TAS and SRC are safe and effective treatment options for C1-C2 instability but require a thorough knowledge of atlantoaxial anatomy for successful insertion of screws. Slightly higher rates of fusion and less risk of injury to the vertebral artery during screw placement were observed with the SRC technique. However, differences in graft material and techniques were noted. Prospective, randomized studies with validated radiographic and clinical outcome metrics are necessary for proper comparison of these techniques.

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Object Some centers report a lower incidence of vertebral artery (VA) injury with C-2 pars screws compared with pedicle screws without sacrificing construct stability, despite biomechanical studies suggesting greater load failures with C-2 pedicle screws. The authors reviewed published series describing C-2 pars and pedicle screw implantation and atlantoaxial fusions and compared the incidence of VA injury, screw malposition, and successful atlantoaxial fusion with each screw type. Methods Online databases were searched for English-language articles between 1994 and April of 2011 describing the clinical and radiographic outcomes following posterior atlantoaxial fusion with C-1 lateral mass and either C-2 pars interarticularis or pedicle screws. Thirty-three studies describing 2975 C-2 pedicle screws and 11 studies describing 405 C-2 pars screws met inclusion criteria for the safety analysis. Seven studies describing 113 patients treated with C-2 pars screws and 20 studies describing 918 patients treated with C-2 pedicle screws met inclusion criteria for fusion analysis. Standard and formal meta-analysis techniques were used to compare outcomes. Results All studies provided Class III evidence. Ten instances of VA injury occurred with C-2 pedicle screws (0.3%) and no VA injury occurred with pars screws. The point estimate of VA injury for C-2 pedicle screws was 1.09% (95% CI 0.73%–1.63%) and was similar to that of C-2 pars screws (1.48%, 95% CI 0.62%–3.52%). Similarly, there was no statistically significant difference in the rate of clinically significant screw malpositions (1.14% [95% CI 0.77%–1.69%) vs 1.69% [95% CI 0.73%–3.84%]). Radiographically identified screw malposition occurred in a higher proportion of C-2 pedicle screws compared with C-2 pars screws (6.0% [95% CI 3.7%–9.6%] vs 4.0% [95% CI 2.0%–7.6%], p < 0.0001). Pseudarthrosis occurred in a greater proportion of patients treated with C-2 pars screws (5 [4.4%] of 113) compared with those treated with C-2 pedicle screws (2 [0.22%] of 900). Point estimates with 95% confidence intervals show a slightly higher rate of successful atlantoaxial fusion in the pedicle screw cohort (97.8% [CI 96.0%–98.8%] vs 93.5% [CI 86.6%–97.0%]; p < 0.0001). Q-testing ruled out heterogeneity between the study groups. Conclusions With a thorough knowledge of axis anatomy, surgeons can place both C-2 pars and C-2 pedicle screws accurately with a small risk of VA injury or clinically significant malposition. There may be subtle trade-off of safety for rigidity when using axial pedicle instead of pars screws, and the decision to use either screw type must be made only after careful review of the preoperative CT imaging and must take into account the surgeon's expertise and the particular demands of the clinical scenario in any given case.

With training, experience, and anatomic knowledge, both TAS and C2PS can be inserted accurately and safely. However, improper insertion and VAI can have catastrophic consequences. Our review identified a higher risk of VAI, neurological injury, and clinically significant malpositions with TAS compared with C2PS. These data provide preliminary support for the supposition that C2PS have a lower risk of morbidity.

Study Design: A prospective cohort study. Objective: Quantify the extent of change in dynamic balance and stability in a group of patients with cervical spondylotic myelopathy (CSM) after cervical decompression surgery and to compare them with matched healthy controls. Summary of Background Data: CSM is a naturally progressive degenerative condition that commonly results in loss of fine motor control in the hands and upper extremities and in gait imbalance. Whereas this was previously thought of as an irreversible condition, more recent studies are demonstrating postoperative improvements in balance and stability. Materials and Methods: Thirty subjects with symptomatic CSM and 25 matched asymptomatic controls between the ages of 45 and 75 years underwent functional balance testing using a 3D motion capture system to gather kinematic and spatiotemporal parameters. CSM subjects underwent testing 1 week before surgery and again 3 months postoperatively. Results: Patients with CSM exhibited markedly diminished balance as indicated by increased sway on a Romberg test and requiring significantly more time and a wider stance to complete tandem gait tests. The surgical intervention resulted in improved balance at the 3-month postoperative time point; however, kinematic and spatiotemporal parameters did not completely normalize to the levels observed in asymptomatic controls. Conclusions: Human motion video capture can be used to robustly quantify balance parameters in the setting of CSM. Compared with healthy controls, such patients exhibited increased standing sway and poorer performance on a tandem gait task. The surgical intervention resulted in significant improvement in many of the measures of functional balance, but overall profiles had not completely returned to normal when measured 3 months after surgery. These data reinforce the importance of operative intervention in the treatment of symptomatic CSM with the goal of halting disease progress but the expectation that balance may actually improve postoperatively.

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