Objective: To provide the scientific theoretical basis for clinical practice by comparing biomechanical characteristics of single compressed plate with intramedullary pin, locking intramedullary nail and simple arm external fixator with simple internal fixation devices.
Methods: Eighteen wet humeral bone specimens of adult cadaver were made complicated fracture models of humeral shaft and divided into 3 groups according to fixation methods. Fracture was fixed by single compressed plate with intramedullary pin in plate group, by locking intramedullary nail in intramedullary nail group and by external fixator with simple internal fixation devices in external fixator group. The intensity and rigidity of complicated fracture models of humeral shaft was measured in compress test and torsion test.
Results: In compress test, the maximum load in plate group (6,162.09 +/- 521.06) N and in intramedullary nail group (6,738.32 +/- 525.89) N was significantly larger than that in external fixator group (2,753.57 +/- 185.59) N (P < 0.05); but there was no significant difference between plate group and intramedullary nail group (P > 0.05). Under 600 N physiological compress load, the rigidity was (171.69 +/- 6.49) N/mm in plate group, (333.04 +/- 36.85) N/mm in intramedullary nail group and (132.59 +/- 2.93) N/mm in external fixator group; showing no significant difference between plate group and external fixator group (P > 0.05), and showing significant difference between intramedullary nail group and plate, external fixator groups (P < 0.05). In torsion test, the maximum torque in plate group (38.24 +/- 7.08) Nm was significantly larger than those in intramedullary nail group (17.12 +/- 5.73) Nm and external fixator group (20.26 +/- 6.42) Nm (P < 0.05), but there was no significant difference between intramedullary nail group and external fixator group (P > 0.05). Under 0.80 Nm physiological torque, the rigidity was (16.36 +/- 2.07) Ncm/degree in plate group and (18.79 +/- 2.62) Ncm/degree in external fixator group, which was significantly larger than that in intramedullary nail group (11.45 +/- 0.22) Ncm/degree (P < 0.05); but there was no significant difference between plate group and external fixator group (P > 0.05).
Conclusion: 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.