Stretch-induced nerve injury as a cause of paralysis secondary to the anterior cervical approach

The anterior approach to the cervical spine, first described 40 years ago, has become a popular and widely used procedure by spine surgeons to expose the anterior vertebral bodies from C3 to T1. A significant complication of this procedure is transient or permanent ipsilateral recurrent laryngeal nerve paralysis. In a previous review at our institution of patients with hoarseness after an anterior cervical approach, 15 of 16 patients demonstrated right-sided paralysis. The asymmetry in the anatomic courses and lengths of the recurrent laryngeal nerves are proposed to place the right recurrent laryngeal nerve at an increased risk of stretch-related injury during this surgical procedure. We developed a cadaver model to evaluate the in-line stretch on the recurrent laryngeal nerve during the right- and left-sided approaches to the C4 and C7 vertebral bodies. To assess the difference in risk of injury to the two recurrent laryngeal nerves,we performed the anterior approach to the cervical spine in four anatomic positions: the left neck and right neck at the levels of C4 and C7 on 10 fresh human cadavers during the immediate postmortem period. The blades of a Cloward retractor were progressively spread to 2, 3, and 4 cm in the four anatomic positions while the corresponding degrees of ipsilateral recurrent laryngeal nerve stretch resulting from retraction were simultaneously measured. The left recurrent laryngeal nerve herd sufficient redundancy in its course within the tracheoesophageal groove in 10 of 10 cadavers such that it exhibited no in situ stretch during the left-sided approach to either the C4 or C7 vertebrae. In contrast, the right recurrent laryngeal nerve has little redundancy in its course and is not protected within the tracheoesophageal groove. The right-sided approach to C7 resulted in an average in situ stretch on the ipsilateral recurrent laryngeal nerve of 12% and 24%, with 3 cm and 4 cm of Cloward retraction, respectively. The right-sided approach to C4 resulted in significant levers of stretch in 3 (30%) of 10 cadavers and no stretch in 7 (70%) of TO cadavers. The relevance of these data is demonstrated by the review of numerous studies demonstrating the potential for significant neural damage with nerve stretch greater than 12%.