Arthroplasty of the proximal humerus positions a prosthetic articular surface in relation to the humeral canal. Most descriptions of surgical technique recommend positioning the humeral component in 30 degrees to 45 degrees of retroversion. This study measured retroversion in relationship to the surgically reamed canal and introduced a method of measurement pertinent to prosthetic reconstruction. The canals of 21 cadaveric humeri were surgically reamed, the articular margins of the humeral heads were outlined with steel wire, and the trochlear axes were transfixed with Steinman pins. Under fluoroscopy the humeri were rotated on a jig that allowed rotation around the reamer and measurement of retroversion relative to the plane of the articular surface. Retroversion of the proximal humerus is highly variable, ranging in this study from 10 degrees to 55 degrees (mean 29.8 degrees). Anatomic reconstruction of the retroversion angle must be individualized. Palpation of the rotator cuff insertion is recommended prior to humeral head resection to avoid inadvertant cuff injury.

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