gms | German Medical Science

Objective: C1 screw placement via the lateral arch, i.e. transpedicular (TP) screw placement, has biomechanical advantages over the traditional lateral mass (LM) technique and could potentially reduce the risk of injuries to the C2 nerve root and the paravertebral venous plexus. However, anatomic variability of the intramedullary height (IMH) of the C1 pedicle seems to be crucial for the success of this technique. We conducted a prospective study to analyze the feasibility of the C1 TP-technique based on preoperative evaluation of the C1 IMH.

Methods: Prospective single center analysis of patients for whom a C1 screw placement as part of a C1/C2-instrumentation or instrumented fusion with help of intraoperative 3D-imaging and navigation guidance was planned. The C1 pedicle IMH [1] was measured at the midpoint of the vertebral artery groove on preoperative coronal CT scans. When IMH was ≥1mm the technique was judged to be potentially possible (PP), when the IMH was <1mm the technique was judged to be potentially impossible (PI) and was discarded. Only in PP pedicles the surgical approach was planned for TP screw placement (no dissection of C2 nerve or paravertebral plexus) and the intraoperative success rate was recorded. Furthermore, pedicle violations were graded using the Neo classification (Neo et al., Spine 2005).

Results: The median age of our 7 patients (f: n=3) was 76 years (range: 69-85 years). The pathologies were 2 C1 arch fractures, one of them combined with an odontoid fracture, 2 odontoid fractures, and 3 odontoid pseudarthroses. 10 C1 pedicles were rated as PP with an IMH of 1.6±0.5 mm while 4 pedicles were classified as PI; in these pedicles the IMH was 0.4±0.4 mm. The TP-technique was feasible in all PP pedicles (success rate: 100%) while the traditional LM technique was applied in the 4 PI pedicles. The median duration of surgery was 135 min. (range 95-200 min), the median blood loss was 400 ml (range: 100-700 ml). According to Neo et al. 5 screws presented no pedicle perforation, minor pedicle violations <2mm were documented in 4 screws, a pedicle violation between 2 and 4 mm occurred in 1 screw. There was no violation >4mm. No revision surgery was needed due to screw malposition.

Conclusion: Our prospective evaluation demonstrated that an IMH ≥1mm measured on preoperative coronal CTs is a good selection criterion and leads to a high success rate of the transpedicular C1 screw placement technique.