Abstract
An improved cortico-cancello-cortical screw (FIG. 8a-c) to hold properly in the cortical portion at the two ends of vertebral-body which has a threaded portion (L) provided with cortical thread for the cortical bone and cancellous thread for cancellous bone; a neck portion; a shoulder portion that connects the threaded portion to the screw head; a taper of approximately 2° along entire length of the screw to ensure smooth insertion and progress as the screw is fastened so that proximal portion of the screw would engage cortical bone the same way as the intermediate portion that would engage the cancellous bone. L is divided into L1 (proximal section) that engages the cortical bone of vertebra, L2 (intermediate section) that engages the cancellous bone and has flanges bent on itself and L3 (distal section) that engages distal cortical bone to provide increased surface area and better pull out strength.
Claims
1. An improved cortico-cancello-cortical screw (FIG. 8a-c) to hold properly in the cortical portion at the two ends of injured bone WHEREIN the screw has: a threaded portion marked by L which is further provided with cortical thread for the cortical bone and cancellous thread for cancellous bone; a neck portion; a shoulder portion that connects the threaded portion to the screw head; a taper of approximately 2° along entire length of the screw to ensure smooth insertion and progress as the screw is fastened; and WHEREIN the proximal portion of the screw would engage cortical bone the same way as the intermediate portion that would engage the cancellous bone.
2. The improved cortico-cancello-cortical screw (FIG. 8a-c) as claimed in claim 1 WHEREIN the threaded portion L is divided into L1 (proximal section) the distal most portion of the screw that engages the cortical bone of vertebra, L2 (intermediate section) that engages the cancellous bone and L3 (distal section) that engages the distal cortical shell.
3. The improved cortico-cancello-cortical screw (FIG. 8a-c) as claimed in claim 1 WHEREIN the threaded portion L consists of flanges (f of FIG. 8c, FIG. 9c) of variable pitch (p3 of FIG. 9a) along its length such that the intermediate portion L 2 has longer flanges with bent rims that provides a larger surface area.
4. The improved cortico-cancello-cortical screw (FIG. 8a-c) as claimed in claim 1 WHEREIN the length of L 1 is 3-5 mm and the length of L 3 is 3-4 mm, L2 is 16-20 mm.
5. The improved cortico-cancello-cortical screw (FIG. 8a-c) as claimed in claim 1 WHEREIN the length of L 1 is 3-5 mm and the length of L3 is equal to L2 depending on the vertebral level, for pedicle screws at thoraco-lumbar region.
6. The improved cortico-cancello-cortical screw (FIG. 8a-c) as claimed in claim 1 WHEREIN proximal section L1 has following features: the pitch (p3 of FIG. 9a) or the distance between 2 adjacent flanges is 1.20-1.30 mm for smaller/thinner screw used in cervical spine and 1.35-1.45 mm for larger/thicker screw used in lumbar spine; the root is broader than the crest of the flange and is a buttress thread; the root forms an angle of approximately 45° with core proximally (pra3) and distal is 90° to the core (dra3); the Outer diameter (OD) of this portion is 3.0-3.5 mm for upper cervical spine and 6.0-6.5 for the lumbar spine; the core diameter (CD) of this portion is 2.3-2.5 mm for cervical spine and 4.0-5.0 mm for larger screws of lumbar spine;
7. The improved cortico-cancello-cortical screw (FIG. 8a-c) as claimed in claim 1 WHEREIN intermediate section L 2 has following features: the length of intermediate section L 2 (FIG. 9 c) of the threaded portion of the screw is 14 mm for upper cervical spine and 14 mm to 30 mm for subaxial spine and thoraco-lumbar spine; the outer diameter (OD) is 3.0-3.6 mm for upper cervical spine and 5-6.5 mm for larger lumbar spine; core diameter (CD) is 2 mm for thinner screws for cervical spine and 2.8 to 3.5 mm for larger screws meant for lumbar spine; the pitch is 1.75 mm-2 mm for thinner/thicker screws; the flange (FIG. 9 c) bends on itself at ⅔ length from the root; the proximal root angle (pra2) is 120-130° to core and the distal root angle (dra 2) is 65-75° to core; the proximal crest angle (pca—angle between proximal surface of flange edge and that towards the root) is 120-130′ and the distal crest angle (dca—angle between under surface of flange edge and that toward the root) is 45-55°; the angle between the crest surface and flange undersurface is 60°-62°; and the crest is 0.5-0.8 mm thick.
8. The improved cortico-cancello-cortical screw (FIG. 8a-c) as claimed in claim 1 WHEREIN distal section L3 (FIG. 9d) has following features: the length of this portion would be approximately 3 mm to 5 mm for cervical and thoraco-lumbar vertebra respectively; the pitch (p1) is 0.9 mm for the smaller/thinner screws and 1.25 mm for larger/thicker screw; the core diameter (CD) is rapidly tapering in this section from approximately 2-4 mm at proximally to 0.8 mm at the tip; the outer diameter (OD) is rapidly tapering as well from 3.4-5 mm proximally to 1.5 mm at the tip; the thread geometry is buttress with proximal root angle of 45° (pra1) and distal root angle of 90° to the core (dra1); adding cutting flutes to the tip would make the screw self-tapping;
9. The improved cortico-cancello-cortical screw (FIG. 8a-c) as claimed in claim 1 WHEREIN direction of the flanges of L2 is vertically reversible (FIG. 9c and FIG. 9e).
10. The improved cortico-cancello-cortical screw (FIG. 8a-c) as claimed in claim 1 WHEREIN the outer diameter of the screw head is at least 5.0 mm and more for the thoraco-lumbar spine.
Description
BRIEF DESCRIPTION OF THE DRAWINGS
[0052] FIG. 1-FIG. 7 are prior art figures of existing Bone screws
[0053] FIG. 8a—The section of vertebral body showing the cancellous center with outer cortical shell. In addition the entire screw as viewed from sides and top with inserts to further show each section of the screw
[0054] FIG. 8b—The detailed drawing of the screw showing thread, neck and shoulder
[0055] FIG. 8c—The detailed drawing of the screw showing the gentle tapering angle (2.sup.0) with dashed line
[0056] FIG. 9a—The proximal part of the threaded portion of the screw
[0057] FIG. 9b—The intermediate section of the threaded portion of the screw
[0058] FIG. 9c—The detailed flange anatomy of the L2 section of the screw
[0059] FIG. 9d—The distal portion of the screw
[0060] FIG. 9e—The flange anatomy of the L2 section of the screw in reverse direction
[0061] FIG. 10—The view of the screw-head as seen from top
OBJECT OF THE PRESENT INVENTION
[0062] It is an object of the present invention to disclose a screw to properly hold the cortical portion at the two ends of injured bone.
[0063] Yet another object is to disclose a screw which is useful for bones with relatively poor quality and density.
[0064] One more object is to disclose a screw which can help in greater manipulation without the fear of pull out to achieve good alignment of the bone, so that the construct failure rates would drop.
DETAILED DESCRIPTION OF THE INVENTION
[0065] The present invention discloses a screw that has threads suitable for each particular part of the vertebral body; i.e., cortical thread for the cortical bone and cancellous thread for cancellous bone. FIG. 8a represents the vertebral body that has a central cancellous bone and has a peripheral cortical bone of approximately 3-5 mm thickness. The cortical bone is also seen along the pedicle and isthmus, the part that connects the vertebral body to the lamina. The picture of entire screw has been provided with various views. Referring to FIG. 8b, the screw is made of threaded portion marked by L the neck and shoulder that connects the threaded portion to the head. The threaded portion, L is further divided into 3 different segment. L 1 represent the distal most portion of the screw that engages the distal cortex of vertebral body whereas L 3 engages the proximal cortex of vertebral body. The intermediate section of the threaded portion, L 2 engages the cancellous bone. The length of L 1 is nearly constant irrespective of the vertebral level (cervical, thoracic or lumbar). The L1 is approximately 3-5 mm, the length of L3 depends on the vertebral level. For atlas or C1 lateral mass, the L 3 will be 3-4 mm. The same may be good for the subfacetal or pedicle screw. For pedicle screws below that level, L3 will be approximately equal to L2. The reason for this is subaxial spine, thoracic and lumbar spine have longer pedicles and proximal portion of the screw would engage cortical bone almost the same as the intermediate portion that would engage the cancellous bone. In general the screw has a gentle taper of approximately 2° along its entire length. This is depicted in the FIG. 8c with dashed lines. Prior drilling of the cortical portions of vertebrae is essential to avoid fracturing the cortex while fastening the screw. The taper along the entire length assures smooth insertion and progress as the screw is fastened. The outer diameter would be described for each portion (L 1-3) separately (vide infra). The pitch, P is separate for L 1, L 2 and L 3 and is described with each section. The flange (f) geometry is unique geometry for each section of the screw and has been described separately.
[0066] FIG. 9a represents the proximal part of the threaded portion that would engage the cortical bone of vertebra. The pitch (p3) or the distance between 2 adjacent flanges is 1.2-1.3 mm for smaller/thinner screw used in cervical spine and 1.4-1.6 mm for larger/thicker screw. The root is broader than the crest of the flange and is a typical buttress thread. The root forms an angle of approximately 45° with core proximally (pra3) and distal is 90° to the core (dra3). The Outer diameter (OD) of this portion depends on the vertebral segment where it would be used. For e.g. it would be 3.5 mm for upper cervical spine and 6.5 for the lumbar spine. Similarly the core diameter (CD) of this portion is 2.4 mm for cervical spine and approximately 4.5 mm for larger screws of lumbar spine. As described above the L 3 (length of this portion would depend on the vertebral body level where it would be used.
[0067] FIG. 9b represents the intermediate section of the threaded portion of the screw. The L 2 or the length would depend on the level of the vertebra. It would be around 14 mm for upper cervical spine and for subaxial spine and thoraco-lumbar spine it would approximately 14 mm to 30 mm. The outer diameter (OD) is 3.4 mm for upper cervical spine and 5-6.mm for larger lumbar spine. Core diameter (CD) is 2 mm for thinner screws for cervical spine and 2.8 to 3.5 mm for larger screws meant for lumbar spine. The pitch is 1.75 mm for thinner screws and approximately 2 mm for thicker screws. This portion would engage the softer cancellous bone and the thread geometry is the more complex. The flange anatomy is better described in FIG. 9c. The flange bend on itself at ⅔ length from the root. The proximal root angle (pra2) is 120-130° to core and the distal root angle (dra 2) is 65-75° to core. The proximal crest angle or pca (angle between proximal surface of flange edge and that towards the root) is 120-130° and the distal crest angle or dca (angle between under surface of flange edge and that toward the root) is 45-55°. The angle between the crest surface and flange undersurface is around 55-65°. The crest is approximately 0.5-0.8 mm thick
[0068] FIG. 9d represents the distal portion of the screw. The pitch (p1) is 0.85-0.95 mm for the smaller/thinner screws and 1.20-1.30 mm for larger/thicker screw. The length (L1) of this portion would be approximately 3 mm to 5 mm for cervical and thoraco-lumbar vertebra respectively. The Core diameter (CD) is rapidly tapering in this section from approximately 2-4 mm mm at proximally to 0.8 mm at the tip. The outer diameter (OD) is rapidly tapering as well from 3.4-5 mm proximally to 1.5 mm at the tip. The thread geometry is typical buttress one with proximal root angle of 40-50° (pra1) and distal root angle of 90° to the core (dra1). Adding cutting flutes to the tip would make the screw self-tapping.
[0069] FIG. 10 represents the view of the screw-head as seen from top. The outer diameter would be 5.0 to 5.5 mm. The inner portion is a hexagonal notch that would engage in the screw driver.
[0070] The inventor being a neurosurgeon himself, has designed and developed a screw (FIG. 8a-c) that is tapered and has flanges (f, FIG. 8c, FIG. 9c) and pitch (p3, FIG. 9a) to hold appropriately in the cortical portion at the two ends. The proximal portion of the screw would engage cortical bone the same way as the intermediate portion that would engage the cancellous bone. The flanges in the intermediate portion have a larger surface area and are shaped in a manner to counter toggle in multiple axes. The screw is a tapered one with buttress thread for the cortical surfaces. The intermediate portion for cancellous bone has threads with longer flanges with bent rims. The angulation of the threads on itself not only provides a larger surface area but also counters the torque and forces in various angles. This significantly would increase the holding strength and larger surface area good for bone with poorer quality. This would help in greater manipulation without the fear of pull out to achieve good alignment.
[0071] The construct failure rates would drop too. The screw would be of benefit in bones with poorer density as well.
NOVELTY, INVENTIVE STEP AND INDUSTRIAL APPLICATION
[0072] Novelty—In this present invention, a newly designed screw that is tapered and has flanges and pitch to hold properly in the cortical portion at the two ends of injured bone has been developed. This unique design would help in greater manipulation without the fear of pull out to achieve good alignment, so that the construct failure rates would drop. This unique idea has neither been disclosed nor anticipated by any of the prior art publications.
[0073] Inventive Step—The technical advancement of knowledge lies in the unique design of the screw wherein the intermediate portion for porous cancellous bone has threads with longer flanges with bent rims that provides a larger surface area, which is good for bones with relatively poor quality and density. The angulation of the threads counters the torque and forces in various angles to increase the holding strength. This would significantly help in greater manipulation without the fear of pull out to achieve good alignment. At the same time, the construct failure rates would drop. Therefore the present invention is technically more advanced than other available similar screws qualifying it for inventiveness.
[0074] Industrial application—The present invention can be easily manufactured on industrial scale and the production cost is not much as the raw material is cheap and readily available.
