External midface distractor system
The external midface distractor is a distraction osteogenesis device that attaches to the cranium and midface and is used to gradually lengthen the midface at the Le Fort I, II, and III levels (including monobloc). It addresses the clinical need for an external distraction device to treat patients with congenital craniofacial anomalies with severe midface retrusion, which can lead to airway obstruction and nutrition difficulties. It meets requests for an external device to achieve controlled advancement of the midface where internal devices are not desirable. Therefore, it is particularly well suited for younger patients who are not skeletally mature and have mixed dentition. It can be placed and removed more easily than its internal counterpart and allows for postoperative vector control of the bone segments.
Some of the most common syndromes that are treated with the external midface distractor are Pfeiffer syndrome, Apert syndrome, and Crouzon syndrome. It can also be used on patients with cleft lip and palate as a secondary procedure in their teenage years to address their anterior maxillary growth deficiency.
The external midface distractor consists of an external head frame, a vertical carbon fiber rod assembly, horizontal crosspieces containing distraction screws, and separate internal footplate assemblies that attach to the zygoma and maxilla. The external components are connected to the internal hardware with wires. Scalp fixation pins are used to attach the device to the lateral aspects of the cranium.
The device is assembled prior to placement on the patient. The head frame, vertical carbon fiber rod assembly, and horizontal crosspiece with distraction screws are joined together and secured by set screws. For Le Fort I and II advancement one horizontal crosspiece is joined to the vertical carbon fiber rod assembly primarily at the level of the maxilla. For Le Fort III and monobloc advancement two horizontal crosspieces are joined to the vertical rod assembly; one primarily at the level of the zygoma or infraorbital rim and one primarily at the level of the maxilla.
The head frame can be adjusted to fit a range of patient head sizes. The head frame expands laterally as a unit using a central adjustment screw located in its hub. Rear adjustment screws located in the mounting plates of the head frame adjust the anterior projection of the device. The vertical carbon fiber rod can be adjusted laterally for placement along the patients midline, independent of the head frame position on the skull. The vertical carbon fiber rod can also be rotated both anteriorly/ posteriorly and right/left to minimize obstruction of the patients path of vision and enable to the patients to have an unobstructed access to deliver food to the mouth.
Mounting pins in rounded, conical, and self-drilling versions are used to secure the device to the patient. Rounded pins do not pierce the soft tissue and are used for initial stabilization of the device on the cranium. Conical pins pierce the soft tissue to apply clamping pressure to the lateral skull bones for securing the device. Self-drilling pins are offered as an alternative to conical pins to engage and secure the headframe to the bone by threading into the bone in the same manner similar to standard cranial bone screws.
Active distraction is accomplished by the patient using a screwdriver that mates with a hex nut on each distraction screw assembly. The mid-face can be advanced in 0.5 mm increments by the patient. According to the surgeons instruction. Further refinements of the position of the midface are accomplished by the surgeon using the adjustment capabilities of the device. This is achieved by loosening the wires connecting the external device to the internal hardware, repositioning the horizontal cross pieces, and retightening the wires. Removal of the device is accomplished by cutting the wires between the internal and external hardware, removing the mounting pins from the cranium, and removing the internal hardware. Depending on the type of internal hardware used, a secondgeneral anesthesia may or may not be needed for device removal.
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