Three-part humeral head fractures treated with a definite construct of blocked threaded wires: finite element and parametric optimization analysis

Abstract

Background Mini open reduction and percutaneous fixation of three-part humeral head fracture with blocked threaded wires has demonstrated functional results similar to locking plates or intramedullary nails but with significantly lower major complication rate. In the context of three-part humeral head fractures, we performed a parametric optimization through a finite element analysis of a recently published construct to verify if the encouraging clinical results can be supported by a more rigorous investigation from a mechanical viewpoint. Materials and Methods The 2-dimensional geometry of a three-part proximal humerus fracture synthetized with a system of blocked threaded wires was created. Tension/bending/shear and compression load tests were simulated. A parametric optimization analysis was performed considering four design parameters (height of wire couples; wire material; interdistance between two wires). Eighteen simulations were carried out. Additional analyses were performed also considering a varying diameter of the external rod. Results Four points where the largest gap occurs and three points associated with the highest stress concentration were considered. As per the tension/bending/shear loading, a slight gap increase was observed in two different points (8.494 μm; 7.540 μm), while a slight decrease was detected along the greater tuberosity fracture line (1.445 μm). The maximum von Mises stress up to 64.4 MPa was achieved in the humeral head. As per the compression loading, the gap increased along the greater tuberosity fracture line (1.445 μm; 7.545μm); the maximum von Mises stress attains the value of 64.42 MPa. The smallest gap distance (15.37μm) and the lowest von Mises stress (51.51 MPa) were obtained in two different alternative constructs. The diameter of the external rod had no significant effect. Conclusions The studied construct is biomechanically valid; it only allows micromovements (one-thousandth of the characteristic humerus size) that are not able to cause humeral head rotation and translation. Furthermore, the construct generates acceptable pressure stresses on sensible areas of the fractured humeral head. Compared to the original construct, we propose to space the pair of horizontal wires for the great tuberosity by at least 1 cm.

Experimental characterization of humerus bones with complex fracture patterns and fixation systems via laser vibrometry

“…One sample represents the healthy, non fractured bone, another sample is the fractured bone subject to the gold standard surgery operation and the remaining three fractured humerus are trated with the BTWs technique. The system of BTWs was tested in three different configurations: the first configuration was composed of 4 couples of wires according to the pattern used by the authors for the treatment of complex PHFs for which excellent clinical and radiological outcomes are documented in recent biomechanical validation studies [29][30][31]. The second configuration differs from the previous one for the lack of the proximal couple of TW (from the greater tuberosity to the medial calcar).…”

“…The authors documented, after a medium term follow-up, similar clinical and radiological outcomes with respect to locking plate and nail with a significant quite lower rate of major complication. A finite element analysis and a parametric optimization of the system documented the biomechanical properties of the construct [30] and the satisfactory cyclic load to failure [31].…”

Humeral Head Three-Part Posterior Fracture-Dislocation Reduced through a Posterior Approach and Fixed with Blocked Threaded Wires: A Consecutive Case Series

“…We aimed to evaluate the clinical and radiological outcomes of patients with humeral head three-part posterior fracture dislocation treated by reduction through a posterior approach and fixed with a biomechanically validated configuration [40,41] of blocked threaded wires, after a minimum follow-up of 24 months.…”