Friction-fit implantable devices and assemblies

A receiver for a polyaxial bone screw assembly, the receiver comprising:

• a body, comprising:
• a rod receiving channel sized and shaped to receive a fixation rod therein;
• an axial bore extending longitudinally through the receiver to a distal opening, the distal opening being sized and shaped to receive a head of a bone shank therethrough;
• a conical chamber disposed adjacent to the distal opening, the conical chamber being wider at a proximal end of the conical chamber than at a distal end of the conical chamber;
• and
• a ridge protruding from a surface of the axial bore;
• a split retainer ring disposed in the conical chamber, the split retainer ring comprising a conical exterior surface, wherein the split retainer ring is configured to expand within the conical chamber to allow a head portion of a bone shank to pass therethrough and thereafter support the head portion in a pivotable relationship;
• and
• a pressure insert disposed at least partly above the split retainer ring, the pressure insert comprising:
• a saddle surface configured to seat the fixation rod;
• a distally-facing concave surface configured to abut the head portion of the bone shank;
• a groove formed in an exterior surface of the pressure insert;
• and
• a rounded corner adjacent to a proximal end of the pressure insert,
• wherein the groove is configured to engage the ridge in the receiver to maintain the pressure insert in a first state associated with a first longitudinal position within the receiver;
• wherein the pressure insert is configured to flex inward to disengage the groove from the ridge;
• and
• wherein the groove is configured to abut the rounded corner of the pressure insert in a second state associated with a second longitudinal position within the receiver, wherein, in the second state, the groove urges the pressure insert distally such that:
• the head portion of the bone shank forms a first friction fit with the concave surface of the pressure insert;
• the head portion of the bone shank forms a second friction fit with an interior surface of the split retainer ring;
• and
• the conical exterior surface of the split retainer ring is urged against a surface of the conical chamber.

A receiver body for a polyaxial bone screw assembly, the receiver body comprising:

• a longitudinal axis;
• a rod receiving channel oriented transverse to the longitudinal axis and being sized and shaped to receive a fixation rod therein;
• an axial bore extending along the longitudinal axis from a proximal opening to a distal opening, the distal opening being sized and shaped to receive a head of a bone shank therethrough;
• a conical chamber disposed adjacent to the distal opening and in communication with the axial bore, the conical chamber being wider at a proximal end of the conical chamber than at a distal end of the conical chamber, wherein the conical chamber is wider than the axial bore at both the proximal end and the distal end of the conical chamber;
• a ridge protruding inward into the axial bore from an interior surface surrounding the axial bore, the ridge disposed proximally of the conical chamber;
• and
• a set of threads on a proximal portion of the interior surface and disposed proximally of the ridge.

A fastener kit for a spinal fixation system, comprising:

• a bone shank comprising a head portion and a distal threaded portion configured to be implanted into bone;
• a receiver comprising:
• a channel configured to receive a fixation rod therein;
• an axial bore extending longitudinally through the receiver from a proximal opening of the receiver to a distal opening, the distal opening being sized and shaped to receive the head portion of the bone shank therethrough;
• a chamber disposed adjacent to the distal opening, the chamber comprising a conical interior surface, the conical interior surface comprising a distal portion having a first diameter, and a proximal portion having a second diameter larger than the first diameter;
• and
• a ridge protruding from a surface of the axial bore;
• a split retainer ring sized and shaped to be positioned in the chamber;
• and
• a pressure insert sized and shaped to be positioned at least partly above the split retainer ring, the pressure insert comprising:
• a saddle configured to seat the fixation rod;
• a distally-facing concave surface configured to contact the head portion of the bone shank;
• a depression formed in an exterior surface of the pressure insert;
• and
• a rounded corner adjacent to a proximal end of the pressure insert.

A fastener assembly for a spinal fixation system, comprising:

• a bone shank comprising a head portion and a distal threaded portion configured to be implanted into bone;
• a receiver comprising:
• a channel for receiving a fixation rod therein;
• an axial bore extending longitudinally through the receiver from a proximal opening of the receiver to a distal opening, the distal opening being sized and shaped to receive the head portion of the bone shank therethrough;
• a chamber disposed adjacent to the distal opening, the chamber comprising a conical interior surface, the conical interior surface comprising a distal portion having a first diameter, and a proximal portion having a second diameter larger than the first diameter;
• and
• a depression in the surface of the axial bore;
• a split retainer ring disposed in the chamber, the split retainer ring being configured to expand within the chamber to allow the head portion of the bone shank to pass therethrough and thereafter support the head portion in a pivotable relationship;
• and
• a pressure insert disposed at least partly above the split retainer ring, the pressure insert comprising:
• a saddle configured to seat the fixation rod;
• a distally-facing concave surface configured to contact the head portion of the bone shank;
• and
• a ridge protruding from the exterior surface of the pressure insert;
• wherein, when the pressure insert is in a first longitudinal position relative to the receiver, the ridge is configured to engage the depression in the receiver to maintain the pressure insert at the first longitudinal position;
• and
• wherein, when the pressure insert is in a second longitudinal position, the ridge is disengaged from the depression and positioned in a manner that the head portion of the bone shank is maintained in a friction fit with both the pressure insert and the split retainer ring.