too low and the deltoid must undergo some contraction prior to starting to move the arm the height adjusting mechanism allows the surgeon to temporarily set the height of the head and then evaluate the deltoid tension in particular as shown in fig1 and 19 height adjusting mechanism 136 includes a guide bar 150 which is moveably mounted to a carriage 152 which is driven up and down along a threaded rod 154 with the implant in a humeral shaft 156 the guide bar is positioned to sit on top 158 of the humeral shaft the surgeon can then adjust the implant up or down by turning the threaded rod the guide bar establishes a predetermined height which can be maintained while retroversion is set and even if the implant is removed and reinserted as when bone cement is used after establishing the correct height the surgeon can use the retroversion guide to set correct retroversion as shown in fig2 the retroversion guide includes an l shaped rod 160 with a lower sighting arm 162 rod 160 is pivotally and slidably mounted to template 132 to allow the height and angular orientation of the sighting arm to be adjusted a set screw 164 allows the position of the rod to be fixed once it is in the desired orientation in use the sighting arm is set for a predetermined retroversion angle relative to the.