Tests recorded in the Journal of Prosthetics and Orthotics indicate that, as early as 950 B.C., Egyptians were making functional and comfortable prosthetic toes to aid in walking. The earliest were made out of wood and leather. Later examples (about 600 B.C.) were made of a mixture of glue, linen and plaster. Prior to these discoveries the oldest prosthetic device was thought to have been an artificial leg made by the Romans about 300 B.C.
I think your 950 BC prosthetic toe and 300 BC prosthetic leg would have been preceded by a prosthetic phallus by many thousands of years. The earliest dated phallic symbol is 28,000 years so people had the basic idea.