Mechanical testing of scapular neck fracture fixation using a synthetic bone model

Abstract

Background: Trauma can fracture the scapular neck. Typically, a single plate along the lateral scapula border affixes the glenoid fragment to the scapula. This method is limited by difficulty in screw placement, frequent excessive soft tissue dissection, and risk for neurovascular injury. Substituting 2 smaller plates bridging the scapular neck mitigates these limitations, but no comparative mechanical data between techniques exists. Therefore, we compared the mechanical properties of two constructs securing a simulated scapular neck fracture.

Methods: Twenty synthetic human scapulae underwent a templated scapular neck fracture. Repairs were performed with a single plate on the lateral scapular border (Column method), or two small plates parallel to the lateral border (Neck method). Measures of displacement, force, and stiffness were quantified during cyclic testing (20-150 N, 1 Hz, 1000 cycles) and loading to failure. Statistical comparisons were made with t-tests (p ≤ 0.050).

Findings: The column constructs had higher displacements than neck constructs after 1000 cycles, but differences were small (mean) 0.18 (SD 0.01) vs. 0.15 (0.02) mm (p ≤ 0.004). Cyclic stiffness was 655 (43) and 790 (88) N/mm for the column and neck constructs, respectively (p ≤ 0.003). Both techniques performed comparably in failure loading: at 1 mm of gap reduction the compressive loads were 426 (61) N and 428 (48) N and stiffness was 354 (129) and 334 (80) N/mm for the column and neck constructs, respectively.

Interpretation: Given the surgical advantages, the neck fixation may be more suitable without biomechanical compromise compared to traditional lateral column fixation.

Keywords: Fracture; Mechanics; Plate; Sawbones; Scapular neck.