A system for use during a surgical procedure on a patient, the system comprising: (a) an implant having a modular cage and a shim with a tool holding feature, an upper bracket, and a lower bracket, the modular cage including four modules: (i) a first endplate adapted to press against anatomical structures of the patient, (ii) a second endplate adapted to press against opposing anatomical structures of the patient, (iii) a body with a top surface on which the first endplate is positioned and a track which engages the upper bracket of the shim and guides the shim into engagement with the modular cage, and (iv) a column with a bottom surface on which the second endplate is positioned, a track which engages the lower bracket of the shim and guides the shim into engagement with the modular cage, and at least one leg over which the body slides so that the at least one leg is contained at least partially within the body, and (b) a tool having an expander and an inserter, the tool engaging a tool holding feature (454, 474) on the modular cage and adapted to position the modular cage at a surgical site within the patient, the expander sliding the body along the at least one leg to separate the body from the column in situ and thereby define the height of the implant, and the inserter positioning the shim between the body and the column, wherein the height of the implant can be adjusted in situ to a potentially infinite number of possible heights between a starting height where the body is fully seated on the column and an upper limit where the body exceeds the height of the at least one leg, and the shim when positioned between the body and the column fixes the distance between the body and the column, wherein the body has a chamfer above the track to facilitate insertion of the upper bracket of the shim, wherein the track of the body has a final detent recess for seating the upper bracket of the shim under the chamfer and in the track, and wherein the track further comprises a backup detent recess to retain the shim should the shim become dislodged from the final detent recess. (a) an implant having a modular cage and a shim with a tool holding feature, an upper bracket, and a lower bracket, the modular cage including four modules: (i) a first endplate adapted to press against anatomical structures of the patient, (ii) a second endplate adapted to press against opposing anatomical structures of the patient, (iii) a body with a top surface on which the first endplate is positioned and a track which engages the upper bracket of the shim and guides the shim into engagement with the modular cage, and (iv) a column with a bottom surface on which the second endplate is positioned, a track which engages the lower bracket of the shim and guides the shim into engagement with the modular cage, and at least one leg over which the body slides so that the at least one leg is contained at least partially within the body, and (i) a first endplate adapted to press against anatomical structures of the patient, (ii) a second endplate adapted to press against opposing anatomical structures of the patient, (iii) a body with a top surface on which the first endplate is positioned and a track which engages the upper bracket of the shim and guides the shim into engagement with the modular cage, and (iv) a column with a bottom surface on which the second endplate is positioned, a track which engages the lower bracket of the shim and guides the shim into engagement with the modular cage, and at least one leg over which the body slides so that the at least one leg is contained at least partially within the body, and (b) a tool having an expander and an inserter, the tool engaging a tool holding feature (454, 474) on the modular cage and adapted to position the modular cage at a surgical site within the patient, the expander sliding the body along the at least one leg to separate the body from the column in situ and thereby define the height of the implant, and the inserter positioning the shim between the body and the column, wherein the height of the implant can be adjusted in situ to a potentially infinite number of possible heights between a starting height where the body is fully seated on the column and an upper limit where the body exceeds the height of the at least one leg, and the shim when positioned between the body and the column fixes the distance between the body and the column, wherein the body has a chamfer above the track to facilitate insertion of the upper bracket of the shim, wherein the track of the body has a final detent recess for seating the upper bracket of the shim under the chamfer and in the track, and wherein the track further comprises a backup detent recess to retain the shim should the shim become dislodged from the final detent recess. wherein the height of the implant can be adjusted in situ to a potentially infinite number of possible heights between a starting height where the body is fully seated on the column and an upper limit where the body exceeds the height of the at least one leg, and the shim when positioned between the body and the column fixes the distance between the body and the column, wherein the body has a chamfer above the track to facilitate insertion of the upper bracket of the shim, wherein the track of the body has a final detent recess for seating the upper bracket of the shim under the chamfer and in the track, and wherein the track further comprises a backup detent recess to retain the shim should the shim become dislodged from the final detent recess.