Anterior odontoid screw fixation

J.V. Mollá-Torró; J.Sales-Llopis

Neurosurgery Department, General University Hospital Alicante, Spain

• Non contiguous dual level spinal injuries - A tertiary care centre institutional experience
• Full-endoscopic assisted surgery using anterior double odontoid screw fixation in type II odontoid fractures: A clinical study of the surgical technique
• Evaluating the prognostic role of computed tomography Hounsfield units in anticipating spinal outcomes post-instrumentation: a systematic review and meta-analysis
• Endoscope-Assisted Anterior Odontoid Screw Fixation for Odontoid Fracture
• Anterior C2 Odontoid Fixation Using Cranial Brainlab Navigation: A Novel Approach and Case Report
• Robot-assisted anterior odontoid screw for the treatment of type odontoid fractures: Safety and effectiveness analysis
• Controversies in the Management of Type II Odontoid Fractures
• Odontoid Fractures: A Review of the Current State of the Art

50% of axial rotation of the head occurs at the C1–2 complex. Treatment of odontoid fractures by C1–2 fusion significantly reduces this mobility (although subaxial articulations will compensate to some degree over time). Odontoid screw fixation (OSF) attempts to treat odontoid fractures by restoring the structural integrity of the odontoid process (osteosynthesis) without sacrificing the normal mobility.

Stability of the C1–2 joint depends primarily on the integrity of the odontoid process and the transverse ligament of the atlas (which is the most important structure holding the odontoid process in position against the anterior arch of C1).

A full set of C-spine X-rays is needed, including an open mouth odontoid radiograph. MRI is recommended to rule out disruption of atlantal transverse ligament. Cervical axial CT with coronal and sagittal reconstructions are also recommended to demonstrate the orientation of the fracture path and to verify the integrity of the posterior elements. Complex motion polytomography may be used if the CT findings are unclear.

Anterior odontoid screw fixation indications.

1. fractures of the C2 vertebral body (except cephalad Type III fracture)

2. disruption of transverse atlantal ligament (TAL): see Transverse ligament injury. May be directly demonstrated on MRI. Indirect evidence: if the sum of the overhang of the lateral masses of C1 on C2 exceeds 7mm (rule of Spence)

3. large odontoid fracture gap

4. irreducible fracture

5. age of fracture: controversial. Fusion rates in fracture > 18 months old was 25% ¹⁾. Fracture < 6 months old have ≈ 90% fusion rate.

6. patients with short, thick necks and/or barrel chest: makes it difficult to achieve the proper angle. May be circumvented by the instrumentation distributed by Smith-Nephew which utilizes a cannulated flexible drill, tap, and screwdriver

7. pathologic odontoid fracture

8. fracture line in oblique orientation to frontal plane (shearing forces can cause malalignment during screw tightening).

1. position: supine head on horseshoe headrest, halter traction

2. anesthesia: video laryngoscopy, or second choice, asleep fiberoptic bronchoscopy are the intubation methods of choice (awake fiberoptic intubation is rarely used). Do NOT use a wire reinforced endotracheal tube

3. equipment: 2 C-arms for biplane fluoro, or O-arm image guidance

4. instrumentation:

a) ACDF surgical set

b) tube retractor (e.g. METRx® by Medtronic)

c) some surgeons use specialized instrumentation (e.g. Apfelbaum set)

5. implants: cannulated screw set

6. consent (in lay terms for the patient—not all-inclusive):

a) procedure: surgery to place screw(s) from the front of the neck across the fractured odontoid bone. Possible posterior approach in case the anterior approach cannot be completed

b) alternatives: nonsurgical management in a collar, fusion

c) complications: screw breakage/pullout, failure to fuse which might require additional surgery (which will reduce neck motion)

The anesthesiologist is positioned at the foot of the table. Video laryngoscopy, or second choice, asleep fiberoptic bronchoscopy are now the intubation methods of choice (awake fiberoptic intubation is rarely used).

Do NOT use a wire reinforced endotracheal tube since the wire interferes with the AP imaging.

Supine. The neck is placed in extension (critical to performing the procedure) either with Holter traction and a small shoulder roll with the head on a gel donut (a strip of tape across the forehead stabilizes the head), or a radiolucent head holder may be used. Place the lateral fluoro unit first, then the AP unit slides into the “C” of the lateral unit. Lateral fluoroscopy is used to assess reduction of the fracture fragment, and the head is repositioned to try and achieve reduction. If there is retrolisthesis of the odontoid, the neck may need to be slightly less extended. A radiolucent mouth gag is placed to hold the mouth open for AP transoral imaging (a small tape roll works well). Abort the procedure if AP and lateral fluoroscopic views do not adequately image the odontoid.

A Cloward-type of horizontal skin incision at ≈ C5–6 (the entry site can be localized by placing a guidewire adjacent to the patient’s neck and taking a lateral fluoro) and approach identical to anterior cervical discectomy are used (all the way to exposing the longus coli muscles. A Kittner is used to dissect superiorly anterior to the longus coli muscles in the loose areolar tissue up to C2. A self-retaining retractor (e.g. Caspar retractor—not distractor) with a superior retractor blade is attached (or a hand-held retractor, preferably radiolucent, may be used). Alternatively, a retractor tube system (e.g. METRx® by Medtronic, which manufactures a specialized extra-angled bevelled tube for this procedure) may be used. The bovie is used to remove the soft tissue over the inferior front of C2.

Localization: lateral fluoro is used to place the tip of an awl as far anteriorly as possible on the inferior endplate of C2 (a common error is to go too far back along the inferior margin of C2, which results in the guidewire ending up toward the back of the dens). AP fluoro is used place the awl in the exact center of the C2 body in the lateral dimension. The awl is used to make a pilot hole at this location.

Guidewire placement, drilling, tapping, and ultimately screw placement are performed while monitoring the progress on frequent fluoro images, aiming for the exact middle of the dens on AP fluoro, and aiming toward the apex of the odontoid fracture fragment (skimming just within the anterior part of the C2 vertebral body) on lateral fluoro.

Drilling is performed under fluoro all the way through the apical cortex of the dens to avoid cracking the dens with the screw (the area just distal to the apex of the dens is safe). A titanium partially threaded (lag) screw is placed. If an appropriately sized lag screw is not available, one can overdrill the part of the path through the body of C2 up to the fracture. In this way, a fully threaded screw can be used, which will slip through the overdrilled hole and still have a lag effect on the fracture fragment. If a second side-by-side screw is used, it may be fully threaded. In chronic nonunion cases, prior to advancing the screw, a bifaced curette may be inserted within the fracture space to freshen the fracture site. The screw(s) should be drawn up tightly to the inferior edge of C2.

At the end of the procedure confirm integrity of the transverse ligament by carefully flexing the neck under lateral fluoro.

The cement augmentation of a conventional anterior screw fixation in type II odontoid process fractures for elderly patients significantly increased stiffness and load to failure under anterior-posterior load in comparison with non-augmented fixation. The amount and quality of bone cement are usually taken ad hoc in clinical practise.

A study showed that the low porous cement was able to significantly influence the stiffness of the augmented odontoid screw fixation in vitro, although further in vivo clinical studies should be undertaken. Our results suggest that only a small amount of non-porous cement is needed to restore stiffness at least to its pre-fracture level and this can be achieved with the injection of 0.7-1.2 ml of cement ²⁾.

The immediate post-op strength of the odontoid + screw is only ≈ 50% of the normal odontoid. Therefore, a cervical brace is recommended for 6 weeks (although some authors don’t use one). If the patient has significant osteoporosis, a halo brace is recommended.

A patient hospitalised in the Neurosurgery Department of St Lukas Hosital in Tarnów in 2016. A literature review was performed using PubMed; search criteria included the phrases 'odontoid fracture perforation' and 'anterior cervical spine perforation'. The search returned 235 articles, of which 55 publications were in line with the subject of this paper, with only 12 deemed appropriate for consideration.

The authors present the case of an elderly patient with a history of odontoid fracture. Ten weeks after primary AOSF, the patient came to the Neurosurgery Department due to expectorating screws. This implied the need for further examination and even oesophageal reconstructive surgery or another spinal surgery. In laryngological examination and in gastroscopy there were no signs of fistula. In this case conservative treatment was proceeded. Due to odontoid fracture, non-union cervical posterior stabilisation was necessary ³⁾.

Healing takes ≈ 3 months (or longer with chronic nonunion). With fractures < 6 months old, the union rate was 95%. Chronic nonunions > 6 months old have a significant risk of hardware failure (screw breakage or pull-out), with a bony union rate of 31%, and 38% rate of presumed fibrous union. Thus, in cases of chronic nonunion > 6 months old, C1–2 arthrodesis is probably a better choice unless the need to maintain motion is worth the risk of needing a second operation if this one fails. The average technical complication rate is ≈ 6% (2% screw malposition, 1.5% screw breakout).

Common surgical option is an anterior odontoid screw. Some of the fractures are not suitable for anterior odontoid screw (anterior oblique, displaced distal fragments and those with atlantoaxial instability) and these are usually offered posterior transarticular screws (Magerl's) or posterior atlantoaxial screw rod/plate fixation (Goel-Harms technique).

Anterior odontoid screw fixation was first reported by Nakanishi ⁴⁾ and Bohler ⁵⁾. This procedure provides immediate spinal stability, preserves the normal rotation between C1-2, allows the best anatomical and functional outcome for type II odontoid fracture, and is associated with rapid patient mobilization, minimal postoperative pain and a short hospital stay. Acute odontoid fractures treated by anterior screw fixation have a fusion rate of approximately 90 percent ⁶⁾.

see Anterior odontoid screw fixation case series.