The invention relates to surgical instrumentation (101) custom-designed for a given patient, comprising a patient-specific femoral block (110) defining a stationary bearing surface (110A) which bears on the patient's femur (F) and which is shaped so that it is specifically adjusted to said femur. According to the invention, the instrumentation also comprises a mechanical system (120) for adjusting to the external/internal rotation of the femur, which system, when in use, is partially connected to the femoral block in a fixed manner.
