The reliability of the Bellhouse test for evaluating extension capacity of the occipitoatlantoaxial complex.

Unlabelled: We examined the reliability of an airway evaluation test to assess the occipitoatlantoaxial (OAA) extension capacity described by Bellhouse et al. (Bellhouse test) in 20 adult volunteers with normal cervical spines. Each subject sat upright with the head in the neutral position and was then asked to extend the head maximally while attempting to move the neck as little as possible. The angle from the neutral position to the extreme extension was measured using the goggle-goniometer. Lateral cervical radiographs were taken in these positions, and the OAA extension angle was radiographically measured. Median values for OAA extension measured radiographically and extension of the head measured with the Bellhouse test were 21.5 degrees and 30 degrees, respectively. Extension of 9.5 degrees occurred at the subaxial regions, which could not be detected by inspecting surface contours of the neck. The extent of the subaxial extension was almost consistent with the degree of overestimation of the OAA extension capacity by the Bellhouse test. Because the subaxial extension occurred independent of the degree of the OAA extension, a strong relationship between the angle measured with the goggle-goniometer and the OAA extension angle measured radiographically was not established (P < 0.01, r(2) = 0.44). These findings mean that the test is not always accurate to evaluate the OAA extension capacity and will fail to detect a reduction of the OAA extension capacity if the subaxial regions are normal. Therefore, these problems derived from the Bellhouse test offer a potential for missing a prediction of difficult tracheal intubations because reduced OAA extension is one of the important factors that make intubation difficult.

Implications: The Bellhouse test was not always accurate to evaluate the actual occipitoatlantoaxial extension capacity because of the inevitable occurrence of the subaxial extension. This may mean that some difficult endotracheal intubations will be unpredictable.