According to the disclosure, a variable tissue volume circular stapler instrument (9) may be adapted from those currently used for the removal and treatment of haemorrhoids. An exemplary instrument comprises a handle, a shaft extending from the handle, and a stapling head assembly extending from the shaft. The stapling has a hollow casing that allows a certain amount of tissue to be drawn into the housing via the use of draw string sutures placed in the mucosal layers of the anal wall. The amount of tissue drawn into the housing with current instrumentation may be controlled by providing a variable tissue-volume control mechanism (16) mounted between the casing, the staple pusher mechanism (15) and the central shaft (19) and having fenestrations (18) which correspond to external stapler housing fenestrations (17).
