A Method to Facilitate Improved Positioning of a Reverse Prosthesis Stem During Arthroplasty Surgery: The Metaphyseal-centering Technique.

Because humeral head offset values vary widely from patient to patient, the final position of the proximal portion of a stemmed humeral prosthesis will sometimes not align well with respect to the center of rotation of the humeral head. This is especially notable when a humeral component with limited modularity is used. To address this problem, a prosthesis-specific method is presented for orienting a reverse shoulder humeral component (AltiVate Reverse, DJO Surgical, Austin, TX). With the metaphyseal-centering technique, priority is given to the positioning of the shell portion of the prosthesis over that of the stemmed portion during bone preparation. To ensure that a centralized shell position is achieved within the proximal humerus bone in patients with extreme posterior and medial offset measurement values, the stem portion of the humeral prosthesis is sometimes purposely undersized and positioned eccentrically within the humeral diaphysis. Bone autograft is used in such cases to improve the fit and fixation of the stem within the humeral canal. The metaphyseal-centering technique facilitates: (1) consistent positioning of the shell portion of the humeral prosthesis relative to the center of rotation of the humeral head, and (2) conversion from a standard to a reverse prosthesis, or vice versa, during revision surgery without the need for stem removal or alteration of the humerus bone. Preliminary outcomes of this surgical technique are encouraging, but formal studies are warranted to validate its clinical utility and longevity of results.