Abstract: A surgical instrument (100) and system incorporating such instruments, the instrument comprising: a stem (112), the stem having a proximal end (116) and having a distal end (110); a handle portion (114), the handle portion being provided towards the proximal end of the stem; and a guide element (108), the guide element being provided towards the distal end of the stem, wherein the guide element provides: a body element (131) defining a guide channel (128), the guide channel having a longitudinal axis (X-X) and being open at both ends along the longitudinal axis; and one or more positioning elements (130a, 130b). The instrument and system are suited to the removal of a polyethylene acetabular liner (25) from an implanted shell (27), for instance to remove that liner and replace it with another, whilst minimising the risk of damage to the shell holding it.