The unique anatomical articulation of the C1–C2 complex allows for a wide range of motion predominantly rotational motion than any other single level in the remaining cervical spine. The transverse ligament plays the main role in limitation of the translation movement at the C1–C2 complex, which can be lost in cases of odontoid fracture type II associated with ligamentous tear causing antero- or retrolisthesis of the C1–C2 complex in relation to the C2 body with subsequent spinal cord compression producing severe neurological deficits .
In type II odontoid fracture, the union rate is related directly to the strategy of treatment. Conservative management with a cervical collar or halo vest has a high nonunion rate that can reach 40% . Thus, surgical treatment of odontoid fracture type II has the cornerstone role for management, especially in elderly patients and those that have a higher risk for nonunion . Anterior odontoid screw placement is considered as an optimum surgery in fresh cases; however, in osteoporotic patients, short neck, C1–2 displacement, and oblique line of fracture, or patients with failure of union after conservative management, posterior cervical C1–C2 fixation became the optimum management. Surgical treatment with posterior cervical instrumented fusion (PCIF) increases the fusion rate to more than 80% in many patient series .
Posterior cervical instrumented fusion (PCIF) C1–C2 fixation is a commonly used procedure in the management of odontoid type II fracture especially in cases associated with significant displacement of the fractured segment and avulsion of the transverse ligament and cases associated with C1 Jefferson fracture who are not amenable for anterior odontoid screw .
Different ways for a posterior approach are described. Gallie, Brooks et al., and Sonntag et al. techniques aimed to put a bone graft between the posterior arch of C1 and the C2 lamina with sublaminar wiring. These procedures have a satisfactory fusion rate of about 74% but there is a loss of the normal C1–2 rotatory motion that is responsible for 50% of the cervical spine rotation and limitation by 10% for the cervical flexion-extension movement [11,12,13,14,15]. Magerl in 1986 introduced a transarticular atlantoaxial screw fixation with a high biomechanical stability with superiority upon the wiring technique in the fusion rate. However, in cases associated with atlantoaxial dislocation or subluxation with loss of C1–C2 alignment, drawbacks will appear with a high difficulty of transarticular screw trajectory [16,17,18,19,20,21].
The Goel technique, in which C1–2 intraarticular spacers are used, may be performed to restore stability to a disrupted atlantoaxial complex by placing polyaxial screws and plates . In 2001, Harms described a new way for atlantoaxial stabilization that could bypass the limitations found in both the previous wiring posterior fixation and the transarticular screws in cases associated with C1–C2 alignment loss and posterior arc involvement. Harms developed Goel’s work on atlantoaxial screw fixation by a technique based on lateral mass polyaxial screw in C1 and pars or pedicle polyaxial screw in C2. This technique showed biomechanical results that are comparable to those with Magerl’s technique [23, 24]. With surgeons with good expertise and well-equipped operative rooms, Harms technique shows less intraoperative complications with satisfactory postoperative biomechanics results .
Comparable to our results for the postoperative complications, we achieved results that were nearly achieved in previous series using the same technique. There was no injury for the neural element or the vertebral artery among all cases; however, vertebral artery injuries were reported in 10% of literature [23,24,25]. Limitation in pedicle screw was reported in literature, including vertebral artery injuries especially in congenital anomalies in the course of arteries including the high right vertebral artery and we can overcome that by performing preoperative 3D angiography .
In 2011, Park et al. showed there were good unions for all cases in his series for C1–C2 posterior fixation after odontoid fracture type II. There was limitation in the rotatory movement after fixation and fusion by about 20% . In our series, the limitation in the rotatory movement can reach about 17% for each side in lateral bending, thanks to a wide range allowed by the polyaxial screws. However, recent studies began to solve this issue by a temporary fixation of C1–C2 for 6 months then removing the screws to maintain the rotatory movement .
A remarkable limitation in our study is that we depended on postoperative X-ray in the evaluation of fusion which is considered not sufficient in other literature, and CT cervical spine is more accurate in the assessment of postoperative fusion .