Superior glenoid inclination and glenoid bone loss : Definition, assessment, biomechanical consequences, and surgical options.

Correct anatomical alignment of the glenoid component is of central importance for wear and loosening in shoulder endoprostheses. The aim of this article is to review and clarify the biomechanical and clinical effects of incorrect glenoid inclination in reverse and anatomical joint replacements. Based on the literature and on our own work, statements are made about the following: (1) the glenoid inclination of a normal glenoid, a degenerative glenoid and a glenoid implant, and the consequences if superior inclination is too large, and (2) the surgical technique as well as tips and tricks for correct adjustment of the inclination. The inclination of the glenoid plane is a morphological parameter of the scapula with high individual variation and is best measured using reformatted computed tomography using three-dimensional software for reconstruction and evaluation. The standard value is between 0 and 10°. Excessive superior inclination promotes translation of the humeral head and the formation of rotator cuff tears-in a degenerative glenoid, to superior wear. The correct amount of superior inclination of the glenoid component is essential for the survival of the implant. Positioning without excessive superior inclination is therefore mandatory. Precise preoperative determination of glenoid inclination and wear is important in order to correctly plan the positioning of an implant. This serves as the basis for deciding whether a bone graft or patient-specific instrumentation is necessary. Thus, the surgeon also has prognostic parameters for the anticipation of possible complications as a result of the bone defect and abnormal orientation. However, the evaluation must always include the position of the scapula in these considerations.