[Development and biomechanical study of anatomical locking plate of sternoclavicular joint]

To develop an anatomical locking plate in accordance with the anatomical characteristics of the sternoclavicular joint, which is reliable fixation and easy to operate, so as to provide an ideal internal fixation device for the treatment of sternoclavicular joint dislocation or peripheral fractures.

Gross measurement and CT measurement were performed on the 8 adult antiseptic and moist cadaver specimens (16 sides) to measure the parameters of surrounding bone structure of the sternoclavicular joint. The parameters included the thickness of presternum, sternal notch width, anteroposterior diameter of proximal 1/3 of clavicle, upper and lower diameters of proximal 1/3 of clavicle, angle between proximal end of clavicle and presternum in coronal plane, and angle of thoracoclavicular joint at anatomic position forward. According to the anatomical parameters and biomechanical properties of the specimens, the anatomical locking plate was designed and developed. The sternoclavicular ligament and joint capsule of all the specimens were completely cut off to make the sternoclavicular joint dislocation model. The left and right sternoclavicular joint of each specimen were randomly divided into experimental group (anatomic locking plate fixation) and control group (oblique T shape locking plate fixation). The sternoclavicular joint activity and common force mechanism was simulated on the universal mechanical testing machine, and the clavicular distal load test, sternoclavicular joint torsion test, and anti-pulling of steel plate manubrium part test were performed.

The differences between the anatomical parameters of gross measurement and CT measurement were not significant ( P>0.05). In the clavicular distal load test, when the anatomical position perpendicular to the distal clavicle back loading to 20 N, the displacement of loading point in the experimental group was (8.455±0.981) mm, which was significantly less than that in control group [(10.163±1.379) mm] ( t=-3.012, P=0.020); the distal clavicle displacement of loading point of experimental group and control group were (5.427±1.154) mm and (6.393±1.040) mm, respectively, showing no significant difference ( t=-1.459, P=0.188)。In the sternoclavicular joint torsion test, the torque of experimental group was significantly greater than that of control group when the clockwise torsion angle was at 2, 4, 6, 8, and 10 degrees and the counterclockwise torsion angle was at 4, 6, 8, and 10 degrees ( P<0.05). The torsional stiffness in the experimental group under clockwise and counterclockwise condition was 0.122 and 0.108 N·m/° respectively, which were significantly higher than those in the control group (0.083 and 0.078 N·m/° respectively) ( F=67.824, P=0.000; F=20.992, P=0.002). In the anti-pulling of steel plate manubrium part test, the maximum pullout force of experimental group [(225.24±16.02) N] was significantly higher than that in control group [(174.40±21.90) N] ( t=5.785, P=0.001).

The new type of anatomical locking plate can realize the sternoclavicular joint three-dimensional fixation, and has the advantages of reliable fixation, simple operation, less trauma, superior biomechanical properties, and earlier functional exercise. It may be an ideal internal fixation device in clinical treatment of sternoclavicular joint dislocation or peripheral fractures.