Comparison of safety and stability of C-2 pars and pedicle screws for atlantoaxial fusion: meta-analysis and review of the literature

Abstract

<jats:sec> <jats:title>Object</jats:title> <jats:p>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.</jats:p></jats:sec> <jats:sec> <jats:title>Methods</jats:title> <jats:p>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.</jats:p></jats:sec> <jats:sec> <jats:title>Results</jats:title> <jats:p>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 &lt; 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 &lt; 0.0001). Q-testing ruled out heterogeneity between the study groups.</jats:p></jats:sec> <jats:sec> <jats:title>Conclusions</jats:title> <jats:p>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.</jats:p></jats:sec>

Posterior atlantoaxial fixation: a review of all techniques

“…The direction of the screw is 15 -30 medial and 20 -25 cephalad. Although a biomechanical study has shown that C2 pedicle screws have twice the pullout strength of C2 pars screws [68], the clinical results of the two fixation techniques are similar [69]. Both the C2 pedicle screw and C2 pars screw are widely used for screw-rod system fixation of C1-C2 fusion [69].…”

Biomechanical analysis of screw constructs for atlantoaxial fixation in cadavers: a systematic review and meta-analysis

“…30,36 C1-C2TL constructs are commonly used for cases in which contraindications for C1-C2TA and C1LM-C2PS constructs exist, primarily to avoid vertebral artery injury; the reported fusion rate is 92.9%. 30 Elliott et al 10 performed a meta-analysis and found a slightly higher incidence of vertebral artery injury in C1LM-C2PS constructs than in C1LM-C2 pars constructs, with reported fusion rates higher for C1LM-C2PS constructs (97.8%) than for C1LM-C2 pars constructs (93.5%). Given our findings of insufficient biomechanical stabilization of lateral bending by the C1-C2TL construct, clinical studies to compare long-term fusion rates and the incidence of hardware failures to the other constructs may help provide a clinical correlation.…”

Comparison of structural allograft and traditional autograft technique in occipitocervical fusion: radiological and clinical outcomes from a single institution

“…Recently, Elliott et al 7 reviewed atlantoaxial grafting options and found no significant difference in fusion rates between allograft and autograft constructs but noted wide variability in the use of autograft, allograft, and bone morphogenetic protein. The study found a 99.7% fusion rate among 652 patients treated with autograft and a 100% fusion rate among 60 patients treated with allograft in 7 studies; however, the majority of these included morselized allografts rather than the structural allograft described in the current study.…”