Minimally Invasive Subaxial Cervical Pedicle Screw Placement with Routine Fluoroscopy: Cadaveric Feasibility Study and Report of 6 Clinical Cases

Abstract

Objective: Conventional cervical pedicle screw insertion necessitates extensive paraspinal muscle dissection and retraction in order to achieve the lateral to medial angulation needed to achieve the optimal screw trajectory. Minimally invasive transmuscular approach can comfortably achieve this angulation without significant injury to the midline structures and its musculo-ligamentous attachments.Methods: Minimally invasive cervical pedicle screws were inserted in 4 fresh frozen cadaveric specimens. Pre-procedure and post-procedure CT scans were done to assess the pedicle dimensions, suitability for screw insertion and integrity of the screws. The same technique was applied in a clinical cohort of six cases – 3 cases of traumatic subluxation; one case of traumatic vertebral fracture and 2 cases of infective facet destruction (Koch’s); with successful outcomes.Results: Among the 38 screws in the cadaver specimens, a total of 11 screws (28.9%) had breached the pedicle wall (Lateral wall breach–9; Medial wall breach–2). Of the 9 screws (23.6%) that had a lateral breach into the vertebral canal, 4 (10.5%) each had Grade IIa breach and one (2.6%) had Grade III breach. The mean transverse screw angle in the subset of pedicle screws with no breach was 34.1 whereas it was 22.1 in screws that had lateral breach and 43.6 in those with medial breach. Among the 22 screws inserted in the clinical cohort of 6 cases, 4 screws (18.1%) had breached the pedicle wall. All the identified breaches were in the lateral wall (Grade IIa – 3; Grade IIb–1; Grade III–nil). Conclusion: Minimally invasive subaxial pedicle screw insertion can be utilized in cases where a robust posterior fixation is required, either in isolation or as an adjunct to anterior surgery, in cases where a direct posterior decompression is not warranted. It is a safe and effective approach which minimizes injury to the paraspinal structures and midline attachments.