A Biomechanical Study Of Internal And External Fixation Devices For The Treatment Of Humeral Shaft Fracture

Objective The incidence rate and the serious level of injury of humeral shaft fracture have a tendency of increase. Because of the limitations of the traditional conservative treatment, orthopedist always prefer to selecting operative treatment. These operative treatments mainly include fracture fixation with compressed plate, locking intramedullary nail and external fixator. But every treatment has its advantages and disadvantages, it is hard to reach a definite consensus when orthopedist want to make a choice. To search for the advantages and disadvantages of the operative treatment of humeral shaft fracture by comparing biomechanical characteristics of single compressed plate with intramedullary pin, locking intramedullary nail and external fixator with simple internal fixation devices, so as to decrease the incidence rate of delayed union or disunion of bone after fracture operation and provided the scientific theoretical basis for clinical practice.Methods Complicated fracture models of humeral shaft are produced in 18 wet humeral bone specimens of adult cadaver. The fracture models are randomly divided into three groups. Six fracture models of group one is fixed by single compressed plate with intramedullary pin and is named as group plate. Six fracture models of group two is fixed by locking intramedullary nail and is named as group intramedullary nail. Six fracture models of group three is fixed by external fixator with simple internal fixation devices and is named as group external fixator. Six fracture models of each group are randomly divided into two subsets and each subset contains three fracture models. The intensity and rigidity of complicated fracture models of humeral shaft is measured in compress test and torsion test.Results The data of experiment is analyzed by spss13.0. In compress test, the maximum load of each group is 6162.09±521.06N, 6738.32±525.89N, 2753.57±185.59N. The intensity of group plate and group intramedullary nail are better than that of group external fixator, difference exists from statistics view (P<0.05), no difference exists between group plate and group intramedullary nail (P>0.05). Under 600N physiological compress load, the rigidity of each group is 171.69±6.49 N/mm, 333.04±36.85N/mm, 132.59±2.93N/mm. The rigidity of group intramedullary nail is better than that of group plate and group external fixator, difference exists from statistics view (P<0.05), no difference exists between group plate and group external fixator (P>0.05). In compress test, the maximum torque of each group is 38.24±7.08Nm,17.12±5.73 Nm,20.26±6.42 Nm. The intensity of group plate is better than that of group intramedullary nail and group external fixator, difference exists from statistics view (P<0.05), no difference exists between group intramedullary nail and group external fixator (P>0.05). Under 0.80Nm physiological torque, the rigidity of each group is 16.36±2.07Ncm/(°), 11.45±0.22 Ncm/(°), 18.79±2.62 Ncm/(°).The rigidity of group plate and group external fixator are better than that of group intramedullary nail, difference exists from statistics view (P<0.05), no difference exists between group plate and group external fixator (P>0.05).Conclusions Those fracture models fixed by single compressed plate with intramedullary pin have better compress and torsion intensity, they also have better torsion rigidity but less compress rigidity. Those fracture models fixed by locking intramedullary nail have better compress intensity but less torsion intensity, they also have better compress rigidity but less torsion rigidity. Those fracture models fixed by external fixator with simple internal fixation device have less compress and torsion intensity, they also have less compress rigidity but better torsion rigidity.