Biomechanical Analysis of Combined Medial Calcar and Lateral Locked Plating Versus Isolated Lateral Locked Plating of Proximal Humerus Fractures.

Abstract

Medial calcar buttress plating combined with lateral locked plating is biomechanically tested against isolated lateral locked plating in synthetic humeri models for the treatment of proximal humerus fractures. Proximal humerus fractures (OTA/AO type 11-A2.1) were manufactured in 10 pairs of Sawbones humeri models (Sawbones, Pacific Research Laboratories, Vashon Island, WA). Specimen were randomly assigned and instrumented with either medial calcar buttress plating combined with lateral locked plating (CP) or isolated lateral locked plating (LP). Nondestructive torsional and axial load tests were performed to evaluate construct stiffness. Large-cycle axial tests were conducted followed by destructive ramp-to-failure tests. Cyclic stiffness was compared in both nondestructive and ultimate failure loads. Failure displacement was recorded and compared between groups. The addition of medial calcar buttress plating to lateral locked plating constructs significantly increased the axial ( P < 0.01) and torsional ( P < 0.01) stiffness of the construct compared with isolated lateral locked plating by 95.56% and 37.46%, respectively. All models demonstrated greater axial stiffness ( P < 0.01) after 5000 cycles of axial compression, not dependent on the fixation method. During destructive testing, the CP construct withstood 45.35% larger load ( P < 0.01) and congruently exhibited 58% less humeral head displacement ( P = 0.02) before failure when compared with the LP construct. This study demonstrates the biomechanical superiority of medial calcar buttress plating when combined with lateral locked plating as compared with isolated lateral locked plating of OTA/AO type 11-A2.1 proximal humerus in synthetic humeri models.