Radial-capitellar implant

Abstract

A radial-capitellar implant for surgical replacement of the capitellum of the humerus and, optionally, the head of the radius. The radial-capitellar implant includes a capitellar implant or surface replacement arthroplasty of the capitellum and a radial prosthesis for replacement of the head of the radius. In one embodiment the radial prosthesis includes an articular head which moveable articulates with a stem implantable in the radius.

Claims

1. An implantable joint prosthesis for implantation at the radiocapitellar joint, the joint prosthesis comprising: a capitellar prosthesis configured to replace a capitellum while leaving an adjacent trochlea substantially intact, the capitellar prosthesis comprising: a body having a smooth convex articular surface having a lateral flat adapted to allow for excursion of the radial nerve over the articular surface, and a bone interface surface on a side of the body opposite to the convex articular surface, the bone interface surface having a first facet and a second facet positioned inferior to the first facet, the first facet being oriented relative to the second facet at an obtuse angle on the side of the body opposite the convex articular surface; and a first stem extending outwardly away from the bone interface surface, the stem including a lateral side, a medial side, a superior side and an inferior side, the medial side having a bend along a portion of the medial side and the lateral side is angled approximately 5 degrees relative to a centerline of the stem.

2. The joint prosthesis as claimed in claim 1, wherein the convex articular surface is substantially a partial spheroid.

3. The joint prosthesis as claimed in claim 1, wherein the convex articular surface extends along an arc of about one hundred seventy to about one hundred ninety degrees in a first direction and along an arc of about eighty to about one hundred degrees in a second direction, the second direction being substantially normal to the first direction.

4. The joint prosthesis as claimed in claim 1, wherein the first stem is treated to promote osseointegration.

5. The joint prosthesis as claimed in claim 1, wherein the first stem has a substantially quadrilateral cross section.

6. The joint prosthesis as claimed in claim 1, wherein the first stem is substantially tapered along its length.

7. The joint prosthesis as claimed in claim 1, wherein the first stem extends outwardly from the bone interface surface at a junction between the first facet and the second facet.

8. The joint prosthesis as claimed in claim 1 further comprising: a radial head prosthesis, the radial head prosthesis comprising a second stem and a head, the head having a concave articular surface.

9. The joint prosthesis as claimed in claim 8, wherein the concave articular surface is formed of UHMWPE.

10. The joint prosthesis as claimed in claim 8, wherein the concave articular surface is formed of a polymeric substance.

11. The joint prosthesis as claimed in claim 8, wherein the convex articular surface of the capitellar prosthesis is substantially a partial spheroid.

12. The joint prosthesis as claimed in claim 8, wherein the convex articular surface of the capitellar prosthesis has a lateral flat adapted to allow for excursion of the radial nerve over the articular surface.

13. The joint prosthesis as claimed in claim 8, wherein the convex articular surface extends along an arc of about one hundred seventy to about one hundred ninety degrees in a first direction and along an arc of about eighty to about one hundred degrees in a second direction, the second direction being substantially normal to the first direction.

14. The joint prosthesis as claimed in claim 8, wherein at least a portion of the capitellar prosthesis is treated to promote osseointegration.

15. The joint prosthesis as claimed in claim 8, wherein the first stem has a substantially quadrilateral cross section.

16. The joint prosthesis as claimed in claim 8, wherein the first stem is substantially tapered along its length.

17. The joint prosthesis as claimed in claim 8, wherein the first stem extends outwardly from the bone interface surface at a junction between the first facet and the second facet.

18. The joint prosthesis as claimed in claim 1 further comprising: a radial head prosthesis, the radial head prosthesis comprising a second stem and a head, the head having a concave articular surface, the head being formed entirely from UHMWPE.

19. The joint prosthesis as claimed in claim 1 further comprising: a radial prosthesis, the radial prosthesis comprising a second stem and a head, the head being articulated to the second stem by a ball joint.

20. The joint prosthesis as claimed in claim 19, wherein the ball joint comprises a primary ball articulable into a primary joint socket and a secondary ball articulable into a secondary joint socket.

21. The joint prosthesis as claimed in claim 20, wherein the primary ball is supported by the second stem, the primary socket is defined by the head, the secondary ball is supported by the head and the secondary socket is defined by the second stem.

22. The joint prosthesis as claimed in claim 20, wherein the primary ball, the primary socket, the secondary ball and the secondary socket share a substantially commonly located center.

23. The joint prosthesis as claimed in claim 1, wherein the first stem further comprises at least one of the lateral side, inferior side and superior side as planar from proximate an end of the first stem to proximate the bone interface.

24. The joint prosthesis as claimed in claim 23, wherein a portion of the medial side proximal to the bend is angled approximately 95 degrees relative to the first facet.

25. The joint prosthesis as claimed in claim 23, wherein a portion of the medial side distal to the bend is angled approximately 3 degrees relative to a centerline of the stem.

26. The joint prosthesis as claimed in claim 23, wherein each of the lateral side, inferior side and superior side is planar.

27. The implantable joint prosthesis of claim 26, wherein a cross-section of the end of the first stem is substantially quadrilateral.

28. The joint prosthesis as claimed in claim 1, wherein the convex articular surface of the capitellar prosthesis includes a first lateral surface and a second lateral surface.

29. The joint prosthesis as claimed in claim 28, wherein the first lateral surface is planar and the second lateral surface includes a planer portion and a curved portion.

30. The joint prosthesis as claimed in claim 1, wherein the bend is on a medial side of the first stem relative to the radiocapitellar joint when the joint prosthesis is implanted.

31. The joint prosthesis as claimed in claim 1, wherein the bend is formed between a proximal surface and a distal surface, the proximal surface forming an angle with the first facet of approximately 95 degrees.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a plan view of the radial-capitellar implant in accordance with the present invention in a flexed position;

(2) FIG. 2 is a plan view of the radial-capitellar implant in a partially extended position;

(3) FIG. 3 is a plan view of the radial-capitellar implant in a fully extended position;

(4) FIG. 4 is a perspective view of the radial-capitellar implant in a flexed position;

(5) FIG. 5 is a perspective view of the radial-capitellar implant in a partially extended position;

(6) FIG. 6 is a perspective view of the radial-capitellar implant in a fully extended position.

(7) FIG. 7 is an exploded perspective view of the radial-capitellar implant;

(8) FIG. 8 is another exploded perspective view of the radial-capitellar implant;

(9) FIG. 9 is an exploded perspective view of another embodiment of the radial-capitellar implant;

(10) FIG. 10 is an additional exploded perspective view of the radial-capitellar implant;

(11) FIG. 11 is an elevational view of a capitellar implant in accordance with the present invention;

(12) FIG. 12 is a plan view of the capitellar implant;

(13) FIG. 13 is a front elevational view of the capitellar implant;

(14) FIG. 14 is a perspective view of the capitellar implant;

(15) FIG. 15 is another perspective view of the capitellar implant;

(16) FIG. 16 is another perspective view of the capitellar implant;

(17) FIG. 17 is a plan view of the head of the radial implant;

(18) FIG. 18 is a sectional view of the head of the radial implant;

(19) FIG. 19 is a perspective view of the head of the radial implant;

(20) FIG. 20 is a perspective view of the head of the radial implant;

(21) FIG. 21 is a plan view of a stem interface component of the head of the radial implant;

(22) FIG. 22 is a sectional view of the stem interface component of the head of the radial prosthesis with internal structures shown by phantom lines;

(23) FIG. 23 is a perspective view of the stem interface portion of the head of the radial implant;

(24) FIG. 24 is a perspective view of the stem interface portion of the head of the radial implant;

(25) FIG. 25 is a plan view of the capitellar interface portion of the head of the radial implant;

(26) FIG. 26 is a sectional view of the capitellar interface portion showing internal structures in phantom.

(27) FIG. 27 is a perspective view of the capitellar interface portion;

(28) FIG. 28 is another perspective view of the capitellar interface portion;

(29) FIG. 29 is a plan view of an alternate embodiment of the radial prosthesis head;

(30) FIG. 30 is a sectional view with phantom lines showing internal structures;

(31) FIG. 31 is a perspective view of the radial component head;

(32) FIG. 32 is another perspective view of the radial component head;

(33) FIG. 33 is a plan view of a stem of an alternate embodiment of the radial head implant;

(34) FIG. 34 is an elevational view of the stem showing internal structures in phantom;

(35) FIG. 35 is a perspective view of an alternate embodiment of the stem of the radial implant; and

(36) FIG. 36 is another perspective view of an alternate embodiment of the stem of the radial implant;

DETAILED DESCRIPTION OF THE INVENTION

(37) The radial-capitellar implant 40 of the present invention generally includes capitellar prosthesis 42 and radial prosthesis 44. Referring initially to FIGS. 1-5 capitellar prosthesis 42 and radial prosthesis 44 are shown in various views as articulated with one another in various degrees of flexion and extension.

(38) Referring particularly to FIGS. 1-6 and 11-16 capitellar prosthesis 42 generally includes body 46 and stem 48. Stem 48 is joined to body 46 extending outwardly from bone interface surface 52 of body 46. Articular face 50 presents a substantially spheroidal surface. Body 46 and stem 48 may be integrally formed from a single piece of material such as by casting or machining.

(39) Articular face 50 is smooth and may be mirror polished to facilitate smooth articulation. Articular face 50 may present a substantially spheroidal convex surface Articular face 50 extends over an arc of approximately 170 to 190 degrees in a first direction and an arc of 80 to 100 degrees in a second direction generally perpendicular to the first direction. In one embodiment, articular face 50 extends along an arc of about 170 to about one 190 in a first direction and along an arc of about 80 to about 100 degrees in a second direction, the second direction being substantially normal to the first direction. Articular face 50 further presents medial flat 54 and lateral curved flat 56. Lateral curved flat 56 presents straight portion 58 and curved portion 60. Lateral curved flat 56 allows for excursion of the radial nerve over the lateral aspect of articular face 50.

(40) Bone interface surface 52 presents a first facet 62 and a second facet 64. First facet 62 and second facet 64 meet at juncture 66 and form an obtuse angle 68 of approximately 130 to 150 degrees.

(41) Stem 48 extends outwardly away from bone interface surface 52 substantially at juncture 66.

(42) Stem 48 may be substantially square in cross section and presents lateral side 70, medial side 72, superior side 74 and inferior side 76. These designations correspond to the positions of the sides when capitellar prosthesis 42 is implanted in the humerus. Stem 48 extends outwardly from bone interface surface 52 and is angled medially relative to bone interface surface 52. All corners 90 of stem 48 may be radiused.

(43) Desirably medial side 72 of stem 48 displays bend 78. Thus medial side 72 presents proximal surface 80 proximal to bend 78 and distal surface 82 distal to bend 78. Proximal surface 80 forms an angle with first facet 62 of approximately ninety five degrees. A centerline of stem 48 is angled approximately ten degrees from a perpendicular extending outwardly from first facet 62. Distal surface 82 of medial side 72 is angled approximately three degrees relative to the centerline of stem 48. Lateral side 70 of stem 48 is angled approximately five degrees relative to the centerline of stem 48. Stem 48 presents a substantially quadrilateral distal end 84. Superior side 74 of stem 48 is angled approximately two degrees relative to a centerline of stem 48. Inferior side 76 of stem 48 is angled approximately eight degrees relative to centerline of stem 48. Stem 48 and bone interface surface 52 meet at fillet 86. Articular face 50 and bone interface surface 52 meet at edges 87. Edges 87 are radiused around the perimeter 88 of articular face 50 and bone interface surface 52 where articular face 50 and bone interface surface 52 meet.

(44) Capitellar prosthesis 42 is formed of cobalt chrome alloy per ASTM F-1537 or another biocompatible, corrosion resistant material. Capitellar prosthesis 42 is desirably a unitary structure formed from a single piece of material. Bone interface surface 52 and stem 48 may be roughened to encourage osseointegration such as by commercially pure titanium plasma coating.

(45) Referring particularly to FIGS. 7 and 8, one embodiment of radial prosthesis 44 generally includes head 92 and stem 94. Referring particularly to FIGS. 17-25, head 92 generally includes articular portion 96 and stem interface portion 98.

(46) Referring particularly to FIGS. 25-28 articulation portion 96 of radial prosthesis 44 may be formed of UHMWPE or another durable self-lubricating material. Other polymers, composites or metals may also be suitable.

(47) Referring particularly to FIGS. 26 and 27, articulation portion 96 presents concave articular face 100 and engagement portion 102. Concave articular face 100 may be spheroidal in curvature. Concave articular face 100 is surrounded by rim 104. Engagement portion 102 extends outwardly from articulation portion 98 on the opposite side from concave articular face 100. Engagement portion 102 presents integral snap ring 106 that extends radially outward defining indented circular groove 108.

(48) Referring particularly to FIGS. 21-24, stem interface portion 98 may be formed from a rigid biocompatible material such as cobalt chrome alloy. Referring particularly to FIGS. 22 and 23, stem interface portion 98 includes articular face cavity 110 which is dimensioned to accept engagement portion 102 and snap ring 106 therein. Articular face cavity 110 presents circular catch ring 112 surrounding the inner edge 114 thereof. Circular catch ring 112 is dimensioned to fit into circular groove 108 while snap ring 106 fits into the perimeter 116 of articular face cavity 110.

(49) Referring particularly to FIGS. 22 and 24 stem interface portion 98 further presents stem cavity 118. Stem cavity 118 is generally cylindrical in shape and may be formed with a morse taper. Stem interface portion 98 also presents concave portion 120 and convex portion 122. Stem interface portion may be formed of cobalt chrome alloy similar to capitellar prosthesis 42 above. Stem interface portion may be mirror polished over its entire surface with particular attention being paid to concave portion 120 and convex portion 122 which may articulate with soft tissues when implanted within the human body.

(50) In another embodiment of the invention, head 92 may be formed having the same shape and external structure as are articulation portion 96 and stem interface portion 98 together. In this embodiment, the entirety of head 92 may be formed from UHMWPE or another durable self-lubricating material or another polymer or composite.

(51) Referring particularly to FIGS. 7 and 8, stem 94 generally includes bone interface portion 124, collar 126 and extension 128. Bone interface portion 124 has a generally tapering shape with a rounded end 130. Bone interface portion 124 may include a bend 132 occurring approximately halfway between collar 126 and rounded end 130. Bone interface portion 124 may also form a continuous curve. Collar 126 has a diameter larger than both bone interface portion 124 and extension 128. Collar 126 may present an index notch 134 or other marking to indicate the direction of bend 132. Extension 128 is substantially cylindrical in structure and may be formed with a morse taper proportioned to fit into stem cavity 118. Extension 128 and face 136 of collar 126 that make contact with stem interface portion 98 may be mirror polished. The remainder of stem 48 including bone interface portion 124 and the remainder of collar 126 may be roughened to encourage osseointegration such as by application of a commercially pure titanium plasma coating. Stem 48 may take the form of the stem of the radial prosthesis disclosed in U.S. Pat. No. 6,709,459, the contents of which are incorporated herein in their entirety by reference.

(52) Referring particularly to FIGS. 9, 10 and FIGS. 29-36, another embodiment of radial prosthesis 44 is depicted. In this embodiment, radial prosthesis 44 generally includes head 92 and stem 94. Head 92 and stem 94 may be articulated at ball joint 138.

(53) Referring particularly to FIGS. 29-31, in this embodiment, articular head 140 presents concave articular surface 142 surrounded by a radiused rim 144. Articular head 140 further presents primary joint socket 146 and secondary ball 148. Primary joint socket 146 is a substantially spheroidal cavity within articular head 140 including a narrowed portion 150 and tapered portion 152. Secondary ball 148 includes spheroidal portion 154 and is surrounded by flat 156.

(54) Referring particularly to FIGS. 33-36, in this embodiment stem 94 is articular stem 158. Articular stem generally includes bone interface portion 160 which is substantially similar to bone interface portion 124 of the prior discussed embodiment. Articular stem 158 further presents grooved collar 162 and head interface portion 164.

(55) As seen in FIGS. 34 and 35, articular stem 158 presents primary joint ball 166 and secondary socket 168. Primary joint ball 166 includes spheroidal portion 170 supported by base 172. Secondary socket 168 defines a generally spheroidal cavity surrounding base 172 of primary joint ball 166. Articular stem 158 may be formed from cobalt chrome steel or another biocompatible material such as titanium.

(56) Bone interface portion 160 of articular stem 158 may be roughened to encourage osseointegration such as by application of commercially pure titanium plasma coating. The portions of grooved collar 162 not expected to contact bony tissues and the remainder of head interface portion 164 may be mirror polished to facilitate smooth articulation with soft tissues of the elbow.

(57) In operation, capitellar prosthesis 42 is implanted to replace and/or resurface the capitellum of the humerus. To prepare a space to implant capitellar prosthesis 42 a portion of the capitellum is resected utilizing a resection guide (not shown) corresponding to the location of the first and second facets 62, 64 and a sagittal saw (not shown). Transverse and oblique cuts are made to the deep base of the capitellum and the resected portions are removed. After the capitellum is resected a pilot hole is prepared in the capitellum and drilled into the distal humerus. A broach is then used to enlarge the pilot hole and to shape it appropriately to create a cavity to receive stem 48 of capitellar prosthesis 42. Capitellar prosthesis 42 is intended for cemented implantation. Prior to insertion of capitellar prosthesis 42, stem 48 and bone interface surface 52 are coated with bone cement. If capitellar prosthesis 42 is being utilized for a hemi-arthroplasty of the capitellum without replacement of the head of the radius, then the procedure is complete and the site is closed.

(58) If the radial-capitellar implant 40 is utilized for a complete arthroplasty including replacement of the capitellum with capitellar prosthesis 42 and replacement of the head of the radius with radial prosthesis 44, the following procedure is also performed. Resection of the radial head is performed by making a cut at the radial neck utilizing a resection guide (not shown.) During resection the forearm is pronated and supinated while the cutting guide is used to align the saw blade perpendicular to the axes of rotation of the radius.

(59) The intramedullary canal of the radius is entered using a starter awl in a twisting motion. The intramedullary canal is then broached to the appropriate size and shape to receive stem 94 of radial prosthesis 44. With capitellar prosthesis 42 in place, stem 94 of radial prosthesis 44 is inserted into the broached cavity in the radius and radial prosthesis 44 is assembled by installing head 92 on stem 94. Following assembly of radial prosthesis 44, capitellar prosthesis 42 is articulated with head 92 of radial prosthesis 44. Articular face 50 of capitellar prosthesis 42 articulates with concave articular face 100 of radial prosthesis 44.

(60) If the embodiment of radial prosthesis 44 is utilized that includes articular head 140 connected to articular stem 158 by ball joint 138, articular head 140 also articulates with articular stem 158 about ball joint 138. It is notable that the load born by ball joint 138 is transferred largely at the interface between secondary ball 148 and secondary socket 168 while primary joint ball 166 articulates with primary joint socket 146 and bears a lesser portion of the load. Concave articular face 100 articulates with articular face 50 in both a sliding and a rotational fashion. In addition, ball joint 138 allows conical rotation of articular head 140 relative to articular stem 158 thus adjusting for possible misalignment between articular head 140 and capitellar implant 142.

(61) The above summarizes the technique of implantation of the invention, however a more detailed surgical procedure can be found below.

(62) Surgical Technique

(63) Initial Incision

(64) Place the patient under a general or a regional anesthesia. Make a classic Kocher skin incision identifying the interval between the anconeus muscle and the extensor carpi ulnaris. The incision should extend approximately 6-7 cm. Carry dissection down to the joint capsule. The origin of the anconeus can be released subperiosteally and retracted posteriorly to permit adequate exposure of the capsule.

(65) Capsular Exposure

(66) If the elbow is stable, expose the capsule by elevating a portion of the extensor carpi ulnaris sufficiently to allow identification of the lateral collateral ligament complex. Alternatively, split the extensor carpi ulnaris longitudinally in line with its fibers staying anterior to the attachment of the lateral collateral ligament. Divide the lateral capsule slightly anteriorly to the collateral ligament and the annular ligament and reflect the capsule anteriorly and posteriorly to expose the radial head. A portion of the lateral collateral ligament and anterior capsule can be reflected off the lateral epicondyle and anterior humerus to expose the capitellum. The lateral ulno-humeral ligament should not be disturbed. If the ligament has been disrupted, then proceed through the site of disruption to expose the radiohumeral joint. Retract the common extensor tendon and elbow joint capsule as needed to maximize exposure.

(67) Capitellar Resection Guide

(68) Place the capitellar resection guide (not shown) over the capitellum. Perform transverse and oblique cuts to the deep base of the capitellum. Using a rongeur, remove the capitellar head and trim remaining fragments, as needed.

(69) Capitellar Trial and Drill Guide

(70) Place a capitellar trial (not shown) against the resected humerus. Insert K-wires through holes in the trial and into the distal humerus to firmly seat the trial component. Using an appropriately sized drill, drill a broach pilot hole into the distal humerus. If using the capitellar implant alone as a hemi-arthroplasty of the capitellum, radial head resection is not necessary, therefore proceed to the step of Intramedullary Preparation, Distal Humerus below.

(71) Radial Head Resection Guide

(72) Resect the radial neck utilizing a resection guide (not shown.) Resection of the radius utilizing a resection guide is disclosed in U.S. Pat. No. 6,709,459.

(73) During the resection, the forearm is pronated and supinated while the cutting guide is used to align the sawblade perpendicular to the axis of rotation defined by the resection guide. The extent of resection of the radius should be minimized. For example, the distal extent of resection may be the minimal amount that is consistent with the restoration of function as dictated by a fracture line in the radius or a previous radial head resection. In addition, radial length should be restored using a lamina spreader to apply axial traction if there is a positive ulna variance.

(74) Intramedullary Preparation, Proximal Radius

(75) If the elbow is unstable, varus stress and rotation of the forearm into supination allows improved access to the medullary canal. If the elbow is stable but the exposure is not adequate to access the medullary canal, careful reflection of the origin of the collateral ligament from the lateral epicondyle may be necessary to permit subluxation to access the medullary canal. Enter the canal with a starter awl using a twisting motion. Broach the canal taking care to identify the proper axial orientation. The forearm should be in mid-rotation with the tuberosity directed medially. This position is favorable for broaching and implantation as the curve of the broach/implant points lateral or away from the radial tuberosity. Serial sized broaches are used until the broach fits snugly in the canal to an appropriate depth.

(76) Trial Reduction, Proximal Radius

(77) A trial stem is inserted into the broached cavity and a trial radial head is placed on the trial stem. Assure that the stem's collar is flush with the resected head of the radius. Tracking, both in flexion and extension and forearm rotation should be carefully assessed. Misalignment of the radial osteotomy will cause abnormal tracking during flexion-extension and/or forearm pronation and supination. Remove the radial head and stem trials if tracking and alignment is satisfactory.

(78) Intramedullary Preparation, Distal Humerus

(79) Remove the capitellar trial and K-wires to allow access to the broach pilot hole. Insert broach into the pilot hole and impact. Care should be taken to maintain proper alignment with the drilled pilot hole. Continue broaching the distal humerus until the broach fits snugly in the canal to an appropriate depth.

(80) Implanting the Final Components

(81) Once acceptable alignment has been determined, a permanent prosthesis can be inserted. Distraction of the proximal radius may be necessary to allow sufficient access for capitellar prosthesis 42 insertion. Insert the stem 48 into the canal and tap into place using an impactor (not shown). Polymethyl methacrylate (PMMA) bone cement is recommended for the capitellar component. If using the capitellar prosthesis 42 as a hemi-arthroplasty of the capitellum, proceed to the step of Closure below.

(82) Insert the radial stem 94 of radial prosthesis 44 into the intramedullary canal of the proximal radius and tap it into place with an impactor. Bone cement is recommended unless a secure fixation is present at the time of the insertion of the trial stem (i.e. stem cannot be easily extracted from the medullary canal). Next, place head 92 over extension 128 using longitudinal distraction and/or varus stress to distract the radio capitellar interface sufficiently to permit head 92 to be placed on extension 128. Once inserted, secure head 92 using an impactor or an assembly tool. Reduce the elbow and again test the range of motion in flexion/extension and pronation/supination.

(83) Closure

(84) Close the incision. The forearm is placed in full or partial rotation before sutures are tied. The elbow is splinted at 90 degrees flexion and in neutral to full pronation.

(85) Aftercare

(86) Passive flexion and extension is permitted on the second day assuming the elbow is considered stable. The goal of radial head replacement and soft tissue repair is to achieve elbow stability.

(87) Both flexion/extension and pronation/supination arcs are allowed without restriction. Active motion can begin by day five. Long term aftercare requires monitoring as with any prosthetic replacement.

(88) The present invention may be embodied in other specific forms without departing from the central attributes thereof, therefore, the illustrated embodiment should be considered in all respects as illustrative and not restrictive, reference being made to the appended claims rather than the foregoing description to indicate the scope of the invention.