The specific aim of this pilot project is to develop a laboratory model to investigate rigid internal fixation (plates and screws) of maxillary fractures. The long term objective is to identify the least complex method of rigid internal fixation that will produce stability sufficient to allow for healing of maxillary fractures without prolonged jaw immobilization. At present, the use of multiple miniplates across each maxillary fracture line is advocated. However, a complex combination of multiple plates and screws is expensive and carries the risk of producing a serious malunion and subsequent malocclusion if an adaptation error occurs when the plates are contoured and attached to the fracture fragments. The initial hypothesis to be tested is that short-term resistance to occlusal forces by a single plate, strategically placed to reconstruct the key maxillary stress trajectory (zygomaticomaxillary (ZM) buttress), will be comparable to that of two plates placed to reconstruct both the ZM buttress and the nasomaxillary (NM) buttress. Simulated bilateral low maxillary fractures will be created in 6 fresh cadaver heads. Fixation in 3 heads will consist of one stainless steel plate per side placed across the fracture line in the area of the ZM buttress. The plates will be anchored with 2 screws above and 2 screws below the fracture line. Fixation in the other 3 heads will consist of 2 plates per side across each fracture line, one again in the area of the ZM buttress and the other over the NM buttress. Controlled loads simulating vertical occlusal forces in centric occlusion will be applied through the mandible to the maxilla using a servo-hydraulic test frame. Micromotion transducers will be used to measure relative motion of the fracture fragments when a sinusoidal cyclic load approximating the typical masticatory force per chew is applied for 5000 cycles. Fracture gap motion will be quantified and compared for the fixation modalities of settling, pistoning, migration and net displacement. The proposed pilot project will establish the validity of the laboratory model and provide preliminary data that will lead into a larger investigation of such variables as plate configuration, plate material (stainless steel, titanium, vitallium), number of screws used to anchor each plate, and the influence of uneven occlusal forces on fixation stability.
| Funk, G F; Stanley Jr, R B; McKellop, H A et al. (1994) Motion observed across maxillary continuity defects stabilized with plates and screws. Arch Otolaryngol Head Neck Surg 120:187-94 |
