A prosthesis, in particular for the ankle, has two nesting elements (2,4) assigned to a respective bone (12,22) and an intermediate element (6) interposed between them for relative articulation. Instruments for implanting the prosthesis are provided. The tibial element (2) comprises a centring brace (10) provided with elements to be gripped by the practitioner for extraction, consisting of a bend (24) in the brace (10) and by facets (26,28) provided at its distal end. The ankle bone element (4) comprises a plane (44) for longitudinal support against the ankle bone (22). A specific instrument enables to centre the ankle bone element (4) relative to the tibial element (2).