- a sleeve having an open end to accommodate a needle assembly and a portion of a syringe cylinder and a closed end that has an opening to receive a needle of the needle assembly therethrough - a positioning member within the sleeve, the positioning member having an opening to engage the needle assembly and the sleeve having at least one formation for releasably engaging the positioning member and - a biasing member situated in the sleeve between the positioning member and the closed end of the sleeve. In use, counter-pressure exerted by the patients skin against the closed end causes the positioning member to be rotatably released from the formation thereby releasing the sleeve from the operative position and biases it to the rest position. The sleeve is biased to cover the needle to the extent that the needle is withdrawn from the patient.
