A medical infusion device, comprising: a base; a flexible catheter movable from a first catheter position disposed substantially entirely within said base to a second catheter position in which a free end of said catheter is disposed externally of said base; and an introducer needle located within said catheter and movable between a first introducer needle position disposed substantially entirely within said base and a second introducer needle position in which a free end of said introducer needle is disposed externally of said base; wherein the medical infusion device further comprises a torsion spring (181, 281, 381, 481, 581) for initially rotating a rotating member (171, 271, 303, 505) in a rotational direction to move said catheter from said first to said second catheter position and said introducer needle from said first to said second introducer needle position to facilitate insertion of said catheter, said torsion spring (181, 281, 381, 481, 581) then further rotating said rotating member (171, 271, 303, 505) in the same rotational direction to move said introducer needle back toward said first introducer needle position to store said introducer needle within said base with said free end of said catheter remaining disposed externally of said base characterised in that a linking arm (151, 251, 351, 451) is coupled to said introducer needle and to said rotating member (171, 271, 303, 505), the coupling between said rotating member (171, 271, 303, 505) and said linking arm (151, 251, 351, 451) being at fixed points on each of said rotating member (171, 251, 303, 505) and said linking arm (151, 251, 351, 451), wherein said rotating member (171, 271, 303, 505) and said linking arm (151, 251, 351, 451) together form a rotary crank mechanism for converting rotary motion from said torsion spring (181, 281, 381, 481, 581) to linear motion of said introducer needle. a base; a flexible catheter movable from a first catheter position disposed substantially entirely within said base to a second catheter position in which a free end of said catheter is disposed externally of said base; and an introducer needle located within said catheter and movable between a first introducer needle position disposed substantially entirely within said base and a second introducer needle position in which a free end of said introducer needle is disposed externally of said base; wherein the medical infusion device further comprises a torsion spring (181, 281, 381, 481, 581) for initially rotating a rotating member (171, 271, 303, 505) in a rotational direction to move said catheter from said first to said second catheter position and said introducer needle from said first to said second introducer needle position to facilitate insertion of said catheter, said torsion spring (181, 281, 381, 481, 581) then further rotating said rotating member (171, 271, 303, 505) in the same rotational direction to move said introducer needle back toward said first introducer needle position to store said introducer needle within said base with said free end of said catheter remaining disposed externally of said base characterised in that a linking arm (151, 251, 351, 451) is coupled to said introducer needle and to said rotating member (171, 271, 303, 505), the coupling between said rotating member (171, 271, 303, 505) and said linking arm (151, 251, 351, 451) being at fixed points on each of said rotating member (171, 251, 303, 505) and said linking arm (151, 251, 351, 451), wherein said rotating member (171, 271, 303, 505) and said linking arm (151, 251, 351, 451) together form a rotary crank mechanism for converting rotary motion from said torsion spring (181, 281, 381, 481, 581) to linear motion of said introducer needle.