ABSTRACT
The presence or absence of both tunical layers, the thickness of the tunica itself and of the intracavernous pillars varies throughout the course of the penis, as does the histological composition, reflecting the relationship between anatomical ‘design ’ and function. The strength and thickness of this layer correlates with location, with the thinnest portion noted to be between the 5 o ’ clock and 7 o ’ clock positions. 5 This coincides with the absence of the outer longitudinal layer at the ventral groove over the urethra; extrusion of penile prosthesis is most common at this location. 6 As the crura diverge proximally, circular fibers provide sole support.A higher elastin-to-collagen ratio, as well as the absence of the outer layer and struts, for the tunica overlying the corpus spongiosum ensures a lowpressure structure during erection. 7
The average thickness of the tunica is also seen to relate to the stress forces applied to this structure prior to penetration (i.e. during rigid erection). The 0.8 ± 0.1mm thickness between the 6 o ’ clock and 7 o ’ clock positions has associated forces of 1.6 ± 0.2 × 107 Newtons (N)/m 2 , there is 1.2 ± 0.2 mm thickness at the 9 o ’ clock position, with 3.0 ± 0.3 × 10 7 N/m 2 , and 2.2 ± 0.4 mm thickness at the 11 o’ clock position, with 4.5 ± 0.5 × 10 7 N/m 2 (mirror-image measures are nearly identical).5
