Abstract
Objective : To evaluate the accuracy of free-hand pedicle screws placement at the seventh cervical vertebra. Methods : The authors have exposed the cervicothoracic junction of 9 adult cadavers (7 male and 2 female) preserved in formalin from the Faculty of Medicine of the Universidad Andina Néstor Cáceres Velásquez, city of Juliaca, Puno - Peru, locating the C7 vertebra based on anatomical parameters. According to previous publications, the entry point for the C7 pedicle was determined as 3-4mm lateral and 5-6mm superior to the center of the lateral mass, and the pedicle was drilled manually and instrumented with 3.5mm screws. After the screws placement, the C7 vertebrae were removed for radiographic analysis. Results : The authors were able to adequately locate the C7 entry point in 12 pedicles (66.6% accuracy), finding a great variability both laterally (2-5mm) and cranially (3-10mm). The angulation in the coronal plane was correct in 13 pedicles (72.3%), despite the incorrect location of the entry point. Angle values in the coronal plane ranged from 38 to 62 degrees. In the sagittal plane angulation, 2 screws were placed in the C6-C7 disc. The midtransversal diameter of the 18 pedicles ranged from 4 to 7mm. Conclusions : The location of the entry point for placement of C7 pedicle screws with pure free-hand technique is very variable due to anatomical differences and the authors recommend some type of guidance for increased safety and accuracy.
Highlights
The cervicothoracic junction is a complex region, in which dramatic anatomic and biomechanical changes take place
The purpose of this study is to evaluate the accuracy of free hand pedicle screw insertion at C7 in cadaveric specimens
The authors found great variability in terms of the point of entry of the pedicle in the C7 lateral mass in relation to its center point, with values ranging from 2mm to 5mm laterally and 3mm to 10mm superior to it. (Table 1) The angulation in the coronal plane was correct in 13 pedicles (72.2%, figure 3), where the screws were parallel to the pedicles, despite some of them having breached any of the walls
Summary
The cervicothoracic junction is a complex region, in which dramatic anatomic and biomechanical changes take place. Within the field of anatomy, changes in vertebral diameter, mineral density and fixation points from the mid cervical to the upper thoracic spine are challenges that need to be overcome in order to accommodate biomechanical adaptations from the lordotic and mobile portion to a rigid and kyphotic upper thoracic region. Lateral mass screws have proven to be safe and biomechanically stable fixation points in most cases, and thoracic pedicle screws have become a standard fixation option for the T1 and caudal vertebrae. The C7 vertebra remains a challenge for those operating on the cervicothoracic junction. The biomechanical stability offered by pedicle screws for treating traumatic, degenerative, inflammatory, and neoplastic conditions of the spine is well known.[3,4,5] cervical pedicle screw insertion is technically demanding because of the anatomical variations in cervical pedicle size, the lack of anatomical landmarks, and the transverse angle of cervical pedicles.[3,6,7,8]
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