Ponticulus Posticus: Definition and Clinical Significance
Ponticulus posticus (PP), also known as arcuate foramen or Kimmerle's anomaly, is a bony bridge on the posterior arch of the atlas (C1 vertebra) that forms over the vertebral artery groove, creating a complete or partial ossification of the posterior atlanto-occipital membrane 1, 2.
Anatomical Description
The structure represents ossification of the posterior atlanto-occipital membrane over the vertebral artery as it passes through the superior-lateral surface of the atlas posterior arch. This creates a foramen (arcuate foramen) that contains:
- The vertebral artery
- The suboccipital nerve root (posterior branch of C-1 spinal nerve) 3
Classification
PP is categorized into two distinct types:
- Complete PP: A circumferential bony bridge that fully connects the superior articular process to the posterior arch of the atlas 4
- Partial PP: An incomplete bony spike protruding from either the superior articular process or posterior arch, extending above the vertebral artery sulcus 4
Prevalence
The prevalence varies across populations, ranging from 7% to 17.5% in different studies 1, 2. The condition shows higher prevalence in males 1 and increases with age, suggesting a degenerative component 5, 6.
Clinical Significance
Symptomatic Presentations
PP is associated with multiple clinical manifestations:
- Cervicogenic headaches (particularly chronic tension-type headaches) 7, 3, 4
- Vertebrobasilar insufficiency 2
- Vertigo and dizziness 2
- Neck and shoulder pain 2, 7
- Neurosensory hearing loss 3
- Orofacial pain 4
Patients with complete PP experience more severe symptoms (82.22% symptomatic) compared to partial PP (72.22% symptomatic) 7.
Surgical Implications
The presence of PP poses significant risk during atlas lateral mass screw insertion, as the altered anatomy increases the potential for vertebral artery injury 2. The posterior arch lamina with PP is thinner (mean 3.3-3.4 mm) compared to normal anatomy, though this difference is not statistically significant 5.
Diagnostic Detection
PP is commonly identified on:
- Lateral cephalometric radiographs (routine orthodontic imaging) 1, 4
- Cone-beam CT (provides superior anatomical detail) 2
- CT scans (for surgical planning) 5
Critical pitfall: The cervical spine region on lateral cephalograms is frequently overlooked by orthodontists and radiologists, leading to missed diagnoses 4. This anatomical variant should be systematically evaluated in all lateral cephalometric images.
Associated Findings
Research demonstrates that the superior articular facet (SAF) on the PP side is significantly larger in both complete and partial variants, with greater left-right asymmetry compared to patients without PP 2. Additionally, PP shows a significant association with the GoGn-SN angle (vertical skeletal pattern), suggesting cranio-cervical posture may contribute to its development 6.