RESUMO
A clavicle is an S-shaped long bone whose biomechanical behavior is unlike that of a straight tubular long bone. When a clavicle is under a compression load along the axis, the force produces a middle one-third clavicular fracture. The present study is a biomechanical study to confirm the clinical observations of the mechanism of the fracture and to discover the tension site and compression site of the fracture, using 12 fresh cadaveric clavicles, a universal testing machine and two special grips. One grip was constructed with a contour like a sternoclavicular articulation. The grip was mounted at the medial end of the clavicle. Another grip was constructed with a contour like an acromioclavicular articulation. The grip was mounted at the lateral end of the clavicle. A load was applied to the lateral clavicle like a force transmitting from the weight of the shoulder girdle. A load was also applied to the medial clavicle like a force from the sternocleidomastoid muscle. A compression load was applied along the axis of the testing clavicle through the upper grips by using a universal testing machine. The result found that the average load of the clavicular fracture was 1526.19 N. The fracture occurred at the middle one-third of the clavicle in the region of the curve of the lateral clavicle changing to the curve of the medial clavicle. While primatic cross section of the clavicle at the fracture site determined a tension and a compression site of the fracture, the fracture took the superoanterior aspect of the clavicle as a tension site and posteroinferior aspect as a compression site. The fracture had a ratio of length of the lateral fragment to the total length of the clavicle of 0.49. This study confirmed that a compression load along the axis of the clavicle produces a middle one-third clavicular fracture as in clinical observation and the fracture took the superoanterior aspect of the clavicle as a tension site.