The Effects of Latarjet Reconstruction on Glenohumeral Kinematics in the Presence of Combined Bony Defects: A Cadaveric Model. (July 2016) - Patel, Ronak M.
Background: Recurrent glenohumeral instability is often a result of underlying bony defects in the glenoid and/or humeral head. Anterior glenoid augmentation with a coracoid bone block (ie, Latarjet procedure) has been recommended for glenoid bone loss in the face of recurrent instability. However, no study has investigated the effect of Latarjet augmentation in the setting of both glenoid and humeral head defects (Hill-Sachs defects). Purpose: To evaluate the glenohumeral kinematics of the Latarjet procedure in the presence of combined bony defects. Study Design: Controlled laboratory study. Methods: Eighteen fresh-frozen cadaveric specimens void of all surrounding soft tissue were tested at all combinations of glenohumeral abduction (ABD) angles of 20°, 40°, and 60° and 3 external rotation (ER) levels of 0°, 40°, and 80°. Each experiment comprised anterior dislocation by translating the glenoid under a 50-N medial load applied on the humerus, simulating the static load of soft tissue. The primary outcome measurement was defined as the percentage of intact translation (normalized distance to dislocation). Specimens were tested in an intact condition (no defect), with different combinations of defects, and with Latarjet augmentation. The Latarjet procedure was performed for 20% and 30% glenoid defects by transferring the specimen′s coracoid process anterior to the glenoid so that it was flush with the articulating surface. Results: Results depended on the position of the arm. At 20° of ABD and 0° of ER, a 20% glenoid defect decreased the percentage of intact translation regardless of the humeral head defect size ( P ≤ .0001). In this same setting, Latarjet reconstruction restored translation to dislocation greater than the native intact joint for all sizes of humeral head defects. At 60° of ABD and 80° of ER, a 20% glenoid defect led to an overall decrease in translation to dislocation with increasing humeral head defects. While Latarjet augmentation resulted in increased translation to dislocation for all humeral head defect sizes, it was not able to restore translation greater than the native intact joint for large humeral head defects (31% and 44%); the normalized percentages of intact translation to dislocation were 65% and 30%, respectively. Conclusion: These results demonstrate that some degree of translation can be regained for combined bony glenoid and humeral head defects with the Latarjet procedure. However, for humeral defects larger than 31%, the rotational effect of the humeral head defect led to persistent decreased translation and to dislocation despite glenoid augmentation. Thus, directly addressing the humeral defect to restore the articular surface should be considered in these cases. Clinical Relevance: This study provides a critical value limit for combined anterior glenoid bone loss and humeral head defects. While this is a biomechanical study, the results indicate that in patients with humeral head defects greater than 31%, additional humeral-sided surgery may be needed.