Positional change of hyoid bone after anesthesia in anterior surgery of upper cervical spine.

BACKGROUND CONTEXT The hyoid bone is used as a landmark in anterior upper cervical spine operations and is supposed to represent the level of C3 body. However, this correspondence between hyoid bone position and cervical level is not static and changes during surgery (extension after anesthesia). PURPOSE To find the cervical level corresponding to the position of hyoid bone before and after anesthesia and to evaluate the adequacy of its usage as a surgical landmark. STUDY DESIGN A retrospective study. PATIENT SAMPLE One hundred twenty-eight patients with degenerative cervical diseases who had undergone anterior cervical discectomy and fusion. OUTCOME MEASURE Radiologic measure. METHODS For each patient, preanesthesia neutral, preanesthesia extension, and postanesthesia induction extension C-spine lateral image were obtained. The level of cervical vertebra that midline of hyoid bone indicated was measured by radiological method. A cervical vertebra was divided into three segments, consisting of upper half, lower half, and disc space, and each of these segments was considered as one level. The differences between pre- and postanesthesia induction hyoid positions were classified as minimal change (one level or less) and significant change (two levels or greater). Relationship between positional change of hyoid bone to gender, obesity, and age were respectively investigated. RESULTS There were 20 cases of one-level distal displacement of the hyoid bone, 40 cases of two-level distal displacement, 34 cases of three-level distal displacement, 16 cases of 4-level distal displacement, and two cases of five-level distal displacement. In eight cases, there was no level change, and in the remaining 8 cases, the hyoid bone had been displaced proximally. There were 34 cases of minimal change. The remaining 94 cases (73.4%) had significant changes. No respective relationship was found between sex, obesity, age and pre-and postanesthesia induction positional change of hyoid bone. CONCLUSIONS Among the 128 cases studied, 73.4% hyoid bone positions had changed by more than one cervical vertebra body between the pre- to postanesthesia induction X-ray images. Sex, age, and body mass index were not associated with statistically significant differences in these positions. The hyoid bone should not be trusted as a landmark for upper cervical operations, and the cervical level to be operated should be confirmed by a radiological method before a skin incision is made.