The present invention proposes a device (1) for assisting in the placementof a trapeziometacarpal prosthesis comprising a cup intended to be fixed inthetrapezium (4) of a patient and a stem intended to be fixed in the patient'sfirstmetacarpal (6). Said device comprises a first guide (2) able to be interposedbetween the trapezium (4) and the first metacarpal (6), said first guide (2)comprising a first body (8) having a first surface (8a) intended to bepositioned onthe articular surface of the trapezium (4), said first surface (8a) beingcongruentwith said articular surface of the trapezium (4) and a second surface (8b)intendedto face the articular surface of the first metacarpal (6) before resection,saidsecond surface (8b) preferably being congruent with the articular surface ofthefirst metacarpal (6) so as to be suitable to be positioned on said articularsurface ofthe first metacarpal (6). The first guide (2) also comprises locating members(20)carried by the first body (8) and arranged to define resection lines (22) forthe firstmetacarpal (6).
