a modular hip joint prosthesis is assembled from a head section having a connection for the ball of the joint and from a shaft section . the shaft section is joined by a insert connection to the head section , and provision is made for fixing the insert connection . the insert connection is situated in the region of shenton &# 39 ; s arc . the respective contours , in longitudinal section , of the head and shaft sections in the region of the connection merge smoothly , without any substantial change in direction , irrespective of the relative mutual alignments of the sections at any given time , with the exception of a gap in the immediate vicinity of the connection .