[Improvement of Hoffmann external fixation apparatus].
The resurgence of external fixators for the management of skeletal and joint injuries has generated an increasing number of reports. In addition, many types of fixators have been developed in the last ten years. Of these, the Hoffmann external fixator is the most popular one. Is it possible for the patient with a tibial comminuted fracture to walk with the fixator? This study has been pursued to investigate this question and to improve on the fixator. Bone models were made from tubed polyester resin strengthened by glass fiber (elastic module: 9.46 kg/mm2, outside diameter: 35 mm, inside diameter: 30 mm). Each bone model was transfixed by two Steinmann pins (phi: 4.5 mm) with 43 mm between, and a pair of models was framed with two straight bars, with 30 mm from model to bar. The Steinmann pins and straight bars were connected to each attachment. The experiment focused on four main studies: Measurement of the Young's modulus of the Steinmann pin. Compression load test and bending load test framed bone models with each attachment. Observation and measurement of the ground reaction force of ambulation on stilt framed with experimental external fixator. Determination of S-N curve of the Steinmann pin. Results were as follows: The Young's modulus of the Steinmann pin were 1.8 X 10(4) kg/mm2. 0.2% proof of the pin was 110 kg/mm2. The bone models framed with the conventional method were destructed at the universal ball joint at 68 kgf in the compression load test, and 6.8 kgf in the bending load test. The models framed with the conventional method fitted with spring washers at ball joints were not destructed until 203 kgf in compression load, but after several trials the spring washers were crushed. The models fabricated by using a vice with rods and articulation coupling were not damaged until 210 kgf in compression load and were not damaged until 15 kgf in bending load even after several trials. The displacement between the models were 2.8 mm at 80 kgf and 8.5 mm at 210 kgf in compression load. The models fabricated by experimental external fixators were not damaged until 250 kgf in compression load and were not damaged until 30 kgf in bending load, and the displacement between the models were 2.1 mm at 80 kgf and 6.9 mm at 210 kgf in compression load.(ABSTRACT TRUNCATED AT 400 WORDS)
D001696:Biomechanical Phenomena; D005592:Fracture Fixation / Q000295:instrumentation*; D006801:Humans; D008953:Models, Anatomic; D013978:Tibial Fractures / Q000503:physiopathology / Q000601:surgery