Humeral head arthroplasty and its ability to restore original humeral head geometry

Background prosthetic components are designed to enable restoration of proximal humeral morphology, provided that a precise osteotomy of the humeral head at the level of the anatomic neck is performed. To determine whether a simulated osteotomy and replacement arthroplasty with an idealized implant were able to restore original head geometry. als and methods held digitizer and surface laser scanner were used to digitize 24 humeri. Computer models were used to simulate an osteotomy, performed at the anterior cartilage–metaphyseal interface, and reconstruct the head with a spherical prosthetic head. The head diameter, radius of curvature, and inclination and retroversion angles were calculated for each specimen and compared with the original humeral head. s mulated osteotomy resulted in a 4.8° decrease in inclination (P < .01) and 11.3° increase in retroversion (P < .001). The radius of curvature in the coronal plane was not significantly different (P = .284). However, in the axial plane, the prosthesis was significantly larger than the original head for both head diameter (P < .001) and radius of curvature (P < .05). sion udy suggests that the humeral head is not a perfect segment of a sphere and an osteotomy along the anterior cartilage–metaphyseal interface does not remove only the proximal humeral articular surface. Even with a fully adaptable prosthetic implant, replacement arthroplasty is not able to restore original head geometry. sions tions to head geometry with the osteotomy described may alter the line of force through the prosthetic joint, producing eccentric loading at the glenoid, and contribute to early failure.