Rear Tip Extenders and Penile Prosthesis Rigidity: A Laboratory Study of Coloplast Prostheses

Abstract

Background: Rear tip extenders (RTEs) are used commonly in penile prostheses, but their effect on erectile rigidity has not been extensively studied.

Aim: To determine whether RTEs affect erectile rigidity in inflatable penile prostheses and determine what length of RTE should be used for a given corporal length-in this case, 22 cm.

Methods: To assess the effect of RTEs on erectile rigidity, we created a penile model simulating 2 corpora cavernosa that accommodated cylinders of varying lengths. Once the cylinders were inflated, a 200-g weight was then uniformly placed on the tip of the cylinders and deflection was measured using a ruler. Measurements were repeated for varying cylinder/RTE lengths to total 22 cm of overall corporal length.

Outcomes: Differences in rigidity and angular deflection based on RTE length were assessed.

Results: Increasing the length of RTEs increased the deflection in our model, indicative of decreased axial rigidity.

Clinical translations: The current work implies that having additional RTEs may decrease penile rigidity and in turn, patient satisfaction.

Strengths and limitations: Though assessing effect of RTEs on erectile rigidity is novel, the exact ability of our model to predict in-vivo behavior is unknown.

Conclusion: An inflatable penile prosthesis represents a heterogeneous beam given that it is composed of a non-inflatable rear combined to an inflatable cylinder. In this model greater bending deflection was associated with more RTE length. Greater RTE length decreases the size of the inflatable device that can be implanted. The erect penis is subject to axial stress and bending deflection. Though further work is needed, these data support the notion that maximizing inflatable length by minimizing RTEs will improve overall erectile rigidity dynamics. Thirumavalavan N, Cordon BH, Gross MS, et al. Rear Tip Extenders and Penile Prosthesis Rigidity: A Laboratory Study of Coloplast Prostheses. J Sex Med 2018;15:1030-1033.

Keywords: Inflatable Penile Prosthesis; Model; Rear Tip Extender; Rigidity.