SPECIAL attention should be paid to airway management in rheumatoid patients with atlantoaxial subluxation (AAS) because they may be at risk of life-threatening neurologic injury caused by worsening the subluxation in the head and neck position during airway maneuver.1–5Atlantoaxial subluxation is found in 11–46% of patients with rheumatoid arthritis and is classified into four groups according to the direction of the subluxation, including anterior AAS, posterior AAS, vertical AAS, and lateral AAS.6,7Anterior AAS is the most prevalent form, accounting for 80% of all types of subluxations.6,7In rheumatoid patients with anterior AAS, the degree of subluxation has been estimated in association with flexion and extension at the entire cervical spine (the head and neck) as a functional unit.6,7During flexion of the entire cervical spine, the atlas separates anteriorly from the axis, and the subluxation is worsened. On the contrary, during extension, the atlas slides backward until it rests against the dens of the axis, and the subluxation is reduced. Therefore, standard anesthesia textbooks advocate avoiding flexion of the head and neck in rheumatoid patients with anterior AAS.3,4The sniffing position is widely recommended as the standard head and neck position for conventional laryngoscopy.8,9This position consists of two components, which are severe extension of the head at the occipitoatlantoaxial (OAA) complex and slight flexion of the neck at the subaxial cervical segments.8,9In this position, the direction of movement of the OAA complex (head movement) and that of the subaxial segments (neck movement) are opposite.8,9Theoretically, extension of the OAA complex reduces the subluxation, and flexion of the subaxial segments makes it worse in rheumatoid patients with anterior AAS. In general, it is believed that accomplishment of the sniffing position is tolerated in these patients because the OAA complex where the subluxation occurs is extended, and the degree of the subaxial flexion is mild.2,10However, whether this position is safe is still unknown. We report a case of the rheumatoid patient with anterior AAS that was markedly worsened by the sniffing position.
A 61-yr-old, 160-cm, 47-kg woman with rheumatoid arthritis was admitted for reconstruction of the rheumatoid distal radioulnar joint. She had had rheumatoid arthritis for 18 yr. Three years previously, the patient had undergone bilateral total knee replacements during combined spinal epidural anesthesia. Airway examination consisted of Mallampati class 2 with a hyomental distance of 5 cm and a mouth opening of 5 cm. The patient could move her head and neck without limitation and was asymptomatic in every head and neck position. Radiographic examination of the cervical spine for rheumatoid patients was performed in our radiology center the day before surgery. When the patient lay down on a flat table, lateral cervical radiographs were taken in three head and neck positions, which were the head on the flat table without a pillow, extension of the entire cervical spine obtained by bending part of the table, and the sniffing position obtained by placing 7 cm of a pillow under the head.8,9These positions were determined by actively positioning with the patient’s effort. Radiographs revealed marked AAS of the anterior atlas–dens interval (AADI) of 10 mm and the posterior atlas–dens interval (PADI) of 12 mm in the sniffing position, compared with an AADI of 2 mm with both the head on the flat table without a pillow and extension of the entire cervical spine (fig. 1). The AADI and PADI were defined as the distance between the posterior surface of the anterior arch of the atlas and the anterior surface of the dens and the distance between the posterior surface of the dens and the anterior surface of the posterior arch of the atlas, respectively.7Preoperative laboratory results were normal except for mild anemia. The patient requested to have general anesthesia because of the stress she had experienced during regional anesthesia during a previous operation. We planned fiberoptic intubation, with the patient awake and under sedation, using manual in-line stabilization because of the necessity of providing a guaranteed airway for the surgical procedure lasting for 1.5–3 h and the technique minimizing the head and neck motion with which we had the most expertise. After the patient was counseled, she agreed to the procedure.
The patient received atropine (0.5 mg) 30 min before surgery. In the operating room, the patient lay supine on the operating table, and her head was placed on the flat table without a pillow. We confirmed that the patient was neurologically asymptomatic in this position. The standard monitors, including electrocardiography, indirect arterial pressure, pulse oximetry, and capnography, were applied, and midazolam (2 mg) was administered intravenously. After appropriate topical anesthesia, fiberoptic intubation was performed with manual in-line stabilization while the patient was awake. After successful intubation was confirmed, anesthesia was induced with propofol. Oxygen saturation did not decrease below 98% throughout intubation. The operation proceeded uneventfully. After the patient fully awakened, the trachea was extubated using manual in-line stabilization. We confirmed that the patient did not have any neurologic deficits.
The stability of the OAA complex is mainly maintained by the transverse, apical, and alar ligaments.1,7Of these, the transverse ligament is pivotal for keeping the dens securely in place, but it is prone to be affected by synovial inflammation and hyperemia of the adjacent articulations related to rheumatoid arthritis.1,7When the transverse ligament alone is disrupted, AAS of the AADI of up to 5 mm occurs.1,7If the apical and alar ligaments in addition to the transverse ligament are disrupted, the AADI amounts to more than 10 mm.1,7At this stage, the occiput and the atlas are separated from the axis and the lower cervical vertebrae, and the cervical spine is divided into the occiput–atlas component and the axis–lower component. In the current patient, all of the ligaments stabilizing the OAA complex were disrupted because of an AADI of more than 10 mm. We considered mechanisms for occurrence of the subluxation in the sniffing position in our patient as follows. When the neck was flexed by placing a pillow under the occiput for achieving the sniffing position, the occiput–atlas component was pushed forward, leaving the axis–lower component behind, and AAS occurred. Head extension was expected to correct the subluxation as a result of placement of the pillow. However, because all of the ligaments contributing to the stability of the OAA complex were disrupted, force at the occiput–atlas component producing by head extension was not transmitted to the axis–lower component, and the AAS remained unchanged. If the apical and alar ligaments were intact even with disruption of the transverse ligament, the AAS might be corrected because the occiput–atlas component was connected to the axis–lower component. Whether AAS is corrected may depend on degree of disruption of ligaments stabilizing the OAA complex. That is, AAS is not always corrected by head extension in rheumatoid patients with anterior AAS. Therefore, achievement of the sniffing position is dangerous in these patients.
Compression of the spinal cord occurs when the AADI is more than 9 mm or the PADI is less than 14 mm in patients with anterior AAS.1,7,11However, despite an AADI of 10 mm and a PADI of 12 mm in the sniffing position, our patient was asymptomatic. There are some patients with AAS who are entirely asymptomatic, and AAS can occur without obvious abnormalities at other peripheral joints.1,4,7The subluxation, even if severe, is not always easy to diagnose with only symptoms and signs. Also, in the current patient, the head and neck position during radiography was determined by actively positioning with the patient’s effort. Dvorak et al. 12showed that the degree of the cervical spine motion found by passively positioning by an examiner was greater than that by actively positioning with the patient’s effort. Moreover, when general anesthetics, muscle relaxants, or both are used, the splinting action of the cervical muscles on the cervical spine is lost, which may enhance motion of the cervical spine by passively positioning. Calder et al. 10reported that the prevalence of difficult laryngoscopy was high in patients with rheumatoid arthritis. Also, with routine preoperative airway evaluation tests, prediction of difficult laryngoscopy is often difficult. These facts indicate that preoperatively undiagnosed AAS can be worsened in patients with rheumatoid arthritis as a result of excessive motion of the cervical spine if a laryngoscopist passively achieves the sniffing position while the patient is under general anesthesia, muscle relaxation, or both to improve the view of the larynx during direct laryngoscopy when unanticipated difficult laryngoscopy is encountered, which may cause life-threatening neurologic injury. Bollensen et al. 5reported a case of a patient with rheumatoid arthritis and unrecognized AAS in whom tetraplegia with respiratory insufficiency due to dislocation of the dens occurred after airway management. To overcome this problem, it is essential to recognize AAS and to plan an appropriate strategy for airway management. Therefore, the cervical spine should be evaluated radiographically before anesthesia in all patients with rheumatoid arthritis. Airway techniques minimizing head and neck movement are recommended in rheumatoid patients with anterior AAS. Fiberoptic intubation is useful not only for this purpose but also for managing difficult airways. Wattenmaker et al. 13demonstrated that the fiberoptic intubation reduced postoperative upper airway complications in patients who had posterior operations on the cervical spine for rheumatoid arthritis. Fiberoptic intubation is a reliable method. When conventional laryngoscopy is necessary for tracheal intubation, attention must be paid to the head and neck position during the maneuver.
In summary, this case illustrates that accomplishment of the sniffing position for laryngoscopy can result in exacerbation of the subluxation with resultant neurologic injury in rheumatoid patients with anterior AAS. Therefore, these patients’ tracheas should be intubated in a manner in which head and neck movement is minimized. In addition, preoperative radiologic assessment of the cervical spine is recommended because of the difficulty in diagnosis of AAS with merely clinical evaluation in these patients.