Biomechanical Evaluation of Glenoid Reconstruction With an Implant-Free J-Bone Graft for Anterior Glenoid Bone Loss

Background: The anatomic restoration of glenoid morphology with an implant-free J-shaped iliac crest bone graft offers an alternative to currently widely used glenoid reconstruction techniques. No biomechanical data on the J-bone grafting technique are currently available. Purpose: To evaluate (1) glenohumeral contact patterns, (2) graft fixation under cyclic loading, and (3) the initial stabilizing effect of anatomic glenoid reconstruction with the implant-free J-bone grafting technique. Study Design: Controlled laboratory study. Methods: Eight fresh-frozen cadaveric shoulders and J-shaped iliac crest bone grafts were used for this study. J-bone grafts were harvested, prepared, and implanted according to a previously described, clinically used technique. Glenohumeral contact patterns were measured using dynamic pressure-sensitive sensors under a compressive load of 440 N with the humerus in (a) 30 degrees of abduction, (b) 30 degrees of abduction and 60 degrees of external rotation, (c) 60 degrees of abduction, and (d) 60 degrees of abduction and 60 degrees of external rotation. Using a custom shoulder-testing system allowing positioning with 6 degrees of freedom, a compressive load of 50 N was applied, and the peak force needed to translate the humeral head 10 mm anteriorly at a rate of 2.0 mm/s was recorded. All tests were performed (1) for the intact glenoid, (2) after the creation of a 30% anterior osseous glenoid defect parallel to the longitudinal axis of the glenoid, and (3) after anatomic glenoid reconstruction with an implant-free J-bone graft. Furthermore, after glenoid reconstruction, each specimen was translated anteriorly for 5 mm at a rate of 4.0 mm/s for a total of 3000 cycles while logging graft protrusion and mediolateral bending motions. Graft micromovements were recorded using 2 high-resolution, linear differential variable reluctance transducer strain gauges placed in line with the long leg of the graft and the mediolateral direction, respectively. Results: The creation of a 30% glenoid defect significantly decreased glenohumeral contact areas (P < .05) but significantly increased contact pressures at all abduction and rotation positions (P < .05). Glenoid reconstruction restored the contact area and contact pressure back to levels of the native glenohumeral joint in all tested positions. The mean (SD) force to translate the humeral head anteriorly for 10 mm (60 degrees of abduction: 31.7 12.6 N; 60 degrees of abduction and 60 degrees of external rotation: 28.6 +/- 7.6 N) was significantly reduced after the creation of a 30% anterior bone glenoid defect (60 degrees of abduction: 12.2 +/- 6.8 N; 60 degrees of abduction and 60 degrees of external rotation: 11.4 +/- 5.4 N; P < .001). After glenoid reconstruction with a J-bone graft, the mean peak translational force significantly increased (60 degrees of abduction: 85.0 +/- 8.2 N; 60 degrees of abduction and 60 degrees of external rotation: 73.6 +/- 4.5 N; P < .001) compared with the defect state and baseline. The mean total graft protrusion under cyclical translation of the humeral head over 3000 cycles was 138.3 +/- 169.8 mu m, whereas the mean maximal mediolateral graft deflection was 320.1 +/- 475.7 mu m. Conclusion: Implant-free anatomic glenoid reconstruction with the J-bone grafting technique restored near-native glenohumeral contact areas and pressures, provided secure initial graft fixation, and demonstrated excellent osseous glenohumeral stability at time zero.