Fundamental Study On The Mechanism Of Cubitus Varus Due To Supracondylar Fracture Of Humerus

Fundamental Study on the Mechanism of Cubitus Varus due to Supracondylar Fracture of HumerusObjective: To investigate the mechanism of cubitus varus due to the supracondylar fracture of humerus(SFH) and the methods for prevention of cubitus varus. Methods: (1) Using six upper limbs of three normal children cadavers (age 3-4years,average 3.3years),we measured the stress and strain of bilateral supracondylar area of humerus under the compressive load. (2) Osteotomies were made at the level of the top of olecranon fossae in the six upper limbs to simulate the SFH. Each fractures was anatomically reduced and fixed seriatim with 1.5-millimeter Kirschner wires in three methods(two medial and lateral crossed pins, two lateral crossed pins, two lateral parallel pins),then measured the resistance to rotation and tilt of the distal fragment of the simulated supracondylar fracture fixed by the three methods.(3) Using Image Analysis ,we measured the X-ray density of the medial and lateral supracondylar area in the anteroposterior roentgenogram of elbow joint in group A (15 cases,10 boys,5 girls ,age 5-7years,averge 4.7 years, all have type I SFH in roentgenogram) and group B (20 cases, 13 boys,7 girls, age 3-7years,averge 4.7years,all normal in roentgenogram). Results:(l) The medial supracondylar area of humerus has more stress and strain than the lateral supracondylar area under compressive load(P<0. 01). (2) The group of two medial and lateral crossed pins has more advantage in the resistance to rotation and tilt of the distal fragment of the simulated supracondylar fracture than the group of two lateral crossed pins and the group of two lateral parallel pins(P<0.05) .(3) The X-ray density of the medial supracondylar area in the anteroposterior roentgenogram of elbow joint in group A was higher than group B(P<0.05). Conclusion:(1) In the SFH ,the medial wall of supracondylar is more likely to collapse than the lateral wall. If this factor is not taken into account in the reduction of the fracture when the degree of the collapse of the medial wall of supracondylar is big enough to decrease the carrying angle, it will cause the cubitus varus after the reduction. (2) The method of two medial and lateral crossed pins can provide the most stability in the fixation of the SFH.lt can prevent the cubitus varus due to unreliable fixation after the reduction of the SFH.PU Liyong(Pediatric surgery) Directed by ZHANG Xiqing...