Bicentric polyaxial locking screw and coupling element

Details Bicentric polyaxial locking screw and coupling element Bicentric polyaxial locking screw and coupling element

1995-11-13

1997-07-15

Tucker, Guy V.

Surgery

Instruments

Orthopedic instrumentation

606 73, A61B 1770

Patent

active

056478739

ABSTRACT:
A polyaxial orthopedic device for use with rod implant apparatus includes a screw having a curvate head, a bicentric locking shell disposed therearound, and a coupling element having a curvate tapered socket into which both the screw and the shell nest. The bicentric shell is slotted and has a semi-spherical interior volume into which the screw head is initially polyaxially held. The coupling element has an axial bore through which the screw and shell may be inserted, and a curvate bottom having a smaller radius of curvature than the shell, which provides a radially inward force on the locking shell when forced thereinto. This radially inward force causes the shell to crush lock against the head of the screw, therein locking the two at the instant angulation. In an initial disposition, however, the screw and the shell head remain polyaxially free with respect to each other, and to the coupling element. The coupling element also includes a transverse channel in which a rod may be disposed. In a first embodiment the channel is formed between a pair of upwardly extending members, and in a second embodiment, the channel is formed in the side of the element. In either case, a rod which is inserted in the channel seats against the top of the shell and the head of the screw. Engagement of a locking nut on the top of the coupling element provides a downward force against the rod, and forces the locking shell into the socket in the bottom of the bore, thereby locking the rod, locking shell, and screw simultaneously.

REFERENCES:
patent: 5151103 (1992-09-01), Tepic et al.
patent: 5360431 (1994-11-01), Puno et al.
patent: 5443467 (1995-08-01), Biedermann et al.

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