A medical implant for supporting skeletal structures is disclosed. The implant includes an expandable central portion formed of a first material that at least partially inhibits the monitoring of bone in-growth using a medical diagnostic technique. The implant further includes end caps for mating with the central portion and the skeletal structure. The end caps are made of a second material different than the first material that inhibits the monitoring of bone in-growth using the medical diagnostic technique to a lesser degree than the first material. In another aspect, a polymer end member for use with a metallic implant for supporting a skeletal structure is disclosed. The polymer end member facilitates the monitoring of fusion or bone in-growth using fluoroscopy. In another aspect, a spinal implant is disclosed. The implant includes a central portion made of a first material and an end cap made of a different material.