顎関節突起骨折に対する各種骨内固定法の生体力学的評価 A biomechanical evaluation of bone stability with different types of rigid internal fixation techniques for subcondylar fractures
The purpose of this study was to evaluate the biomechanical stability of various rigid internal fixation systems for subcondylar fractures.<BR>Fifteen identical synthetic polyurethane mandibles with a cancellous bone structure (Synbone (R), Switzerland) were used. The left condylar processes were cut with a band saw to mimic subcondylar fractures directed perpendicularly to the long axis of the ramus, and the right sides were cut to mimic oblique fractures to the ramus. The fixation systems used were a single 4-hole titanium mini-adaptation plate (Synthes), double fixation with the same plates, a single 5-hole titanium mini-dynamic compression plate (Synthes), an Eckelt lag screw (R) system (Martin), and a Wurzburg lag screw plate (R) system (Leibinger). Biomechanical testing was done as described by Haug et al.(1996). The bone models were held with a custom-made jig to keep the occlusal plane horizontal. The canine region was pressed with a cantilever beam design using a servohydraulic testing machine (Autograph, Shimadzu) at a rate of 1mm/sec. The force-displacement curve, maximum load for breakage, and stiffness were measured.<BR>In perpendicular fractures, double mini-plate fixation and Eckelt lag screw fixation provided the best stability. The maximum loads of the former and the latter were 46.7±9.5N and 44.7±11.6N, respectively. Their stiffness was 4.1±1.1N/mm and 4.7±1.9N/mm, respectively. Single mini-plate fixation was weakest, i. e., 13.2±2.4N maximum load and 1.3±1.0N/mm stiffness. In oblique fractures, double mini-plate fixation also had the best tolerance for load and stiffness, i.e., 55.1±11.6 N and 5.2±2.7N/mm, respectively. The Eckelt lag screw, however, showed considerably less fixation strength than that for perpendicular fractures, i.e., 22.8±11.3N for load tolerance and 1.0±0.2N/mm for stiffness.<BR>In this laboratory setting, double mini-plate fixation proved superior in both types of fractures with regard to resistance to movement and breakage strength. The Eckelt lag screw showed good stability for perpendicular fractures; however, stability was weak for oblique fractures. Not only single mini-plate fixation but also minidynamic compression plate fixation or a Wurzburg lag screw plate system may provide insufficient fixation strength for this type of fracture on early functional loading.
日本口腔外科学会雑誌 50(9), 515-521, 2004-09-20
Japanese Society of Oral and Maxillofacial Surgeons