Importance of the Occipitoaxial Angle and Posterior Occipitocervical Angle in Occipitocervical Fusion

Abstract

ObjectiveTo observe the effects of occipitoaxial angle (O‐C2 angle, OC2A) and posterior occipitocervical angle (POCA) selection on postoperative clinical efficacy and lower cervical curvature in patients with acute acquired atlantoaxial dislocation after occipitocervical fusion (OCF).MethodsA total of 150 healthy subjects without cervical disease (healthy group) were randomly selected based on gender and age. Three spine surgeons measured the OC2A and POCA of the healthy group and averaged the values. A total of 30 patients with an average age of 51.0 years (range, 18–70 years; 16 male and 14 female) with trauma or rheumatoid arthritis (disease group) who underwent occipitocervical fusion (OCF) for atlantoaxial dislocation between January 2012 and June 2016 were reviewed. OC2A, POCA, and cervical spinal angle (CSA) were measured postoperative/soon after surgery and ambulation, and at the final follow‐up visit. The preoperative and final follow‐up visual analog scale (VAS), Japanese orthopedics association score (JOA), neck disability index (NDI), and dCSA (change of CSA from postoperative/soon after surgery and ambulation to final follow‐up) were recorded.ResultsThe values of OC2A and POCA in 150 healthy subjects were 14.5° ± 3.7° and 108.2° ± 8.1°, respectively, and the 95% confidence interval (CI) were 7.2°–21.8° and 92.3°–124.0°, respectively. There was a negative correlation between OC2A and POCA (r = −0.386, P < 0.001). There were 18 patients (group one) of ideal OC2A and POCA (both within 95% CI of the healthy group) postoperative/soon after surgery and ambulation with a mean follow‐up time of 26.3 ± 20.9 months in disease group. The remaining patients (group two) with a mean follow‐up time of 31.3 ± 21.3 months. There was no statistically significant difference in the baseline data as well as pre‐operative outcomes, including VAS score, JOA score, and NDI between the two groups. Likewise, the post‐operative outcomes in final follow‐up, including VAS and JOA score, had no distinct difference in the two groups. However, NDI (11.0 ± 2.9) in group two at the final follow‐up was significantly higher than that in group one (7.0 ± 2.3) (P < 0.001). And group two showed statistically greater dCSA (5.9 ± 7.5°) than group one (−2.3° ± 6.2°) (P = 0.003).ConclusionsThe negative correlation between OC2A and POCA plays an important role in maintaining the biodynamic balance of the occipital‐cervical region. OC2A and POCA should be controlled of a normal population in patients with acute acquired atlantoaxial dislocation during OCF, which can further improve the clinical efficacy and prevent loss of lower cervical curvature after surgery.

Optimizing Alignment Parameters During Craniocervical Stabilization and Fusion: A Technical Note

“…The POCA is that angle subtended by the tangent to the flat posterior aspect of the occiput between the opisthion and occipital protuberance, and a line drawn along the posterior aspect of the third and fourth cervical facets. An increased POCA reflects a downward head tilt and is associated with increased adjacent segment degeneration due to increased biomechanical stresses [20].…”

Immersive Surgical Anatomy of the Craniocervical Junction

“…• The posterior occipitocervical angle (POCA) is described as the intersection of a tangential line along the flat squamous portion of the occipital bone (from the foramen magnum to the external occipital protuberance) with a line formed by the posterior aspect of the C3 and C4 facets ( Figure 7B). The values of this angle vary from 108.3°± 7.8° and 108.0° ± 8.4°, respectively in males and females [18].…”

“…• The occipitoaxial angle (C0-C2 McGregor) is determined by the crossing of an oblique line drawn along the inferior endplate of the axis with the McGregor line ( Figure 7B). This angle ranges between 14.8° ± 3.1° in males and 14.2° ± 4.3° in females [18].…”

Flexion Dysfunction of Atlanto‐Occipital Joint Associated with Cervical Spondylosis

“…In contrast, the atlanto‐occipital joint accommodates 25° of flexion and extension and 5° of axial rotation 7 . Significant relationships between the alignments of the upper and subaxial cervical spine have been clearly established in asymptomatic subjects 4, 8 . Several studies demonstrated that atlantoaxial instability can result in compensatory change in subaxial alignment of cervical spine and further lead to spinal degeneration like osteophyte formation, ligamental hypertrophy, and disc space reduction due to the pathological factors related to the instability, including weakness of paraspinal muscles, facetal telescoping, and “listhesis” 4, 9 .…”