A computer implemented medical method of calibrating a spinal cage, comprising the steps: acquiring (S10), by using a pointer tip of a pointing device , a cage tip point (S) at a cage tip of the spinal cage , wherein the cage tip is disposed at a first end of the cage in a length direction (L) of the cage; acquiring (S20), by using the pointer tip of the pointing device , a cage end point (E) at a cage end of the spinal cage , wherein the cage end is disposed at a second end of the spinal cage , opposing to the first end , in the length direction (L); characterized by acquiring (S30), by using a pointer shaft of the pointing device , at least one axis (X1, X2, X3, X4) along a side (Sl1, Sl2, St, Sb) of the spinal cage ; determining (S40) a calibrated virtual model (V1, V2) of the spinal cage using the cage tip point (S), the cage end point (E) and the at least one cage axis (X1, X2, X3, X4); wherein acquiring the cage end point (E), the cage tip point (S) and the at least one cage axis (X1, X2, X3, X4) comprises: determining a cage-to-holder-coordinate-transformation (CageToHolder), which describes a transformation between a holder coordinate system (Holder) of a holding device and a cage coordinate system (cage) of the spinal cage ; providing a pointer-to-holder-coordinate-transformation (PointerToHolder), which describes a transformation between the pointer coordinate system (Pointer) and the holder coordinate system (Holder); determining the cage-to-holder-coordinate-transformation (CageToHolder), by using the pointer-to-holder-coordinate-transformation (PointerToHolder). acquiring (S10), by using a pointer tip of a pointing device , a cage tip point (S) at a cage tip of the spinal cage , wherein the cage tip is disposed at a first end of the cage in a length direction (L) of the cage; acquiring (S20), by using the pointer tip of the pointing device , a cage end point (E) at a cage end of the spinal cage , wherein the cage end is disposed at a second end of the spinal cage , opposing to the first end , in the length direction (L); characterized by acquiring (S30), by using a pointer shaft of the pointing device , at least one axis (X1, X2, X3, X4) along a side (Sl1, Sl2, St, Sb) of the spinal cage ; determining (S40) a calibrated virtual model (V1, V2) of the spinal cage using the cage tip point (S), the cage end point (E) and the at least one cage axis (X1, X2, X3, X4); wherein acquiring the cage end point (E), the cage tip point (S) and the at least one cage axis (X1, X2, X3, X4) comprises: determining a cage-to-holder-coordinate-transformation (CageToHolder), which describes a transformation between a holder coordinate system (Holder) of a holding device and a cage coordinate system (cage) of the spinal cage ; providing a pointer-to-holder-coordinate-transformation (PointerToHolder), which describes a transformation between the pointer coordinate system (Pointer) and the holder coordinate system (Holder); determining the cage-to-holder-coordinate-transformation (CageToHolder), by using the pointer-to-holder-coordinate-transformation (PointerToHolder). determining a cage-to-holder-coordinate-transformation (CageToHolder), which describes a transformation between a holder coordinate system (Holder) of a holding device and a cage coordinate system (cage) of the spinal cage ; providing a pointer-to-holder-coordinate-transformation (PointerToHolder), which describes a transformation between the pointer coordinate system (Pointer) and the holder coordinate system (Holder); determining the cage-to-holder-coordinate-transformation (CageToHolder), by using the pointer-to-holder-coordinate-transformation (PointerToHolder). <EOS>