[A preliminary study of risk factors for the stress fracture in treated with clavicle hook plate]

Objective: To investigate the effects of bone density, plate bending degree and proximal screw type on the stress fracture of clavicle hook.

Methods: Three sows weighing between 45 and 50 kg were selected, from which a total of 40 rivs were collected. The 15 ribs of sows were divided into 3 groups according to bone density and bone hardness with 5 rivs in each group. And then the 3 groups were fixed with 6-hole collarbone hook plates and 3 locking screws. Measure the maximum torsion force when the ribs were fractured by force. The same size 15 rids were divided into 3 groups, named forward bending group, 0° group(the angle between the plate surface and the rib surface) and reverse bending group. All fixed with 6-hole collarbone hook plates and locking screws to measure the maximum torsion force of rib stress fracture. Then the same size 10 rids were divided into 2 groups, the normal screw group and the locking screw group with 5 ribs in each group. Both groups were fixed with 6-hole collarbone hook plates and screws. The normal screw group was a normal screw, fixed in proximal end, and two locking screws. The locking screw group was fixed by locking screws. Measure the maximum torsion force of the two groups when the ribs fracture by force.

Results: In the bone density experiment, the torque force of hard bone group (104.51±6.27) N was greater than the normal bone group (75.04±3.81) N(t=8.979, P<0.05). The force of normal bone group was greater than the osteoporosis group (49.99±2.12) N(t=12.832, P<0.05). In the bending collarbone hook experiment, the order of the torque force generated by each group as follow:the forward bending group (343.59±6.18) N greater than the 0° group (106.01±5.29) N(t=65.279, P<0.05) greater than the reverse bending group (95.82±4.12) N(t=3.398, P<0.05). The force of the normal screw group (98.68±0.70) N was greater than the locking screw group (50.20±0.95) N(t=91.484, P<0.05). The data comparisons of each group were statistically significant.

Conclusion: Bone density, plate bending degree and proximal screw type had an impact on stress fracture of clavicle hook plate. Higher bone density, forward bending of the steel plate, and ordinary screws in proximal end can reduce the rates of stress fractures of clavicle hooks.