Second milling
With the appropriate spigot in place (in this case a 3), use the spherical mill to remove the required additional thickness of bone from the condyle. Remove the corners of bone with a chisel tangential to the milled surface. If a collar of bone has appeared around the 6 mm hole, this should be removed with the bone collar remover [35]. Reinsert the trial femoral component and remeasure the gaps. The flexion gap should not have changed. The extension gap should now equal the flexion gap. Occasionally if the extension gap is still too narrow, a third milling is necessary.
Third milling
By subtracting the extension gap from the flexion gap the amount of bone to be removed is determined (say 1 mm). Add this to the size of the spigot used for the second milling (3) to determine the size (4) needed for the third milling. Insert the appropriate spigot, but do not hammer it in. As the small central collar of bone has been removed the spigot should not be touching the surface of the bone but is referenced off the bottom of the hole. Repeat milling and reassess gaps.
