A retractor system comprising: a first tower which is mountable on a first surgical screw (12.1), the first tower comprising: a first tube having a distal end defining a distal opening, a proximal end defining a proximal opening, and the first tube defining an axial bore extending between the distal opening and the proximal opening, the first tube defining at least first and second slots (32.1, 32.2) extending axially from the distal end partially towards the proximal end, to form a screw gripping formation which comprises at least first and second axially extending tube parts (20.1, 20.2) which are spring biased towards a first configuration to grip a head of the first surgical screw by pinching the head between them, wherein the at least first and second tube parts (20.1, 20.2) are manipulatable against the bias to a second configuration to release the head; a centre shaft comprising a transverse formation at a distal end thereof; and an inner tube having an external diameter which is less than an inner diameter of the first tube and which is coaxially receivable in the first tube and which inner tube comprises an external thread towards a distal end thereof, wherein the centre shaft is coaxially receivable in the bore of the first tube with the transverse formation locating in diametrically opposed notches (19.1, 19.2) of the head of the screw and wherein the inner tube is coaxially receivable between the centre shaft and the first tube and the external thread cooperates with a complementary internal thread in the first tube to bear onto and lock the transverse formation of the centre shaft in the diametrically opposed notches (19.1, 19.2); a second tower which is mountable on a second surgical screw (12.2); a link extending between the first and second towers (102, 104); and at least a first elongate retractor element for at least one of muscle, tissue and nerve structures and which at least first element is movably mountable on the link. a first tube having a distal end defining a distal opening, a proximal end defining a proximal opening, and the first tube defining an axial bore extending between the distal opening and the proximal opening, the first tube defining at least first and second slots (32.1, 32.2) extending axially from the distal end partially towards the proximal end, to form a screw gripping formation which comprises at least first and second axially extending tube parts (20.1, 20.2) which are spring biased towards a first configuration to grip a head of the first surgical screw by pinching the head between them, wherein the at least first and second tube parts (20.1, 20.2) are manipulatable against the bias to a second configuration to release the head; a centre shaft comprising a transverse formation at a distal end thereof; and an inner tube having an external diameter which is less than an inner diameter of the first tube and which is coaxially receivable in the first tube and which inner tube comprises an external thread towards a distal end thereof, wherein the centre shaft is coaxially receivable in the bore of the first tube with the transverse formation locating in diametrically opposed notches (19.1, 19.2) of the head of the screw and wherein the inner tube is coaxially receivable between the centre shaft and the first tube and the external thread cooperates with a complementary internal thread in the first tube to bear onto and lock the transverse formation of the centre shaft in the diametrically opposed notches (19.1, 19.2); a second tower which is mountable on a second surgical screw (12.2); a link extending between the first and second towers (102, 104); and at least a first elongate retractor element for at least one of muscle, tissue and nerve structures and which at least first element is movably mountable on the link.