The specimens were thawed at room temperature at 12 h before tests. All specimens were subjected to deep cryopreservation (− 100 ☌). Those specimens had no congenital malformations, fractures, and tumors. Sixteen female humerus specimens (average age of 73 ± 3, range of 69–83 years old) provided by Tianjin Hospital were used in this study. The treatment combining internal fixation and plates was used as control. The biomechanical characteristics including load bearing and torsional resistance were assessed. Therefore, this study was designed to evaluate the biomechanical characters of external fixator and closed intersection pinning in treating two-part surgical neck fracture of humerus in elderly patients with osteoporosis. proposed that minimally invasive fixation with percutaneous pinning should be ideal for treating elderly patients whose main demand is functional recovery of the joint under painless circumstances rather than restoring muscle strength. It is reported that percutaneous pinning can be applicable in elderly patients with satisfactory efficacy. Screw pin fixation has more remarkable advantages, although about 27% patients may still display loss of fracture contraposition, which is mainly caused by fixation failure due to old age and osteoporosis. The percutaneous pinning technique represents a minimally invasive procedure, which avoids extensive exposure and complications. Percutaneous pinning is characterized by minimal invasion and low cost, but its biomechanical stability is not satisfactory, which may result in loss of reduction position and withdrawal of internal fixation. Antegrade intramedullary pinning can provide fracture reduction fixation with minimal invasion, but it may induce rotator cuff injury. However, it requires extensive surgical exposure, thus it is prone to complications of soft tissues as well as aseptic necrosis of the humeral head. Plate fixation tends to achieve better biomechanical stability. Every method has advantages and drawbacks. Although some studies have compared the treatments results between intramedullary pinning, plate fixation and percutaneous fixation, no consensus has been reached. According to the Neer classification, 28% patients have two-part fracture and it mostly occurs in the patients over 50 years old, with a mean age of 72 years old. Recent epidemiological survey revealed that the annual incidence of proximal humerus fracture was as high as 2.48/1000. It has an increasing incidence with the increasing aging population in China.
Proximal humerus fractures are very common and often accompanied by osteoporosis. In the fixation of two-part humeral fracture in elderly patients with osteoporosis, the new external fixator seemed to be superior to plate fixation in load bearing and resistance to torsional stress. As for resistance to torsional stress, plate’s torque fluctuated between 1 Nm and 5 Nm, while the external fixator’s torque values were more evenly ( P < 0.01) distributed with the fluctuation within 1 Nm. Ultimate bearing capacity and load bearing at different parts with the humerus rotation were higher ( P < 0.05) in the external fixator group (145.16 ± 17.42 N and 140 N respectively) than those in the plate group (120.21 ± 13.15 N and 69.63 ± 25.16–90.78 ± 17.18 N respectively). The parameters of the two groups were compared using independent t-test. Biomechanical testing of the specimens was performed to assess the resistance to load bearing and torsional stress. In the control group, a clover plate and 6 cortical bone screws were applied. In the test group, the fracture was firstly fixed with intersection pinning using 3 Schanz pins (3.5 mm), followed by the novel external fixation frame. Models with the surgical neck two-part fracture of the proximal humerus were built, in which a novel external fixator (test group) and a clover plate (control group) were applied separately. Sixteen female elderly humeral shaft specimens with osteoporosis were randomized into 2 groups. This study was aimed to evaluate the biomechanical characteristics of a novel external fixator in treating two-part surgical neck fracture of the proximal humerus in the elderly patients with osteoporosis. No consensus exists on the treatment of proximal humerus fractures, especially in the elderly patients with osteoporosis.
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