HKU Bulletin January 2011 (Vol. 12 No. 1)

Distraction simulation surgery for mandibular advancement in a child with OSAS A new grant has allowed surgeons in the Faculty of Dentistry to extend their service to the economically deprived. Obstructive Sleep Apnoea Patients Get Free Treatment Research Obstructive sleep apnoea is an under recognized and under diagnosed medical condition, characterized by abnormal pauses in breathing, or instances of abnormally low breathing, during sleep. Each pause in breathing, called an apnoea, can last from a few seconds to minutes, and may occur five to 30 times or more an hour. It can lead to serious conditions such as hypertension, type 2 diabetes, stroke and even sudden death during sleep. Traditional treatments rely on the use of Continuous Positive Airway Pressure (CPAP) or oral appliances during sleep both which are uncomfortable and inconvenient. With that in mind, in 2000, the Oral and Maxillofacial Surgery Discipline in the Faculty of Dentistry began employing corrective surgery as a permanent solution. As obstructive sleep apnoea is often caused by an underdeveloped mandible, lengthening the mandible can result in corresponding enlargement of the oro-pharygeal airway. The jaws can be lengthened by surgical methods that include orthognathic surgery and distraction osteogenesis. Thanks to a grant from the S.K. Yee Medical Foundation, a number of patients from lower income families are now receiving the treatment free of charge. This kind of surgery can also be extended to children and infants suffering from this debilitating sleep apnoea problems. Professor L.K. Cheung, Chair Professor of Oral and Maxillofacial Surgery explains, “Distraction osteogenesis is a biological tissue engineering method, by stretching a divided bone segement slowly and progressively, and by creating tension, new bone will spontaneously form. This technology involves a device fitted into the jaw to gradually lengthen the jawbone to correct the dental occlusion and simultaneously enlarge the airway. A History of Correcting Facial Deformities “This method was developed at our University based on our experience of distraction osteogenesis in correcting facial deformities in non-apnoeic patients. Our experience of distraction of the cranio- maxillofacial skeleton dates back to 1995 and our research and clinical experience have been extensively reported in about 30 publications.” Although the application of internal distractors has been practiced on adults for some time, the method is more difficult when applied to children because their bones are softer and smaller, and there are developing permanent teeth inside the jawbones. One child that Professor Cheung has operated on has such severe sleep apnoea from micro-gnathic jaw that he required a tracheostomy (an opening on the windpipe for air to bypass) to breath. To ensure that the apnoea can be resolved, Professor Cheung aimed to move the child’s jaw forward by 40 mm. “The distraction process is not painful for the child,” he says. “But it requires the involvement of parents and child to turn the distractors every day to lengthen the jaw which can be done at home.” “The reason it’s called distraction osteogenesis is because we cannot simply force the jaw forward by 40 mm, because we will tear the nerves and blood vessels inside the lower jaw. This process involves gradual lengthening of not only the jaw bone but also the nerves and vessels. In most cases, distraction is applied to the lower jaw, although it may involve the upper jaw or a combination of both.” It moves one millimetre a day and, if it goes smoothly, should take 40 days to reach the target. During a period of consolidation bone will spontaneously form inside the stretched fibrous soft tissues. Once the jaw has been extended, the patient is assessed by a sleep study to ensure he or she can breathe unaided with no, or few, apnoea events. The distractors, which offer a permanent solution, are usually removed after three to six months. The sponsored treatment is only available to those diagnosed with obstructive sleep apnoea, who are unable to tolerate the CPAP or oral appliance, or those hoping for a permanent cure of their apnoea. “The distractor devices are very expensive. Unfortunately many patients and child sufferers are from poor families and they can’t afford to pay for the distractor devices which cost $20,000 each. In sleep apnoea patients, we need two for each side of the jaw. 29 “We applied for a grant from the S.K. Yee Medical Foundation and they acknowledged our efforts by giving us slightly less than $900,000. Unfortunately we originally applied for $2.7 million, with which we hoped to pay for 120 devices for 60 patients. With only one third of the requested funding, we will try to treat as many patients as possible by appealing to other charities and research foundations, as well as trying to request the company that supply these devices provide a substantial discount. We would appreciate anyone generous enough to donate funds to complete the project.” Professor Cheung has also applied for the government’s Matching Fund for what he sees an extremely worthwhile charity project. Post-operation distraction Professor Cheung Lim-kwong Pre-operation distraction The University of Hong Kong Bulletin January 2011