• Mikinobu Takeuchi, Norimitsu Wakao, Mitsuhiro Kamiya, Koji Osuka, Naoki Matsuo, Toshiaki Terasawa, Toshimasa Asai, and Masakazu Takayasu.
• From the Departments of *Spine Center †Neurological Surgery ‡Orthopedic Surgery, Aichi Medical University, Nagakute, Aichi, Japan §Department of General Surgery, Shirayama Surgical Clinic, Kasugai, Aichi, Japan; and ¶Department of Internal Medicine, Asai Hospital, Seto, Aichi, Japan.
• Spine. 2014 Jul 15;39(16):E944-9.

Study DesignA prospective study.ObjectiveTo examine the diameter (mm), transverse diameter (mm), and cross-sectional area (mm²) of the C5, C6, and C7 nerve roots using ultrasonography.Summary Of Background DataEach 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.MethodsAll 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.ResultsThe 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 mm²; C6, 10.7 and 11.0 mm²; and C7, 8.8 and 8.8 mm². 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).ConclusionThe C5 nerve root was significantly 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.

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