AU1545502A

AU1545502A - Surgical cutting instrument

Info

Publication number: AU1545502A
Application number: AU15455/02A
Authority: AU
Inventors: Karen Drucker
Original assignee: Smith and Nephew Inc
Current assignee: Smith and Nephew Inc
Priority date: 1997-12-11
Filing date: 2002-02-06
Publication date: 2002-03-21
Anticipated expiration: 2018-12-04
Also published as: AU768557B2

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION FOR A STANDARD PATENT .o Name of Applicant: Actual Inventors: Address for Service: Invention Title: Smith Nephew, Inc.

DRUCKER, Karen DAVIES COLLISON CAVE, Patent Attorneys, 1 Little Collins Street, Melbourne, 3000 Surgical Cutting Instrument The following statement is a full description of this invention, including the best method of performing it known to Q:\OPER\CAE\2002UAN 02\ 500960 COP 035DOC 4/2/02 P OPER'CAE 2500960di, 035 dc-OS02 02

-I-

SURGICAL CUTTING INSTRUMENT This invention relates to surgical instruments, and in particular to powered arthroscopic surgical instruments.

Powered arthroscopic surgical instruments typically include a rigid, stationary outer tube within which an inner tube is rotated by a motor: A cutting implement is disposed on the distal end of the inner tube. Tissue is exposed to the cutting implement through an opening in the distal end of the outer tube, and tissue or bone fragments cut by the cutting implement are often drawn through the interior of the inner tube along with irrigating fluid by the use of suction applied at the proximal end of the instrument. Examples of such surgical instruments are described in U.S. Patent Nos. 4,203,444, 4,274,414, 4,834,729, and 4,842,578.

In one aspect of the invention there is provided a surgical cutting instrument 15 comprising: a first member extending distally from a base along an axis and having distal and proximal ends, the first member being rotatable to transmit torque from e• the base to the distal end of the member; a cutter carried at the distal end of the first member, the cutter having distal 20 and proximal ends and defining a first cutting edge oriented in a right-handed direction and a second cutting edge oriented in a left-handed direction; and the distal end of the cutter defining a generally planar area that lies at an acute angle to the axis of the first member, the generally planar area intersecting the first and second cutting edges at respective first and second points.

One aspect of the invention is a surgical cutting instrument disposed generally along an axis, the cutting instrument comprising a first member extending distally from a base and having distal and proximal ends, the first member being rotatable to transmit torque from the base to the distal end of the member; a cutter carried at the distal end of the first member, the cutter having a first cutting edge defined by a symmetrical revolved surface.

P: OPER'CAE 2i00960 di 035 doc-050202 -2- Among other advantages, as the member rotates, the edge defined by the symmetrical revolved surface can cut tissue during a surgical procedure, e.g., medium tissue such as cartilage.

Preferred embodiments of this aspect include the following features.

The symmetrical revolved surface defines two cutting edges, one oriented in a right-handed direction and the other oriented in a left-handed direction. Both edges are forward-swept, and symmetrical with respect to one another about a 10 plane of symmetry. The symmetrical right-handed and left-handed cutting edges enable the instrument to cut, tissue as the member rotates either clockwise or counterclockwise. By selecting the appropriate direction of rotation, the cutter can *oo o thus be moved tangentially in either direction across the surface of the material being cut. For strength during cutting, an uninterrupted circumferential band 15 extends between the two edges. The distal end of the cutter defines a generally planar area that intersects the cutting edges at distal points. The planar area lies at a 300 to 900 650) to the longitudinal axis of the cutter, and includes a go ***notch.

20 A relatively rigid hollow outer member terminates at its distal end in a pair of longitudinally extending tabs. Each tab defines a pair of right-handed and lefthanded cutting edges, which edges define a pair of openings extending along the longitudinal axis of the outer member. The distal end of the second member is substantially entirely open to expose the distal end of the cutter.

Among other advantages, the generally planar area intersects the edges to form a point that facilitates the initiation of the cut. The angle at which the planar area lies to the axis of rotation of the instrument 300 to 750, preferably 650) determines the 3 "pointedness" of these cut-initiating points. Moreover, the edge of the generally planar surface forms an additional cutting edge that extends between the right-handed and left-handed cutting edges of the cutter.

In another aspect of the invention, a rotatable member of a surgical cutting instrument transmits torque to a cutter carried at its distal end. The cutter has forward-swept right-handed and lefthanded cutting edges. The rotatable member is coaxially disposed with and rotates within a relatively rigid hollow outer member. The distal end of the outer member is substantially entirely open to expose the distal end of the cutter Among other advantages, the substantially entirely open o .t 15 distal end of the outer member permits axial boring, or end-on °oooo cutting, by the forward-swept cutting edges.

Other features and advantages of the invention will be apparent from the description of the preferred embodiments, and •from the claims.

FIG. 1 is a front view of a surgical cutting instrument.

FIG. 2 is a sectional view of the surgical cutting instrument taken through line 2-2 in FIG. 1.

FIG. 3 is a side view of an outer tube of the surgical cutting instrument shown in FIG. 1.

FIG. 4 is a distal end view of the outer tube shown in FIG. 3.

FIG. 5 is a side view of an inner tube of the surgical cutting instrument shown in FIG. 1.

FIGS. 6-7 are front views of a distal region of the inner tube shown in FIG. 4 FIG. 8 is a sectional view of the inner tube taken through line 8-8 in FIG. Referring to FIGS. 1 and 2, a surgical cutting instrument suitable for cutting tissue, particularly medium tissue such as cartilage, during, e.g, arthroscopic knee surgery, includes an inner member 12 and an outer member 14. Tissue is cut at the distal end of the surgical cutting instrument 10 by a cutting implement Referring also to FIGS. 3 and 4, the outer member 14 includes a hollow outer tube 16, the proximal end of which is connected to a base 18. The outer tube 16 has a length of, e.g., 146.256 mm an outer diameter of 4.231 mm and an inner diameter of 3.590 mm 3.615 mm (0.140" 0.141"). The inner diameter of the outer tube 16 is constant along its length. The distal end of the outer tube 16 includes a pair of tabs 26, 28. The tabs 26, 28 extend longitudinally and are located along the circumference of the outer tube 16. Each one of the tabs 26, 28 defines a right-handed cutting edge 30, 34 and a left-handed cutting edge 32, 36.

The tabs 26, 28 define three openings in the distal end of the outer tube 16: two side-facing openings 38, 40 and one distal-end .opening 42. The tabs 26, 28 are configured so that the openings 38, 40, and 42 form one contiguous open area. Each of the tabs 26, 28 is, 2.564 mm (0.100") long with comers radiused to 0.385 mm The side-facing openings 38, 40 are substantially semicircular with a radius of 1.282 mm (0.050").

Referring to FIG. 5, inner member 12 includes an inner tube 20, the proximal end of which is connected to a drive shaft 22 (FIGS. 1 and The inner tube 20 has, a length of 176.231 mm (6.873") including the length of a cutter 44 discussed below, an outer diameter of 3.436 mm and an inner diameter of 2.641 mm 2.718 mm (0.103" 0.106"). The inner tube is inserted into the outer tube 16 so that both are coaxially disposed along a longitudinal axis 24. The inner tube 20 includes an internal passageway 52 that extends along the longitudinal axis 24 from the proximal to the distal end of the inner tube 20. The proximal end of the internal passageway 52 is connected to a suction source when the surgical cutting instrument 10 is in operation.

S.:i Referring to FIGS. 5-7, the cutter 44 is carried at the distal ~15 end of the inner tube 20. The outer diameter of the cutter 44 is larger than the outer diameter of the inner tube 20 to provide a closely toleranced fit with the inner diameter of the outer tube 16, 3.5692 mm 3.5820 mm (0.1392"- 0.1397") The cutter44 includes three cutting edges, a right-handed edge 46, a left-handed edge 48, and an upper edge 50. Lying in the U-shaped region defined by the three edges 46, 48, 50, an opening 54 is in fluid communication with the internal passageway 52 of the inner tube 20. The right-handed edge 46 is oriented in a clockwise direction along the outer circumference of the cutter 44, and the left-handed edge 48 is oriented in a counterclockwise direction along the outer circumference of the cutter 44. The upper edge 50 is located on the distal end of the cutter 44, and extends from the right-handed edge 46 to the left-handed edge 48. The three edges 46, 48, 50 are arranged symmetrically about a plane of symmetry 66 that extends along the longitudinal axis 24 and bisects the cutter 44.

6 The distal ends of the right-handed and left-handed edges 46, 48 terminate in two points. The right-handed edge 46 terminates at a right point 64 and the left-handed edge 48 terminates at a left point 62. The right point 64 is formed at the intersection of the right-handed edge 46 and the upper edge 50, and the left point 62 is formed at the intersection of the left-handed edge 48 and the upper edge 50. The right-handed and left-handed edges 46, 48 are "forward swept", i.e: the right point 64 projects in the clockwise direction, and the left point 62 projects in the counterclockwise direction.

Referring to FIGS. 5 and 8, the edges 46, 48, 50 and the opening 54 are formed by a revolved cut at the distal end of the :•:°.inner tube 20, by electro-discharge machining (EDM) in which 15 an electrode with a geometric shape is used to remove material from a closed-ended cutter "blank", a cup shaped metal item used to manufacture the cutter 44. The revolved cut is defined by a circular ~segment 80 that is rotated about a circumferential axis 78 that lies on the outer circumference of the cutter 44 and that extends parallel 20 to the longitudinal axis 24. The plane of symmetry 66 is the plane defined by the circumferential axis 78 and the longitudinal axis 24.

When viewed in a section taken along the plane of symmetry 66, the circular segment 80 has, a radius of 3.846 mm (0.150") that ~extends from an origin lying 1.615 mm (0.063") from the circumferential axis 78 in the plane of symmetry 66. The end points of the circular segment 80 define a chord that, has a length of 4.103 mm (0.160") and extends parallel to the longitudinal axis 24.

The revolved cut creates a revolved surface 58, shown in FIG. 7. The intersection of the revolved surface 58 and the outer circumference of the cutter 44 forms the right-handed edge 46 and 7 the left-handed edge 48. The intersection of the revolved surface 58 and a planar area 60 located on the distal end of the cutter 44 forms the upper edge 50. As shown in FIG. 5, the planar area 60 lies at an angle 82 to axis 24 in the plane of symmetry 66. The angle 82 measures between approximately 30 degrees and 90 degrees, e.g., degrees.

The cutter 44 has a solid region 74 of material that extends approximately 180 degrees around the outer circumference of the cutter 44 from the right-handed edge 46 to the left-handed edge 48.

This solid and continuous region 74 provides circumferential support ".for the edges 46, 48 during cutting.

The cutter 44 further includes a notch 68, as shown in FIGS.

15 6 and 7. The notch 68 runs along the planar area 60 and is bisected oo i by the plane of symmetry 66. The notch 68 intersects the planar area 60 forming two notch edges 70, 71. The notch edges 70, 71 are additional cutting edges that lie symmetrically, each on either *side of and parallel to the plane of symmetry 66. The notch 68 forms, a curved surface with a radius from 0.513 mm 0.641 mm (0.020"-0.025"), measuring 1.462 mm 1.615 mm (0.057"- 0.063") at its widest point, measuring 0.385 mm (0.015") in depth, and forming a notch angle 72 measuring 90 degrees.

When the inner tube 20 is inserted into the outer tube 16, the cutter 44 is positioned in close proximity to the tabs 26, 28. The right-handed and left-handed edges 46, 48 of the cutter 44 are periodically exposed through the side-facing openings 38, 40 as the inner tube 20 rotates relative to the outer tube 16 acting in conjunction with the cutting edges 30, 32, 34, 36 of the tabs 26, 28 to sever or shear tissue.

N When the inner tube 20 is fully inserted, the distance from the left and right points 62 and 64 to the ends of the tabs 26, 28 is 0.513 mm This short distance is tolerable because the tabs 26, 28 do not have lips that extend over and cover the points of the cutting edges when viewed in the axial direction. The instrument optionally utilizes a "blade lock" feature. When not rotating, the "blade lock" holds the edges 46, 48 in place against the tabs 26, 28 so that the cutter 44 is shielded and does not rotate as it is moved about the tissue. Therefore, when not rotating, the edges 46, 48 do not require "zeroing", i.e, the points 62, 64 do not need to be positioned underneath the lip to shield the edges 46, 48 and prevent rotation as the instrument 10 is moved within the tissue.

15 A lip requires an increase in the length of the tab so that the tab can be tapered from the lip to the desired width. The increased length as well as the lost exposure of the blade, which results from partially covering the blade with the lip, decreases the cutting ability of the blade. Because the distance between the points 62, 64 and the ends of the tabs 26, 28 can be reduced and because the cutting edges 46, 48 are not partially covered, cutting is improved, especially in the axial direction.

In operation, the cutter 44 can cut tissue in both directions of rotation: the right-handed edge 46 cuts tissue in cooperation with the left-handed cutting edges 30, 34 of the tabs when the cutter 44 rotates in a clockwise direction, and the left-handed edge 48 cuts tissue in cooperation with the right-handed cutting edges 32, 36 of the tabs when the cutter 44 rotates in a counterclockwise direction.

Tissue is severed in a shearing motion caused by an edge 46, 48 of i. i .o iXTli~Li.i"j~:-Ps~i; ~i~iijix~l~iii~- 9 the cutter 44 moving closely past one of the cutting edges 30, 32, 34, 36 of the outer tube 16.

Because the left and right points 62, 64 are "forward swept", the points 62, 64 initiate the cut. The left point 62 initiates the cut in the counterclockwise direction, and the right point initiates the cut in the clockwise direction.

Tissue can be cut laterally or longitudinally (also known as axial boring) through the distal-end opening 42. The short distance from the ends of the tabs 26, 28 to the points 62, 64 aids the cutting, especially during axial boring.

The structure of the cutter 44, with the edges 46, 48, 15 oriented around a single opening 54, allows the opening 54 to be large relative to the size of the blades. Thus, the surgical cutting instrument 10 is capab! of removing both relatively large fragments -,of tissue as well as relatively high volumes of tissue and fluid when suction is applied to the distal end of internal passageway 52. In 20 addition, because the cutter 44 contains only a single opening 54, °o the suction is not split between multiple openings.

Other embodiments are within the scope of the following claims.

For example, a revolved cut can be geometric shapes other than the shape used to form the revolved surface 58. Thus, the revolved cut can be, spherical, cylindrical, or ovoid. In addition, multiple revolved cuts could be made, thus forming an instrument that has multiple sets of opposed right-handed and left-handed cutting edges. The cutting edges defined by the revolved cut can .7 P.'OPER'CAE'250090 di' 035 doc 05/02'02 alternatively be asymmetrical. The revolved surface can be formed by techniques other than EDM, metal injection molding.

One or more of the cutting edges 30, 32, 34, 36, 46, 48, 50, 70 need not be smooth, but instead can be serrated.

The cutter also can have multiple openings similar to opening 54, oriented, along the solid region 74 or along the distal end in the planar area 60 to further facilitate the evacuation of severed tissue and fluid.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other 15 integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be .o taken as, an acknowledgment or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

Claims

1. A surgical cutting instrument comprising: a first member extending distally from a base along an axis and having distal and proximal ends, the first member being rotatable to transmit torque from the base to the distal end of the member; a cutter carried at the distal end of the first member, the cutter having distal and proximal ends and defining a first cutting edge oriented in a right-handed ":direction and a second cutting edge oriented in a left-handed direction; and 10 the distal end of the cutter defining a generally planar area that lies at an .:i acute angle to the axis of the first member, the generally planar area intersecting the first and second cutting edges at respective first and second points. .oeo°i

2. The surgical cutting instrument of claim 21 wherein the angle between the 1. 5 generally planar area and the axis of the first member is between 30 degrees and degrees.

3. The surgical cutting instrument of claim 22 wherein the angle is approximately 65 degrees.

4. The surgical cutting instrument of claim 21 wherein the generally planar area includes a notch.

The surgical cutting instrument of claim 21 wherein the first and second cutting edges are forward swept.

6. A surgical cutting instrument disposed generally along an axis, the cutting instrument comprising: a first member extending distally from a base and having distal and proximal ends, the first member being rotatable to transmit torque from the base to the distal end of the member; I i. P.'OPERCAE'2500960 diw 035 do-05,02;02 -12- a cutter carried at the distal end of the first member, characterised in that the cutting edges of the cutter are formed by a single cut of a symmetrical revolving cutting surface.

7. The surgical cutting instrument of claim 6 wherein the cutting edges comprise a first cutting edge oriented in a right-handed direction and a second cutting edge oriented in a left-handed direction.

8. The surgical cutting instrument of claim 7 wherein the cutting edges 10 comprise a first and second cutting edges are forward-swept.

9. The surgical cutting instrument of claim 7 wherein the first and second oeooo cutting edges are symmetrical with respect to one another about a plane of symmetry.

The surgical cutting instrument of claim 7 wherein the cutter comprises an uninterrupted circumferential band extending from the first cutting edge to the S"second cutting edge. 20

11. The surgical cutting instrument of claim 7 wherein the first and second cutting edges terminate in first and second distal points.

12. The surgical cutting instrument of claim 11 wherein the distal end of the cutter includes a generally planar area that intersects the first and second cutting edges at the respective first and second distal points.

13. The surgical cutting instrument of claim 12 wherein an angle between the planar area and a longitudinal axis of the cutter is between 30 degrees and degrees. P OPER'CAE 2500960 di 035 doc-05102102 -13-

14. The surgical cutting instrument of claim 13 wherein an angle between the planar area and a longitudinal axis of the cutter is between 30 degrees and degrees.

15. The surgical cutting instrument of claim 14 wherein the angle is approximately 64 degrees.

16. The surgical cutting instrument of claim 12 wherein the generally planar °:area includes a notch.

17. The surgical cutting instrument of claim 7 further comprising a relatively rigid hollow second member coaxially disposed around the first member, the second member having a proximal end and a distal end and the first member being rotatable within the second member.

18. The surgical cutting instrument of claim 17 wherein the second member defines a first opening extending along a longitudinal axis of the second member and corresponding to the location of the cutter. 20

19. The surgical cutting instrument of claim 18 wherein the first opening is defined by an opposed pair of right-handed and left-handed cutting edges.

The surgical cutting instrument of claim 19 wherein the first cutting edge moves towards and closely past the left-handed edge of the first opening as the first member rotates clockwise with respect to the second member.

21. The surgical cutting instrument of claim 19 wherein the second cutting edge moves closely past the right-handed edge of the first opening as the first member rotates counterclockwise with respect to the second member. P'OPER'C AE'25009O di' 035 doc-.050202 -14-

22. The surgical cutting instrument of claim 18 wherein the second member defines a second opening extending along the longitudinal axis of the second member and corresponding to the location of the cutter.

23. The surgical cutting instrument of claim 17 wherein the distal end of the second member is substantially entirely open to expose a distal end of the cutter.

24. The surgical cutting instrument of claim 23 wherein the distal end of the o: second member terminates in a pair of longitudinally extending tabs, wherein 10 longitudinal edges of the tabs define first and second openings extending along a longitudinal axis of the second member and corresponding to the location of the cutter.

The surgical cutting instrument of claim 6 wherein the first member defines 15 an internal passageway in fluid communication with an opening defined in the cutter.

26. A surgical cutting instrument disposed generally along an axis, the cutting instrument comprising: 20 a first member extending distally from a base and having distal and proximal ends, the first member being rotatable to transmit torque from the base to the distal end of the member; a cutter carried at the distal end of the first member, the cCitter defining a first cutting edge oriented in a right-handed direction and a second cutting edge oriented in a left-handed direction, the first and second cutting edges being forward-swept; a relatively rigid hollow second member coaxially disposed around the first member, the first member being rotatable within the second member characterised in that a distal end of the second member is substantially entirely open to expose a distal end of the cutter and that the cutting edges of the cutter are formed by a single cut of a symmetrical revolving cutting surface. li--ii -i~ P 'OPER'CAE'2500960 di, 035 do-05,0202

27. The surgical cutting instrument of claim 26 wherein the first and second cutting edges are symmetrical with respect to each other about a plane of symmetry.

28. The surgical cutting instrument of claim 26 wherein the first and second cutting edges terminate in first and second distal points.

29. The surgical cutting instrument of claim 28 wherein the distal end of the cutter includes a generally planar area that intersects the first and second cutting 10 edges at the respective first and second distal points. o oo oooo

30. The surgical cutting instrument of claim 29 wherein an angle between the ooo planar area and a longitudinal axis of the cutter is between 30 degrees and degrees. o *S w

31. The surgical cutting instrument of claim 30 wherein an angle between the planar area and a longitudinal axis of the cutter is between 30 degrees and degrees. 20

32. The surgical cutting instrument of claim 31 wherein the angle is "oSo° approximately 65 degrees.

33. A surgical cutting instrument disposed generally along an axis, the cutting instrument comprising: a first member extending distally from a base and having distal and proximal ends, the first member being rotatable to transmit torque from the base to the distal end of the member; a cutter carried at the distal end of the first member, the cutter having a first cutting edge defined by a symmetrical revolved surface.

34. The surgical cutting instrument of claim 33 wherein the first cutting edge is rs, Q;ii r~9-ri.n~i ~~i~i~ii lri r~ P 'OPER'CAE2500960 di, 035 doc-05,02,OSOO -16- oriented in a right-handed direction and wherein the symmetrical revolved surface further defines a second cutting edge oriented in a left-handed direction.

The surgical cutting instrument of claim 34 wherein the first and second cutting edges are forward-swept.

36. The surgical cutting instrument of claim 34 wherein the first and second cutting edges are symmetrical with respect to one another about a plane of symmetry.

37. The surgical cutting instrument of claim 34 wherein the cutter comprises an uninterrupted circumferential band extending from the first cutting edge to the second cutting edge.

38. The surgical cutting instrument of claim 34 wherein the first and second cutting edges terminate in first and second distal points.

39. The surgical cutting instrument of claim 38 wherein the distal end of the cutter includes a generally planar area that intersects the first and second cutting edges at the respective first and second distal points.

The surgical cutting instrument of claim 39 wherein an angle between the planar area and a longitudinal axis of the cutter is between 30 degrees and degrees.

41. The surgical cutting instrument of claim 40 wherein an angel between the planar area and a longitudinal axis of the cutter is between 30 degrees and degrees.

42. The surgical cutting instrument of claim 41 wherein the angle is approximately 65 degrees. P 'OPER CAE'2500960 div 035do-05i02'02 -17-

43. The surgical cutting instrument of claim 39 wherein the generally planar area includes a notch.

44. The surgical cutting instrument of claim 34 further comprising a relatively rigid hollow second member coaxially disposed around the first member, the second member having a proximal end and a distal end and the first member being rotatable within the second member.

The surgical cutting instrument of claim 44 wherein the second member defines a first opening extending along a longitudinal axis of the second member 00 and corresponding to the location of the cutter.

46. The surgical cutting instrument of claim 45 wherein the first opening is defined by an opposed pair of right-handed and left-handed cutting edges.

47. The surgical cutting instrument of claim 46 wherein the first cutting edge moves towards and closely past the left-handed edge of the first opening as the first member rotates clockwise with respect to the second member.

48. The surgical cutting instrument of claim 46 wherein the second cutting edge moves closely past the right-handed edge of the first opening as the first member rotates counterclockwise with respect to the second member.

49. The surgical cutting instrument of claim 45 wherein the second member defines a second opening extending along the longitudinal axis of the second member and corresponding to the location of the cutter. The surgical cutting instrument of claim 44 wherein the distal end of the second member is substantially entirely open to expose a distal end of the cutter.

P"OPER'CAE'2500960 di O35.do-050202 -18-

51. The surgical cutting instrument of claim 50 wherein the distal end of the second member terminates in a pair of longitudinally extending tabs, wherein longitudinal edges of the tabs define first and second openings extending along a longitudinal axis of the second member and corresponding to the location of the cutter.

52. The surgical cutting instrument of claim 33 wherein the first member defines an internal passageway in fluid communication with an opening defined in the cutter.

A surgical cutting instrument disposed generally along an axis, the cutting instrument comprising: a first member extending distally from a base and having distal and proximal ends, the first member being rotatable to transmit torque from the base to the distal end of the member; a cutter carried at the distal end of the first member, the cutter defining a S.i :first cutting edge oriented in a right-handed direction and a second cutting edge oriented in a left-handed direction, the first and second cutting edges being forward-swept; a relatively rigid hollow second member coaxially disposed around the first member, the first member being rotatable within the second member and a distal end of the second member being substantially entirely open to expose a distal end of the cutter.

54. The surgical cutting instrument of claim 53 wherein the first and second cutting edges are symmetrical with respect to each other about a plane of symmetry. The surgical cutting instrument of claim 53 wherein the first and second cutting edges terminate in first and second distal points.

P OPER'CAE 250090 div 035 doc-05! 0202 19-

56. The surgical cutting instrument of claim 55 wherein the distal end of the cutter includes a generally planar area that intersects the first and second cutting edges at the respective first and second distal points.

57. The surgical cutting instrument of claim 56 wherein an angle between the planar area and a longitudinal axis of the cutter is between 30 degrees and degrees.

58. A surgical cutting instrument substantially as herein described with 10 reference to the accompanying figures. DATED this 31st day of January, 2002 Smith Nephew, Inc. :by DAVIES COLLISON CAVE 15 Patent Attorneys for the Applicant i