An orthopedic implant device (100, 200, 300, 301, 320, 340, 400, 500, 600, 700', 720, 740, 760, 770, 800, 900, 1000, 1100, 1200, 1300, 1400, 1500, 1600, 1700, 1800) is non-rigid, i.e., flexible and/or malleable, in a first form for insertion into a desired in vivo site, and then transformable into a rigid, or hardened, form for providing a load-bearing function or providing other structural and/or mechanical function after implantation. The device includes a biocompatible sheath (110) and a curable material (120) sealed within the sheath (110). The curable material (120) is provided in a first form that provides flexibility to the device and is structured to rigidize in a second form after insertion to an in vivo location at least one minute after application of a cure-initiating energy to the material (120) prior to insertion. Related methods and kits are also provided.