 However, it is not attached to the ulna, as the distance between these two bones varies with supination and pronation of the forearm.Instead the medial attachment is to the most medial of the carpal bones, the triquetrum (or triquetral bone) and pisiformis (or pisiform bone).The retinaculum is also attached in its passage across the wrist, to the ridges on the dorsal surface of the radius.