There was a considerable degree of instability, pain and actual extrusion through the skin or the urethra. Silicone was first tried outside the corpus cavernosum between Buck's fascia and the tunica albuginea. In the late 1960s, silicone became popular for prostheses due to its qualities: it induced minimal tissue reaction, it was unbreakable, had a nice mix of rigidity and resiliency, and could be bent to allow easier surgical insertion. In 1966 Beheri reported longterm results with over 700 patients, presenting a surgical technique for the intracavernous placement of his polyethylene rods much in the fashion that we place prosthetic cylinders today. This placement seemed superior in suppleness and malleability to the earlier placement of the rods outside the corporus cavernosal tissue. In 1958, Beheri began using two separate polyethylene rods placed inside the corpus cavernosal space as rigid stents.' During the 1950s complications with acrylic rods placed outside the corpora cavernosa became evident, including perforations and ulcerations. This was subsequently modified by Jonas with a prosthesis consisting of silicone rubber with a core of twisted silver wire, enabling the bending of the prosthesis into any desired position. This device was later modified by Finney with a hinge section allowing for penile flexion at the pubic level.

Small and his workers introduced the Small-Carrion device in the early seventies as a pair of sponge-filled silicone prosthetic cylinders to be implanted inside the natural erectile cylinders. In the 1970s we saw the introduction of the two broad categories of penile implants which are still utilized today: the semirigid or malleable prosthesis and the multi-component inflatable prosthesis. However, when the silicone rubber cylinders were placed within the erectile cylinders, they conformed more to the normal tumescent form of the penis and provided satisfactory vaginal penetration without interfering with normal daily activities and without being uncomfortable with most clothing. Others used perforated acrylic rods for treatment of impotence with the similar placement in the top part of the penis between the two corpus cavernosum, referring to this location of the acrylic rods as creating an "artificial os penis."