Measurements:
(1) dorsal length: from the pubo-penile angle to the urethral meatus (proximal end at the pubic bone to reduce effect of prepubic fat pad)
(2) ventral length: from the peno-scrotal angle to the urethral meatus
ratio of stretched to flaccid length =
= (stretched penile length in cm) / (flaccid penile length in cm)
ratio of erectile to flaccid length =
= (erected penile length in cm) / (flaccid penile length in cm)
ratio of ventral erectile to flaccid length =
= (1.113 * (ratio of ventral stretched to flaccid lengths)) - 0.031
ratio of dorsal erectile to flaccid length =
= (0.849 * (ratio of dorsal stretched to flaccid lengths)) + 0.3657
where:
• R squared for the ventral equation = 0.76 and for the dorsal equation = 0.48
• The end point for stretching was onset of patient discomfort.
• Ventral means near the abdomen and dorsal towards the back (or underside of a leave in Botany). I would have thought the aspect terms would have been reversed.
If this equation is expanded based on the definition of the ratios:
ventral length erected in cm =
= (1.113 * (ventral length of penis stretched in cm)) - (0.031 * (ventral flaccid length in cm))
dorsal length erected in cm =
= (0.849 * (dorsal length of penis stretched in cm)) + (0.3657 * (dorsal flaccid length in cm))
The correlation between the stretched and erect lengths is affected by:
(1) penile elasticity (which is greater in younger men)
(2) the force used on stretching
Based on engineerng analysis the authors found that the stretched length using a force of 450 grams (4.41 Newtons) approximated the erected length. Most of the time stretching is done with a much lower force because of patient discomfort. The recommendation was to use a standard stretching pressure to reduce variability in the readings.
where:
• 1 Newton = 101.97 grams
