A medical needle assembly comprising: a needle cannula having a body and a tip, wherein the tip is disposed at a distal end of the cannula; a feature secured to the body of the cannula; a shield slidingly mounted to the needle cannula for movement between a proximal position in which the tip is exposed from the shield to a distal position in which the tip is trapped within the shield, wherein the shield comprises: a shield body having a central chamber, a distal end, and a proximal end; and a plate secured to the proximal end of the shield body and defining an aperture; characterised in that there is an elongate member disposed proximal to the feature, wherein the elongate member is biased radially outward from the needle cannula when the shield is in the proximal position, wherein the aperture is sized to permit passage of a body of the needle cannula and to prevent passage of the feature; and wherein in response to the shield sliding from the proximal position to the distal position, the elongate member compresses to pass through the aperture and the tip enters the central chamber, wherein when the shield is in the distal position, the elongate member is biased radially outward from the needle cannula and prevents the shield from moving proximally with respect to the needle cannula. a needle cannula having a body and a tip, wherein the tip is disposed at a distal end of the cannula; a feature secured to the body of the cannula; a shield slidingly mounted to the needle cannula for movement between a proximal position in which the tip is exposed from the shield to a distal position in which the tip is trapped within the shield, wherein the shield comprises: a shield body having a central chamber, a distal end, and a proximal end; and a plate secured to the proximal end of the shield body and defining an aperture; characterised in that there is an elongate member disposed proximal to the feature, wherein the elongate member is biased radially outward from the needle cannula when the shield is in the proximal position, wherein the aperture is sized to permit passage of a body of the needle cannula and to prevent passage of the feature; and wherein in response to the shield sliding from the proximal position to the distal position, the elongate member compresses to pass through the aperture and the tip enters the central chamber, wherein when the shield is in the distal position, the elongate member is biased radially outward from the needle cannula and prevents the shield from moving proximally with respect to the needle cannula. a shield body having a central chamber, a distal end, and a proximal end; and a plate secured to the proximal end of the shield body and defining an aperture; characterised in that there is an elongate member disposed proximal to the feature, wherein the elongate member is biased radially outward from the needle cannula when the shield is in the proximal position, wherein the aperture is sized to permit passage of a body of the needle cannula and to prevent passage of the feature; and wherein in response to the shield sliding from the proximal position to the distal position, the elongate member compresses to pass through the aperture and the tip enters the central chamber, wherein when the shield is in the distal position, the elongate member is biased radially outward from the needle cannula and prevents the shield from moving proximally with respect to the needle cannula.