1. A bone anchor assembly for securing a longitudinal connecting member to a bone, the bone anchor assembly comprising: a receiver having a through bore around a central vertical axis, the receiver including a lower body with a bottom opening and an internal cavity communicating with an upper portion having a pair of opposed arms defining a first channel therebetween opening onto a top thereof, the first channel having opposed inner surfaces and a transverse axis perpendicular to the central vertical axis, the first channel sized and shaped for receiving a portion of the longitudinal connecting member, the arms having a discontinuous helically wound guide and advancement structure thereon, and the receiver including interior opposed recesses having downwardly-facing top surfaces located entirely below the helically wound guide and advancement structure; a bone attachment structure having a body and an upper head portion having a substantially spherical surface above a hemisphere thereof, the body extending through the receiver bottom opening and pivotal with respect to the receiver; and an insert having a body with upright arms forming a second channel therebetween, the second channel being alienable with the receiver transverse axis to receive the portion of the longitudinal connecting member, the upright arms having uppermost top surfaces, the insert body further including a central through-and-through tool receiving opening and oppositely-directed opposed radial extending portions with outer surfaces in the direction of the receiver transverse axis engageable with the receiver first channel inner surfaces to inhibit rotation between the receiver and the insert, the opposed radial extending portions having top surfaces that extend radially outward and underneath a most bottom surface of the portion of the longitudinal connecting member positioned within the receiver first channel, wherein when the uppermost top surfaces of the upright arms of the insert are snapped under and engaging the downwardly-facing top surfaces of the receiver opposed recesses, the bone attachment structure has a non-floppy relationship with respect to the receiver, and the insert is prevented from moving back up within the receiver prior to the longitudinal connecting member being positioned within the receiver and the insert first and second channels and locked by a closure structure.
1. A bone anchor assembly for securing a longitudinal connecting member to a bone, the bone anchor assembly comprising: a receiver having a through bore around a central vertical axis, the receiver including a lower body with a bottom opening and an internal cavity communicating with an upper portion having a pair of opposed arms defining a first channel therebetween opening onto a top thereof, the first channel having opposed inner surfaces and a transverse axis perpendicular to the central vertical axis, the first channel sized and shaped for receiving a portion of the longitudinal connecting member, the arms having a discontinuous helically wound guide and advancement structure thereon, and the receiver including interior opposed recesses having downwardly-facing top surfaces located entirely below the helically wound guide and advancement structure; a bone attachment structure having a body and an upper head portion having a substantially spherical surface above a hemisphere thereof, the body extending through the receiver bottom opening and pivotal with respect to the receiver; and an insert having a body with upright arms forming a second channel therebetween, the second channel being alienable with the receiver transverse axis to receive the portion of the longitudinal connecting member, the upright arms having uppermost top surfaces, the insert body further including a central through-and-through tool receiving opening and oppositely-directed opposed radial extending portions with outer surfaces in the direction of the receiver transverse axis engageable with the receiver first channel inner surfaces to inhibit rotation between the receiver and the insert, the opposed radial extending portions having top surfaces that extend radially outward and underneath a most bottom surface of the portion of the longitudinal connecting member positioned within the receiver first channel, wherein when the uppermost top surfaces of the upright arms of the insert are snapped under and engaging the downwardly-facing top surfaces of the receiver opposed recesses, the bone attachment structure has a non-floppy relationship with respect to the receiver, and the insert is prevented from moving back up within the receiver prior to the longitudinal connecting member being positioned within the receiver and the insert first and second channels and locked by a closure structure. 14. The bone anchor assembly of claim 1 , wherein a length of the insert second channel between outer ends of the opposed radial extending portions, as measured along the transverse axis, is greater than the greatest width between inner surfaces of the insert upright arms forming the second channel therebetween, as measured perpendicular to both the transverse axis and the central vertical axis.