Spinal Implant with Screw Retention and Removal Mechanisms

Abstract

The presented device is an orthopedic spinal cage that is inserted from an anteriorly aspect into a patient's intervertebral disc space. The device includes a cage to maintain vertebral separation and allow for fusion. Threaded screws allow for a matting and lag feature to prevent screw back out, provide a tactile event once fully inserted, and then to provide a stepped feature for reliable screw removal with minimal axial force. These features may be adapted to any orthopedic or other application requiring the thread screw features.

Claims

1. A fixation device for bones, comprising: a member configured to be fixed to one or more bones and has at least one bore for receiving a bone screw for insertion through at least one bore in the bone, wherein the at least one bore comprises a first internal cavity having an annular feature, annular cavity, and a reduced diameter passage; the bone screw having: a first shaft section provided with a first external thread portion configured to thread into the reduced diameter passage portion of the at least one bore; a head section having a diameter larger than reduced diameter passage portion of the at least one bore to provide a catch configured and where the head section is larger than annular feature of the at least one bore to provided restricted passage; and a second shaft section comprising a clearance groove extending between the diameter of the head section and the external thread of the first shaft section wherein the member allows passage of the threaded portion of the bone screw by means of tapping into the reduced diameter passage and to capture and accommodate the hemispherical shaped head of the bone screw.

2. The fixation device according to claim 1 wherein the annual feature has a least a partially smaller radius on at least one side of the internal cavity wherein it deforms to allow the bone screw head to pass by with a tactile feel.

3. The fixation device according to claim 2 wherein a fully introduced bone screw will first engage the member reduced diameter passage with the bone screw first external thread portion before the bone screw head section contacts the member annular feature during screw removal.

4. The fixation device according to claim 3 where the member is a polymer and the bone screw is a metallic device.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIGS. 1A-1C are side and cross-sectional views of the device within common vertebra bodies with the bone screw partially engaged within the cage.

[0019] FIGS. 2A-2C are side and cross-sectional views of the device within common vertebra bodies with the bone screw nearing full engagement into the cage.

[0020] FIGS. 3A-3C are side and cross-sectional views of the device within common vertebra bodies with the bone screw past the tactical engagement of the cage.

[0021] FIGS. 4A-4C are side and cross-sectional views of the device within common vertebra bodies with the bone screw fully engagement into the cage with the screw free to rotate or lag the vertebral body as needed.

[0022] FIGS. 5A-5C are side and cross-sectional views of the device within common vertebra bodies with the bone screw fully engagement into the cage with the screw free to rotate or lag the vertebral body as needed with noted diametric references.

[0023] FIGS. 6A-6C are side and cross-sectional views of the device within common vertebra bodies with the bone screw partially engaged within the cage with noted diametric references.

[0024] FIGS. 7A-7C are side and cross-sectional views of the cage device within common vertebra bodies showing the treading of the material.

DETAILED DESCRIPTION OF THE INVENTION

[0025] Referring to FIG. 1A, the interbody implant consists of a polymer spacer body 1 and a plurality of bone screws 2 used to secure the polymer implant 1 to the surrounding vertebral bodies 13.

[0026] Referring to FIGS. 1B & C apertures 11 in the polymer implant 1 are fabricated with a cavity 3 designed to allow passage of the threaded portion 16 of the bone screw 1 and to capture and accommodate the hemispherical shaped head 4 of the bone screw 2.

[0027] One opening of the cavity 3 has an annular feature 6 that is smaller in diameter than the hemispherical diameter of the bone screw 4 head. An opposing opening in the cavity 3 has a spherical shaped surface 14 and reduced diameter passage 15.

[0028] Referring to FIGS. 2A, B & C, as the bone screw 2 is being threaded into the vertebral end plate 14, its hemispherical head 4 will come in contact with the smaller diameter region 6 of the implant bone screw aperture 11. Referring to FIGS. 3A, B & C, during the bone screw 2 placement portion of the procedure, the largest diameter region 5 of the bone screw head 4 will be driven through the smaller diameter annular feature 6, in the polymer implant 1. The smaller diameter annular feature 6 will reduce any tendency to back out of the vertebral end plate 14 the bone screw 2 may exhibit.

[0029] FIG. 4C shows the hemispherical head of the bone screw 4 completely seated in a mating spherical pocket 14 the implant 1. The practitioner will receive both tactile and audible feedback during bone screw 2 placement indicating the bone screw 2 is nearly completely seated in the implant 1 as shown in FIG. 4C.

[0030] FIGS. 5A, B & C illustrates additional features of the polymer implant 1 and bone screw 2 intended to reduce any tendency to back out of the vertebral end plate 14 the bone screw 2 may exhibit. A region 15 at one end of the cavity 3 formed in apertures 11 in the polymer implant 1 has a diameter 8 less than the major diameter 7 of the bone screw 2. Threads 17 on the bone screw 2 are relieved to the minor diameter 18 of the thread form near the head 4 of the bone screw 2. Any tendency of the bone screw to back out of the vertebral end plate 14 will be resisted as the non-relieved portion of thread on the bone screw 2 encounters the reduced diameter portion 15 of the implant aperture 11.

[0031] Bone screw 2 placement will create grooves 10 in the reduced diameter region 15 of the implant aperture 11 wall as the polymer material will plastically deforms to accommodate passage of the bone screw 2 threads 17. Significant elastic deformation of the polymer material will also occur allowing the grooves 10 to recover to a diameter 19 less than that of the major diameter 7 of the bone screw. This material interference 9 is illustrated in FIG. 6C and will reduce any tendency to back out of the vertebral end plate 14 the bone screw 2 may exhibit.

[0032] Flat section X allows, during screw removal, the threads to first engage under axial torque prior to the hemispherical head 4 coming into contact with the smaller diameter region 6. This will allow the applied axial torque to be converted to linear motion from the created grooves 10 in the reduced diameter region 15 of the implant aperture 11 in corporation with the bone screw 2 threads 17.