Angular stable intramedullary nail versus locking plate fixation of osteoporotic surgical neck proximal humerus fractures: A biomechanical comparison

Abstract

Background: Our study's purpose was to compare biomechanical performances of a proximal humerus locking plate (PHLP) with an antegrade intramedullary nail (IMN) in an osteoporotic two-part surgical neck proximal humerus fracture model.

Methods: Simulated fractures were made through the surgical neck of synthetic osteoporotic humeri. One group had identical transverse fractures instrumented with a PHLP with seven screws (PHLP-7; n = 4), a PHLP with nine screws (PHLP-9; n = 2), or an IMN (n = 4). Each underwent pre-fatigue testing, an identical fatigue protocol, and post-fatigue testing. A second high oblique fracture line was tested identically with PHLP-9 (n = 4) and IMN (n = 4) constructs.

Results: Statistical analyses of transverse specimen pre-fatigue stiffness revealed that the PHLP-7 and PHLP-9 were stiffer in anteroposterior bending and torsion compared to the IMN. There was no difference between the three constructs in varus-valgus bending or compression. Post-fatigue stiffness comparisons revealed no difference between the three constructs. For the oblique fracture, pre-fatigue differences were found with the IMN stiffer in varus-valgus bending and the PHLP-9 stiffer in torsion.

Discussion: The biomechanical performance of an angular-stable proximal humeral nail design was comparable, especially following fatigue, to locked plate/screw constructs in a synthetic osteoporotic two-part surgical neck proximal humerus fracture model.

Keywords: biomechanics; intramedullary nail; locked; osteoporosis; proximal humerus fracture; proximal humerus locking plate.

Figure 1.

Synthes PHILOS proximal humerus locking plate. Note: The two screw holes left open in the PHLP-7 construct were from the row circled in red (row C) which, when placed, provide divergent screw fixation in the anterior and posterior regions of the mid-aspect of the humeral head and neck. The most distal screws, row E, provide fixation into the anterior and posterior aspects of the inferomedial humeral neck and have been shown to prevent loss of reduction and screw loosening.

Figure 2.

Wright Medical Aequalis proximal humeral nail (IMN).

Figure 3.

Radiograph of representative specimens. Note: Left—intramedullary nail; right—proximal humerus locking plate. Superimposed lines demonstrate fracture line position; (green line = “transverse” fracture line, red line = “oblique” fracture line).

Figure 4.

Potting technique and set up of the tested specimens.

Figure 5.

The servohydraulic biomechanical testing set up of specimens.

Figure 6.

Ph_FINAL. Note: Lack of tuberosity/proximal segment cortical fixation in the “oblique” fracture pattern leading to significant loosening of the fixation constructs during fatigue.