Biomechanical evaluation of straight antegrade nailing in proximal humeral fractures: the rationale of the “proximal anchoring point”

Abstract

Purpose Varus failure is one of the most common failure modes following surgical treatment of proximal humeral fractures. Straight antegrade nails (SAN) theoretically provide increased stability by anchoring to the densest zone of the proximal humerus (subchondral zone) with the end of the nail. The aim of this study was to biomechanically investigate the characteristics of this Bproximal anchoring point^(PAP). We hypothesized that the PAP would improve stability compared to the same construct without the PAP. Methods Straight antegrade humeral nailing was performed in 20 matched pairs of human cadaveric humeri for a simulated unstable two-part fracture. Results Biomechanical testing, with stepwise increasing cyclic axial loading (50-N increments each 100 cycles) at an angle of 20°abduction revealed significantly higher median loads to failure for SAN constructs with the PAP (median, 450 N; range, 200-1.000 N) compared to those without the PAP (median, 325 N; range, 100-500 N; p = 0.009). SAN constructs with press-fit proximal extensions (endcaps) showed similar median loads to failure (median, 400 N; range, 200-650 N), when compared to the undersized, commercially available SAN endcaps (median, 450 N; range, 200-600 N; p = 0.240). Conclusions The PAP provided significantly increased stability in SAN constructs compared to the same setup without this additional proximal anchoring point. Varus-displacing forces to the humeral head were superiorly reduced in this setting. This study provides biomechanical evidence for the Bproximal anchoring point's^rationale. Straight antegrade humeral nailing may be beneficial for patients undergoing surgical treatment for unstable proximal humeral fractures to decrease secondary varus displacement and thus potentially reduce revision rates.

Straight antegrade humeral nailing and risk of iatrogenic injury of supraspinatus tendon footprint: An MRI study

“…The PAP provided significantly increased stability in SAHN constructs. 4 This dense subchondral bone stock lateral to the nail's proximal end depends on the CD and the nail's radius. The smaller the CD or bigger the nail diameter, greater is the risk that the nail does not anchor sufficiently bone at proximal humerus.…”

“…1–3 Biomechanically, the lever arm of an intramedullary device is lower, potentially counteracting posteromedial varus displacing forces. 4 Technically, SAHN allows a medial insertion, preserving the supraspinatus tendon footprint (SSP-F). 5–7…”

“…[1][2][3] Biomechanically, the lever arm of an intramedullary device is lower, potentially counteracting posteromedial varus displacing forces. 4 Technically, SAHN allows a medial insertion, preserving the supraspinatus tendon footprint (SSP-F). [5][6][7] The poor results associated with second-generation antegrade humeral nailing (locked, bent design) were related to the curvilinear design with increased risk for iatrogenic rotator cuff injury.…”

Intramedullary Nail for Treatment of Proximal Humeral Fracture: A Credible Fixation in Comminuted Calcar

“…The use of nails to treat comminuted metaphyseal fractures may be suspicious; however, compared to plating, the proximal humeral nail has several theoretical advantages, such as minimal soft tissue damage and preservation of the blood supply to the already injured humeral head. Furthermore, centrally placed nails possess biomechanical advantages in resisting loss of reduction and varus displacement 27 …”

“…Furthermore, centrally placed nails possess biomechanical advantages in resisting loss of reduction and varus displacement. 27 In our trauma center, an angle-stable, straight, short humerus nail (TRIGEN Humeral Nail; Smith & Nephew, Cordova, TN, USA) is commonly utilized for PHFs. This study aims to investigate (1) the radiographic results after intramedullary nail fixation, (2) evaluate the clinical outcomes, (3) and focus on the impact of medial calcar integrity.…”