Anatomical analysis of medial branches of the dorsal rami of cervical nerves for radiofrequency thermocoagulation

Abstract

Objective: Blocking of the cervical medial branches has been used to successfully treat patients with chronic neck pain. The aim of this study was to clarify the anatomical aspects of the cervical medial branches to improve the accuracy and safety of thermocoagulation denervation. Methods: Forty cervical spine specimens (20 right and 20 left specimens) were harvested from 20 cadavers and dissected. Therein, the anatomical parameters of the C4 – C7 cervical medial branches from the dissected specimens were measured. Three-dimensional computed tomography (3D-CT) reconstruction images were then obtained after coating the nerve with barium. The parameters were measured using the electronic calipers provided by Picture Archiving Communication System (PACS).Results: Based on cadaveric analysis, most of the cervical dorsal rami gave off one medial branch; however, the cervical dorsal rami gave off two medial branches in 27 % at the vertebral level C4, in 15% at level C5, in 2 % at level C6, and in 0 % at level C7. The diameters of the medial branches varied from 1.0 to 1.2 mm, and the average distance from the notch of inferior articular process to the medial branches was about 2 mm. The averaged contact lengths of the medial branches with a straight electrode needle under a parasagittal approach and a 30-degree angular approach at levels C4 – C6 were 4.9±2.1 mm and 2.7±0.9 mm, respectively. Lateral branches emerged from the dorsal rami at the medial portion of the posterior tubercle in more than 80% of all 40 specimens at all vertebral levels, while bifurcation sites on the upper portion of the posterior tubercle were observed in six, six, four and zero specimens at vertebral levels C4, C5, C6 and C7, respectively. On the analysis of three-dimensional computed tomography reconstruction images, cervical medial branches (C4 to C7) passed through the upper 49% – 53% of a line between the tips of two consecutive superior articular processes (anterior line). Also, cervical medial branches passed through the upper 28% – 35% of a line between the midpoint of two consecutive facet joints (midline). Conclusions: The present study demonstrated that cervical medial branches run dorsally along a line that passes through the midpoint of the anterior line and through the upper one third of the midline of the facet column at vertebral levels C4 – C6, respectively. The results of the present study indicate that needle tip placement at the middle of the anterior line and the upper one third of the midline, respectively, in cervical radiofrequency thermocoagulation may be superior to conventional approaches.