a biodegradable implant for placement in nonunion bone fractures as a substitute for bone graft material is provided which is a flat plate or disk having a thickness of between about 1 mm and about 15 % of the length of the bone , interconnected micropores , and canals substantially equivalent in size and spacing to naturally - occurring haversian canals . the implant may additionally comprise additives such as growth factors , including bone morphogenic protein . in a preferred embodiment the implant is formed from a biodegradable polymer such as a polylactic acid - polyglycolic acid copolymer by a gel casting technique followed by solvent extraction to precipitate the implant as a microporous solid .