Surgical assembly, and bone anchor screw and device for extending one such screw that belong to said surgical assembly

A surgical assembly, comprising:

• a bone anchorage screw having an anchorage portion for anchoring in a vertebral column, and a head comprising a socket;
• and
• an extension device adapted to fit over the socket the bone anchorage screw for forming a longitudinal extension thereto;
• wherein:
• said extension device comprises a first tubular element referred to as an “inner tube”, of inside diameter greater than or equal to an inside diameter of the socket of the bone anchorage screw, and extended longitudinally by two diametrically opposite branches, said branches having resilience allowing the branches to be moved apart from each other and towards each other, and the free ends of the two branches forming jaws for clamping onto an outside surface of the socket so as to lock onto the socket;
• the extension device further comprises a second tubular element referred to as an “outer tube”, mounted around the inner tube and of inside diameter matching an outside diameter of said inner tube to an extent such that said outer tube slides along said inner tube between a “non-locking position” and a “locking position”, in which the outer tube respectively does not lock onto and locks onto the bone anchorage screw, the outer tube being extended longitudinally by two diametrically opposite branches superposed on the branches of the inner tube, free ends of the two branches of the outer tube being in register with the free ends of the two branches of the inner tube, and each of said free ends of the outer tube being provided with retaining means adapted, when the extension device is fitted over the socket of the bone anchorage screw and when said outer tube is slid into the locking position, for co-operating with complementary retaining means arranged on the socket to prevent said branches of the outer tube from moving apart from each other, thereby preventing the branches of the inner tube from moving apart from each other so as to make it possible to keep the extension device locked on the socket of the bone anchorage screw.