Hybrid blade and locking plate fixation for proximal humerus fractures: a comparative biomechanical analysis

Abstract

Background: Open reduction and internal fixation of proximal humerus fractures can be difficult to achieve adequate, complication free results due to osteopenia of the proximal humerus and unstable fracture patterns. This study aimed to compare the biomechanical properties of a novel hybrid fixed angle blade plate (Fx plate) with an established fixed angle locking plate (PHILOS plate).

Methods: A two-part fracture was simulated in synthetic composite humeri by creating a transverse osteotomy and 10 mm fracture gap at the surgical neck. After treating the fractures with either an Fx plate or a PHILOS plate, humeral head was fixed and the shaft was displaced in a cantilever fashion. For elastic tests, loading was along the frontal and sagittal plane to achieve varus/valgus and extension/flexion, respectively. In plastic tests, loading was in a varus direction to determine the constructs' resistance to varus collapse.

Results: In elastic tests, both construct types had higher peak load and stiffness in extension/flexion than varus/valgus. Fx plate constructs were significantly stiffer than PHILOS constructs in varus/valgus (mean: 7.590/6.900 vs. 6.609/6.091 N/mm; p < 0.001 for both) but significantly less stiff in extension/flexion (8.770/9.541 vs. 9.533/9.997 N/mm; p < 0.001 for extension, p < 0.05 for flexion). In varus plastic tests, significantly higher peak loads were reported for Fx plate than PHILOS (134.391 vs. 115.531 N; p < 0.001).

Conclusions: In this fracture gap model, humeri implanted with a novel Fx plate provided higher varus/valgus stiffness but lower extension/flexion stiffness than a more traditional proximal humeral locking plate design (PHILOS).

Keywords: Biomechanical analysis; Blade plate; Locking plate; Plate fixation; Proximal humerus fractures.

Fig. 1

Numbering of screws and blade on DePuy Synthes PHILOS plate (a) and the Fx plate (b)

Fig. 2

Experimental setup for performing bending tests, shown with Fx plate in varus

Fig. 3

Mean stiffness (S) for PHILOS and Fx plate constructs during elastic loading of 5 mm cantilever displacement in extension, flexion, valgus and varus directions. For each direction, stiffness is presented as the mean for five specimens (25 trials) in each construct group. A single asterisk (*) indicates p ≤ 0.05; and triple asterisks (***) indicate p ≤ 0.001

Fig. 4

Mean peak load (F₅) for PHILOS and Fx plate constructs during elastic loading of 5 mm cantilever displacement in extension, flexion, valgus and varus directions. For each direction, peak load is presented as the mean for five specimens (25 trials) in each construct group. A single asterisk (*) indicates p ≤ 0.05; and triple asterisks (***) indicate p ≤ 0.001

Fig. 5

Mean load for PHILOS and Fx plate constructs during plastic loading at 15 mm displacement before (F_15a) and after (F_15b) eight-minute intermission and at 30 mm displacement (F₃₀). Load is presented as the mean for five specimens (5 trials) in each construct group. A single asterisk (*) indicates p ≤ 0.05; and double asterisks (**) indicate p ≤ 0.01

Fig. 6

Typical load–displacement curves at load point for PHILOS and Fx plate constructs during plastic loading. A drop of 4–5 N in load is noted at 15 mm displacement due to the stress relaxation of construct during the eight-minute intermission