Volumetric three-dimensional computed tomographic evaluation of the upper airway in patients with obstructive sleep apnoea syndrome treated by maxillomandibular advancement

Obstructive sleep apnoea syndrome is the periodic reduction or cessation of airflow during sleep together with daytime sleepiness. Its diagnosis requires polysomnographic evidence of 5 or more episodes of apnoea or hypopnoea/hour of sleep (apnoea/hypopnoea index, AHI). Volumetric 3-dimensional computed tomographic (CT) reconstruction enables the accurate measurement of the volume of the airway. Nasal continuous positive airway pressure (CPAP) is the conventional non-surgical treatment for patients with severe disease. Operations on the soft tissues that are currently available give success rates of only 40%-60%. Maxillomandibular advancement is currently the most effective craniofacial surgical technique for the treatment of obstructive sleep apnoea in adults. However, the appropriate distance for advancement has not been established. Expansion of the air-flow column volume did not result in an additional reduction in AHI, which raises the important issue of how much the maxillomandibular complex should be advanced to obtain an adequate reduction in AHI while avoiding the risks of overexpansion or underexpansion. We have shown that there is a significant linear relation between increased absolute upper airway volume after advancement and improvement in the AHI (p=0.013). However, increases in upper airway volume of 70% or more achieved no further reduction in the AHI, which suggests that the clinical improvement in AHI reaches a plateau, and renders further expansion unnecessary. This gives a new perspective to treatment based on the prediction of changes in volume, so the amount of sagittal advancement can be tailored in each case, which replaces the current standard of 1cm.