Remplissage of an Off-track Hill-Sachs Lesion Is Necessary to Restore Biomechanical Glenohumeral Joint Stability in a Bipolar Bone Loss Model

Abstract

To validate the glenoid track concept in a cadaveric bipolar bone loss model and to test whether "on-track" and "off-track" lesions can be stabilized with Bankart repair (BR) with or without Hill-Sachs remplissage (HSR). Eight fresh-frozen cadaveric shoulders were tested in a custom apparatus with passive axial rotation and then progressive translational loading (10 to 40N) at mid-range (60°) and end-range external rotation (90°). Injury conditions included glenoid bone loss of 15% with on-track (15%) and off-track (30%) Hill-Sachs lesions. Repair conditions included BR with HSR and BR without HSR. For on-track lesions, engagement occurred with translation testing in one shoulder (12.5%) at end-range rotation. After BR, engagement was prevented for this shoulder. For off-track lesions, engagement with translation testing occurred in 8 shoulders (100%) at end-range rotation and in 6 (75%) at mid-range rotation. AfterBR, engagement was prevented in 4 of 6 engaging shoulders (67%) at mid-range rotation but was prevented inzero of 8 (0%) at end-range rotation. Adding HSR prevented engagement in all 14 engaging shoulders with off-track lesions (100%). BR with HSR resulted in supraphysiological stiffness for off-track lesions at mid- and end-range rotation(13.3N/m vs 7.0N/m and 10.0N/m vs 5.0N/m, P= .0002) and for on-track lesions at end-range rotation (10.1N/m vs 5.0N/m, P= .0002). Stiffness of BR with HSR was not different from the intact shoulder for on-track lesions at mid-range rotation (7.2N/m vs 7.0N/m, P > .99). The patterns of engagement of Hill-Sachs lesions with a 15% glenoid defect in this model give support to the glenoid track concept. BR plus remplissage resulted in supraphysiological shoulder stiffness but was necessary to prevent engagement of off-track bipolar bone lesions. This biomechanical study provides evidence to aid in surgical decision making by examining the effects of bipolar bone loss and soft-tissue reconstruction on shoulder stability.