Optimizing intramedullary entry location on the proximal humerus based on variations of neck-shaft angle

Abstract

The purpose of this study was to define the relationship between the humeral neck-shaft angle (NSA) and variations in the ideal entry portal aligned with the long axis of the intramedullary canal of the proximal humerus. Three-dimensional images of 36 cadaveric humeri with various NSAs were reconstructed by a computerized surgical simulation program. The anteroposterior, mediolateral, and linear distances between a line from the center of the proximal medullary canal to the bicipital groove were measured. Differences among humeri with various NSAs were analyzed. The intramedullary axis line was located a mean of 9±2mm posteriorly and 11±3mm medially from the bicipital groove. The axis line was 9±2mm posterior and 11±2mm medial with a standard NSA. The axis line in humeri with a varus NSA was 8±2mm posteriorly and 9±2mm medially, whereas the axis line was 10±3mm posteriorly and 14±3mm medially with a valgus NSA. The differences in the mediolateral distances between the groups were significant (P<.00009). Care should be taken in choosing the entry portal position in humeri with various NSAs as the entry portal position differs according to the NSA. It is recommended that the location of the entry portal be moved toward the center of the humeral head to align with the centerline of the intramedullary canal in humeri with a valgus NSA in particular.