|Title of Invention||
RENEW COMPRESSION SCREW DEVICE
|Abstract||The Renew Compression Screw Device for internal and external fixation of bone, consisting of a rod like implant with a first end, and a thread at the said first end; and a second end, with a means of gripping at the said second end; with a specified intercalated head between the said thread and the said second end.|
THE PATENTS ACT, 1970
(39 ot 1970)
(SECTION 10; rule 13)
"RENEW COMPRESSION SCREW"
24 MAR 2005
Dr. KARTIKEYA P. PATHAK,
An Indian National having his address at
260/5, Harinav,Near Punjabi Hall,
Gujarat State, India.
The following specification particularly describes the nature of this invention:-
It is very well known that bone is a living structure and sometimes breaks due to direct or indirect forces acting upon it. Bone being alive has the capacity to repair itself by the biological process of healing.
It may be necessary occasionally to eliminate and fuse a joint between two or more bones because the joint has become most troublesome due to infection or degeneration.
In such cases it is not always possible to replace the joint with an artificial joint, or such an artificial joint might have already been failed. In such cases the bones participating in the joint may have to be permanently fixed to each other without movement at the diseased joint. Such bone surfaces must join and heal to each other to become one bone.
Joining of one bone piece to another in good position is facilitated by:
• Positioning them in the original anatomical shape rotation and angle,
• Eliminating any gap,
• Compressing the surfaces of bone together,
• Holding them without harmful movement,
• Preserving the circulation of bone and other tissues,
• Allowing rest only to healing parts, encouraging activity of the other parts,
• And all these factors being provided, until the bone is sufficiently healed to take care of itself.
The following methods are available in prior art, with their respective advantages and defects.
A. Strapping of the part. This can be done with adhesive and non-adhesive
bandaging and has very limited applications to certain injuries such as of the
collar bone or toe bones.
B. Traction, or continuously pulling on the part to restore length of the limb for
severalAveeks until healing.
C. External splints like Plaster of Paris, wooden splints etc. They cover too much
of the part and conceal any wounds within that area. They may give pressure
sores on bony points, insects may get inside, and splints may allow displacement
of the fragments.
D. Internal fixation, consisting of screws, plates of various sizes and shapes, and
nails into the canal or substance of a bone.
They are most often capable of holding the bones very securely and in good position. However, large skin incision is required with disturbance to muscles and circulation. If revitalization of bone pieces occurs, healing may get delayed or nonunion may occur. Same implants can be inserted by less invasive methods with smaller incisions, but soft tissue interpositions may remain, with loosening and fresh uncertainties.
It is possible to compress the fragments at the time of operation, by using compression devices or by utilizing the LAG-SCREW principle while driving some of the screws.
After applying the device, the wound is closed in layers and the device stays deep inside the body. However, the compression always wears off within hours or days either due to crumbling of compressed bone or due to absorption of the bone, and there is no way of renewing the lost compression.
Nails are inserted through the entire or almost entire length of the bone canal, by closed or open methods. They act more as splints and need interlocking at both ends to prevent rotational and tilting forces to disturb bone healing. Patient and staff receive a lot of x-ray radiation during such operations. E. External bone fixator devices.
Screws and pins are inserted into the bone pieces to gain control over them, after which the pins project outside the skin and are connected together by clamps to rods and tubes to each other for stability.
There is minimum disturbance to any soft tissue or to circulation, if they are driven through "safe corridors". Only stab incisions in the skin are required. The problems are of LOOSENING of screws in the bone, and infection; with loss of control. Loosening and infection are also complimentary to each other.
There is a technique of "RADIAL PRELOAD" in which the screw is driven into a drill hole of a smaller diameter then the core diameter of the screw. This gives more stiffness and some longevity to the stability, but there is no way of renewing the stability after loosening. Once loosened, it stays loose. Coating the surface with substances like Hydroxyapatite lengthens the duration by "bonding", but without scope for renewable stability.
There is an external fixator screw implant patented by Taylor et al for exerting lag screw compression, but its major drawback is the plane of engagement of its head, which in all cases is at right angles to the rod axis. Due to this, the head stands on edge if the rod is driven at any angle other than 90 degrees to the bone surface (FIGURE VII). A lag screw has to be at 90 degrees to the Fracture Plane to be most effective, in which case it cannot be at 90 degrees to the outer bone surface. This is because the fracture plane itself is
always at an angle to the bone surface. 90 degrees to fracture is never 90 degrees to surface. Apart from the radial preload technique, there is nothing inherent in the design of any prior external fixator implant to give any other preloads in different directions, to distribute stress more widely.
F. Combined methods of internal and external fixation.
Whenever the surgeon feels insecure about the quality of bone or of stability achieved, He / She may have to combine internal and external fixation for improved stability. Significant damage to the nutrition of the part might have already occurred, without sufficient stability to achieve union. It is a good combination, but without the element of any renewable stability.
G. The invention of RENEW COMPRESSION SCREW is an original device of basic
external fixation implant with the following features.
• It has the advantage like other external fixation implants, of requiring only small stab incisions.
• It is also inserted along "Safe corridors" to prevent injury to any vital structures.
• It is inserted into a drill hole of smaller diameter to exert a RADIAL PRELOAD as in the older method.
• In addition to the radial preload, it also exerts a SURFACE PRELOAD by the screw head resting on the bone, resisting tilt. (FIGURE X)
• On tightening the screw further, the screw thread exerts also an AXIAL PRELOAD on the surface of the bone thread cut into the bone substance. This gives more rigidity and durability, with tensioning of the implant along its long axis against the bone thread. This is due to the presence of the intercalated screw head in the invention.
• The screw, like other external fixator implants, projects outside the skin. It is therefore possible to renew its stability later on by retightening the screw. This is by virtue of an intercalated screw head in the device that presses upon the bone surface.
• It can be driven in a LAG SCREW mode, to achieve compression of bone surfaces of different fragments which possibly does not exist efficiently in any of the present devices of external fixation. For this, the invention device is driven across at about 90 degrees to the fracture line through a gliding hole in the nearer fragment.
• Even if the lag screw compression wears off, the screw can be tightened from outside to renew it. This is not possible with an internally fixed screw, because the screw lies deep within the body and there is no approach. It is not possible to cut open the wound every time to approach the screw for turning it tight.
• Also, the Renew Compression Screw is connected to an external construct by means of clamps and tubes or rods to give a stable fixation of fragments.
• To gain the advantages of renewable stability and renewable compression in lag screw mode, it does not newly acquire any adverse qualities.
DESCRIPTION OF THE INVENTION:
The invention is a rod like bone fixation device made out of materials, which will be compatible with the living tissues of the body, so as not to suffer rejection by the body. It consists of a thread at one end. The diameter of the rod, the
thread, and the core of the thread depend on the size and pattern of bone
structure for which it is intended.
At the other end is a provision for gripping, in the form of a milled or triangulated
or a quick coupling pattern etc, which will help to drive the device in or out with
Between the thread and the other end, is an intercalated screw head. The first
end may have a full thread from the tip to the screw head, or may be partly
threaded and have a smooth portion of screw shaft between the thread and
the head, when intended in the lag screw mode. The screw head is spherical; or
when so required, should be hollow dome shaped or conical or bell shaped.
The portion between the head and the grip end is the drive shaft, which turns the
device and projects outside the body for participation in the outside fixation
construct, and also serves to renew the compression when called for, by turning
the screw later.
The entire device can be canalized lengthwise to allow a guide wire to pass
through, which will guide the insertion of device.
FIGURE NUMBER I. This shows a common fracture 13 of the human hip, fixed by a
commonly used device for internal fixation of prior art.
It is an angulated device in two pieces, in which a partly threaded screw 8 is
inserted into the head and neck 11 of the femur bone. The barrel of the plate 9
is slipped over the screw that has a required angle of junction with the plate,
which secured to the shaft 12 of the bone with screws 10. This completes the
assembly, but one can add a compression screw between the screw 8 and the
barrel 9 (not shown). This will compress the fracture surfaces 13 together.
After this the wound is closed including skin at 27, and the connpression effect may wear off within hours or days. After this the device is not accessible from outside. Sliding of the screw 8 in the barrel 9 may occur allowing contact of bone at 13, but the compression is lost. Jamming of screw may prevent sliding, to create a gap at 13.
FIGURE NUMBER II. The same fracture 13 is shown fixed with a prior art external fixation device. > It is also in an angular mode with Schanz Screws 16 into the head and neck segment 11 of femur, and same screws 16 on the outer side of the shaft 12 of femur, connected outside the body with a construct of tube 14 and clamps 15. The implants are at an angle to each other.
Due to the absence of any screw head, no compression in lag screw mode can be exerted, and even a gap may remain at the fracture 13. Sliding may or may not occur, to allow contact of surfaces, and only immobilization is achieved. The skin of the part is at 27.
FIGURE NUMBER III. The same fracture 13 is reduced and fixed with the invented device. Due to the presence of the screw heads 5 and smooth unthreaded section 4 across the fracture 13, a lag screw effect is achieved on tightening the device. This gives firm compression of the fracture surfaces 13. Skin cover is marked 27. If the compression wears off later on, the invention device can be turned tighter at any later date, by loosening the clamp 15 of one screw at a time and driving it tight. The same procedure is repeatable. If the invention implant in the shaft side 12 loosens, turning it on a later occasion will re-stabilize the same.
FIGURE NUMBER IV. This shows the features of the invention in one form. The grip
end 7 is triangulated in this drawing, meant for gripping with a Jacob's chuck, if
can be also milled, or any other suitable surface to suit the gripping handle
The drawing shows the intercalated screw head 5 between the thread 3 and the
grip end 7. Drawing shows a spherical head 5, for use either at a right angle to
the bone surface, or at other angles, to be seated in a matching countersink in
bone surface (not shown) to distribute stress evenly and broadly at all angles of
There is a smooth portion of screw shaft 4 between the thread 3 and screw head
5, which is intended for use in the lag screw mode. For use in a single bone
fragment as a basic external fixator implant, a fully threaded device is preferred
(not shown), for maximum bone thread contact. The drawing shows a short
In this drawing, the invention device is shown having a self-cutting tip 2. This has
advantages in some situations, without which the thread will have to be cut with
a bone tap. The drawing shows a canalized invention device, with a canal 1
from one end through head 5 to the other end. Due to this facility, first an
acceptable location in bone is achieved with a small diameter guide wire (not
shown), and then the device is threaded over the guide wire and driven home.
Between 5 and 7 is the drive shaft 6 used for turning the device in or out, and for
securing to an external fixator construct.
FIGURE NO V. The drawing shows a cone shaped hollow head 5, with a wavy
margin 28 of the rim, intended for interrupted contact with bone surface.
FIGURE NO VI. The drawing shows a dome shaped head 5 with an open base and a wavy rim margin 28.
FIGURE NO VII. The drawing shows serially placed holes 18 in the central rod of the device. There is a spherical head 5, which is fixed in a desired position by means of a transverse screw 17 through head and rod.
FIGURE NO VIII. The drawing shows prior art device of Taylor and Taylor. To get good lag screw compression, the device should be driven at about 90 degrees to the fracture plane as at 22. This will cause the device to subtend about 45 degrees angle with the surface of bone, as at 21. The fracture plane 13 is running at an angle of about 45 degrees to the outer bone surface seen at 20. 12 is the other fragment of bone. At this angle, the flat under surface 29 of their patented head 5 will stand on edge at about 45 degrees to the bone surface of fragment 11. Such a loading is uneven, eccentric, and strenuous both for bone and implant, as seen at 19.
FIGURE NO. IX. The drawing shows the claimed device with spherical head 5, which under conditions similar to figure no viii, exerts a comfortable, even, and broad contact in a matching countersink 23. This discourages loosening. A matching excavated washer (not shown) also can be used, instead of countersinking. The invention device is seated across fracture plane 13, at an angle of about 90 degrees (at 22). The plane of the fracture is about 45 degrees (at 20) to the surfaces of fragments of bone 11 and 12, and the implant is at 45 degrees to bone at 21. A broad interface between head 5 and countersink 23 is a more durable relationship.
FIGURE NO X. The drawing shows the claimed invention being used not in lag screw mode, but in the basic implant mode to grip a single fragment 11 on one
side of a fracture, which is always inserted at 90 degrees to bone surface for efficient mechanics. Radial preload 24 at the rod/drill hole interface, is ensured by driving the device through a smaller drill hole. When the base of the head touches the bone surface of 11, any tilting of the rod at 6 and 7 is transmitted to the bone surface at 25 via the head, and diverted from the rod/drill hole interface 24 which is the site for loosening. This point at 25 is the SURFACE preload, a feature only of the claimed device. On driving the device tight against the bone thread, an AXIAL preload 26 is created by the claimed device in which the implant is tensioned axially against the none thread. These three combined factors distribute stresses widely away from the implant/drill hole junction 24, where loosening occurs. Radial preload at 24 is not renewable, but if is protected by the surface 25, and AXIAL 26 preloads, which are renewable. Looking to the descriptions in the above FIGURES I to X, it is clear that the prior art device of internal fixation of FIG I fail in sustaining any compression achieved at the end of operation. Compression is inevitably lost over hours or days, due to crumbling or absorption of bone ends, or due to pressure necrosis of any soft tissue which at times interposes between bone and metal. The device is deep in the body, unapproachable. In FIG II prior art external fixator, the Schanz screw merely passes through the fracture plane, without compressing the surfaces in lag screw mode, due to absence of any intercalated head. Gap may occur later, due to bone absorption, being bad for healing.
FIG III shows the claimed invention in action, the upper two devices compress the fracture plane in lag screw mode due to the intercalated heads. If the compression wears off, the screws can be loosened at the clamps one at a time to RENEW the compression, a very good thing for quick bone healing.
FIG IV shows one form of the claimed device more ideally suited for lag screw compression. It is well known that lagging the fragments in compression heals them early, which is best at nearly 90 degrees to the fracture plane. Due to this, direction is a more important consideration. To find a proper direction, the device may have to be repeatedly driven until a good position is achieved. This damages the bone too much. Instead, a small diameter guide wire is passed with minimal damage, and when the position is ideal, the claimed invention is threaded over it and driven home. The central canal 1 weakens the rod to some extent, but gives the advantage of keeping the bone strong. For lagging, the thread must catch only in the fragment near the tip of the screw. All nearer fragments towards the head must slide over the smooth shaft 4, being pushed by the head, to achieve compression. The smooth shaft 4 is preferred in the claimed invention because it will never catch in any irregularity in the bone drill hole. The alternative is to keep the thread full from tip to head, and to make an oversized gliding hole in the near fragments to prevent the thread from catching in it. The larger drill hold weakens the bone, and the thread may still catch somewhere in it.
It is known that self tapping screws (2) loosen a little earlier than screws driven after using a bone tap, but it is most convenient to have a self tap for a lag mode. This is because the lag screw by itself though compressing the surfaces tightly, has little resistance to other forces across the fracture such as muscle pulls and gravity. A lag screw must be followed by other measures to neutralize the other forces and to protect the good work of the lag screw. In this case it is the external fixator construct which protects, and in which the invention participates.
FIG V and FIG VI show hollow heads 5 with interrupted contact at 28 on bone surface. The significance is that blood supply must be allowed to reach under
the head 5 to nourish the bone underneath. Cutting off the nutrition kills the bone, which allows loosening of device. It is a well known phenomenon that new bone forms around implants like plates and screws when the surrounding bone is well nourished. This ensures some strength at the time of removal of the implant, and is always to be preserved.
FIG VII shows a movable spherical head, for use as lag screw. This reduces the inventory. There may be some minimal micro movement between the head and rod, but the lag screw is well protected by the basic external construct, making it
FIG VIII shows the device of Taylor et al, and how it will give problems in surgery. Too much concentration of stress on a small area of bone in a lopsided manner causes micro fractures in the bone surface and loosening. The stress is beyond the mechanical tolerance of bone, and unbalanced. There is no conceivable washer to redeem the mismatch situation created. The only angle at which it will seat evenly is 90 degrees, which is seldom possible in working. This is because the fracture line being at an angle to the bone surfaces will demand a lag screw which also at a similar angle to the surface. FIG IX shows how the claimed device will always make a broad, stable, concentric and even contact with a matching countersink in bone surface, at all angles to the surface. If there are any reservations about countersinking the bone, a surface washer can be easily added, with a matching spherical excavation towards the head 5. FIG X shows the claimed invention in basic mode, driven in a single bone fragment. The ideal angle of insertion for mechanical advantage is 90 degrees,
which is easily judged without any guide wire technique. Thus there is no canal, which makes this a stronger rod, and no self cutting flutes at the tip, which makes it last longer in bone being driven after a proper use of a bone tap for cutting the thread.
The very wide distribution of contact and stresses between the invention and the bone around it, makes it very much more durable in this situation. The Radial preload is retained as in prior art, and Surface and Axial preloads are added which protect the Radial preload. Surface and Axial preloads are also renewable, subsequent to the initial procedure. The threaded section of this screw may either be coated with hydroxyapatite or any bonding substance, or be uncoated.
|Indian Patent Application Number||885/MUM/2004|
|PG Journal Number||42/2008|
|Date of Filing||16-Aug-2004|
|Name of Patentee||DR. PATHAK KARTIKEYA PRANJIVAN|
|Applicant Address||260/5, HARINAV, NEAR PUNJABI HALL, NAVRANGPURA, AHMEDABAD 380 009, GUJARAT STATE, INDIA.|
|PCT International Classification Number||N/A|
|PCT International Application Number||N/A|
|PCT International Filing date|