The invention relates to a surgical assembly which comprises: a cap (2) comprising an outer thread (2c) and a central recess for inserting a screw bit； a cap-holder in the form of a hollow sleeve (10) comprising a connection end (11) for connecting with the cap (2), and a locking pin (15) slidably mounted in the hollow sleeve (10) between a neutral position and a locking position of the cap； the cap (2) comprises at least two diametrically opposed radial notches (7), arranged away from an outer side wall of said cap (2), each of the notches (7) comprising at least one side groove (8)； the connection end (11) is extended longitudinally by two diametrically opposed lugs (12) capable of being inserted into the notches (7) and each including a side shoulder (12a) which complements the groove (8) of the notch (7) capable of being inserted into said groove in order to lock the sleeve (10) axially onto the cap.
