Instrument for implanting a sensor

An instrument for implanting a sensor in a body part, in which the sensor has at least one cord extending therefrom which is connected to an external device, includes a guide sheath for defining a path to the surface of the body part through overlaying soft tissue, the sheath having a bore extending along its length between first and second open ends through which the tool can pass and a slot that extends along its length between its first and second open ends. A delivery sheath for implanting the sensor in the hole has a bore extending along its length between a first open end at which the sensor can be mounted and a second end, with the cord extending from the sensor along the bore, in which the sheath has a slot that extends along its length between its first and second end, and wherein the delivery sheath can be received within the guide sheath by sliding the delivery sheath within the bore of the guide sheath. The slots of the guide and delivery sheaths can be aligned to allow the cord to be removed from the bores other than at the ends of the bores.