Morphometric study and anatomical variation with its incidence of foramina transversaria on the lower cervical vertebrae / Estudio morfométrico y variación anatómica con la incidencia de forámenes transversos en las vértebras cervicales inferiores

SUMMARY: Anatomical variation of the foramina transversaria (FT) is associated with vertebral neurovascular symptoms and can cause complications after lower spine surgery, especially cervical pedicle screw (CPS) insertion. FT variation has been documented and classified in various populations, as this information can help increase cervical stability in subaxial vertebral surgery. Although the morphometry of the upper cervical spine in Thai populations has been reported, there have yet been no studies examining the features of FT. The FT of dried cervical spines (C3-C7; left and right side; n = 107, male = 53 and female = 54) were examined for morphological variation, and their anteroposterior (AP) and transverse (T) diameters were measured using a digital vernier caliper. Morphometric data and variations were compared by sex and lateral side. It was that the C3-C6 FT in both sexes were round, and the C7 FT was elliptical with an oblique right side. FT diameters did not differ significantly by sex except for the AP diameters of C6-C7 and for T diameters of C4 and C7. The left AP diameters of C3-C6 were significantly longer than the right, as were the T diameters of C4 and C7 FT. Additionally, T diameter was significantly longer than that of the AP, except that of the left C6 in male spines, which did not differ from the AP. Most FT examined were round. These findings should be considered in the provisional diagnosis of vertebral neurovascular symptoms caused by FT variation as well as that of neurovascular damage after cervical pedicle screw placement.

La variación anatómica del foramen transverso (FT) se asocia con síntomas neurovasculares vertebrales y puede causar complicaciones después de la cirugía de columna cervical inferior, especialmente la inserción de tornillos pediculares cervicales (TPC). La variación del FT se ha documentado y clasificado en varias poblaciones, ya que esta información puede ayudar a aumentar la estabilidad cervical en la cirugía vertebral subaxial. Aunque se ha informado sobre la morfometría de la columna cervical superior en poblaciones tailandesas, aún no se han realizado estudios que examinen las características de FT. Se examinó la variación morfológica del FT de vértebras cervicales secas (C3-C7; lado izquierdo y derecho; n = 107, hombres = 53 y mujeres = 54), y se midieron sus diámetros anteroposterior (AP) y transverso (T) usando un pie de metro digital. Se compararon datos morfométricos y variaciones por sexo y lado. Los FT de C3-a C6 en ambos sexos eran redondos, y el FT C7 era elíptico con el lado derecho oblicuo. Los diámetros del FT no difirieron significativamente por sexo excepto para los diámetros AP de C6- C7 y para los diámetros transversos de C4 y C7. Los diámetros AP izquierdos de C3-C6 eran significativamente más largos que los del lado derecho, al igual que los diámetros transversos de C4 y C7. Además, el diámetro transverso fue significativamente mayor que el AP, excepto el C6 izquierdo en las vértebras de hombres, que no difirió del AP. La mayoría de los FT examinados eran redondos. Estos hallazgos deben ser considerados en el diagnóstico provisional de síntomas neurovasculares vertebrales causados por la variación del FT, así como en el de daño neurovascular tras la colocación de tornillos pediculares cervicales.

Application of guide combined with probing the internal wall of pedicle screw trajectory for subaxial cervical pedicle screw placement / 中国骨伤

<p><b>OBJECTIVE</b>To investigate the skill and evaluate the accuracy for application of guide combined with probing the internal wall of pedicle screw trajectory for subaxial cervical pedicle screw placement.</p><p><b>METHODS</b>Subaxial cervical pedicle screw was inserted in 11 patients by the guide combined with probing the internal wall of pedicle screw trajectory from January 2014 to October 2016, including 7 males and 4 females with an average age of 48.1 years(ranged 32 to 63 years). There were 4 cases with cervical spondylotic myelopathy, 4 with fracture and dislocation of cervical vertebrae, 1 with cervical cord injury without fracture and dislocation, and 2 with atlantoaxialfracture and dislocation. The target pedicle's diameter, optimal entry point, sagittal angle and cross-sectional angle were measured by CT before operation. During operation, the pedicle screw inserted angle was controlled by a guide with a self-designed protractor and probed the internal wall of pedicle screw trajectory as medial safety margin of insertion screw. The accuracy of cervical pedicle screw was evaluated by CT with classification of four grades and assessed whether there was injury of spine cord or vertebral artery postoperatively.</p><p><b>RESULTS</b>Seventy-one cervical pedicle screws were placed among 11 patients, and no one had been found with clinical manifestations of injury of spine cord (or nerve root) or vertebral artery after operation. According to postoperative CT scan for evaluating the grade of screw position, 52 screws were in grade 0, 13 in grade 1, 4 in grade 2, 2 in grade 3, and 91% (65/71) located in good position. In total, 6 screws were incorreted in placement, and 4 cases of them broke medial wall and 2 cases broke lateral wall.</p><p><b>CONCLUSIONS</b>The method of probing the internal wall of pedicle screw trajectory for subaxial cervical pedicle screw placement is safe and reliable, but the studying curve is long. Probing the internal wall of pedicle screw trajectory and controlling the insertion angle by guide with a protractor are key points of this technology.</p>

A Novel Patient-Specific Drill Guide Template for Pedicle Screw Insertion into the Subaxial Cervical Spine Utilizing Stereolithographic Modelling: An In Vitro Study

STUDY DESIGN: Cadaveric study. PURPOSE: The purpose of this study was to assess the accuracy and feasibility of cervical pedicle screw (CPS) insertion into the subaxial cervical spine placed using a patient-specific drill guide template constructed from a stereolithographic model. OVERVIEW OF LITERATURE: CPS fixation is an invaluable tool for posterior cervical fixation because of its biomechanical advantages. The major drawback is its narrow corridor that allows very little clearance for neural and vascular injuries. METHODS: Fifty subaxial pedicles of the cervical vertebrae from five cadavers were scanned into thin slices using computed tomography (CT). Digital imaging and communications in medicine images of the cadaver spine were digitally processed and printed to scale as a three-dimensional (3D) model. Drill guide templates were manually moulded over the 3D-printed models incorporating pins inserted in the pedicles. The drill guide templates were used for precise placement of the drill holes in the pedicles of cadaveric specimens for pedicle screw fixation. RESULTS: The instrumented cadaveric spines were subjected to CT to assess the accuracy of our pedicle placement by an external observer. Our patient-specific drill guide template had an accuracy of 94%. CONCLUSIONS: The use of a patient-specific drill guide constructed using stereolithography improved the accuracy of CPS placement in a cadaveric model.

Recent progress in pedicle screw placement in the subaxial cervical spine and clinical applications / 天津医药

Pedicle screw fixation is biomechanically most reliable for reconstruction of the cervical spine, which can ef?fectively restore cervical sagittal profiles, provide rigid fixation and higher fusion rate. Because of the large individual differ?ences in cervical pedicle, vertebral artery and nerve root, preoperative evaluation should be individualized. Cervical pedicle screw techniques include freehand technique and the computer-assisted navigation technology developed recently. Although complications associated with cervical pedicle screw fixation cannot be completely obviated, they can be minimized by com?bination of sufficient preoperative imaging studies of the pedicles and meticulous surgical techniques of screw placement. Cervical pedicle screw fixation techniques have been used in the treatment of various cervical disorders, with fewer complica?tions and good clinical efficacy, and a wide range of clinical applications.

Mid-Term Results of Computer-Assisted Cervical Pedicle Screw Fixation

STUDY DESIGN: A retrospective study. PURPOSE: The present study aimed to evaluate mid-term results of cervical pedicle screw (CPS) fixation for cervical instability. OVERVIEW OF LITERATURE: CPS fixation has widely used in the treatment of cervical spinal instability from various causes; however, there are few reports on mid-term surgical results of CPS fixation. METHODS: Record of 19 patients who underwent cervical and/or upper thoracic (C2-T1) pedicle screw fixation for cervical instability was reviewed. The mean observation period was 90.2 months. Evaluated items included Japanese Orthopaedic Association (JOA) score and C2-7 lordotic angle before surgery and at 5 years after surgery. Postoperative computerized tomography was used to determine the accuracy of screw placement. Visual analog scale (VAS) for neck pain and radiological evidence of adjacent segment degeneration (ASD) at the 5-year follow-up were also evaluated. RESULTS: Mean JOA score was significantly improved from 9.0 points before surgery to 12.8 at 5 years after surgery (p=0.001). The C2-7 lordotic angle of the neutral position improved from 6.4degrees to 7.8degrees at 5 years after surgery, but this was not significant. The major perforation rate was 5.0%. There were no clinically significant complications such as vertebral artery injury, spinal cord injury, or nerve root injury caused by any screw perforation. Mean VAS for neck pain was 49.4 at 5 years after surgery. The rate of ASD was 21.1%. CONCLUSIONS: Our mid-term results showed that CPS fixation was useful for treating cervical instability. Severe complications were prevented with the assistance of a computed tomography-based navigation system.

Cervical Pedicle Screw Placement in Sawbone Models and Unstable Cervical Traumatic Lesions by Using Para-Articular Mini-Laminotomy: A Novice Neurosurgeon's Experience / 대한신경손상학회지

OBJECTIVE: This retrospective study was conducted to analyze the novice neurosurgeon's experience of cervical pedicle screw placement by using the technique with direct exposure of pedicle via para-articular mini-laminotomy. METHODS: Fifteen sawbone models of subaxial spine were used (124 pedicles) to evaluate efficacy of repetitive training improving accuracy of cervical pedicle screw insertion. After that, we retrospectively reviewed 9 consecutive patients presented with traumatic cervical lesion. A total 38 cervical pedicle screws had been inserted. We analyzed the direction and grade of pedicle perforation on the postoperative computed tomography scan, and learning curve by using sawbone model. RESULTS: In sawbone model group, the correct position was found in 102 (82.3%) screws, and the incorrect position in 22 (17.7%) screws. The incidence of incorrect screw position was 26.9% in the initial 9 sawbone model, and 0% after that. Among the 38 screws inserted in 9 patients, the correct position was found in 36 (94.7%) screws, and the incorrect position in a 2 (5.3%) screw. There was no neurovascular complications related with cervical pedicle screw insertion. CONCLUSION: In vitro training to insert pedicle screw by using sawbone models could improve an accuracy of cervical pedicle screw placement by using this technique. Preliminary result revealed that cervical pedicle screw placement would be feasible and provide good clinical results in traumatic cervical lesions.

Cervical Pedicle Screw Insertion Using the Technique with Direct Exposure of the Pedicle by Laminoforaminotomy

OBJECTIVE: To present the accuracy and safety of cervical pedicle screw insertion using the technique with direct exposure of the pedicle by laminoforaminotomy. METHODS: We retrospectively reviewed 12 consecutive patients. A total of 104 subaxial cervical pedicle screws in 12 patients had been inserted. We also assessed the clinical and radiological outcomes and analyzed the direction and grade of pedicle perforation (grade 0: no perforation, 1: 50% of screw diameter) on the postoperative vascular-enhanced computed tomography scans. Grade 2 and 3 were considered as incorrect position. RESULTS: The correct position was found in 95 screws (91.3%); grade 0-75 screws, grade 1-20 screws and the incorrect position in 9 screws (8.7%); grade 2-6 screws, grade 3-3 screws. There was no neurovascular complication related with cervical pedicle screw insertion. CONCLUSION: This technique (technique with direct exposure of the pedicle by laminoforaminotomy) could be considered relatively safe and easy method to insert cervical pedicle screw.