal plane (D1), the shortest distance between the ICA wall and the anterior cortex of the lateral mass of atlas (LMA) (D2) on the most caudal and cranial levels of LMA and the angle (A) between the sagittal plane passing through the screw entry point of C1 lateral mass(C1LM) screw and the medial tangent line of the vessel passing through the entry point were measured. Besides, the location of ICA in front of the atlantoaxial vertebra was divided into 4 categories (Z1-Z4). RESULTS: There was a statistically difference between the male and female patients regarding D1, and the difference between D2 at level a and level b as well as angle A between the left and right sides were statistically different (p < 0.05). Ninety-two ICAs (57.5%) were anteriorly located in Z3, 50 (31.3%) were located in Z4, 17 were located in Z2, and only one ICA was located in Z1 in all 80 patients. CONCLUSIONS: In "sandwich" AAD patients, particular attention should be paid to excessively medialized ICA to avoid ICA injury during trans-oral procedures, and the risk of injuring the ICA with more cranially and medially angulated C1LM screw placement was relatively less during posterior fixation procedures. A novel classification of ICA location was used to describe the relationship between ICA and LMA.

Reconstruction of C1 lateral mass with an expandable cage in addition to vertebral artery preservation: presenting two cases.

PURPOSE: C1 lateral mass reconstruction is recommended, in cases of instability caused by tumor involvement or extensive C1 lateral mass resection. However, because of the anatomical complexity of the area and, most importantly, the proximity to vertebral arteries, few cases of reconstruction have been reported to date. The purpose of this report is to present technical details of C1 lateral mass reconstruction in conjunction with vertebral artery preservation from a posterior approach. METHODS: Two cases of one stage craniovertebral junction instrumentation and C1 lateral mass reconstruction in conjunction with vertebral artery preservation from a posterior approach are presented. RESULTS: In both cases of extensive resection of lateral mass due to tumor involvement, an expandable cage was used for C1 lateral mass reconstruction, which has been used only in one patient in literature. Complementary pathological examinations of the two cases indicated two rare tumors that had been reported in the upper cervical region so far. The first case became an unknown origin metastatic cancer and the second was reported to be a primary non- Hodgkin lymphoma. CONCLUSIONS: C1 lateral mass reconstruction with an expandable cage together with VA preservation is recommended in cases of extensive C1 lateral mass resection to increase the total strength and to shorten the length of the posterior device and probably better fusion. The expandable cage is preferred because of safer placement under compression instead of the lateral mass.

Complications associated with subaxial placement of pedicle screws versus lateral mass screws in the cervical spine: systematic review and meta-analysis comprising 1768 patients and 8636 screws.

Lateral mass screw (LMS) fixation for the treatment of subaxial cervical spine instability or deformity has been traditionally associated with few neurovascular complications. However, cervical pedicle screw (CPS) fixation has recently increased in popularity, especially with navigation assistance, because of the higher pullout strength of the pedicle screws. To their knowledge, the authors conducted the first meta-analysis comparing the complication rates during and/or after CPS and LMS placement for different pathologies causing cervical spine instability. A systematic literature search of PubMed and Embase from inception to January 12, 2021 was performed to identify studies reporting CPS and/or LMS-related complications. Complications were categorized into intraoperative and early postoperative (within 30 days of surgery) and late postoperative (after 30 days from surgery) complications. All studies that met the prespecified inclusion criteria were pooled and cumulatively analyzed. A total of 24 studies were conducted during the time frame of the search and comprising 1768 participants and 8636 subaxially placed screws met the inclusion criteria. The CPS group experienced significantly more postoperative C5 palsy (odds ratio [OR] = 3.48, 95% confidence interval [CI] = 1.27-9.53, p < 0.05). Otherwise, there were no significant differences between the LMS and CPS groups. There were no significant differences between the CPS and LMS groups in terms of neurovascular procedure-related complications other than significantly more C5 palsy in the CPS group.

Suitability of 3.5-mm screw for the atlas in children: a retrospective computed tomography analysis.

BACKGROUND: The growth and development of the atlas in children has not been studied to date using a large sample size. OBJECTIVE: To study whether a 3.5-mm screw is suitable for the atlas in children, to explore the anatomical size and development of the atlas in 0-14-year-old children, and to provide morphological basis for lateral mass screw internal fixation. METHODS: A Computed Tomography (CT) morphometric analysis was performed on 420 pediatric atlases. In the atlas, D1, D2, D3, D4, and α of the atlas lateral mass were measured. Statistical analysis was performed using one-way ANOVA and Students' t test. The least square method was used for the regression analysis of the change trend in anatomical structure. The curve with the greatest goodness of fit was used as the anatomic trend regression curve. RESULTS: D1, D2, D3, and D4 generally showed an increasing trend with age. The ranges of averages of D1, D2, D3, D4, and α in 0-14 year-old children were as follows: 4.576-9.202 mm, 9.560-25.100 mm, 3.414-10.554 mm, 11.150-27.895, and 12.41°-20.97°, respectively. The trends of the fitting curves of L1 and L3 were power functions, and those of L2 and L4 were logarithmic curves. CONCLUSIONS: CT examination could help in preoperative decision-making, and 3.5-mm screw was found to be suitable for lateral mass screw internal fixation in children aging 2 years and older. D1-D4 increased with age. This provided a certain reference to perform posterior atlantoaxial fusion in children and is of great significance to design posterior atlantoaxial screw in children.

Atlas (C1) lateral mass screw placement using the intersection between lateral mass and inferomedial edge of the posterior arch: a cadaveric study.

PURPOSE: To compare the Atlas (C1) lateral mass screw placement between screw trajectories of 0° and 15° medial angulation while using the intersection between lateral mass and inferomedial edge of the posterior arch. METHODS: Forty-eight Atlas lateral masses were prepared and divided into 2 groups: Group 1; screws inserted at 3 mm lateral to the reference point with screw trajectory of 0° angulation(N = 24) and Group 2; those inserted with screw trajectory of 15° medial angulation(N = 24). We evaluated the atlas anatomy, screw purchase and the presence of any breaches using CT scan. RESULTS: The radiographic parameters for Groups 1 and 2 were found statistically different (p-value < 0.05): bilateral intraosseous screw lengths (17.92 ± 1.47 mm. vs. 20.71 ± 2.4 mm.), bilateral screw length (29.92 ± 1.72 mm. vs. 33.13 ± 1.78 mm.), left screw medial angulation (x°) (0.67° ± 0.78° vs.14.17° ± 3.51°), right screw medial angulation (y°) (0.83° ± 1.03° vs.14.25° ± 2.53°) and bilateral screw medial angulation (0.75° ± 0.9° vs. 14.21° ± 2.99°). Twenty-two screws (91.67%) using the 0° medial angulation and nineteen screws (79.17%) using the 15° medial angulation had no cortical violations (Grade 0). However, two screws (8.33%) with 0° medial angulation and five screws (20.83%) with 15° medial angulation had breach less than 2 mm (Grade 1). There were no screws with breach between 2 and 4 mm (Grade 2) or greater than 4 mm. (Grade 3). CONCLUSION: A starting point of 3-mm lateral to the intersection between lateral mass and inferomedial edge of the Atlas posterior arch can be safely and effectively used to insert C1 lateral mass using both 0° and 15° medial angulation.

Unilateral biportal endoscopic laminectomy with lateral mass screw fixation for treating cervical spinal stenosis.

BACKGROUND: The unilateral biportal endoscopic (UBE) technique is less invasive and has a faster recovery time than open surgery. Compared with the uniportal technique, the biportal technique has a larger field of vision and a wider operation range. METHOD: We attempted the posterior UBE approach for cervical stenosis at the C4-C6 levels. UBE decompression of C4-C6 with unilateral lateral mass screw fixation at the C4-C5 levels was performed under general anesthesia. CONCLUSIONS: We successfully performed cord decompression at the C4-C6 levels using the UBE technique. This approach could be used as an alternative method to treat cervical stenosis with instability.

Innovative C-Arm-Free Navigation Technique for Posterior Spinal Fixation for Atlantoaxial Subluxation: A Technical Note.

Study design: Technical note. Objectives: To present a novel C-arm-free technique guided by navigation to insert and place a C1 lateral mass screw. Background and Objectives: Atlantoaxial subluxation (AAS) is a relatively common sequelae in patients with rheumatoid arthritis (RA) and upper cervical trauma. If they present with severe symptoms, surgical intervention such as posterior fusion is indicated. The established treatment for AAS is fixation with a C1 lateral mass screw and C2 pedicle screw (modified Goel technique) to achieve bony fusion. However, this technique requires fluoroscopy for C1 screw insertion. To avoid exposing the operating team to radiation, we present here a novel C-arm-free C1 lateral mass screw insertion technique for AAS. Materials and Methods: A 67-year-old man was referred to our hospital with neck pain, quadriparesis, and clumsiness and numbness of both upper and lower limbs. He had undergone C3-6 posterior fusion previously in another hospital. In physical examination, he had severe muscle weakness of bilateral upper limbs and hypoesthesia of all four limbs. He had hyper-reflexia of bilateral lower limbs and pollakiuria. His Japanese orthopedic score was 8 points out of 17. Preoperative radiograms showed AAS with an atlantodental interval (ADI) of 7 mm. MRI indicated retro-odontoid pseudotumor and severe spinal cord compression at the C1-2 level. The patient underwent posterior atlantoaxial fixation under navigation guidance. To prevent epidural bleeding during the insertion and placement of a C1 lateral mass screw, we have here defined a novel screw insertion technique. Results: The surgical time was clocked as 127 min and blood loss was 100 mL. There were no complications per-operatively or in the postoperative period. The patient showed almost full recovery (JOA 16/17) at two months follow-up and a solid bony fusion was noticed in the radiograms at one year follow-up. Conclusions: This novel surgical procedure and C1 lateral mas screw placement technique is a practical and safe method in recent advances of AAS treatment. Procedurally, the technique helps prevent epidural bleeding from the screw entry point and also allows for proper C1 screw insertion under navigation guidance without exposing surgeons and staff to the risk of fluoroscopic radiation.

Surgical challenges in posterior cervicothoracic junction instrumentation.

The cervicothoracic junction (CTJ) is a region of the spine submitted to significant mechanical stress. The peculiar anatomical and biomechanical characteristics make posterior surgical stabilization of this area particularly challenging. We present and discuss our surgical series highlighting the specific surgical challenges provided by this region of the spine. We have analyzed and reported retrospective data from patients who underwent a posterior cervicothoracic instrumentation between 2011 and 2019 at the Neurosurgical Department of the Geneva University Hospitals. We have discussed C7 and Th1 instrumentation techniques, rods design, extension of constructs, and spinal navigation. Thirty-six patients were enrolled. We have preferentially used lateral mass (LM) screws in the subaxial spine and pedicle screws (PS) in C7, Th1, and upper thoracic spine. We have found no superiority of 3D navigation techniques over 2D fluoroscopy guidance in PS placement accuracy, probably due to the relatively small case series. Surgical site infection was the most frequent complication, significantly associated with tumor as diagnosis. When technically feasible, PS represent the technique of choice for C7 and Th1 instrumentation although other safe techniques are available. Different rod constructs are described although significant differences in biomechanical stability still need to be clarified. Spinal navigation should be used whenever available even though 2D fluoroscopy is still a safe option. Posterior instrumentation of the CTJ is a challenging procedure, but with correct surgical planning and technique, it is safe and effective.

Correlation between different instrumentation variants and the degree of destabilization in treating cervical spondylotic spinal canal stenosis by unilateral hemilaminectomy with bilateral decompression: a biomechanical investigation.

PURPOSE: Unilateral hemilaminectomy with bilateral decompression (BDZ) was proposed as an alternative decompressive procedure in cervical spondylotic myelopathy (CSM). Despite promising clinical results, the destabilizing effect is yet unknown. We therefore performed a biomechanical study to investigate whether lateral mass screw fixation should follow BDZ. METHODS: Six human C2-C7 cervical specimens were tested under various conditions: native, unilateral hemilaminectomy with bilateral decompression without/with fixation (BDZ/BDF), unilateral hemilaminectomy with bilateral decompression and unilateral foraminotomy without/with fixation (UFZ/UFF), unilateral hemilaminectomy with bilateral decompression and bilateral foraminotomy without/with fixation (BFZ/BFF), and laminectomy without/with fixation (LAZ/LAF). Instrumention was applied from C3-C6. For each condition, the three-dimensional kinematics of the cervical specimen were measured in three main loading directions with an ultrasonic motion analysis system. ANOVA was used to determine differences between the specific segment conditions to assess the parameter's range of motion (ROM) and neutral zone (NZ). RESULTS: For flexion-extension, lateral bending and axial rotation, ROM of BDZ, UFZ, BFZ and LAZ remained at the level of the native condition (p > 0.74), whereas fixation reduced ROM significantly (p < 0.01). Between BDF, UFF, BFF and LAF, no significant differences in reduction in ROM were seen (p > 0.49). Results for NZ were equivalent to ROM in flexion-extension and lateral bending. For axial rotation, NZ remained almost constant on the native level for all tested conditions. CONCLUSION: Bilateral decompression via a hemilaminectomy, even if combined with foraminotomy, could be a less invasive treatment option for multilevel CSM in patients with lordotic cervical alignment and absence of segmental instability.

A novel surgical protocol for safe and accurate placement of C1 lateral mass screws in patients with atlas assimilation, basilar invagination and atlantoaxial instability: technical details, accuracy assessment and perioperative complications.

PURPOSE: To introduce a novel surgical protocol for safe and accurate placement of C1 lateral mass screws in patients with atlas assimilation, basilar invagination and atlantoaxial instability, and to categorize the screw accuracy and perioperative complications regarding this technique in a large case series. METHODS: Between January 2015 and January 2020, patients who had atlas assimilation, basilar invagination and atlantoaxial instability, and underwent atlantoaxial fixation using C1 lateral mass screws were reviewed. C1 lateral mass screws were placed with a novel surgical protocol following a series key steps, including posterior para-odontoid ligament release, panoramic exposure of the invaginated lateral mass, and diligent protection of the abnormal VA. Screw accuracy and related complications were specifically evaluated. RESULTS: A total of 434 C1 lateral mass screws were placed. Fifteen screws (3.5%) were classified as unacceptable, 54 screws (12.4%) were classified as acceptable, and 365 screws (84.1%) were classified as ideal. Overall, 96.5% of screws were deemed safe. There were no cases of vascular injury or permanent neurological defects. One patient with an unacceptable screw presented with hypoglossal nerve paralysis and recovered after an immediate revision surgery. Thirty-seven patients complained about occipital neuralgia and were successfully managed with medication. CONCLUSION: Placement of C1 lateral mass screws in patients with atlas assimilation, basilar invagination and atlantoaxial instability following this surgical protocol is safe and accurate. Thorough para-odontoid ligamental release, wide exposure of the invaginated lateral mass, and diligent protection of the vertebral artery are critical to maximize the chances of successful screw placement.

Cervical decompressive laminectomy and lateral mass screw-rod arthrodesis: surgical experience and analytical review of 4120 consecutive screws.

BACKGROUND: Cervical decompressive laminectomy with lateral mass arthrodesis is a common neurosurgical procedure used to address a variety of cervical spine pathologies. PURPOSE: This study aimed to determine the safety and efficacy of this neurosurgical procedure using the Anderson-Sekhon technique for screw trajectory. METHODS: The study retrospectively reviewed all clinical and radiological indicators for patients who underwent lateral mass arthrodesis between December 2005 and December 2017. All patients underwent polyaxial screw-rod implants using the Anderson-Sekhon technique for screw trajectory. It additionally reported all intra- and post-operative complications, along with short- and long-term outcomes for these patients. The follow-up period ranged from 2 months to 10 years. RESULTS: The study evaluated 695 patients who received a total of 4120 lateral mass screws. This is considered the largest reported case series up to date. No patients had neuro-vascular injuries. The main complications included 51 (7.3%) cases of screw malposition, as when the screw had breached either of foramen transversarium, neural foramen, or the facet joint; 39 (5.6%) cases of lateral mass breakdown; 29 (4.2%) cases of C5 root pain which has subsided overtime; 22 (3.2%) of incidental durotomy; and 18 (2.6%) cases of postoperative wound infection. There were only 3 cases of screw pullout leading to a stability rate of 99.5%. Most cases demonstrated very good to excellent outcomes on both short- and long-term follow-up. CONCLUSIONS: Cervical decompressive laminectomy with lateral mass arthrodesis is a safe and effective technique for the management of different cervical spine pathologies, which results in favourable short- and long-term outcomes.

The internal carotid artery and the atlas: anatomical relationship and implications for C1 lateral mass fixation.

PURPOSE: The internal carotid artery (ICA) is potentially at risk during posterior fixation of C1. In this study, we performed a CT-based anatomical analysis of the relationship between the internal carotid artery and the lateral mass of the atlas. METHODS: We analysed 30 CT angiography of the cervical spine, and we measured on both sides the distance of the carotid artery from the midline, distance of the ICA from the anterior cortex of C1 and from the ideal C1 screw entry point. We measured the angle between the sagittal plane passing through the entry point and the tangent line of the vessel. Separated statistical analysis between left and right sides, between male and female patients, and differentiation by age were also performed. RESULTS: Sixty ICAs were studied. The mean distance of the ICA from the midline was 23.3 ± 4.3 mm, with a minimum of 15 mm. The distance between the ICA and the anterior cortical layer of C1 was 4.8 ± 2.7 mm, with a minimum of 1.1 mm. The distance between the screw entry point and the arterial wall was 22.6 ± 2.8 mm, with a minimum of 17.5 mm. The mean angle was 10.4°, with a minimum of 11°. CONCLUSIONS: Although rare, intraoperative lesion of the ICA is reported and the spine surgeon must be aware of this risk. Careful preoperative planning is mandatory and the position of the ICA in relation to C1 must be assessed. The anatomical parameters presented in this paper can be useful to reduce the risk of ICA injury.

Instrumentation of C1 lateral mass via insertion of the posterior arch of atlas - a morphometric study.

INTRODUCTION: Instrumentation of the lateral mass of atlas via posterior arch attachment (PALMS) is a method that, unlike the traditional direct screw insertion into the lateral mass, prevents damage to the periarticular venous plexus and C2 nerve root. The method itself may be, however, limited by the anatomical situation. The small cranio-caudal pedicle dimension may lead to vertebral artery damage. The aim of this study was to use morphometric examination of CT findings from the healthy population to evaluate theoretical feasibility of this technique in a randomly selected population sample. METHODS: Morphometric measurements determining dimensions of C1 pedicle at the site of expected screw insertion were performed on reformatted parasagittal CT scans of 42 healthy probands. Using the software of the Jivex browser, we measured the minimum height of posterior arch insertion under the vertebral artery groove and evaluated the possibility of introducing 3.5 mm and 4 mm screws. RESULTS: The mean minimum height of the critical segment was calculated as 4.29 mm (left insertion 4.28 mm, right insertion 4.31 mm, range 3.02-5.62 mm). Despite the highest size in a female and the lowest in a male, the male population showed larger bone stock (mean of 4.71 mm: left connection 4.70 mm, right connection 4.71 mm) than the female one (mean of 4.29 mm: left 4.28 mm, right 4.31 mm). Overall, we found 59.5% insertions higher than 4 mm and 86.9% arch connections bigger than 3.5 mm. CONCLUSION: The anatomical situation allows inserting at least a 3.5mm diameter screw in a vast majority of cases. The posterior arch attachment point thus seems to be a suitable anatomical target for instrumentation of C1 lateral mass. Nevertheless, individual presurgical planning and intraoperative spinal navigation should be implemented, as well.