ressaut means, \"projection; abrupt fall, dip; rise (in saddle).\"
franchissement looks like it comes from the verb franchir, which means, \"to leap, to jump over; to clear; to pass, to pass over or beyond, to overstep; to overcome, to surmount.\"
Perhaps it\'s leapers(franchissement) who fall (ressaut)

I assume this is talking about inserting a needle into a vein, in which case: "penetration is indicated by an often marked jump OR rebound OR recoil (or something along those lines...) [of the needle], and the needle is no longer pushed out when released..."

I'm NOT a medical expert, but this is the sense I get from it, hope you can make somehting from this.

Found the following, discussing ways that a "jump sign" is elicited, including elicitation by needle penetration:

Untitled
... the spot, elicited by needle penetration or pressure held ... pain, and a jump sign characterized by vocalization ... methods include injection or dry ...
internet.apta.org/pt_journal/PTJournal/October2000/v80n10p997.html

UPDATE OF Myofascial Pain from TrPs
... of the taut band. Jump Sign. Pressure on the spot ... the TrP or by needle penetration of an active locus ... for assuring effective injection of a TrP ...
www.pain-education.com/HTML/david simons update.htm

SIMI
... See Fig. 25: needle penetration when injecting the ... he got another similar injection with the same ... Both showed a jump-sign; the patient told me ...
www.inspiration.yucom.be/bpesimi.htm