A surgical instrument comprising a first component (2) having a first face (76) and a second component (4) coupled to the first component (2) such that the first and second components (2, 4) can rotate relative to one another. The instrument further comprises a locking mechanism comprising a third component (32) having a second face (74) coupled to the second component (4). Movement of the third component (32) relative to the second component (4) is arranged to bring the second face (74) into or out of engagement with the first face (76) so as to selectively restrict or allow rotation between the first and second components (2, 4). One of said faces (7, 76) comprises a first array (78) of two or more grooves or teeth spaced apart at a first angular pitch about the centre of rotation between the first and second components (2, 4) and at least one further groove (82) or further tooth which does not correspond to the first angular pitch. The other of said faces (74, 76) comprises a first tooth (84) or a first groove arranged to engage one of the first array (78) of grooves or teeth so as to selectively restrict rotation to two or more predetermined rotational positions within a first range of rotational positions between the first and second components (2, 4). Said other of said faces (74, 76) being arranged to engage the at least one further groove (82) or further tooth so as to selectively restrict rotation between the first and second components (2, 4) at a further predetermined rotational position.La présente invention concerne un instrument chirurgical qui comprend un premier composant (2) ayant une première face (76) et un deuxième composant (4) couplé au premier composant (2) de telle manière que les premier et deuxième composants (2, 4) peuvent pivoter lun par rapport à lautre. Linstrument comprend en outre un mécanisme de blocage qui comprend un troisième composant (32) ayant une seconde face (74) couplée au deuxième composant (4). Le mouvement du troisième co
