Axial-Plane Biomechanical Evaluation of 2 Suspensory Cortical Button Fixation Constructs for Acromioclavicular Joint Reconstruction

Abstract

Background: Although numerous suture-button fixation techniques for acromioclavicular (AC) joint reconstruction have been validated with biomechanical testing in the superior direction, clinical reports continue to demonstrate high rates of construct slippage and breakage.

Purpose: To compare the stability of a novel closed-loop double Endobutton construct with a commercially available cortical button system in both the axial and superior directions.

Study design: Controlled laboratory study.

Methods: Six matched pairs of fresh-frozen cadaveric upper extremities were anatomically dissected and prepared to simulate a complete AC joint dislocation. One side of each pair was reconstructed with the double Endobutton (DE) construct and other side with the dog bone button (DB) construct. The specimens were then tested using a materials testing machine, determining initial superior and axial displacements with a preload, and then cyclically loaded in the axial direction with 70 N for 5000 cycles. Displacement was again measured with the same preloads at fixed cycle intervals. The specimens were then loaded superiorly to failure.

Results: At 5000 cycles, the mean axial displacement was 1.7 mm for the DB group and 1.2 mm for the DE group (P = .19), and the mean superior displacement was 1.1 mm for the DB group and 0.7 mm for the DE group (P = .32). Load at failure was similar (558 N for DE, 552 N for DB; P = .96). There was no statistically significant difference in the modes of failure.

Conclusion: Biomechanical testing of both constructs showed similar fixation stability after cyclical axial loading and similar loads to failure.

Clinical relevance: The strength of both constructs after cyclical loading in the axial plane and load-to-failure testing in the superior plane validate their continued clinical use for achieving stability in AC joint reconstruction procedures.

Keywords: Endobutton; acromioclavicular joint; anatomic reconstruction; biomechanics; coracoclavicular ligament.

Figure 1.

Illustrations depicting 2 acromioclavicular joint reconstruction techniques: (A) continuous-loop double Endobutton construct and (B) dog bone button fixation construct.

Figure 2.

(A) Testing rig. Position of the scapula in the vise, vise angles, and position were adjusted so that scapula was anatomically positioned and vertically oriented. The ring stand position and pulley were adjusted to apply a static perpendicular superior load to the clavicle anterior to the fixation construct. Two marking pins can be seen. (B) Artist depiction of testing rig. AP, anterior-posterior plane; SI, superior-inferior plane.