Visit our Evidence-Based Covid-19 Website and Stay Up to Date with the latest Research.
ACE Report #8961

Pedicle screw more efficacious vs lateral mass screw fixation in atlantoaxial instability

Study Type:Therapy
OE Level Evidence:2
Journal Level of Evidence:N/A

A prospective, double-blind, randomized controlled trial of treatment of atlantoaxial instability with C1 posterior arches >4 mm by comparing C1 pedicle with lateral mass screws fixation

BMC Musculoskelet Disord. 2016 Apr 14;17(1):164

Did you know you're eligible to earn 0.5 CME credits for reading this report? Click Here


140 patients with atlantoaxial instability (AAI), with C1 posterior arches greater than 4mm, were randomized to undergo either C1 pedicle or lateral mass screw fixation. The purpose of this study was to compare the feasibility and clinical outcomes of the two treatments of AAI after a mean follow-up period of 24.5 months. Findings indicated that C1 pedicle screw fixation may be less invasive and yield fewer complications compared to C1 lateral mass screw fixation.

Publication Funding Details +
Non-Industry funded
National Natural Science Foundation of China
None disclosed

Risk of Bias


Reporting Criteria


Fragility Index


Was the allocation sequence adequately generated?

Was allocation adequately concealed?

Blinding Treatment Providers: Was knowledge of the allocated interventions adequately prevented?

Blinding Outcome Assessors: Was knowledge of the allocated interventions adequately prevented?

Blinding Patients: Was knowledge of the allocated interventions adequately prevented?

Was loss to follow-up (missing outcome data) infrequent?

Are reports of the study free of suggestion of selective outcome reporting?

Were outcomes objective, patient-important and assessed in a manner to limit bias (ie. duplicate assessors, Independent assessors)?

Was the sample size sufficiently large to assure a balance of prognosis and sufficiently large number of outcome events?

Was investigator expertise/experience with both treatment and control techniques likely the same (ie.were criteria for surgeon participation/expertise provided)?

Yes = 1

Uncertain = 0.5

Not Relevant = 0

No = 0

The Reporting Criteria Assessment evaluates the transparency with which authors report the methodological and trial characteristics of the trial within the publication. The assessment is divided into five categories which are presented below.




Outcome Measurements


Inclusion / Exclusion


Therapy Description



Detsky AS, Naylor CD, O'Rourke K, McGeer AJ, L'Abbé KA. J Clin Epidemiol. 1992;45:255-65

The Fragility Index is a tool that aids in the interpretation of significant findings, providing a measure of strength for a result. The Fragility Index represents the number of consecutive events that need to be added to a dichotomous outcome to make the finding no longer significant. A small number represents a weaker finding and a large number represents a stronger finding.

Why was this study needed now?

Atlantoaxial instability (AAI) is atypical movement at the cervical region, in between the atlas and axis, caused by malformation of bone or alterations of ligament. Atlantoaxial fixation is required to repair the instability, though various approaches that have been previously used, such as sublaminar wiring, Harms and Magerl techniques, have reported many postoperative complications followed by substantial rates of non-union. The Harms method utilizes polyaxial screws that are independently inserted into the C1 posterior arch and C2 pedicles, thereby allowing C1 posterior arch fixation to be split into pedicle and lateral mass screw fixation. The present study aims to compare the clinical outcomes of C1 pedicle and lateral mass screw fixation methods in treatment of AAI.

What was the principal research question?

In treatment of atlantoaxial instability, how do C1 pedicle and lateral mass screw fixation compare with regards to feasibility and clinical outcomes, as assessed up to 38 months postoperatively?

Study Characteristics -
140 patients, between the ages of 14 and 59, with AAI or reducible dislocation due to trauma, inflammation, or congenital malformation were included. Eligible patients had C1 posterior arches greater than 4mm, as well as differing severity in neck and occipital pain, activity limitation, numbness of limbs, or movement disorders. The study included 36 cases of type II and 43 cases of type III Anderson chronic odontoid fractures, 34 cases of congenital isolated odontoid abnormalities, 19 cases of transverse atlas ligament ruptures, and 8 cases of atlantoaxial dislocation caused by rheumatoid arthritis. All patients were placed in the prone position with the neck in a neutral and immobilized position.
C1 pedicle group: Patients were treated with a C1 pedicle screw inserted from 18-20mm lateral to the posterior tubercle and 3mm inferior to the superior border of the posterior arch. (n=67; Mean age: 43.9 +/- 8.2; 43M/24F)
C1 lateral mass group: Patients were treated with a C1 lateral mass screw inserted where the inferior border of the C1 posterior arch and the midpoint of the C1 lateral mass meet. (n=73; Mean age: 45.2 +/- 8.7; 45M/28F)
Intraoperative outcomes included operation time, volume of blood loss, and intraoperative complications such as venous plexus injury, vertebral artery injury, and spinal cord injury. Clinical outcomes consisted of the Japanese Orthopaedic Association (JOA) score, visual analogue scale (VAS) score for pain, and bone fusion rate.
RCT; prospective, assessor- and patient-blind, single-center
Patients were followed-up at 3 months, 6 postoperative months, and every 6 months thereafter for a total of 12 to 38 months (Mean: 24.5 +/- 13.0 months).

What were the important findings?

  • A significantly shorter mean operation time was reported in the Pedicle screw group compared to the Lateral mass group (85 +/- 11 vs. 110 +/- 17 minutes, respectively; p<0.01).
  • Significantly less volume of blood was lost in the Pedicle screw group compared to the Lateral mass group (180 +/- 40 vs. 370 +/- 80 ml, respectively; p<0.01)
  • Hospitalization time, JOA scores, and VAS scores were similar between groups (p>0.05).
  • JOA and VAS scores were significantly improved within both groups from preoperation to final follow-up (both p<0.01).
  • No postoperative hardware complications were observed in any patient up to final follow-up; however, 6 cases of inferior wall fracture of the posterior arch, 2 cases of penetration of axis pedicle screws into the vertebroarterial foramen, and 2 cases of medial wall fracture of the axis pedicle were reported.
  • 13 cases of burst bleeding from the C1-2 venous plexus during surgery and 9 cases of immediate pain and numbness in the occipitocervical region caused by C2 nerve roots irritation were noted in the Lateral mass group compared to no incidences in the Pedicle screw group (both p<0.01).

What should I remember most?

In treatment of atlantoaxial instability, an operative procedure using C1 pedicle screw fixation was reported to result in a significantly shorter operation time, lower volume of blood loss, and fewer venous plexus and nerve root injuries compared to the C1 lateral mass screw fixation method. However, hospitalization time, Japanese Orthopaedic Association scores, and visual analogue scale scores were comparable between groups.

How will this affect the care of my patients?

The results of this study suggest that the C1 pedicle screw fixation method may be less invasive and less complicated compared to C1 lateral mass screw fixation for patients with atlantoaxial instability. Further trials with longer follow-up periods are required to evaluate the long-term effects between groups.

CME Image

Continuing Medical Education Credits

You could be earning 0.5 CME credits for each report you read.


Please Login or Join to leave comments.