A Posterior Acromial Bone Block Augmentation Is Biomechanically Effective at Restoring the Force Required To Translate the Humeral Head Posteriorly in a Cadaveric, Posterior Glenohumeral Instability Model

Abstract

The purpose of this study was to assess the biomechanical utility of a posterior acromial bone block (PABB) for the treatment of posterior glenohumeral instability. 10 fresh-frozen cadaveric specimens were obtained based upon an a priori power analysis. A 2.5 cm scapular spine autograft was harvested from all shoulders. A custom robot device was used to apply a 50-N compressive force to the glenohumeral joint. The humeral head was translated 10mm posteroinferiorly at 30 degrees from the center of the glenoid at a rate of 1.0 mm/s in 6 consecutive conditions: 1) intact specimen, 2) intact with PABB, 3) posterior capsulolabral tear 4) addition of the PABB, 5) removal of the PABB and repair of the capsulolabral tear (LR), and 6) addition of the PABB with LR. The maximum force required to obtain this translation was recorded. Paired T-tests were performed to compare relevant testing conditions. 10 cadavers with mean age 54.4 years (Standard Deviation (SD) ± 13.1) and mean glenoid retroversion of 6.5 degrees (SD ± 1.0) were studied. The PABB provided greater resistance force to humeral head translation compared to the instability state (instability, 29.3 ± 15.3N versus PABB, 47.6 ± 21.0 N, P = 0.001, 95% confidence interval [CI] -27.6, -10.0). When comparing PABB to LR, the PABB produced higher resistance force than LR alone (PABB, 47.6 ± 21.0 N, LR, 34.2 ± 20.5N, P = 0.012, 95% CI -23.4, -4.1). An instability lesion treated with the PABB, with (P =0.056, 95% CI -0.30, 20.4) or without LR (P = 0.351, 95% CI -6.8, 15.7), produced resistance forces similar to the intact specimen. A posterior acromial bone block is biomechanically effective at restoring the force required to translate the humeral head posteriorly in a cadaveric, posterior glenohumeral instability model. A posterior acromial bone block is a biomechanically feasible option to consider in patients with recurrent posterior instability.