Lag screw fixation of reducible Type II and high Type III odontoid fractures preserving C1-C2 rotation | advanced
Surgical Imaging
The trap: Assuming any Type II fracture is suitable for anterior screw fixation.
The fix: Only posterior-oblique or transverse fracture lines allow lag-screw compression. Anterior-oblique patterns cause the screw to push the odontoid fragment superiorly and are an absolute contraindication — convert to posterior C1-C2 fusion.
Location: The TAL runs behind the odontoid and is the primary restraint to anterior atlanto-axial subluxation.
Risk: Undiagnosed TAL rupture allows persistent instability even after technically perfect screw placement; the construct fails in flexion. Always obtain preoperative MRI or perform intraoperative stress fluoroscopy.
Location: The vertebral artery ascends in the C2 transverse foramen and lies lateral to the intended screw path.
Risk: A laterally directed or excessively long screw can breach the C2 lateral mass or transverse foramen, causing vertebral artery injury, stroke or death. Use simultaneous biplanar fluoroscopy and stay within the medial C2 pedicle walls on the AP view.
The trap: Proceeding with anterior screw fixation in patients with a barrel chest or short neck where the required caudal trajectory cannot be achieved.
The fix: These patients have an unacceptably steep screw angle that risks anterior C2 body breach or inadequate odontoid purchase — convert to posterior Harms-Goel C1-C2 fusion.
Why different: Severe osteoporosis (T-score less than -2.5) or metabolic bone disease compromises screw purchase in the odontoid tip and C2 body.
Implications: High risk of screw cut-out, nonunion or hardware failure. Consider posterior fusion with C1 lateral mass and C2 pedicle/pars screws or augment with bone graft and longer immobilisation.
Location: The high anterior cervical approach places the oesophagus and trachea immediately medial to the exposure.
Risk: Retraction injury, perforation or postoperative dysphagia is more common than in standard Smith-Robinson exposures because of the high level (C2-C3) and prolonged retraction time. Use a right-sided approach, intermittent relaxation of retractors and a nasogastric tube for identification.
S.C.R.E.W.INDICATIONS — Patient Selection for Anterior Odontoid Screw
T.R.A.J.E.C.T.TECHNIQUE — Critical Intraoperative Steps
S.C.R.E.W. FAILCOMPLICATIONS — Recognition and Avoidance
Surgical Indications
Absolute Indications
- Acute Type II odontoid fracture with favourable (posterior-oblique or transverse) fracture line
- High Type III odontoid fracture extending into the C2 body with adequate bone stock for screw purchase
- Reducible fracture with intact transverse atlantal ligament
- Patient preference for motion-preserving surgery over C1-C2 arthrodesis
Relative Indications
- Selected chronic nonunions with good bone quality and favourable anatomy (requires bone grafting)
- Young patients in whom preservation of C1-C2 rotation is functionally important
- Polytrauma patients where shorter operative time and avoidance of prone positioning is desirable
Contraindications
Absolute:
- Anterior-oblique fracture line orientation (screw distracts rather than compresses)
- Comminuted odontoid fracture or large fracture gap
- Established nonunion with sclerotic fracture edges
- Incompetent transverse atlantal ligament (atlanto-dens interval greater than 3 mm)
- Irreducible fracture on preoperative traction or positioning
- Severe osteoporosis (T-score less than -2.5) or metabolic bone disease
- Barrel chest or short neck preventing adequate caudal trajectory
Relative:
- Previous anterior cervical surgery with scarring
- Active infection
- Severe dysphagia or airway compromise preoperatively
Evidence for Anterior Odontoid Screw Fixation
Union Rates and Comparison with Posterior Fusion
- Anterior odontoid screw fixation achieves union rates of 85-95% in appropriately selected acute Type II fractures when the transverse atlantal ligament is intact
- Posterior C1-C2 fusion (Harms-Goel or Magerl) achieves union rates greater than 95% but sacrifices all C1-C2 rotation (approximately 50% of total cervical rotation)
- Anterior screw fixation is therefore preferred in young patients and those requiring preservation of rotation, provided the fracture pattern and TAL are favourable
Key Technical Considerations from the Literature
- Two-screw constructs provide greater rotational stability than single-screw fixation but increase the risk of cortical breach and are technically more demanding
- Intraoperative biplanar fluoroscopy is mandatory; single-plane imaging leads to higher rates of screw malposition
- Bone grafting is not routinely required in acute fractures but is recommended in chronic nonunions
Anterior Odontoid Screw vs Posterior C1-C2 Fusion — Decision Factors
Key Evidence
Direct anterior screw fixation for recent and remote odontoid fractures
Fractures of the odontoid process of the axis
Anterior screw fixation of odontoid fractures: operative technique and results in 18 patients
MRI assessment of the transverse atlantal ligament in odontoid fractures
Complications of anterior odontoid screw fixation: a systematic review
Clinical Decision Scenarios
Practise clinical reasoning and management decisions out loud
“A 42-year-old man sustains a Type II odontoid fracture after a fall from height. Sagittal CT shows a posterior-oblique fracture line at the base of the dens with 3 mm displacement. MRI confirms an intact transverse atlantal ligament. He has no chest deformity and good bone density. What is your surgical plan and why?”
“You are performing anterior odontoid screw fixation on a 35-year-old woman. After guidewire placement you notice on the AP fluoroscopic view that the wire has drifted 3 mm lateral to the medial wall of the C2 pedicle. What do you do?”
“A 68-year-old man with a Type II odontoid fracture undergoes successful anterior odontoid screw fixation. At 12-week follow-up CT shows a persistent fracture line with 2 mm screw cut-out. How do you manage this nonunion?”