Are Locking Screws Advantageous with Plate Fixation of Humeral Shaft Fractures? A Biomechanical Analysis of Synthetic and Cadaveric Bone

Abstract

Synthetic and cadaveric bone testing showed that locking screws offer no obvious biomechanical benefit in this application.

Dual Plating of Humeral Shaft Fractures: Orthogonal Plates Biomechanically Outperform Side-by-Side Plates

“…However, excessive reductions in stiffness may lead to increasing screw and plate stress and early fatigue failure of the construct [7,25,26]. Stiffness resulting from the compressive loading simulations of the humerus may be especially important during crutch weightbearing [18,19]. Moreover, torsional loading also is of interest in the analysis of humeral fracture fixation constructs because it has been reported as a predominant loading mode and possible cause for nonunion of humeral fractures [7,8,29,30].…”

“…The plates in all of the aforementioned models were centered to the fracture gap and locked at a 1-mm offset distance from the outer cortical bone cortex [1,5,25]. The plates are fixed using a total of eight bicortical locking screws [18,25,31] sequentially alternating between the two plates (four screws/plate) resulting in all the models having the same number of fixation points and equal working lengths. Such a staggered placement of the hardware has been suggested to reduce the risk of plate fracture [17].…”

“…Cortical bone was modeled as an orthotropic material characterized by nine independent technical constants (E 1 = 12.0, E 2 = 13.4, E 3 = 20.0 GPa; G 12 = 4.53, G 23 = 6.23, G 13 = 5.61 GPa; m 12 = 0.376; m 23 = 0.235, m 13 = 0.222) [2,3] with density set to 1817 kg/m 3 [22]. To study a worst-case scenario such as an unstable comminuted fracture, a 1-cm transverse fracture gap was created at the middiaphysis of the intact model (simulating an Orthopaedic Trauma Association 12.C.2 fracture) [1,5,6,18,19,23,30,32]. Fracture fixation was performed using five different seven-hole and nine-hole smallfragment (3.5 mm) locking-plate configurations as follows: (1) nine-hole plate anterior and seven-hole plate lateral, 90°a part (Fig.…”

“…This in turn will help limit stress risers and extend the fatigue life and strength of the system. O'Toole et al [18], comparing single-plate locking and nonlocking 3.5-mm small-fragment constructs for humeral shaft fixation, reported both constructs withstood strenuous fatigue and axially failed above anticipated physiologic loads. Results from all of the dual-plate locking constructs compared in our study show the highest stress concentrations occurring at the neck of the screws just below the screw head and plate.…”

“…Furthermore, smallfragment plates for humeral shaft fracture fixation have shown promising clinical results [18]. Questions remain, however, regarding how plate placement on the diaphysis affects the mechanical performance of the dual-plate construct, necessitating further research.…”