Cervical spine is a place of many pathological lesions that could compromise its biomechanical stability. Restoration of stability may ultimately require fixation and placement of hard fixation devices. Posterior cervical spine stabilization is often administered to treat a variable cervical spine lesions that lead to spinal instability that include; cervical spondylotic degenerative disease, traumatic cervical spinal injury with and without fractures or with and without neurological deficits, metabolic -inflammatory lesions, primary and secondary neoplastic cervical spine lesions, infections, and in patients with previous wide cervical laminectomy without fixation. However, numerous surgical techniques and advances in spinal instrumentation have evolved over the last years. Lateral mass fixation has world widely gained popularity among spine surgeons with low morbidity and satisfactory outcome. Sekhon reported the largest series of subaxial lateral mass screw fixation with a total of 1024 screws and no related neuro-vascular injury observed [12, 13].
Many screw entry points and directions have been described since this technique was first introduced, Roy-Camille advocated the entry point of the screw is the midpoint of the lateral mass and the direction of the screw is to be perpendicular to the posterior aspect of the cervical spine and 100 outward . while Magerl proposed starting point is 2-3 mm medial and superior to the midpoint of the lateral mass and angling 300 superiorly and 250 laterally . Anderson recommended that the drilling point is 1 mm medial to the midpoint of the lateral mass and that the screw be angled 30-400 up and 100 lateral . An et al suggested angling 15-180. superiorly and 30-330 laterally, with a starting point 1 mm medial to the center of the lateral mass . Pait et al divided the lateral mass into four quadrants with the upper outer quadrant is the intention for screw insertion in this way its high likely to evade neurovascular injury . finally, sekhon recommended that by using Anderson's starting point and then angling 250 laterally and superiorly; this way is safe and easily applied. In regards to the lateral mass of C7 it can be attained with a steeper course without need for C7 pedicle .
Frequent clinical and cadaver investigations have been done on lateral mass fixation. Focusing on various trajectories to achieve proper placement of the screw and to avoid neural and vascular damage. Ebraheim et al on his cadaver study revealed the foramen transverarium is located in line with the midpoint of the lateral mass. So, the direction of the screw is to be laterally to avoid entry into the vertebral foramen [17, 18]. The work done by Xu et al reached that An technique is high likely to avoid neural damage compared to magerl and Anderson techniques [19, 20]. However, the incidence of nerve root violation when Roy-Camille or Magerl, Sekhon trajectories used is around 3.6%; this is most likely because of the lengthy screw and more lateral trajectory [13, 21, 22].
In terms screw length, Roy-Camille et al recommended 14-17 mm . An et al suggested a screw length of 11 mm is effective . Sekhon suggested that a 14-mm screw is safe and efficient based on the fact that the average vertical distance between the posterior midpoint of the lateral mass and the vertebral foramen from C3 to C6 is approximately 9-12 mm . As a result, insertion of a 14 mm screw obliquely should cross the lateral mass smoothly. In addition to that, a 14 mm screw can be bicorticate which adds further stability to the screw in place and causes no violation to the adjacent foramen, the Cadaveric studies of Heller et al concluded that bicorticate fixation with large diameter and non-self tapping screws had the utmost resistance to pullout [13, 23–25].
In comparison with other fixation techniques such as cervical pedicle screws, lateral mass fixation is safer, has higher success rate and low co-morbidities. In early studies, the failure rate was higher patients who underwent screw/plate constructs compared with the newer polyaxial screw/rod systems. The former systems were semi constricted with no cross link; which augment the stability of the system. In general, the newer polyaxial screw/rod systems are more constrained and essentially avoid screw pullout [25–27].