Ponticulus posticus: Morphometric analysis and Its anatomical Implications for occipito-cervical fusion

Objective: The purpose of this study was to evaluate the morphometric characteristics of ponticulus posticus (PP) and determine the impact of two promising high cervical operations (posterior arch to lateral mass screw fixation (PALMSF) and occipital condyle fixation (OCF)). Patients and methods: We evaluated retrospective data from a total of 2628 head and neck 3-dimensional CT-angiographies (3D-CTA) that did not have bony or vascular abnormalities. The PP anomaly cases were confirmed, then we measured vertebral artery groove height (VAGH), arch to vertebral artery distance (AVD) and posterior arch height (PAH) for PALMSF. We also measured the vertebral artery to occipital bone distance (VOD) for OCF. Results: In 186 patients (7.1%), 227 PP (complete or near complete) were identified and this anomaly was more common in males and on the left side. The mean VAGH and PAH values ranged from 5.0 to 6.0 mm and from 7.0 to 8.8 mm, respectively. The VAGH value was not statistically different, regardless of the presence of PP, and the feasibility ( > 4 mm) of a safe PALMSF (range, 87.7-100%) was not influenced by PP anomalies. The mean value of VOD in the anomaly side (range, 6.0-8.0 mm) was much higher than for normal side (range, 4.2-5.7 mm) and the proportion of patients that had a safe OCF ( > 3.5 mm) was also much higher (range, 90.8-96.9%) than for the normal side. Conclusions: A PP anomaly might have some anatomical feasibility and advantage during PALMSF and OCF, due to the relatively sufficient bony (VAGH) and spatial regions (VOD). However, there are gender differences in anatomical dimensions (VAGH, VOD and AVD); therefore, surgery in female patients should be approached more cautiously in the future.