Receiving part for coupling a rod to a bone anchor
A bone anchoring device includes a receiving part with a head receiving portion defining a seat for pivotably receiving a head of a bone anchor, and a rod receiving portion defining a recess for receiving a rod, the recess forming two legs each having an engagement surface for engaging a locking device to lock the rod in the recess, and an expansion limiting member having a surface configured to engage a portion of the receiving part spaced apart from the engagement surfaces of the legs. When the legs are urged radially outwardly, the head receiving portion is urged radially inwardly to compress and lock the head. The expansion limiting member is adjustable from a first configuration relative to the receiving part where the head receiving portion is expandable to permit the insertion of the head, to a second configuration where expansion of the head receiving portion is restricted.
1 . A bone anchoring device for coupling a rod to a bone anchor, the bone anchoring device comprising:
a receiving part having a first end and a second end below the first end, the receiving part comprising:
a head receiving portion at the second end defining a seat for pivotably receiving a head of the bone anchor, wherein the head receiving portion is expandable to permit insertion of the head into the seat and compressible to lock the head in the seat; and
a rod receiving portion above the head receiving portion that defines a recess for receiving the rod, the recess forming two legs each having an engagement surface for engaging a locking device to lock the rod in the recess, wherein when the legs are urged radially outwardly, the head receiving portion is urged radially inwardly for compressing and locking the head; and
a separate expansion limiting member comprising a surface configured to engage a portion of the receiving part spaced apart from the engagement surfaces of the legs;
wherein when the expansion limiting member is assembled to the receiving part, the expansion limiting member is adjustable from a first configuration relative to the receiving part where the head receiving portion is expandable to permit the insertion of the head while a first stop positioned axially above the entire expansion limiting member restricts movement of the expansion limiting member towards the free ends of the legs, to a second configuration where the expansion of the head receiving portion is restricted while a second stop positioned axially below the entire expansion limiting member restricts movement of the expansion limiting member towards the second end of the receiving part.
2 . The bone anchoring device of claim 1 , wherein the expansion limiting member comprises a ring.
3 . The bone anchoring device of claim 1 , wherein when the expansion limiting member is at the second configuration, the expansion limiting member is configured to exert a compression force onto the head receiving portion such that an angular position of the head relative to the receiving part is held by friction.
4 . The bone anchoring device of claim 1 , wherein the seat is configured to limit axial movement of the head towards the rod receiving portion.
5 . The bone anchoring device of claim 1 , wherein a rod support surface having a substantially V-shaped cross-section is formed at a bottom of the recess for the rod for interchangeably supporting rods with different diameters.
6 . The bone anchoring device of claim 1 , wherein the receiving part comprises a channel configured to provide access for an instrument to directly contact the head while the rod is inserted in the recess.
7 . The bone anchoring device of claim 1 , wherein the expansion limiting member is positionable around at least part of the head receiving portion.
8 . The bone anchoring device of claim 1 , wherein the expansion limiting member is movable axially between the first configuration and the second configuration.
9 . The bone anchoring device of claim 1 , wherein the bone anchoring device is configured to maintain the second configuration while the recess for the rod remains unobstructed.
10 . A bone anchoring device for coupling a rod to a bone anchor, the bone anchoring device comprising:
a receiving part having a first end and a second end below the first end, the receiving part comprising:
a head receiving portion at the second end defining a seat for pivotably receiving a head of the bone anchor, wherein the head receiving portion is expandable to permit insertion of the head into the seat and compressible to lock the head in the seat; and
a rod receiving portion above the head receiving portion that defines a recess for receiving the rod, the recess forming two legs each having an engagement surface for engaging a locking device to lock the rod in the recess, wherein when the legs are urged radially outwardly, the head receiving portion is urged radially inwardly for compressing and locking the head; and
a separate expansion limiting member comprising a surface configured to engage a portion of the receiving part spaced apart from the engagement surfaces of the legs;
wherein when the expansion limiting member is assembled to the receiving part, the expansion limiting member is adjustable from a first configuration where the entire expansion limiting member is positioned higher axially than a bottom of the rod recess of the receiving part while the head receiving portion is expandable to permit the insertion of the head, to a second configuration where the expansion of the head receiving portion is restricted.
11 . The bone anchoring device of claim 10 , wherein the expansion limiting member is positionable around at least part of the head receiving portion.
12 . The bone anchoring device of claim 10 , wherein the expansion limiting member comprises a ring.
13 . The bone anchoring device of claim 10 , wherein the expansion limiting member is movable axially between the first configuration and the second configuration.
14 . The bone anchoring device of claim 10 , wherein the bone anchoring device is configured to maintain the second configuration while the recess for the rod remains unobstructed.
15 . The bone anchoring device of claim 10 , wherein when the bone anchoring device is at the second configuration, at least part of the expansion limiting member extends to an axial position below the bottom of the rod recess of the receiving part.
16 . The bone anchoring device of claim 10 , wherein the seat is configured to limit axial movement of the head towards the rod receiving portion.
17 . A bone anchoring device for coupling a rod to a bone anchor, the bone anchoring device comprising:
a locking device comprising a substantially cylindrical main body and a spreading member that extends away from the main body; and
a receiving part having a first end and a second end below the first end, the receiving part comprising:
a head receiving portion at the second end defining a seat for pivotably receiving a head of the bone anchor, wherein the head receiving portion is expandable to permit insertion of the head into the seat and compressible to lock the head in the seat; and
a rod receiving portion above the head receiving portion that defines a recess for receiving the rod, the recess forming two legs each having a first engagement surface for engaging the main body of the locking device to lock the rod in the recess and a second engagement surface different from the first engagement surface that is inclined and widens as the second engagement surface extends towards free ends of the legs, wherein when the locking device is advanced axially in the recess, the spreading member is configured to engage the second engagement surface to urge the legs radially outwardly and to urge the head receiving portion radially inwardly for compressing and locking the head.
18 . The bone anchoring device of claim 17 , wherein the second engagement surface is provided at at least one of the legs.
19 . The bone anchoring device of claim 17 , wherein the second engagement surface is positioned axially below the entire first engagement surface.
20 . The bone anchoring device of claim 17 , wherein the locking device comprises an outer locking member comprising the main body and the spreading member for urging the legs radially outwardly and urging the head receiving portion radially inwardly for compressing the head, and an inner locking member movable axially relative to the outer locking member for locking the rod in the rod recess.