gms | German Medical Science

Objective: The occipitocervical region poses an anatomical dilemma, given the presence of the V3 segment of the vertebral artery (VA) when performing posterolateral approaches to the odontoid process in cases of pseudarthrosis, tumor or rheumatoid pannus. In such cases, a novel minimally invasive dorsolateral, tubular odontoidectomy and autologous bone augmentation combined with C1-2 instrumentation could provide excellent one stage management. No anatomical studies have described the spatial relationship of a tubular retractor between C1-2 to the surrounding anatomical structures. The objective of this study is to highlight the potential site and mechanisms of injury that can occur during this approach.

Method: 4 adult cadaveric specimens were dissected and studied (8 approaches) and 2 clinical cases of posterolateral minimally invasive odontoidectomy are presented. All cases underwent 3D planning on Dextroscope. The relationship between the vertebral artery, myelon, nerve root und C1-2 lateral masses was analyzed in reference to the minimally invasive dorsolateral approach and a 10 mm wide tubular retractor. Special attention was given to the attachments of the vertebral artery and its relationship to the vertebral foramen during all stages of the approach. In addition, lateral mass screws were placed bilaterally in C1 and pedicle screws were placed in C2, reproducing the modification of the Harms technique.

Results: All 8 approaches were successfully dissected, analyzed, and photographed. The tubular retractor was positioned closer to the VA at C1 (mean distance [SD] 0,6 ± 0,4 mm) than at C2 (mean distance [SD] 1,8 ± 0,5 mm). Within the intertransverse space it coursed closer to the myelon (1,6 ± 4 mm) than to VA (6,8 ± 4,3 mm). The distance between the VA and the uncinate process was less at C2 (3,2 ± 1,1 mm) than at C1 (3,9 ± 1,2 mm). When performing the minimally invasive dorsolateral approach for odontoidectomy, the J groove V3 and the distal V2 segments of the VA must be respected and eventually dissected in order to prevent injury of the vessel. The patients treated had excellent clinical outcomes.

Conclusions: When performing the minimally invasive dorsolateral approach for odontoidectomy, the surgically significant areas of potential vascular injury are the J groove of V3 segment of the VAS at C1 and the distal V2 segment at C2 of the VA which must be respected and eventually dissected in order to prevent injury of the vessel.