Elliptical Humeral Head Implants in Anatomic Total Shoulder Arthroplasty.

Humeral implants for anatomic total shoulder arthroplasty and hemiarthroplasty have typically used spherical humeral heads that have a uniform diameter and radius of curvature. However, the native humeral head has a more elliptical morphology, which has spurred interest in nonspherical implant designs. Cadaveric studies indicate that the native humeral head diameter is 10% longer in the superior-inferior plane than the anterior-posterior plane and has a radius of curvature that is approximately 8% greater. An elliptical implant that more closely replicates native anatomy may allow for more accurate coverage of the humeral resection surface with less implant overhang and risk of overstuffing. Biomechanical evidence suggests that an elliptical implant yields glenohumeral kinematics that mimic the native joint, and early clinical results are promising. As clinical research continues to emerge, it will become clearer whether encouraging cadaveric, biomechanical, and early clinical data translates to meaningful sustained improvements in patient outcomes.