Instrument for assembling a polyaxial bone anchor

A method for assembling a polyaxial bone anchor using an instrument, the polyaxial bone anchor comprising a receiving part and a bone anchoring element having a head and a shank;

• and the instrument comprising a first member having a front end and a rearward end, the front end having a threaded engagement portion configured to releasably attach to the polyaxial bone anchor, a second member having a front portion and a rearward end, the front portion comprising a front end having a tip, a position indicator located at a position away from the front portion of the second member;
• and a spring, wherein the front portion of the second member is movable with respect to the front end of the first member when the second member is inserted into the first member, the method comprising:
• inserting the shank of the bone anchoring element into the bone;
• inserting the second member into the first member;
• biasing with the spring the front portion of the second member to protrude from the front end of the first member;
• attaching the receiving part with the engagement portion of the first member;
• receiving the head of the bone anchoring member into the receiving part such that the head is pivotable within the receiving part;
• contacting the head of the bone anchoring element with the tip of the second member;
• indicating a position of the head of the bone anchoring element relative to the receiving part based on a distance between the front portion of the second member and the front end of the first member.

An instrument for assembling a polyaxial bone anchor, the instrument comprising:

• a first member having a front end and a rear end, the front end having an engagement portion;
• a second member having a front portion and a rearward end, the front portion comprising a front end having a tip, wherein the second member is insertable into the first member;
• a cap member having a front end, a rear end, and a shoulder to abut against the rear end of the first member;
• a position indicator located at a position away from the front portion of the second member and configured to indicate a distance between the front portion of the second member and the front end of the first member when the second member is inserted into the first member;
• and
• a spring configured to bias the front portion of the second member to protrude from the front end of the first member when the second member is inserted into the first member;
• wherein the front portion of the second member is movable with respect to the front end of the first member when the second member is inserted into the first member;
• and
• wherein in a first configuration when the second member is inserted into the first member and the shoulder of the cap member abuts against the rear end of the first member, the rearward end of the second member is retracted relative to the rear end of the cap member, and
• wherein in a second configuration when the second member is inserted into the first member, when the shoulder of the cap member abuts against the rear end of the first member, and when the tip of the second member projects from the front end of the first member, the rearward end of the second member projects out of the rear end of the first member.

An instrument for assembling a polyaxial bone anchor, the polyaxial bone anchor comprising a bone anchoring element having a head and a shank and a receiving part configured to pivotably receive the head of the bone anchoring element, the instrument comprising:

• a first member comprising a front end, a rearward end, and a tubular body defining a cavity extending between the front end and the rearward end, the tubular body having a wall with one or more elongate openings extending through the wall into the cavity, the front end having an engagement portion configured to releasably attach to the polyaxial bone anchor;
• a second member having a front portion and a rearward end, the front portion comprising a front end having a tip, wherein the second member is insertable into the first member;
• a position indicator located at a position away from the front portion of the second member and configured to indicate a distance between the front portion of the second member and the front end of the first member when the second member is inserted into the first member;
• and
• a spring configured to bias the front portion of the second member to protrude from the front end of the first member when the second member is inserted into the first member;
• wherein the front portion of the second member is movable with respect to the front end of the first member when the second member is inserted into the first member;
• and
• wherein when the front portion of the second member protrudes from the front end of the first member, the one or more elongate openings of the first member are positioned entirely between the front end of the first member and a front end of the spring.