Surgical device

Abstract: A surgical device including a handpiece (10) adapted to receive a surgical tool (12) is provided whereby in the handpiece is a motor (18) driven drive shaft (19) for rotating the tool about an axis, a static seal element sealed to the motor assembly, and dynamic seal element sealed to the drive shaft, the seal elements having mating sealing portions defining a face seal in a surface transverse to the axis of rotation of the drive shaft.

Description: The invention relates to surgical devices. More particularly the invention relates to motor driven handpieces which are adapted to receive rotatable surgical tools, and to devices comprising the handpiece and the surgical tool. Surgical devices, eg. for arthroscopic surgery, typically include a handpiece containing a motor and having a distal portion adapted to receive a surgical tool, eg. an arthroplasty resector. In such systems, the distal tip of the surgical tool usually defines a vacuum passage through which fluid and tissue are removed from a patient's body during surgery. The passage extends from the distal tip of the surgical tool through the tool and into a drain tube in the handpiece which is connected to a suction device. Sometimes, however, the fluid and tissue also enter the motor through the space created between the motor housing the rotating drive shaft, causing the motor to malfunction and corrode. It is an object of the present invention to prevent damage to the motor assembly of a surgical instrument from tissue or fluid removed from a patient's body during surgery. One known solution to this problem is to provide flexible lip seals or o-rings around the drive shaft which contact the surface of the drive shaft and seal it parallel to its axis of rotation. The o-rings and the lips of the lip seals, ie. those portions of the seals which contact the drive shaft, are very flexible, eg. formed of silicone rubber, or formed of a cover material and some type of filler such as polytetrafluoroethylene such as that sold under the trade name Teflon and a graphite compound. In addition, systems which use the O-ring and lip sealing techniques are also known to use close tolerance fitting of the bearings with the drive shaft to prevent the surgical device from rotating off centre and pulling away from a portion of the seal, thereby allowing fluids to enter the motor housing. EP-A-0190000 discloses a surgical instrument for removing body tissue having a hand piece according to the preamble of Claim 1 and comprising an auger-like helical cutter which is driven at speeds in excess of 1000 rpm within a stationary outer cylindrical sheath. The sheath has a pair of longitudinally-extending diametrically-opposed tab members each of which has a cutting edge which co-operates with the cutter. The end of the cutter is concave to present a fish-tail shape enabling it to effect an axial boring cut. US-A-3409213 discloses a centrifuge having a rotary seal suitable for allowing blood to be centrifuged in a sterile manner. The seal comprises a first rigid, low-friction member which contacts a moving rigid member with minimal friction to make a dynamic seal, and a second elastomeric member which provides a resilient static seal and a spring action force between the surfaces of the dynamic seal. According to the present invention there is provided a handpiece for receiving and engaging a rotatable surgical tool comprising a drive shaft for engaging said surgical tool and a motor assembly for rotating said drive shaft about its longitudinal axis; characterised in that the handpiece further comprises:- a static seal element sealed to said motor assembly and a dynamic seal element sealed to said drive shaft; wherein said static and dynamic seal elements have mating sealing portions which define a face seal in a surface which is transverse to the axis of rotation of the drive shaft. The present invention further provides a surgical device comprising a rotatable surgical tool and a handpiece as herein described adapted to receive and engage said surgical tool. Aptly the face seal is in a planar surface which more aptly, is perpendicular to the axis of rotation. The dynamic seal element may be biased against the static seal element by a plurality of circumferentially spaced springs. Suitably these springs act through an axially movable drive ring and a resilient buffer ring. The drive ring may surround the drive shaft and be rotatably keyed to the shaft and the dynamic seal element. A seal ring, for example, an o-ring can surround the drive shaft and provide a seal between the shaft and the dynamic seal element. The ring maintains a distance between the shaft and the dynamic seal element. The static seal element may be sealed to the handpiece housing by a pair of silicone o-rings, to prevent fluid from flowing past the motor assembly. In order to provide a good sealing engagement the dynamic seal element and the static seal may be flat lapped within three helium light bands. The advantages of the present invention include prevent fluid from entering the motor by providing the face seal transverse to the axis of rotation, particularly in situations where a fluid passageway from the surgical tool exposed the motor housing to fluid. In addition, the face seal is maintained regardless of whether the drive shaft wobbles, and motor vibrations in the handpiece are reduced. The seals between the dynamic seal element and the drive shaft, and between the static seal element and the handpiece housing, further protect the motor. The invention will be illustrated by reference to the accompanying drawings in which: Figure 1 is a plan view, partially cut away and in cross section of a handpiece according to the present invention. Figure 2 is an enlarged plan view, partially cut away and in cross section, of a portion of the handpiece shown in Fig. 1, including the drive shaft and the motor housing. Figure 3 is a plan view of the portion of the handpiece shown in Figure 2, but rotated approximately 90° and further cut away and in cross section to show additional detail. Figure 4 is a perspective view of a rotatable surgical tool used with the handpiece shown in Figure 1 and connectable to the drive shaft shown in Figures 2 and 3. Figure 4a is an enlarged perspective view, partially cut away and in cross section, of the detail area of Figure 4. Referring to Figure 1 a cylindrical surgical handpiece 10, has an outer housing 11, the length and diameter of which are sized and textured to fit comfortably into the palm of a surgeon. The distal end of the handpiece 10 is adapted to receive a rotatable surgical tool 12 (shown in dotted lines in Figure 1) eg. an arthroplasty resector (shown in Figure 4). The tool 12 engages a rotatable drive shaft 14 (shown in dotted lines in Figure 1) which is bonded, for example, by adhesive, to a rotatable motor shaft 16 extending distally from a conventional electric motor 18 (the motor shaft and the motor also shown in dotted lines in Figure 1) into a recess in the drive shaft 14. This bonding causes the drive shaft 14 to rotate with the motor shaft 16 relative to the handpiece 10, in turn rotating the tool 12. Extending from the proximal end of the handpiece 10, a power line 20 connects the motor 18 to a power source 22 or other control device to regulate the action of the tool 12, eg. its rotation speed. Referring to Figure 4, the distal end of the tool 12 defines an opening 13 which communicates with proximal portions of the tool. Thus, as shown in Figure 1, when the tool 12 is connected to the drive shaft 14, eg. by a flange 15 (shown in detail in Figure 4a) engaged in the distal end of the drive shaft, fluid can flow from a patient's body through an opening in the cutter 13 at the distal end of the tool and collect in a passageway 24 exposed to the drive shaft and motor housing. Referring again to Figure 1, the passageway 24 is defined by the open areas between the tool 12 and the inner walls of the handpiece 10, and between the drive shaft 14 and the inner wall of the handpiece. Most of the fluid exits the passageway 24 through a port 26 and a rotary valve 28 into a channel 30 connected to a drain tube 32. Fluid in the channel 30 is then suctioned through the drain tube 32 by a suction source 34 connected to the tube. Nevertheless, it is possible for some fluid to remain within the passageway 24, which presents a potential hazard should the fluid seep into the motor 18 and cause it to malfunction or corrode. As described below in connection with Figures 2 and 3, the present invention provides an improved sealing assembly to prevent fluid from reaching the motor 18. Referring to Figures 2 and 3, the handpiece 10 further contains a motor housing 36 which includes a ring gear section 38, a ball bearing section 40, and a shoulder section 42, which are pressed and swaged together to form a 3-piece assembly. Adjacent to the distal end of the motor housing 36 and surrounding the proximal end of the drive shaft 14 is a seal assembly 44 which includes a static seal ring 46 and a dynamic seal ring 48. The static ring 46 is rotationally fixed relative to the motor housing 36 by a pin 50 that extends from within the motor housing and fits into a slot 52 cut into the proximal face of the static ring. The static ring 46 is not otherwise attached to the motor housing 36, but rather is held in place against the motor housing by the adjacent dynamic ring 48 which rotates with the drive shaft 14. Referring in particular to Figure 2, a pair of silicone o-rings 53 seal between the static ring 46 and the main housing 11 of the handpiece, to prevent fluid from flowing past the motor assembly. In order that the dynamic ring 48 may rotate with the drive shaft 14, a cap ring 54 is screwed over a threaded portion of the distal U-shaped end of the drive shaft 14, thereby causing the cap ring to rotate with the drive shaft. Adjacent to the cap ring 54 is a spring ring 56 captured between the cap ring 54 and shoulder 55 (Figure 3) of shaft 14 so as to rotate with the shaft. Next, a drive ring 58 is rotatably connected to the spring ring 56 by a tab 60 on the drive ring which fits into a slot 62 cut into the spring ring. Thus, the drive ring rotates with the drive shaft 14. And finally, the dynamic ring 48 is rotatably connected to the drive ring 58 by a pair of tabs 64 (180° apart) which fit into slots 65 in the dynamic ring. Referring to Figure 3, in order to hold the dynamic ring 48 and the static ring 46 together and create a seal, a plurality of springs 66 (for example, nine in total, each may be approximately 6.35mm (0.25 inches) in length, 1.45mm (0.057 inches) in diameter, and formed of 1/4 free length 0.2mm (0.008 inch) wire) are circumferentially spaced around the drive shaft 14 in holes drilled through the spring ring 56. The spring 66 acts against the cap ring 56 and press the drive ring 58, which is axially movable along the drive shaft 14, toward the dynamic ring 48. Disposed around the drive shaft 14, between the drive ring 58 and the dynamic ring 48, is a buffer ring 68, which is preferably formed of silicone rubber. The buffer ring 68 acts as a resilient interface between the drive ring and the dynamic ring to insulate seal rings 46 and 48 from vibrations during operation of the device, and to avoid direct contact between the metal drive ring 58 and the distal surface of the dynamic ring 48, all to increase the operating life of the seal. Referring still to Figure 3, the dynamic ring 48 surrounding the drive shaft 14 is sealed thereto by an o-ring 70 disposed in a groove 71 formed in the drive shaft, thus closing a secondary fluid leakage path to the motor and maintaining a constant distance between the drive shaft 14 and the dynamic ring 48 should the drive shaft 14 begin to wobble, thereby helping to preserve the seal formed between the mating portions of the dynamic ring 48 and the static ring 46. Immediately adjacent to the o-ring, is a tapered proximal end portion 14a of the drive shaft 14. The tapered portion 14a is bonded as described above to the distal end of the motor shaft 16 (shown in dotted lines), thereby causing the drive shaft 14, and all components described above as being rotatably connected thereto, to rotate with the motor shaft 16 relative to the handpiece 10. In addition, surrounding the motor shaft 16, is a washer 72 which acts as a spacer between the tapered portion 14a and the motor housing 36. More specifically, the mating portions of the static ring 46 and the dynamic ring 48 form a face seal 76 in a plane perpendicular to the drive shaft axis 80. Generally, the face seal 76 is formed toward the inner edge of the static ring 46 because the proximal portion of the dynamic ring 46, ie. that portion which makes contact with the static ring 46, is stepped inwardly on the surface of its outer diameter so that the mating portion of the dynamic ring is approximately 1/3 the width of the mating portion of the static ring 46. Although the face seal 76 generally remains at the inner edge of the static ring 46, it can sometimes shift towards an outer edge of the static ring because of a lack of rigidity or a side to side wobble in the drive shaft 14. Nevertheless, the shape of the dynamic ring 48 and its positioning relative to the static ring 46 allow the drive shaft 14 to wobble relative to the motor housing 36 without disturbing the face seal 76, ie. the mating portion of the dynamic ring simply slides radially along the mating portion of the static ring. The dynamic and static rings 48 and 46 are preferably formed of silicon carbide and a carbon graphite composite, respectively. Also, in order to provide as effective a face seal as possible, the contacting faces of the dynamic and static rings 48 and 46 are polished to a very flat surface free of scratches and grooves, eg. flat lapped within two or three helium light bands. The solid arterials chosen are preferred over the more flexible arterials used in previous sealing arrangements, eg. polytetrafluoroethylene or silicone rubber, because they are not sensitive to the material or finish of the drive shaft. Previously used materials were prone to wear out quickly, in part because they contacted the drive shaft itself, a disadvantage that the placement of the rings in the present invention avoids. Finally, the harder materials used in the present invention are resistant to abrasives and other contaminants in the environment, thus ensuring a greater lifetime of use for the motor 18. The surgical device of the present invention provides several advantages over previously known surgical devices using o-ring or lip seal arrangements. Most notably, an effective face seal is achieved transversely to the axis of rotation of the drive shaft, and the seal is maintained regardless of whether the drive shaft wobbles. In addition, the materials of the sealing elements are not prone to warp or wear out quickly, nor are they likely to become contaminated. And finally, vibrations in the handpiece are reduced. In addition to the provision of handpieces as hereinbefore described, the present invention also provides a surgical device comprising a rotatable surgical tool and a handpiece in accordance with the invention which is adapted to receive and engage said tool. Tools for use with the surgical devices of the invention include rotatable cutters and shavers including, for example, the arthroplasty - surgical resector shown in Figure 4 of the accompanying drawings.

Claims: A handpiece (10) for receiving and engaging a rotatable surgical tool (12), comprising: a drive shaft (14) for engaging said surgical tool and a motor assembly (18) for rotating said drive shaft (14) about its longitudinal axis (80); characterised in that the handpiece (10) further comprises:- a static seal element (46) sealed to motor assembly (18) and a dynamic seal element (48) sealed to said drive shaft; wherein said static seal element (46) and said dynamic seal element (48) have mating sealing portions which define a face seal in a surface which is transverse to the axis of rotation of said drive shaft (14). A handpiece (10) as claimed in claim 1 further comprising a passageway (24) for communicating with said surgical tool to receive fluids flowing from a patient's body during surgery, said drive shaft (14) and the housing (36) of said motor assembly (18) being exposed to said passageway, said face seal (46,48) defining a barrier between said passageway (24) and the interior of said motor housing (36). A handpiece (10) as claimed in claim 2 further comprising: a port (26) in its outer wall; a conduit means (30) having one end connected to said port (26) and the other end connected to a suction means (34) for removing at least some of the fluids from said passageway through said port (26) and said conduit (30). A handpiece (10) as claimed in any one of claims 1 to 3 wherein said transverse surface is planar. A handpiece (10) as claimed in any one of claims 1 to 4 wherein said transverse surface is perpendicular to said axis (80). A handpiece (10) as claimed in any one of claims 1 to 5 wherein a plurality of springs (66) are disposed circumferentially about said axis to bias said dynamic seal element (48) axially against said static seal element (46). A handpiece (10) as claimed in claim 6 wherein said springs (66) are parallel to said drive shaft (14). A handpiece (10) as claimed in any one of claims 6 or 7 wherein a buffer ring (68) is disposed around said drive shaft (14) between said springs (66) and said dynamic seal element (48). A handpiece (10) as claimed in any one of claims 1 to 8 wherein said static seal element (46) and said dynamic seal element (48) are rings, the outer diameter of said static seal element (46) being greater than the outer diameter of said dynamic seal element (48). A handpiece (10) as claimed in claim 9 wherein said dynamic seal element (48) defines an inward step which reduces the outer diameter of said dynamic seal element (48) at said mating portions. A handpiece (10) as claimed in any one of claims 1 to 10 wherein the mating portions of said static seal element (46) and said dynamic seal element (48) are lapped flat to within 3 helium light bands. A handpiece (10) as claimed in any one of claims 1 to 11 wherein a portion of said drive shaft (14) defines a groove (70) and a ring seal (71) is positioned within said groove (70) to seal said drive shaft to said dynamic seal element (48). A handpiece (10) as claimed in 12 wherein said ring seal (71) is an O-ring. A handpiece as claimed in claim 12 or claim 13 wherein said ring seal (71) maintains a fixed distance between said drive shaft (14) and said dynamic seal (48). A handpiece as claimed in any of claims 1 to 14 wherein said dynamic seal element (48) is coupled to said drive shaft (14) through a member that is axially slidable along said drive shaft (14) and keyed to be rotatably fixed relative to said drive (14) and said dynamic seal element (48). A handpiece (10) as claimed in claim 15 wherein a plurality of springs (66) bias said member toward said dynamic seal element (48) thereby to urge said dynamic seal element (48) toward said static seal element (46). A handpiece (10) as claimed in claim 15 or 16 wherein a buffer ring (68) is disposed around said drive shaft (14) between said member and said dynamic seal element (48), said buffer ring (68) being adapted to act as a resilient interface between said member and said dynamic seal element (48). A surgical device comprising a rotatable surgical tool (12), and a handpiece (10) adapted to receive and engage said surgical tool (12) as defined in any one of claims 1 to 17.

Inventors: SJOSTROM DOUGLAS DANA, SJOSTROM, DOUGLAS DANA
Applicants: SMITH & NEPHEW DYONICS, SMITH & NEPHEW DYONICS INC
Application year: 1991
Main classification: A61B17
IPC codes: A61B17