The mandibular angle as a landmark for identification of cervical spinal level

Retrospective radiographic review.

To determine the utility of the mandibular angle as a landmark for identification of cervical spinal level.

Improper localization of the skin incision during anterior cervical spine surgery may lead to increased technical difficulty of the surgery. Although the use of traditional palpable anterior neck landmarks (hyoid bone, cricoid cartilage, thyroid cartilage, and carotid tubercle) help identify appropriate spinal levels, their reliability has not been validated in actual surgeries. We hypothesize that the angle of the mandible (AM) is a consistently palpable landmark, and that the mandible can be used to accurately template the distance to subaxial cervical levels using preoperative radiographs.

As a pilot study, we prospectively evaluated 30 consecutive patients who underwent anterior cervical diskectomy and fusion to assess the interobserver accuracy of palpating the mandibular angle, hyoid, carotid tubercle, and thyroid and cricoid cartilages. In a second set of 26 consecutive patients undergoing anterior cervical diskectomy and fusion, we then retrospectively reviewed standing preoperative lateral plain radiographs of the cervical spine, in addition to supine lateral cervical spine radiographs taken at the time of surgery, to assess: (1) the position of the AM relative to the corresponding cervical spinal level, and (2) whether or not the position of the AM relative to the subaxial cervical levels is different on preoperative standing films and intraoperative supine films. In these same 26 patients, we also measured the vertical distance between the AM and the location of each subaxial intervertebral disc space. These measurements were repeated for the hyoid bone as a control for each patient.

The interobserver accuracy was 100% between observers for identifying the AM, hyoid bone, thyroid cartilage, and cricothyroid membrane, and 93% for carotid tubercle. The frequency with which anterior neck landmarks were palpable by the surgeon and assisting senior residents was as follows: AM (100%), hyoid bone (83%), thyroid cartilage and cricothyroid membrane (93%), and carotid tubercle (Surgeon: 63%, Resident: 57%, P = 0.79). There was 100% correlation between the position of the mandibular angle in the preoperative standing lateral radiograph and the intraoperative supine lateral radiograph, compared with 65% with the hyoid bone. The distances between the AM or hyoid to each disc space did not vary significantly between preoperative and intraoperative radiographs (P > 0.05).

The mandibular angle was shown to be the most consistently palpable landmark. Further, the distance from the mandible, measured on preoperative plain lateral cervical spine radiographs, is an accurate template to determine cervical spine levels during anterior cervical spine surgery.