Artificial implant for atlas-axis (C1-2) lateral joints and method of use thereof

Abstract

The joint implant of the present invention is fitted into C1-2 lateral joints through the back of the neck instead of oral approach to avoid infections. It is made of 2 inter-digitating components. One part of the joint implant has a circular railing circumference of a circle, the center of which is odontoid, that inter-digitates in a corresponding circular channel of the other part. Two such implants are fixed on both sides of C1-2 joint simultaneously along the circumference. The circular railings provide mainly circular motion in clockwise and anti-clockwise direction. With some degree of play in channel and rail and making the interacting surfaces of the implant convex on convex, provides the gyroscopic motion with lateral and translational movement and also coupling (vertical translation on rotational movement). This gyroscopic design makes it universal and is likely to work in C1-2 joints of every individual with any possible joint orientation.

Claims

1. An artificial implant (artificial joint) for atlas-axis (C1-2) lateral joints comprising two sets of inter-digitating components called Circular rail (CR1) suitable for fixing in atlas (C1) and Circular channel (CC2) suitable for fixing into axis (C2) wherein: Circular rail (CR1) and the Circular channel (CC2) is fitted along the circumference of an imaginary circle, the center of which is an odontoid; to provide rotational movement almost close to normal; interacting surfaces of the implant are convex on convex to provide a gyroscopic motion with small degree of lateral and translational movement; gyroscopic design makes the implant (joint) universal adapting to varying angles and orientation of C1-2 joints of different individuals; interacting surfaces of the implant are convex on convex to provide coupling (vertical translation on rotational movement); and implant is designed to be fitted from the back of the neck with help of hand tools (T1 and T2) and fixation screws.

2. The artificial implant for atlas-axis (C1-2) lateral joints as claimed in claim 1, wherein implants are fixed on both sides of C1-2 joint simultaneously along the circumference of an imaginary circle, the center of which is the odontoid.

3. The artificial implant as claimed in claim 1, wherein Circular rail (CR1) suitable for fixing in atlas (C1) comprises an upper ledge (UL) and a lower ledge (LL) wherein inner edge (ULi) of the upper ledge (UL) is straight and is connected to Lower ledge (LL) with 3 mm thick connecting stalk (CS); outer edge (ULo) of the upper ledge (UL) is circular, corresponding to the circumference of circle with radius of about 20-23 mm; two projections or the locking pins (LP) are located at ends of the outer edge (ULo) of upper ledge (UL); a perpendicular plate (P1) with of hole (H) is located on top portion; inferior or under surface of Lower ledge (LL) of Circular rail (CR1) is concave (CONC) with central spherical projection (CONV) making interacting surfaces of the implant sphere on sphere; lower ledge (LL) consists of a Monorail (MR) of width about 0.6 mm on its outer edge and follows the circumference of circle with center as odontoid and radius of 18-21 mm and a Groove (G) above the Monorail (MR) about 2-3 mm deep; and upper surface of upper ledge (UL) of circular rail (CR1) comprises ridges (Ro and Ri).

4. The artificial implant as claimed in claim 1, wherein Circular channel (CC2) suitable for fixing into axis (C2) comprises an fused upper half (UL2) and a lower half (LL2) wherein inner edge (UL2i) of the upper half (UL2) is straight and consists of a plate (P2) of 1.5 mm thickness and 4.24.2 mm width and height, angled at 60-70 degrees with respect to the plane of ground and a hole (H2) in the plate (P2); outer edge (UL2o) of the upper half (UL) is circular, corresponding to the circumference of circle with radius of about 20-23 mm and consists of a wall (W1) of 2.5 mm thickness and 2.5 mm height angulated at 60 -70 degrees with respect to the plane of lower surface of CCL; and the lower surface of lower ledge (LL2) comprises of ridges (RLo and RLi) with thickness and height of 2 mm each, running along its entire length at 60 degrees from the surface (perpendicular to plane of ground) fixed inside the Axis (C2) facets in a manner such that ridges (RLo) are positioned higher than the ridges (RLi).

5. The artificial implant comprising a Circular channel (CC2) suitable for fixing into axis (C2) wherein the Wall (W1) as claimed in claim 4 comprises a channel (CMR) in wall (W1) that houses the monorail (MR) of Circular rail (CR1), with an upward projection in the midpoint of its (CMR's) outer circumference acting as a locking pin (LP2) and is narrowest at the center and broadens along the outer lengths of its circumference.

6. The hand tool of claim 1 comprising two arms (UA1 and UA2) 5 cm long and 18 mm wide apart from each other and end in cuboids (CB1) on both ends, for making rough cuttings in CR1 and CC2 facets.

7. The hand tool (T1) as claimed in claim 6, wherein the cuboids (CB1): are at an angle of 20-30 degrees to the horizontal and are sized about 17 mm in length, 7 mm height and 8 mm wide; inner edge of cuboids (CB1) is higher up than the outer on either side; and each cuboid (CB1) has graduated broaches (B1) for ridges of CR1 at upper surface (US1) and graduated broaches (B2) for ridges of CC2 on lower surface (LS1).

8. The hand tool (T2) of claim 1 comprising two arms (UA21 and UA22) 5 cm long and 18 mm wide apart from each other and terminate as cuboids (CB2) on both ends, for making final cuttings in the form of grooves in CR1 and CC2 facets.

9. The hand tool (T2) as claimed in claim 8, wherein the cuboids (CB2): are at an angle of 20-30 degrees to the horizontal and are sized about 17 mm in length, 7 mm height and 8 mm wide; inner edge of cuboids (CB2) is higher up than the outer on either side; and each cuboid (CB2) has regular broaches (BR1) for ridges of CR1 at upper surface (US2) and regular broaches (BR2) for ridges of CC2 on lower surface (LS2).

10. A method of use of the artificial implant for atlas-axis (C1-2) lateral joints as claimed in claim 1, comprising the steps of: fixing CR1 on right and left sides, inter-digitating with the CC2 on each side so that the monorail (MR) (edge of lower ledge of CR1) and the channel of CC2 on each side provides approximately 23 degrees of translational and angular movement on either side, in unison and in either clockwise or anticlockwise direction; and restricting the movement of monorail at its maximum limit by the locking pins (LP 15 and LP2).

11. The artificial implant for atlas-axis (C1-2) lateral joints as claimed in claim 1, wherein railing and the corresponding channel can be circular in cut section with some tolerance (play) making it gyroscopic for adapting to different anatomies of the joint.

12. The artificial implant for atlas-axis (C1-2) lateral joints as claimed in claim 1, wherein there are two railings and channels in each implant to reduce the height of the implant.

13. The artificial implant for atlas-axis (C1-2) lateral joints as claimed in claim 1, wherein: ball bearings of smaller diameter than the channel diameter are in contact with the channel floor to reduce the height of the railing; ends of the channels are partially closed to allow only the entry of railing but preventing the falling of ball bearings; and multiple rails and channels can be used to get the desired result.

14. The artificial implant for atlas-axis (C1-2) lateral joints as claimed in claim 11, wherein: ball bearings of smaller diameter than the channel diameter are in contact with the channel floor to reduce the height of the railing; ends of the channels are partially closed to allow only the entry of railing but preventing the falling of ball bearings; and multiple rails and channels can be used to get the desired result.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIGS. 1, 2, 3 and 4: Anatomical figures of the joints C1-C2

(2) FIG. 5: Actual location of C1-C2 Joints in human neck

(3) FIG. 6: Complete Assembly of the present invention suitable for both sides of human C1-2 lateral joints as seen from behind and left side.

(4) CR1L: Component to be fixed in leftatlas (C1)

(5) CC2L: Component to be fixed in left axis (C2)

(6) CR1R: Component to be fixed in right atlas (C1)

(7) CC2R: Component to be fixed in right axis (C2)

(8) FIG. 6A:Exploded view of CR1L component of FIG. 6

(9) FIG. 6A1:Right side view

(10) UL: Upper ledge of CR1L

(11) ULo: Outer edge of upper ledge (UL)

(12) ULi: The inner edge of the upper ledge (UL)

(13) LL: Lower ledge of CR1L

(14) CONC: Concave undersurface of LL conforming to basic cone on cone design

(15) CONV: Additional Convex surface to make the design gyroscopic and reducing contact point to one

(16) FIG. 6A2:Right Top view

(17) LP: Locking Pin

(18) R: Ridge for securing implant within bone inhibiting any movement within bone and implant

(19) Ri: Inner ridge

(20) Ro: Outer ridge

(21) MR: Monorail to loosely fit into CC2 components channel

(22) TR: Trapezoid

(23) FIG. 6A3:Rear Bottom view

(24) LP: Locking Pin

(25) CS: Connecting stalk

(26) G: Groove

(27) FIG. 6A4:Rear Top view

(28) P1: Plate to fix on the posterior surface of CR1 facet with hole for screw fitting

(29) H1: Hole to fix screw

(30) ULo: Outer edge of upper ledge (UL)

(31) MR: Monorail [outer edge of lower ledge (LL)] to loosely fit into CC2 components channel

(32) FIG. 6B:Exploded view of CC2L component of FIG. 6

(33) FIG. 6B1:Right side view

(34) UL2: Upper ledge of CC2L

(35) UL2i: Inner edge of upper ledge (UL2)

(36) LP2: Locking pin

(37) CONV2: Convex surface conforming to Concave surface CONC of CR1L

(38) CONV3: Additional convexity makes the design gyroscopic and reducing contact point to one with C1 Convex component

(39) FIG. 6B2:Left Side Rear Bottom view

(40) UL2o: Outer edge of the upper ledge (UL2)

(41) W1: Wall on one side of the outer edge (UL2o)

(42) FIG. 6B3:Right Side Rear Top view

(43) CMR: Channel in W1 that houses the monorail (MR) of CR1L

(44) P2: Plate to fix on the posterior surface of facet with hole for screw fitting

(45) H2: Hole to fix screw

(46) FIG. 6B4:Right Side Rear Bottom view

(47) RLi: Inner ridge

(48) RLo: Outer ridge

(49) LL: Lower surface of lower ledge

(50) FIG. 7ATool (T1) in the form of graduated broach for making rough cuttings in CR1 and CC2 facets.

(51) US1Upper surface of graduated broach for ridges of CR1

(52) LS1Lower surface of graduated broach for ridges of CC2

(53) UA1Arm 1 of graduated broach

(54) UA2Arm 2 of graduated broach

(55) CB1Cuboids at 30 degree to horizontal

(56) B1graduated broaches for ridges of CR1 at upper surface (US1)

(57) B2graduated broaches for ridges of CC2 on lower surface (LS1).

(58) FIG. 7BTool (T2) in the form of regular broach for making final cutting of grooves in CR1 and CC2 facets.

(59) US2Upper surface of regular broach for ridges of CR1

(60) LS2Lower surface of regular broach for ridges of CC2

(61) UA21Arm 1 of regular broach

(62) UA22Arm 2 of regular broach

(63) CB2Cuboids of regular broach at 30 degree to horizontal

(64) BR1regular broaches for ridges of CR1 at upper surface (US2)

(65) BR2regular broaches for ridges of CC2 on lower surface (LS2)

(66) FIG. 8Figure of embodiment of the present invention

(67) CCL1Circular Connector Leg 1 to be fitted on the AXIS

(68) CCL2Circular Connector Leg 2 to be fitted on ATLAS

(69) FIG. 8A: Detailed front view of Connector Leg 1

(70) Numbering:

(71) 100L: Locking blocks

(72) 100P: Plate which will rest on Pars-Inter-articularis

(73) 100C: Solid curved section of the Connector leg 1

(74) 100H: Circular Hole for pedicle screw fixation

(75) 100R: Channel for fitting Connector Leg 2

(76) 100W: Width of channel 100R.

(77) 100BW: Total width of the Connector Leg 1 as seen from below

(78) 100T: Solid section below Channel 100 R

(79) FIG. 8B: Front view of Connector Leg 1

(80) Numbering:

(81) 100B: Locking Ratchets in the form of Serrations at the bottom of the Connector Leg 1

(82) 100P: Plate which will rest on Pars-Inter-articularis

(83) 100PW: Width of the Plate 100P

(84) 100L: Locking blocks

(85) FIG. 8C: Exploded side view of 100B

(86) 100H: Circular Hole for pedicle screw fixation

(87) 100BL: Circumference of circular section of Channel 100R

(88) 100BW: Total width of the Connector Leg 1 as seen from below

(89) 100R1: Inner Radius of the Circular Connector Leg 1 (CCL1)

(90) 100R2: Outer Radius of the Circular Connector Leg 1 (CCL1)

(91) FIG. 8D: Front view of Channel 100R

(92) 100RC: Constriction in upper part of channel 100R

(93) FIG. 9A: Detailed front view of Connector Leg 2

(94) Numbering:

(95) 200L: Locking block

(96) 200P: Plate which will rest on isthmus of C2

(97) 200C: Solid curved section of the Connector leg 2

(98) 200H: Circular Hole for pedicle screw fixation

(99) 200R: Rail for fitting Connector Leg 2 in Channel 100R of Connector Leg 1

(100) 200W: Width of channel 200R

(101) 200B: Locking Ratchets in the form of Serrations at the top of the Connector Leg 2

(102) FIGS. 9B, 9C and 9C(1): Views indicating dimensions of Locking Ratchets

(103) FIG. 9D: Exploded view of Rail 200R

(104) 100RC: Constriction in upper part of channel 100R

(105) FIG. 10: Possible Embodiment of the present invention (circular rail and channel in the main interacting surface)

(106) C1: C1 component

(107) C2: C2 component

(108) R: Railing

(109) C: Channel

(110) L: Lock

(111) PC1: Plate for screw in C1 component

(112) PC2: Plate for screw in C1 component

DETAILED DESCRIPTION OF THE INVENTION

(113) The movement of the neck can be in two directionsUp and Down as well as Left and Right.

(114) The dens or the Odontoid Process of AXIS C2 acts as a pivot that allows the atlas (C1) and attached head to rotate on the axis, side to side i.e Movement of neck in Left and Right directions.

(115) The atlanto-occipital joint is a synovial joint which allows the head to nod up and down on the vertebral column i.e movement of neck in Up and Down directions.

(116) Atlanto-axial joint is a complicated joint in the upper part of the neck between the first and second cervical vertebrae; the atlas (C1) and axis (C2).

(117) It provides a significant range of movements. There is a pivot articulation (PA of FIG. 1) between the odontoid process of the axis (C2) and the ring formed by the anterior arch and the transverse ligament of the atlas (C1). There are two lateral atlanto-axial joints (LAJ of FIG. 1) that are relatively flat, slightly slanting downwards, unlike the other vertebral articulations thereby, providing the rotational movement between atlas (C1) with head and axis (C2), apart from providing support. Besides this, there are minimal translational, vertical and lateral bending movements that can occur between C1-2 because of the anatomical flat (in one vertical plane [x-z axis]) and slightly slanting shape (in the other vertical plane [y-z plane]) of lateral atlanto-axial joints.

(118) Therefore, as is obvious now, the Atlas (C1), Axis (C2) and the Atlanto axial joint between C1 and C2 is responsible for majority of the neck movements. Any abnormal displacement between C1 and C2 in single or more than one plane (called AAD) due to congenital reasons or trauma or ligament laxity, can cause restriction in neck movement or sometimes even spinal cord compression thereby causing neurological injuries too.

(119) Sometimes the Atlas (C1) slips over the Axis (C2). Since the pair of lateral atlanto-axial joints lying around the circumference are flat to help in the movement of neck in either in clockwise or anti-clockwise direction. This movement is limited by ligaments. Occasionally, the ligaments become lax or the joints are oblique or the odontoid is fractured. This makes the C1 slip over C2 but in the same direction rather than in a circular motion.

(120) To overcome this restriction in neck movement and to reduce complications due to AAD, the implant of the present invention does not use fusion techniques which permanently restrict the movement of neck to avoid further neurological complications nor does it uses odontoid screw fixation. It also does not use fixing an atlanto-dental joint as these methods have limitations mentioned in the preceding text.

(121) The implant of the present invention fixes into C1-2 lateral joints avoiding the use of oral infection prone route.

(122) Unlike ball and socket joint having a limitation of slipping off vertically, the inventor has developed a novel implant in the form of a joint which can be so fitted along the circumference of a circle, the center of which is odontoid such that it can mimic the natural neck and head movement in clockwise and anticlockwise direction.

(123) In a preferred embodiment (FIG. 6), the present implant is made of 2 inter-digitating components called Circular rail (CR1L) suitable for fixing in atlas (C1) and Circular channel (CC2L) for fixing into axis (C2). On the edge of CC2L there is a circular channel at 60 degrees to the surface which corresponds to railing on the edge of CR1L. The rail and the channel is along the circumference of a circle, the center of which is the odontoid. Such circular rails can provide circular motion in clockwise and anti-clockwise direction. The locking pins (LP and LP2) of CC2L on each side prevent slipping of CC2L and CR1L to sides or excessive translational motion. This provides stability in atlanto-axial joint without compromising the circular motion.

(124) Two such implants as indicated in FIG. 6 (CR1L & CC2L, CR1R & CC2R) are fitted on left and right sides of both C1-2 joints.

(125) Design and Constructional Features of CR1

(126) FIG. 6 A shows CR1L component viewed from various angles and its parts are marked to understand the purpose.

(127) The inner edge (ULi) of the upper ledge (UL) is straight whereas the outer edge (ULo) of the upper ledge (UL) is circular, corresponding to the circumference of circle with radius of about 20-23 mm depending on the size used (center of this imaginary circle is odontoid. Although the outer edge of the lower ledge (LL) is circular, yet it is not a solid circle but consists of a groove (G) and a monorail (MR), tapering with minimal width of about 0.6 mm which gets loosely fitted into the channel in CC2L component. The MR is along the circumference of a circle with radius 18-21 mm. The inner edge (ULi) of the upper ledge (UL) is connected to lower ledge bearing concave (CONC) undersurface with 3 mm thick connecting stalk (CS). The upper surface of upper ledge (UL) is consists of ridges (R) which have thickness and height of 2 mm each, running along its entire length at 60 degrees from the surface (perpendicular to plane of ground) as shown in FIG. 6A2. Due to the shape of trapezoid (TR) (FIG. 6A2), outer ridges (Ro) are positioned lower than the inner ridges (Ri) so as to conform to the angle of C1 facet in y-z plane. These ridges (Ro & Ri) fix inside the atlas (C1) facets and prevent torsional movement. The ends of the outer edge (ULo) of upper ledge (UL) bear two projections or the locking pins (LP) that stop the implant at maximum rotation. On one of the ends of the length, the upper edge (UL) has a perpendicular plate (P1) measuring 1.5 mm thick and 3.53.5 mm length and breadth with of hole (H1) on top portion. This plate (P1) would abut on the surface of facet of atlas (C2). The hole (H1) houses a 2.7 mm screw that would fix the plate (P1) into the lateral mass.

(128) The inferior or under surface of CR1L is concave (CONC) with central spherical projection (CONV) of about 1.5 mm height on this surface. This central spherical projection (CONV) measures about 6 mm in length and 4 mm in width. Only this central spherical projection (CONV) comes in actual contact with convex upper surface of CCL2 during movement.

(129) Design and Constructional Features of CC2L

(130) Referring to FIG. 6B, the upper ledge (UL2) of this component has slightly convex surface. The inner edge (UL2i) of the upper ledge (UL2) is straight with 16 mm length and whereas the outer edge (UL2o) of the upper ledge (UL2) is circular, corresponding to the circumference of circle with radius of about 20-23 mm depending on the size used (odontoid as center). On one side of the outer edge (UL2o) is a wall (W1) of 2.5 mm thickness and 2.5 mm height and is angulated at 60 degrees with respect to the plane of base of CCL2d. This wall (W1) has a channel (CMR) that houses the monorail (MR) of CR1. The channel (CMR) is narrowest at the center and broadens along the outer lengths of its circumference. The channel's (CMR) upper surface has upward projection in the midpoint of outer edge of its circumferences which acts as locking pin (LP2) and rotation would stop where this locking pin (LP2) touches the locking pin (LP) of CR1L. At the end of the inner edge (UL2i) of the upper ledge (UL2), there is a plate (P2) of 1.5 mm thickness and 4.24.2 mm width and height with hole (H2). This plate (P2) is angled at 60-70 degrees w.r.t to the plane of ground. This corresponds to the normal angle between isthmus of axis and its facet. The lower surface of lower ledge (LL) consists of ridges (RLo and RLi) which have thickness and height of 2 mm each, running along its entire length at 60 degrees from the surface (perpendicular to plane of ground). The outer ridges (RLo) are positioned higher than the inner ridges (RLi). These ridges fix inside the axis (C2) facets and prevent torsional movement. The upper surface of CCL2 is convex (CONV 2). There is an additional 0.6 mm convex (CONV 3) component added to CONV 2 which interacts with the CONV surface of C1.

(131) Design and Constructional Features of Entire Assembly

(132) CR1 on right and left sides, inter-digitates with the CC2 on each side. The assembly has been shown in FIG. 6(CR1L & CC2L, CR1R & CC2R). The rotational movement is in unison. It can be clockwise or anticlockwise approximately 23 degrees on either side. The movement at its maximum limit is restricted by the locking pins (LP and LP2). The play provided between the monorail (MR) (edge of lower ledge of CR1) and the channel (CMR) of CC2 on each side provides some degree of translational and angular movement. The excessive translational and angular movements are restricted by the CC2's channels on each side. The convex on convex surface makes the design gyroscopic. This makes it universal as the angles of C1-2 joint in coronal plane (y-z, vertical plane passing through both the C1-2 joints) are variable from 15-45 degrees. With angles the rotational movement is along a conical plane. Conforming to this natural path created, the design has a basic cone on cone pattern (undersurface of CR1 and upper surface of CC2). The small spherical surfaces (CONV and CONV 3) added to these interacting surfaces converts a cone on cone to a sphere on sphere model. This makes the design gyrospcopic and adaptable to the varying coronal angles in individuals. The design is deemed to work even in extreme cases, where the coronal angles may be 60 degrees or as flat as 0-5 degrees.

(133) The sphere on sphere model also provides the coupling action existent in nature. This makes the present invention (artificial C1-2 lateral joints) as close to the natural C1-2 joint as possible.

(134) Design and Constructional Features of the Tools Used:

(135) Two tools are used to fix the entire implant in the form of a joint.

(136) One tool (T1) is a hand tool (FIG. 7A) with two arms (UA1 and UA2) for making rough cuttings in CR1 and CC2 facets. Both the ends of arms (UA1 and UA2) are 5 cm long and 18 mm wide apart from each other and terminate as cuboids (CB1). These cuboids (CB1) which are at an angle of 30 degrees to the horizontal and are sized about 17 mm in length, 7 mm height and 8 mm wide. The inner edge of cuboids (CB1) is higher up than the outer on either side. Each cuboid (CB1) has graduated broaches (B1) for ridges (URi and URo) of CR1 at upper surface (US1) and graduated broaches (B2) for ridges (RLo and RLi) of CC2 on lower surface (LS1).

(137) Another tool (T2) is also a hand tool (FIG. 7B) with two arms (UA21 and UA22) for making final cuttings in the form of grooves in CR1 and CC2 facets. Both the ends of arms (UA21 and UA22) terminate as cuboids (CB2) which are at an angle of 30 degrees to the horizontal. These cuboids (CB2) which are at an angle of 30 degrees to the horizontal and are sized about 17 mm in length, 7 mm height and 8 mm wide. The inner edge of cuboids (CB2) is higher up than the outer on either side. Each cuboid (CB2) has regular broaches (BR1) for ridges of CR1 at upper surface (US2) and regular broaches (BR2) for ridges of CC2 on lower surface (LS2).

(138) The U at its base would have adjusting screw to vary the distance between 2 arms.

(139) The tool (T1) with graduated broaches is just for marking the position of the grooves and making rough cut through the hard cortical shell of bone without fracturing it. The tool (T2) comprising of regular broaches is different than that comprising of graduated broaches as it is used to finally cut grooves of requisite size for fixing the ridges of implant.

(140) Yet another tool with arms similar to above tools would hold the both right and left CR1 and CCL2 together and insert it into the joint space and grooves created.

(141) We cannot use a single tool which can graduate as well as cut because the bone has two layers; outer hard cortical layer and relatively softer inner layer. It is important to cut the cortical layer first with sharp cuts followed by cutting of inner softer layer. If a regular broach is used alone it would fracture the bone rather than cutting it. Using the graduated broach would create partially formed grooves.

(142) Method to Use of the Present Invention:

(143) Step 1: Reduction of dislocation by drilling the facets flat and parallel to each other. The drilling needs to be adequate enough to house the implant (2 mm width of each facet).

(144) Step 2: Rough grooves for fixing the ridges in CR1 and CC2 are prepared using the tool T1 followed by finishing of the grooves using the tool T2.

(145) Step 3: An instrument holding bilateral implants 18 mm apart, would place it within the opened joints simultaneously. The implants would be hammered into bilateral joint spaces with ridges fitting in the grooves created by the broaches using tools T1 and T2.

(146) Step 4: Once the implants are in position, fixing of CR1L on one side (Say Left) with the help of normally available Fixation screws through the hole provided in to insert it in atlas (C1). Another screw would fix the CC2L in axis (C2) facet. Similarly, screws would fix CR1R and CC2R on Right atlas (C1) and axis (C2) respectively.

(147) It is obvious that the surface of implant coming in contact with bone would be rough with ratchets to prevent it from moving out. The surfaces may be sprayed with substances that enhance osseo-integration. The interacting surfaces between CR1 and CC2 (the spherical portions and the channel and rail) would be highly polished. The components can be made of titanium/cobalt-chrome or PEEK or some other strong inert substance or a combination of these or any suitable material, to prevent the metal loss that is likely to occur in a metal on metal surface.

(148) In another embodiment, the interacting surfaces may be flat (CR1 undersurface) on convex (CC2 upper surface) instead of convex on convex. This would make the joint slightly more stable but at the cost of the coupling movement. A cone on cone model (concave on convex) is a feasible and is extremely stable; but is not gyroscopic and has the disadvantage of not being adaptable to varying coronal angles. This would make the implant less universal.

(149) In yet another embodiment, (referring to FIG. 8), the implant is made of 2 inter-digitating components called Circular Connector Leg 1 (CCL1) suitable for fixing in Axis (C2) and Circular Connector Leg 2 (CCL2) suitable for fixing in Atlas (C1). CCL1 acts like a channel and CCL2 acts like a corresponding railing.

(150) The railing and the channel is along the circumference of a circle, the center of which is odontoid. Such circular railings can provide only circular motion in clockwise and anti-clockwise direction, but cannot allow any other motion including slipping of C1-C2. This provides stability in atlanto-axial joint without compromising the circular motion.

(151) The railing has a constriction in the form of a narrow neck as compared to the fundus with a similar corresponding channel. This prevents the railing to come out from the channel.

(152) Two sets of each such implant comprising CCL1 and CCL2 together are fixed on both sides (left and right) simultaneously along the circumference of the C1-C2 joints.

(153) Referring to the accompanying drawings and figures, FIG. 8 shows the complete assembly of the implant of this embodiment. Circular Connector Leg 1 (CCL1) fixed on the Axis (C2) is so designed so as to keep the natural anatomical shape of the Axis in mind which is responsible for the movement of the neck.

(154) Referring to FIG. 8A:

(155) CCL1 comprises of an arc shaped body which has a channel like shape in the centre. The curve of the arc is designed keeping in view the normal human anatomical structure of Axis C2. The inner radius of the arc is 14.64 mm and the outer radius is 25.23 mm. This gives a total width 100BW of CCL1 as (25.2314.64=10.59 mm). More precise dimensions of the curve of the arc is calculated with the help of radiography of individual patient. The upper part of the CCL1 has a solid curved section 100C out of which the channel 100R has been cut leaving behind a solid section of thickness 1.5 mm. Channel 100R for fitting CCL2 is broader at the base and gets constricted towards the top end so as to stop the vertical movement of railing once it is slid in the channel. Solid curved section 100C has locking blocks 100L at the ends to prevent sliding of the railing of CCL2 forward and backward out of the channel of CCL1, once fitted. A plate 100P is provided at the bottom and towards left end of the CCL1. This plate helps to provide stability to CCL1 and rests on Pars-articualris region of the Axis.

(156) Referring to FIG. 1, the Pars-articualris of the Axis is naturally inclined at an angle of 150 degree from the flat surface of atlanto-axial Joint. Therefore, the angle at which the plate 100R is bent outward is 150 degree so as to fix it in the Pars-articualris of the Axis C2 in the best suitable position. The plate 100R has a circular hole 100H in it to accommodate a normally available pedicle screw of width 3.5 mm and length 16-18 mm which is required to fix the CCL1 in the Axis. Vertical height of the plate 100R is 4.20 mm carefully selected to suit the above said pedicle screw. The optimum thickness 100PW of the plate 100R is 2.31 mm which can prevent bending of the plate 100R after fixing the pedicle screw.

(157) Referring to FIGS. 8B and 8C, the bottom face of the CCL1 comprises locking ratchets 100B in the form of serrations. These serrations are required for fitting the implant on the body of the Axis C2 by routine method using a soft hammer. The total curved length or the circumference of circular section (100BL) of the serrations is 19.75 mm. The inner radius 100R1 and the outer radius 100R2 are shown as 14.64 and 25.23 respectively which are the corresponding to curve of the arc of CCL1. The width as shown by 100BW in FIG. 8C corresponds to the total width of the CCL1 as seen from the bottom view of CCL1.

(158) Referring to FIG. 8D, the channel 100R is constricted at the upper end (100RC) to avoid sliding out of the railing of CCL2, in vertical direction, once it is fitted in the channel groove of CCL1.

(159) Design and Constructional Features of CCL2:

(160) Referring to FIGS. 9A,B,C and D, the CCL2 consists of a rail 200R which is cut in a shape suitable for fitting in the channel of CCL1. FIG. 9D describes the dimensions of constriction in the rail 200R which will best fit in the channel 100 R of the CCL2. Constriction in upper side again prevents the railing to come out of CCL1. Therefore, the channel constriction and the Railing constriction get locked with each other once inserted through side groove of the channel. The railing thus can not move out vertically due to this locking arrangement.

(161) To prevent the railing slip horizontally out of the channel, there is provided a Locking Block 200L at the top outer edge of the railing. When the railing moves horizontally and in circular manner inside the channel, it is stopped at the ends by Locking blocks 100L in CCL1 due to the fixing of Locking Block 200L of the railing. Therefore, the railing, cannot move out horizontally also once fitted.

(162) CCL2 also uses a plate 200P which will rest on back side of the lateral mass of Atlas C1 and fixed with a screw that provides stability to CCL2.

(163) The angle at which the plate 200R is bent outward is 150 degree so as to fix it in the best suitable position. The plate 200R has a circular hole 200H in it to accommodate a normally available pedicle screw of width 3.5 mm and length 16-18 mm which is required to fix the CCL2 in the Atlas. Vertical height of the plate 200R is 4.20 mm carefully selected to suit the above said pedicle screw. The optimum thickness 200PW of the plate 200R is 2.31 mm which can prevent bending of the plate 200R after fixing the pedicle screw.

(164) Referring to FIGS. 9B and 9C and 9C(1), the bottom face of the CCL2 comprises locking ratchets 200B in the form of serrations. These serrations are required for fitting the implant on the body of the Axis C2 by routine method using a soft hammer. The total curved length or the circumference of circular section (200BL) of the serrations is 16.75 mm. The inner radius 200R1 and the outer radius 200R2 are shown as 16.48 mm and 24.48 mm respectively which are the corresponding to curve of the arc of CCL2.

(165) Such design has a limitation of being used only in a particular coronal angle. Hence has to be made according to an individual's coronal angle. Since the channels and railings have to be along a circumference of a circle whose center is the odontoid, therefore as a further embodiment to this, railing and the corresponding channel can be circular in cut section instead of a pentagon (FIG. 10). With some play, the implant becomes slightly more gyroscopic, adapting to different anatomies of the joint.

(166) In one more embodiment, there could be two railings and channels in each implant. This would reduce the height of the implant.

(167) In yet another embodiment, the channel floor may be laden with ball bearings of smaller diameter than the channel diameter. The railing would be of smaller height than the one described in FIG. 9. The height of the railing along with the diameter of the ball bearing would be equal to the railing height described in FIG. 9 (2.03). This would make the movement of railing within the channel smooth. The ends of the channels need to be partially closed to allow only the entry of railing but prevent the falling of ball bearings.

(168) Novelty:

(169) Till date, the inventor has not come across any implant for atlanto-axial C1-C2 joint implant which can give freedom of movement to the neck close to natural movement of the neck. There is no atlanto-axial joint implant which can be used for treating congenital abnormalities or inflammatory arthritis with settling apart from traumatic AAD. Also, no implant exists to provide all the degrees of freedom of movement seen in natural C1-2 joints.

(170) The present invention, with the help of a novel concept of using circular Channel and Railing arrangement along with two opposing convex (or convex on flat surface), can successfully overcome all the above limitations. The channel and rail can be on the side or along the opposing surface

(171) Hence the invention seems novel to the best of the knowledge of the inventor.

(172) Inventive Step:

(173) To achieve novelty, the inventor has put in considerable effort to design and develop the implant of the present invention which can be fitted post reduction from the back of the neck avoiding the infected oral cavity route. It can mimic the natural normal movement of the neck in Right-Left directions since the arcs of the channel and railings or any other mechanism used for the purpose such as opposing discs or disc on disc, are designed keeping in view normal human anatomical structure of C1-C2 joints. The implant can thus gives multiple degrees of freedom for neck movements.

(174) It can mimic the natural normal movement of the neck of turning to either sides. The channel and railing implant with play does provide some antero-posterior or lateral translational or bending movement at C1-2. This channel and railing implant is stable. The sphere on sphere model of C1-2 implant provides some lateral and flexion-extension movements. In fact, the rotational movement is associated with coupling vertical movement, closest to the normal.

(175) With the rail and channel alone (model 2) the stability is high but it compromises the natural translational and coupling movement. For patients suffering from Congenital AAD due to deformity in C1-C2 joints can be helped, as this implant takes care of an individual's anatomical structure of the joint and can be easily manufactured by the implant manufacturer.

(176) Hence the invention carries a technological advancement in the field of implants and duly covers the inventive step.

INDUSTRIAL APPLICATION

(177) Since the present invention pertains to the field of surgical and medical implants, it has a lot of societal and commercial significance. It can help save lives of many patients suffering from AAD. It can even treat congenitally deformed patients with AAD, since it can be easily manufactured by any existing implant manufacturer by taking the dimensions of C1-C2 joints of an individual patient with the help of radiography. Hence, the present invention has industrial application.

(178) In the preceding detailed description, the invention is described with reference to exemplary drawings thereof. Various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the description. The specification and drawings are accordingly, to be regarded in an illustrative rather than a restrictive sense. Thus without analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge, readily adapt it for various applications without omitting features that from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention.