Bottom loading poly-axial screw

A method for assembling a modular poly-axial bone screw assembly, the method comprising:

• inserting a collet into a central bore of a tulip head such that an exterior of the collet is accommodated by an interior of the tulip head;
• inserting a bone screw through the central bore of the tulip head such that a bottom portion of a screw head of the bone screw is received within a lower portion of the tulip head;
• applying a force to at least one of the bone screw or the tulip head such that the screw head is displaced into the lower portion of the tulip head;
• and
• wherein:
• the bone screw includes a threaded shank, which extends from the screw head;
• the tulip head is disposed on the screw head and configured to move relative to the screw head before the tulip head is fixed in spatial orientation relative to the bone screw, and configured to receive and hold a spine rod as the spatial orientation of the tulip head is fixed;
• the central bore of the tulip head extends from a first end of the tulip head to a second end of the tulip head and includes an upper portion and inner threading for threaded receipt of a set screw, and wherein the lower portion is sized to receive the screw head in its entirety;
• and
• the collet is disposed in the interior of the tulip head, the collet having a lower section of a first diameter with a first end configured to rest upon a top portion of the screw head, and an upper section comprising a first wall and a second wall opposite the first wall,
• wherein the collet comprises one or more first engagement members disposed along an exterior portion of the collet in the lower section and one or more second engagement members disposed along an exterior of the collet in the upper section.

A method for assembling a modular poly-axial bone screw assembly, the method comprising:

• inserting a collet into a central bore of a tulip head such that an exterior of the collet is accommodated by an interior of the tulip head;
• positioning the collet and the tulip head adjacent a top portion of a screw head of a bone screw, such that a central axis of the central bore is aligned with a central axis of the bone screw;
• and
• applying a force to at least one of the collet and the tulip head such that the collet and the tulip head are displaced relative to the bone screw, wherein the bone screw is received within a lower portion of the tulip head;
• wherein:
• the tulip head is disposed on the screw head and configured to move relative to the screw head before the tulip head is fixed in spatial orientation relative to the bone screw, and configured to receive and hold a spine rod as the spatial orientation of the tulip head is fixed;
• the central bore of the tulip head extends from a first end of the tulip head to a second end of the tulip head and includes an upper portion and inner threading for threaded receipt of a set screw, and wherein the lower portion is sized to receive the screw head;
• the collet comprises a first plurality of depressions disposed along an exterior portion of the collet and a second plurality of protrusions disposed along an exterior portion of the collet;
• in a first position the first plurality of depressions are configured to engage with corresponding one or more protruding members disposed within the interior of the tulip head, and
• in a second position the first plurality of depressions are configured to engage with corresponding one or more protruding members disposed within the interior of the tulip head and the second plurality of protrusions are configured to engage with corresponding plurality of depressions disposed within the interior of the tulip head.