Augmentation of occipitocervical contoured rod fixation with C1-C2 transarticular screws

Occipitocervical Fusion Surgery: Review of Operative Techniques and Results

Objective Varying types of clinicoradiologic presentations at the craniovertebral junction (CVJ) influence the decision process for occipitocervical fusion (OCF) surgery. We discuss the operative techniques and decision-making process in OCF surgery based on our clinical experience and a literature review. Material and Methods A total of 49 consecutive patients who underwent OCF participated in the study. Sagittal computed tomography images were used to illustrate and measure radiologic parameters. We measured Wackenheim clivus baseline (WCB), clivus-canal angle (CCA), atlantodental distance (ADD), and Powers ratio (PR) in all the patients. Results Clinical improvement on Nurick grading was recorded in 36 patients. Patients with better preoperative status (Nurick grades 1-3) had better functional outcomes after the surgery (p = 0.077). Restoration of WCB, CCA, ADD, and PR parameters following the surgery was noted in 39.2%, 34.6%, 77.4%, and 63.3% of the patients, respectively. Complications included deep wound infections (n = 2), pseudoarthrosis (n = 2), and deaths (n = 4). Conclusion Conventional wire-based constructs are superseded by more rigid screw-based designs. Odontoidectomy is associated with a high incidence of perioperative complications. The advent of newer implants and reduction techniques around the CVJ has obviated the need for this procedure in most patients.

Occipitocervical fusion: fix to C2 or C3?

OBJECTIVE

The objective of this study was to explore the differences in clinical outcome between short-segment fixation (SSF; occiput-C2) and multi-segment fixation (MSF; occiput-C2, 3).

METHODS

From January 2008 to January 2012, patients who underwent surgery for instability at the occipitocervical junction were included in the study. Two different groups of surgeons using two different management options completed the surgeries. One group performed SSF, whereas the other group performed MSF. A total of 53 patients met the criteria (33 SSF, 20 MSF). Mean follow-up was 33.9 months (range, 12-62 months). Fusion was demonstrated by plain radiographs and computed tomography imaging. Neurological status, pillow neck pain, operative time, blood loss during operation, and perioperative complications were compared between the SSF and MSF groups.

RESULTS

The fusion rate was 97% in the SSF group and 100% in MSF the group. There was no statistically significant difference in the fusion rate between the two groups (P>0.05). One patient (3%) in the SSF group and two patients (10%) in the MSF group experienced perioperative complications. Of the 25 patients who had neurological symptoms, 22 (88%) showed improvement after the operation in the SSF group and 14 (87.5%) of 16 showed improvement in MSF group. In addition, patients who suffered from pillow neck pain achieved varying degrees of improvement after the operation.

CONCLUSION

SSF may be the better choice for treating occipitocervical instability when no subaxial instability is present. Overall, modern instrumentation can provide the stability needed for successful clinical fusion.

A novel technique of odontoidoplasty and C1 arch reconstruction: anatomical and biomechanical basis

BACKGROUND

Transoral odontoidectomy and resection of the anterior C1 arch destabilize the atlantoaxial joint and risk its stability.

OBJECTIVE

To preserve stability in such cases we devised and evaluated a proof-of-concept study. The arch and dens were dissected and decompression was performed on cadavers. The dens was replaced with an odontoid screw, and the C1 arch was replaced with a rib-graft substitute using miniplates. We assessed the biomechanical strength of the C1 ring and 3D occipitoatlantoaxial flexibility before and after the repair.

METHODS

Five silicon-injected fixed cadaver heads were dissected. The arch of C1 and dens were preserved and reconstructed using odontoid screws and miniplates. Once the feasibility of the technique was established, we biomechanically tested 6 cadaveric occiput-C2 specimens in 3 phases: (1) intact/normal range of motion (ROM), (2) after transection of dens and C1 arch, and (3) with odontoidoplasty using odontoid screws and C1 arch reconstruction.

RESULTS

After odontoidectomy and arch removal, angular ROM increased significantly in all directions of loading. Resection increased flexion-extension at the occiput-C1 and at C1-C2 by 21% and 129%, respectively. Reconstruction slightly increased flexion-extension stability (16% and 107%, respectively) relative to normal.With 70 N applied compression, the C1 ring separation was 1145% greater than normal. After reconstruction, the separation was only 89% greater than normal (statistically significant, P = .002).

CONCLUSION

C1 arch reconstruction with or without odontoidoplasty restores only partial angular stability of the atlantoaxial joint but provides restoration of the ability of the C1 lateral masses to resist splaying, often observed as postodontoidectomy cranial settling.

Biomechanical Implications of Extending Occipitocervical Instrumentation to Include the Subaxial Spine

BACKGROUND

No clear biomechanical data exist regarding where to place the caudal end of a screw-rod occipitocervical instrumentation construct.

OBJECTIVE

This study examines whether range of motion (ROM) from the occiput to C2 is altered by subaxial extension of occipitocervical instrumentation constructs.

METHODS

Cadaver specimens underwent intact biomechanical testing followed by destabilization via an odontoid osteotomy. Subsequent biomechanical testing was performed of four occipitocervical constructs: occipital plate + C2 pars screws (construct 1), occipital plate + C2 pars screws + C4 lateral mass screws (construct 2), occipital plate + C1-C2 transarticular screws (construct 3), and occipital plate + C1-C2 transarticular screws + C4 lateral mass screws (construct 4).

RESULTS

All constructs significantly reduced occiput-C2 ROM in all loading modes compared with the intact cervical spine, with one exception (construct 1, lateral bending). No significant ROM differences were noted when C4 lateral mass screws (construct 4) were added to construct 3. Addition of C4 lateral mass screws (construct 2) to construct 1 decreased the ROM in the flexion mode only. No significant ROM differences were seen between construct 2 and construct 3 in any loading mode.

CONCLUSION

The addition of subaxial instrumentation to occipitocervical instrumentation constructs in this study decreased occiput-C2 ROM only when the construct was anchored by C2 pars screws and only in flexion. Screws that cross the C1 to C2 articulation provide stable fixation when combined with an occipital plate, and the addition of subaxial instrumentation to this construct for stabilizing the occipitocervical junction does not significantly decrease ROM.

Posterior occipitocervical (C0–3) fusion using polyaxial occipital condyle to cervical spine screw and rod fixation: a radiographic and cadaveric analysis

Numerous conditions affect the occipitocervical junction requiring treatment with occipitocervical fixation. In this paper the authors present their technique of craniocervical fixation achieved with the cephalad extension of posterior C1–3 polyaxial screw and rods to polyaxial screws placed in the occipital condyles. They retrospectively analyzed occipital condyle morphology obtained from CT analyses of 40 patients with normal cervical spines, evaluated occipital condyle screw placement feasibility in 4 cadavers, and provided a case report of a 70-year-old woman with rheumatoid arthritis, basilar invagination, and atlantoaxial instability who was treated with this novel technique. Based on radiographic analysis of occipital condyle anatomy, they concluded that on average a 3.5-mm-diameter × 20- to 30-mm-long screw can be safely placed at an angle of 20–33° from the sagittal plane. Overall, measuring the condylar heights (mean [± SD] 10.8 ± 1.5 mm, range 8.1–15.0 mm), widths (mean 11.1 ± 1.4 mm, range 8.5–14.2 mm), lengths (20.3 ± 2.1 mm, range 15.4–24.6 mm), and angles (mean 32.8 ± 5.2°, range 20.2–45.8°) by using CT studies is an accurate and precise method. This finding correlates with the results of prior anatomical studies of occipital condyles and is important in the planning of craniovertebral junction surgery.