Crutch Weightbearing on Comminuted Humeral Shaft Fractures: A Biomechanical Comparison of Large versus Small Fragment Fixation for Humeral Shaft Fractures

Abstract

The results corroborate anticipated plate mechanical behavior with plate stiffness increasing as both plate width and thickness increase. The calculated yield force data suggest that both small and large fragment constructs would experience plastic deformation during bilateral crutch ambulation in a patient weighing 50 kg or more. The large fragment construct is not expected to catastrophically fail when subjected to loads in a patient 90 kg or less. The small fragment construct is predicted to catastrophically fail in patients weighing 70 kg or more.

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

“…In such cases, large-fragment plates may limit the number of screws that can be inserted (ie, less holes/unit length), and lead to increased stress shielding from the greater mismatch in load transfer between bone and plate [19,32]. Dual small-fragment plate constructs may offer a promising alternative.…”

“…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.…”

“…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 smaller size of the humerus in some patients, however, limits the diaphyseal shaft length and/or diameter available for fixation, and therefore makes using a large-fragment plate difficult. Difficulties that arise include the number of screws that can be placed, a resulting bulky fixation with undesirable stress shielding [19], and having to precontour the large-fragment plate to match the diverging anatomy of the humeral metaphysis.…”

Treatment of Humeral Shaft Fractures

“…Recently, there has been an increase in usage of small fragment plates as a reduction tool in fractures where reduction cannot be maintained during the application of a conventional dynamic compression plate. Some surgeons will also use these small fragment plates on patients of small stature 30 .…”