Treatment of the surgical neck fracture of the humerus with a novel external fixator in the elderly with osteoporosis: biomechanical analysis

Abstract

Background: No consensus exists on the treatment of proximal humerus fractures, especially in the elderly patients with osteoporosis. 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.

Methods: Sixteen female elderly humeral shaft specimens with osteoporosis were randomized into 2 groups. 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. 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. In the control group, a clover plate and 6 cortical bone screws were applied. Biomechanical testing of the specimens was performed to assess the resistance to load bearing and torsional stress. The parameters of the two groups were compared using independent t-test.

Results: 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). 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.

Conclusions: 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.

Keywords: External fixator; Load bearing; Plate; Resistance to torsional stress; Surgical neck fracture of humerus.

Fig. 1

Intersection pinning and plate fixation (b) for the surgical neck fracture of the humerus. a, in the external fixator group, three driving screws were locked with fixed links and clamps. b, in the plate fixation group, the end of the humeral shaft was fixed with 3 cortical screws (3.5 mm) and that of humeral head fixed with 3 cancellous screws (4.0 mm)

Fig. 2

Lateral X-ray images of the external fixator (a) and plate fixation (b)

Fig. 3

Specimens with external fixation (a) and plate fixation (b) for measurement of the resistance to load and torsional stress. Ten strain gage pieces were attached along the two sides of the fracture line, with a vertical distance of 2 mm to the broken site

Fig. 4

Compression and torsion experiments and data acquisition for the external fixator group. A gradually-increasing load from 0 to 200 N was applied at a loading rate of 1.4 mm/min. The values of multiple strain gages at both sides of the broken ends were simultaneously acquired. The specimens were rotated for 6 cycles or until damaged

Fig. 5

Compression and torsion experiments and data acquisition for the clover plate group. A gradually-increasing load from 0 to 200 N was applied at a loading rate of 1.4 mm/min. The values of multiple strain gages at both sides of the broken ends were simultaneously acquired. The specimens were rotated for 6 cycles or until damaged

Fig. 6

Comparison of resistance to load stress between the plate and the external fixator groups. It shows that the external fixator had a significantly more uniform load bearing comparing with control group (P < 0.05)

Fig. 7

Comparison of resistance to torsional stress between the plate and the external fixator groups. It shows that the torque was significantly more uniform (P < 0.05) in the external fixator group