Reduction in mouth opening with semi-rigid cervical collars † †Presented as a poster at the Difficult Airway Society Annual Scientific Meeting, Leicester, UK, November 25–26, 2004.

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Abstract
Background. Reduced mouth opening may be a major contributing factor to the deterioration in the view obtained at laryngoscopy when a semi-rigid cervical collar is in place. We set out to assess the degree to which mouth opening is restricted by a cervical collar. Methods. We measured maximal inter-incisor distance in 52 volunteers. It was measured again after application of each of three appropriately sized semi-rigid cervical collars (Stifneck, Miami J, and Philadelphia). Results. Inter-incisor distance was significantly reduced by the application of a cervical collar [No collar 41 (7) mm–mean (sd); Stifneck 26 (8) PPPConclusions. Application of a semi-rigid cervical collar can significantly reduce mouth opening. This could hinder definitive airway placement. Our results support removing the anterior portion of the collar before attempts at tracheal intubation.