A surgical system for machining an anatomical structure of a patient positioned on an operation table, said anatomical structure being part of an anatomical reference system of the surgical system, said surgical system comprising: - a base unit configured to be secured to the operation table, - a machining tool configured to be manually displaced by an operator, - a lockable unit carried by the base unit, said lockable unit including: o at least two linked and manually displaceable elements (23, 24, 26, 28) configured to be manually arranged according to a least one, relatively to the anatomical structure, calculated locked configuration (L 1, L 2, L 3, L 4, L 5, L 6), said locked configuration (L 1, L 2, L 3, L 4, L 5, L 6) being defined within the anatomical reference system, and o a constraining device configured to support and guiding the machining tool, - a grasping element carried by the base unit, said grasping element being designed to secure the anatomical structure, - a sensor unit including at least one sensor configured to follow, in real time, a real time configuration of the lockable unit within the anatomical reference system, - a control unit containing a recording of the at least one locked configuration (L 1, L 2, L 3, L 4, L 5, L 6) of the lockable unit, wherein the at least two elements (23, 24, 26, 28) of the lockable unit are linked to each other by at least one degree of freedom configured to cooperate with lockable means, said lockable means being configured to be activated by the control unit when the real time configuration of the lockable unit corresponds to the at least one locked configuration (L 1, L 2, L 3, L 4, L 5, L 6) recorded inside the control unit, in order to lock the constraining device in a predetermined position which constrains the machining tool within a determined machining plane (P 1, P 2, P 3, P 4, P 5, P 6). - a base unit configured to be secured to the operation table, - a machining tool configured to be manually displaced by an operator, - a lockable unit carried by the base unit, said lockable unit including: o at least two linked and manually displaceable elements (23, 24, 26, 28) configured to be manually arranged according to a least one, relatively to the anatomical structure, calculated locked configuration (L 1, L 2, L 3, L 4, L 5, L 6), said locked configuration (L 1, L 2, L 3, L 4, L 5, L 6) being defined within the anatomical reference system, and o a constraining device configured to support and guiding the machining tool, o at least two linked and manually displaceable elements (23, 24, 26, 28) configured to be manually arranged according to a least one, relatively to the anatomical structure, calculated locked configuration (L 1, L 2, L 3, L 4, L 5, L 6), said locked configuration (L 1, L 2, L 3, L 4, L 5, L 6) being defined within the anatomical reference system, and o a constraining device configured to support and guiding the machining tool, - a grasping element carried by the base unit, said grasping element being designed to secure the anatomical structure, - a sensor unit including at least one sensor configured to follow, in real time, a real time configuration of the lockable unit within the anatomical reference system, - a control unit containing a recording of the at least one locked configuration (L 1, L 2, L 3, L 4, L 5, L 6) of the lockable unit,