A pivotal bone anchor assembly includes a receiver having a central bore with an integral downward facing surface below a helically wound guide and advancement structure and a first interference surface, and a compression insert configured for top-loading into the central bore into a first position and then being rotatable about the receiver longitudinal axis into a second position defined by an engagement between a second protuberant interference surface of the compression insert and a first interference surface of the central bore. The compression insert further includes radially offset upwardly facing surfaces configured for biased engagement with a downward facing surface of the central bore upon completion of rotation to the second position, and the receiver further includes one or more inwardly extending integral non-resilient structure positionable into one or more outer alignment grooves of the compression insert, also upon the completion of rotation to the second position.

A soft dynamic stabilization assembly includes a core, typically in the form of a tensioned cord, at least one pair of bone anchors, a spacer surrounding the core located between the bone anchors, typically, at least one elastic bumper and at least one fixing or blocking member. The core is slidable with respect to at least one of the bone anchors and cooperating spacer.

A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in an integral receiver, the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. A down-loadable compression insert, a down-loadable friction fit split retaining ring having inner and outer tangs and an up-loadable shank upper portion cooperate to provide for pop- or snap-on assembly of the shank with the receiver either prior to or after implantation of the shank into a vertebra. The shank and receiver once assembled cannot be disassembled.

A pivotal bone anchor assembly includes a receiver having a central bore with an integral downward facing surface below a helically wound guide and advancement structure and a first interference surface, and a compression insert configured for top-loading into the central bore into a first position and then being rotatable about the receiver longitudinal axis into a second position defined by an engagement between a second protuberant interference surface of the compression insert and a first interference surface of the central bore. The compression insert further includes radially offset upwardly facing surfaces configured for biased engagement with a downward facing surface of the central bore upon completion of rotation to the second position, and the receiver further includes one or more inwardly extending integral non-resilient structure positionable into one or more outer alignment grooves of the compression insert, also upon the completion of rotation to the second position.

A pivotal bone screw assembly includes a threaded shank body having an integral upper portion receivable in a receiver, with the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. The assembly also includes a downloadable compression insert with a side arm extension for engagement and compression by a vertically-translating insert side compressing member so as to lock the assembly independent of the closure top.

According to some embodiments, systems and methods of ultrasonic detection of implantable medical device distraction are provided. The system includes a first elongate member and a second elongate member. The first elongate member has a first end that is configured to be attached to a first location on the skeletal system of a subject, a second end, and at least one landmark identifiable using ultrasound. The second elongate member has a first end that is movably coupled to the second end of the first elongate member, a second end configured to be attached to a second location on the skeletal system, and at least one landmark identifiable using ultrasound. Movement of the first elongate member in relation to the second elongate member causes a corresponding movement of the at least one first landmark in relation to the at least one second landmark which can be detected using ultrasound.

A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in an integral receiver, the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. A down-loadable compression insert with tool receiving arm extensions, a down-loadable friction fit split retaining ring and an uploadable shank upper portion cooperate to provide for pop- or snap-on assembly of the shank with the receiver either prior to or after implantation of the shank into a vertebra. The shank and receiver once assembled cannot be disassembled.

A polyaxial bone screw assembly includes a threaded shank body having an integral upper portion receivable in an integral receiver, the receiver having an upper channel for receiving a longitudinal connecting member and a lower cavity cooperating with a lower opening. The receiver can have crimp tabs, but is devoid of spring tabs and collet-like flexible structures. A down-loadable compression insert (some with lock and release feature), a down-loadable friction fit split retaining ring and an up-loadable shank upper portion cooperate to provide for pop- or snap-on assembly of the shank with the receiver either prior to or after implantation of the shank into a vertebra. The shank and receiver once assembled cannot be disassembled. The receiver and insert include aligned tool receiving apertures for lock and release of the polyaxial mechanism.

A pivotal bone anchor assembly includes a receiver having an upper channel for receiving an elongate rod and an axial bore extending downward from the upper channel to a bottom opening, and a shank having an anchor portion and an integral upper portion that is positionable in the axial bore of the receiver with the shank extending downward through the bottom opening. In some embodiments an insert provides for a friction fit of the upper portion of the shank in the receiver, resulting in non-floppy placement of the shank with respect to the receiver. A pre-assembled receiver with the insert may be popped-on or snapped-on to the upper portion of the shank prior to or after implantation of the anchor portion into a vertebra. The receiver includes arm break-off extensions attached to a pair of upright arms, with the upright arms also having outer horizontally extending tool engagement grooves.

A reusable surgical implement is provided that is formed of a core positioned within an enclosure. The core is formed of a suitable flexible material to enable the implement, which can be any suitable device such as a reusable surgical trial implant, rod template or flex driver, among others, to be bent to conform to the desired shape for an actual implant to be placed in the location of the implement. The material forming the enclosure is also flexible to accommodate the flexing of the core, and is biologically inert to enable the implement to be sterilized after use for use in subsequent surgical procedures.