Optimal trajectory for the anterior occipital condyle screw

Objective This study aimed to assess the practicality and optimal approach for inserting an anterior occipital condyle screw, as well as to measure the screw placement characteristics. Methods A total of 80 normal head and cervical spine computed tomography scans (40 males/40 females) were used to construct three-dimensional models. The average age of the participants was 45.18 ± 8.86 years (ranging from 25 to 65 years). Three potential entry points for the anterior occipital condyle screw were identified. A simulated screw with a radius of 1.75 mm was created to replicate the screw trajectory and adjusted to establish the maximum and minimum cranial limits for each entry point. The feasibility of screw fixation was assessed, identifying the optimal entry point and analyzing relevant screw placement measurements. Results The success rates for screw placement were 95.6%, 94.4%, and 88.1% for the middle, lateral, and medial entry points, respectively. The success rate for the medial entry point was notably lower than that for the middle and lateral points. No statistically significant differences were found in the measured parameters between the left and right sides. The medial entry point exhibited the highest abduction angulation (35.72° ± 2.01°) for screw placement, followed by the middle (25.96° ± 1.86°) and lateral (15.14° ± 1.82°) points. The middle and lateral entry points displayed a considerably wider safe range of cranial angulation and screw placement length than the medial entry point. All three entry points achieved success rates exceeding 90% when the cranial angulation ranged from 2° to 6°. Conclusion The anterior occipital condyle screw presents a workable choice for anterior craniovertebral fixation. The middle entry point is identified as the optimal approach for placing 3.5-mm diameter screws.