Modular polyaxial pedicle screw assembly with split ring
Inventors
Linder, Eric • Daffinson, Brion
Assignees
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Publication Number
US-11369417-B1
Publication Date
2022-06-28
Expiration Date
Abstract
A modular head polyaxial pedicle screw assembly has a pedicle bone screw, a tulip, a split locking ring and a saddle. The screw has a head and a threaded shank. The split locking ring has a split ring body with one or more positioning tabs extending from a first surface of the split ring body. The split ring locking ring is configured to be placed internal of the tulip positioned in a recess, groove or undercut of an inner surface of the tulip. Upon assembly of the pedicle screw into the tulip, at least a maximum diameter of the head is positioned above the recess, groove or undercut allowing the split locking ring to be inserted into the recess or groove thereby securing the pedicle screw inside the tulip wherein the head of the pedicle screw abuts the one or more positioning tabs.
Core Innovation
The invention is a modular head polyaxial pedicle screw assembly comprising a pedicle bone screw with a head and a threaded shank, a tulip having a distal end opening for receiving the head, and a saddle having a proximal end for engaging a rod and a distal end for receiving the head. The pedicle bone screw head is received in the tulip for polyaxial assembly and securement inside the tulip.
A split locking ring is internal of the tulip upon assembly through the distal end opening and is positioned in a recess, groove or undercut of an inner surface of the tulip. The split locking ring has a split ring body with two or more positioning tabs extending from a first surface, and the split ring body has an outer diameter with an outer surface wall that includes two flexure portions.
During assembly, the split locking ring is compressed as the gap opening is reduced, allowing the split locking ring to move and flex inwardly at the two flexure portions to facilitate assembly through the distal end opening into the recess, groove or undercut, and upon entry past the distal end opening the split locking ring expands. The pedicle bone screw head abuts the positioning tabs, and the tab engagement secures the pedicle bone screw inside the tulip and maintains the tulip angular orientation.
Claims Coverage
The provided independent claims are 1, 16, and 18. They each center on a modular head polyaxial pedicle screw assembly with a tulip and saddle, and an internal split locking ring that is compressed during insertion through a distal tulip opening and then expands in a recess, groove or undercut to secure the pedicle bone screw head by abutment against positioning tabs. The inventive features include the ring insertion-and-expansion arrangement, the head-abutment securing arrangement, and a two-flexure/tab geometry with reduced-thickness flexure portions and symmetric angular spacing.
Internal split locking ring compressed during insertion and expanding in a tulip recess, groove or undercut
A split locking ring is internal of the tulip upon assembly through the distal end opening and positioned in a recess, groove or undercut of an inner surface of the tulip. The split locking ring is compressed as the gap opening is reduced, allowing inward flexure to facilitate assembly through the distal end opening, and upon entry past the distal end opening the split locking ring expands, with the outer diameter larger than the distal end opening.
Pedicle bone screw head abutting positioning tabs to secure head in the tulip
The pedicle bone screw head abuts the two or more positioning tabs or the one or more positioning tabs after the split locking ring is positioned in the recess, groove, or undercut of the tulip, whereby the abutment secures the pedicle bone screw inside the tulip.
Two flexure portions with reduced cross-sectional thickness
The split ring body has an outer diameter with an outer surface wall that includes two flexure portions, each flexure portion being a flat wall having reduced cross-sectional thickness relative to the outer surface wall measured at the outer diameter, and the split locking ring has a split gap opening with two flexure portions located opposed to the split gap opening.
Positioning tabs directly opposite the split gap opening and symmetrically spaced at 120 degrees
Two of the positioning tabs are positioned between the two flexure portions directly opposite the split gap opening, and the center length of each flat portion of the two flexure portions and the center length of the gap opening are symmetrically spaced at an angle of 120 degrees apart.
Saddle and tulip securing arrangement for receiving the pedicle bone screw head
A saddle having a proximal end for engaging a rod and a distal end for receiving the head of the bone screw, together with the tulip having a distal end opening for receiving the head, defines the modular head polyaxial pedicle screw assembly in which the split locking ring secures the head within the tulip.
Force sufficient tab abutment to maintain tulip orientation relative to the screw head
Upon assembly of the split locking ring and the pedicle bone screw into the tulip, the head of the pedicle bone screw abuts the one or more positioning tabs with a force sufficient to maintain the orientation of the tulip with respect to the head of the bone screw.
Across independent claims 1, 16, and 18, the claim coverage is focused on securing a modular head polyaxial pedicle screw by using an internal split locking ring in a tulip recess, groove or undercut. The ring is compressed during insertion through the distal tulip opening and expands after entry; the pedicle bone screw head abuts positioning tabs to secure the screw head inside the tulip, and in dependent members a force-sufficient condition is tied to maintaining tulip orientation.
Stated Advantages
Secures the pedicle bone screw inside the tulip.
Facilitates assembly through the distal end opening into the recess, groove or undercut.
Allows inward flex for assembly and outward expansion after entry past the distal end opening.
Maintains the orientation of the tulip with respect to the head of the bone screw.
Documented Applications
Not explicitly described in patent.
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