There has been an increasing interest in achieving true anatomic replication of native anatomy in unconstrained shoulder arthroplasty. Reconstruction of the humerus is generally done in one of two ways: guided resection of the humeral head using intramedullary cutting guides and version bars and reconstruction with a fixed angle prosthesis or freehand resection of the native humeral head, based on perceived anatomic neck anatomy and reconstruction with a variable angle prosthesis. The purpose of this study is to determine which technique used for proximal humerus reconstruction in shoulder arthroplasty more reliably reproduces native anatomy. Ten sets of cadaveric upper limbs (20 shoulders) were scanned for a pre-resection CT scan to establish preoperative version, neck-shaft angle, center of rotation (COR), and head height. The cadavers were then divided into two groups so that both groups had an equal number of right limbs. Half of the cadavers underwent a freehand cut based on surgeon defined anatomic neck. The other half underwent humeral head resections using a fixed intramedullary guide. The free-hand cut group was reconstructed with a prosthesis that allows the head to be matched to the anatomic cut with 15º of variability in all planes (Depuy-Synthes Global AP). The group cut with the intramedullary guide was reconstructed using a fixed angle stem (Zimmer BF Shoulder). The limbs were then again scanned and the measurements from the reconstructed proximal humeri were compared to those from the native cadavers. The following measurements were taken: humeral head height, neck shaft angle, humeral version (based off the humeral epicondylar axis), and COR in the axial, craniocaudal (CC), and medial to lateral planes (TX). There were no statistically significant differences between the two groups’ delta values with respect to head height (p=.2794), neck shaft angle (p=.8311), version (.1197), or center of rotation as measured in the axial (p=.109), craniocaudal (p=.1754), or medial to lateral planes (p=.7343). However, the fixed angle prosthesis tended to more accurately reproduce native anatomy with regard to humeral height, version, and neck shaft angle. The variable angle prosthesis tended to more accurately replicate COR in the axial, craniocaudal, and medial to lateral planes of reference with standard deviation values that reflected this trend when compared to the fixed angle prosthesis. The results of our study suggest that, with respect to the accuracy of proximal humerus reconstruction in TSA, variable and fixed angle prostheses are equally accurate in reconstructing native proximal humerus anatomy
