Three muscles in the upper costovertebral region: description and clinical anatomy

The aim of the study was to describe three small muscles in the upper costovertebral region that have close proximity to the ventral rami of the lower cervical and upper two thoracic spinal nerves. The study was performed using both anterior and posterior approaches to the costovertebral region. Twenty-five human cadavers, 15 males and 10 females with a mean age of 50 years and with normal spines, constituted the material of the study. Dissection revealed the presence of three triangular muscles that extended from the transverse processes of the seventh cervical through second thoracic vertebrae to the upper borders of the necks of the first through third ribs, respectively. The second and third muscles are described and reported for the first time. The ventral rami of the lower cervical and upper two thoracic spinal nerves emerged through narrow gaps between the described muscles and the bodies of seventh cervical and upper two thoracic vertebrae, respectively. The lateral branch of the dorsal ramus of the corresponding spinal nerve issued posteriorly between the muscle and the articular capsule of the zygapophyseal joint. It then curved round the posterior aspect of the muscle and passed through the gap between the muscle and the levator costarum, after supplying them both. We suggest that these three muscles were suggested to share a common embryogenesis with the intertransverse muscles. In addition, this study suggests that the three muscles described herein could be one of the potential causes of thoracic outlet syndrome.