Morphological Distinction of Cervical Nerve Roots Associated With Motor Function in 219 Healthy Volunteers A Multicenter Prospective Study

Study Design. A prospective study. Objective. To examine the diameter (mm), transverse diameter (mm), and cross-sectional area (mm 2) of the C5, C6, and C7 nerve roots using ultrasonography. Summary of Background Data. Each of the cervical nerve roots affected a different motor or sensory area. Although there were several studies that performed a detailed assessment of cervical nerve root anatomy in cadavers, only a few studies on the thickness of cervical nerve roots in living specimens have been performed. We examined whether the thickness of the C5, C6, and C7 nerve roots, as well as the area supplied by each of the roots, varied. Methods. All 219 subjects (99 males and 120 females; mean age, 47 +/- 15 yr) were healthy volunteers. The diameter and the transverse diameter were measured via ultrasonography, and the cross-sectional area was calculated for each of the C5-C7 nerve roots. Results. The following diameter measurements (right and left, respectively) were obtained: C5, 2.8 and 2.9 mm; C6, 3.6 and 3.8 mm; and C7, 3.3 and 3.4 mm. The following transverse diameter measurements were obtained (right and left, respectively): C5, 2.8 and 3.0 mm; C6, 3.7 and 3.8 mm; and C7, 3.5 and 3.4 mm. The following cross-sectional area measurements (right and left, respectively) were obtained: C5, 6.3 and 6.4 mm(2); C6, 10.7 and 11.0 mm(2); and C7, 8.8 and 8.8 mm 2. Based on the 3 measurement methods, the C5 nerve root was significantly thinner than the other 2 nerve roots (P < 0.001), and the C7 nerve root was smaller than the C6 nerve root (P = 0.001). Conclusion. The C5 nerve root was signifi cantly thinner than the C6 and C7 cervical nerve roots. The fact that the C5 nerve is thinner may render it more susceptible to damage during cervical surgery.