45. BIOMECHANICAL ANALYSIS OF PROXIMAL HUMERAL FIXATION USING LOCKING PLATE FIXATION WITH AN INTRAMEDULLARY FIBULAR ALLOGRAFT

Abstract

Purpose: The purpose of this study is to compare two fixation methods for surgical neck proximal humeral fractures with medial calcar comminution:

1. locking plate fixation alone and

2. locking plate fixation with intramedullary allograft fibular bone peg augmentation.

Method: Eight embalmed pairs of cadaveric specimens were utilized in this study. Dual energy X-ray absorptiometry (DXA) scans were initially performed to determine the bone density of the specimens. Surgical neck proximal humerus fractures were simulated in these specimens by creating a 1-centimeter wedge-shaped osteotomy at the level of the surgical neck to simulate medial calcar fracture comminution. Each pair of specimens had one arm randomly repaired with locking plate fixation, and the other arm repaired with locking plate fixation augmented with an intramedullary fibular autograft bone peg. The constructs were tested in bending to determine the failure loads, and initial stiffness using Digital Imaging Correlation (DIC) technology. The moment created by the rotator cuff was replicated by fixating the humeral head, and applying a point load to the distal humerus. A load was applied with a displacement rate of 4 mm/min, and was stopped approximately every 5 lbs to take a picture and record the load. This process was continued until failure of the specimens was obtained.

Results: The intramedullary bone peg autograft increased the failure load of the constructs by 1.57±0.59 times (p = 0.026). Initial stiffness of the construct was also increased 3.13±2.10 times (p = 0.0079) with use of the bone peg.

Conclusion: The stronger and stiffer construct provided by the addition of an intramedullary fibular allograft bone peg to locking plate fixation may help maintain reduction, and reduce the risk of fixation failure in surgical neck proximal humerus fractures with medial comminution.