Abstract: A pylon assembly for a leg prosthesis including an upper pylon, a lower pylon and a spring. A portion of both the upper pylon and the lower pylon are tubular. The spring is disposed between the upper pylon and the lower pylon inside the tubular portions. Upon assembly, the tubular portion of the lower pylon extends at least partially inside the tubular portion of the upper pylon with the spring extending from a plug inserted in the tubular portion of the lower pylon to a plug inserted in the tubular portion of the upper pylon. The spring biases the lower pylon away from the upper pylon. Compression and extension of the spring allows the lower pylon to reciprocate within the tubular portion of the upper pylon. This reciprocation allows the leg prosthesis to simulate the stride and cadence of a natural leg. In addition, a key may be inserted through the tubular portion of the upper pylon and extending into a key channel cut in the external circumference of the lower pylon.