Failure to completely interrupt sperm migration (very rare):
(1) double vas
(2) polyorchidism
Poor surgical technique:
(1) lack of experience
(2) difficult anatomy (scarring, obesity, etc.)
(3) inferior operating techniques
Failure to wait for azoospermia (may take up to 4 months) before having unprotected sex.
Spontaneous recanalization in which interruption is achieved initially, but later flow is re-established with reappearance of motile sperm in the semen. Risk factors favoring recanalization include:
(1) minimal invasive techniques
(2) ends in close approximation to each other
(3) incomplete division of the vas
Factors reducing the risk of recanalization:
(1) removal of segments >= 2 cm in length
(2) application of clips or sutures
(3) fascia interposition or burying the ends of the ducts in different planes of tissue
(4) use of fibrin glue
(5) fulguration of the ends
