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Dokumentenidentifikation EP1212173 11.09.2003
EP-Veröffentlichungsnummer 1212173
Titel DREHMOMENTBEGRENZER FÜR CHIRURGISCHEN GEBRAUCH
Anmelder Synthes AG Chur, Chur, Graubünden, CH
Erfinder YOUNG, Robert, West Chester, US
Vertreter derzeit kein Vertreter bestellt
DE-Aktenzeichen 60004376
Vertragsstaaten AT, BE, CH, CY, DE, DK, ES, FI, FR, GB, GR, IE, IT, LI, LU, MC, NL, PT, SE
Sprache des Dokument EN
EP-Anmeldetag 17.08.2000
EP-Aktenzeichen 009511726
WO-Anmeldetag 17.08.2000
PCT-Aktenzeichen PCT/CH00/00437
WO-Veröffentlichungsnummer 0001019571
WO-Veröffentlichungsdatum 22.03.2001
EP-Offenlegungsdatum 12.06.2002
EP date of grant 06.08.2003
Veröffentlichungstag im Patentblatt 11.09.2003
IPC-Hauptklasse B25B 23/14
IPC-Nebenklasse A61B 17/88   

Beschreibung[en]

The present invention relates to a device for adjusting and limiting the amount of torque applied to a bone screw during power insertion.

Locking screws, or bone screws, are commonly used during surgery to aid in the proper setting of bone fractures, e.g., to lock a plate to the bone across the area of the fracture in order to align and stabilise the bone fragments and to transfer the load from the bone to the plate. Bone screws are typically self-drilling and self-tapping and therefore require insertion by a drill or other power device, which typically rotate at speeds of the order of 1,000 RPM. If all the torque of the drill were continuously transmitted to the screw head, however, the screw would strip once it meets a certain resistance. As a result, a device is needed for use in a surgical setting to limit the amount of torque that is applied to the screw head.

Torque limiting devices have been developed for other applications to limit the amount of torque applied by a power tool to a workpiece. Examples of prior art devices include those disclosed in U.S. Patent Nos. 5,437,524, 5,004,054, 4,867,019, 4,712,456, and 4,262,501. None of these devices, however, was designed for use in a surgical setting. Tests performed on certain of these prior art devices show that they cannot be autoclaved, as required for use in the sterile environment of an operating room. For example, prior art devices typically use heavy greases or oils that cannot be sterilised or that degrade if autoclaved. In addition, prior art devices commonly use a coil spring to establish the drive connection between the drive plates. The elasticity of a coil spring may change, however, with repeated exposure to the high temperatures required for autoclaving, which affects the ability of the operator to set accurately the maximum torque exerted by the torque limiter. Also, prior art devices accumulate internally dust, grit, or rust as a result of abrasion of their moving parts, which in turn affects the ability to autoclave the device.

From DE-A 33 44 600 a torque limiting device is known according to the preamble of claim 1. The recesses in this known device - receiving the torque transmitting balls - are of spherical shape. From US-A-3 942 337 another torque limiting device is known according to the preamble of claim 1. The recesses in this known device - receiving the torque transmitting balls - are of prismatic shape. In both known devices the rolling action of the balls into and out of the recesses has to occur abruptly which will lead to undesired high friction.

From German Utility Model DE-U 92 00 980 a further torque limiting device is known according to the preamble of claim 1. The recesses in this known device - receiving the torque transmitting balls - are made in the shape of sectors with constant radial width. Such a shape is disadvantageous because the balls are not held firmly in the elongated sector. Besides since the ball will always be positioned at one of the ends of these sectors (in the rotational phase) the same drawbacks as described above for the spherical recesses applies.

As the above discussion illustrates, there is a need for a torque limiting device that can be used in a surgical setting.

The present invention provides a torque limiting device for surgical use as defined in claim 1. In the preferred embodiment, the torque limiting device comprises: (a) a base unit; (b) a housing; (c) an output shaft, about which is mounted a flange; (d) a drive connection; and (e) an elastic element. The base unit, which is preferably screwed into the housing, serves to transmit the rotational energy from the power drill into the drive connection of the device. The drive connection comprises a plurality of transmission balls engaged between divots in the inner surface of the base unit and complementary recesses in the opposing surface of the flange, which is mounted on the output shaft that is operatively connected to the screw-driving bit. The transmission balls are maintained in the divots by the force of a plurality of spring washers, which acts between the flange on the output shaft and the end of the housing opposite the base unit. As the screw tightens in the bone, it will exert a torque on the transmission balls, such torque being transmitted through the output shaft and the flange in which the balls are engaged. The torque generated by the screw is opposite to that generated by the force of the elastic element. Once the counter-torque generated by the screw exceeds the torque generated by the force of the elastic element, the counter-torque will force the balls from the divots in the base unit, thereby severing the drive connection between the base unit and the output shaft and preventing the screw from being overtightened. The maximum torque applied to the screw can be adjusted by screwing the base unit into or out of the housing, thereby compressing or relaxing the elastic element and accordingly increasing or decreasing the force - and hence the torque - exerted by the elastic element on the transmission balls.

The torque limiting device is designed to sustain the high revolutions (of the order of 1,000 RPM) and sterilization procedures required for use in a surgical setting. In the preferred embodiment, the divots in the base unit are shaped in such a manner as to ease the rolling action of the transmission balls into and out of such divots, thereby reducing the abrasion of the moving parts and hence the amount of dirt, grit, or rust that may accumulate as a result of repeated use and autoclaving. This feature also eliminates the need for heavy lubricating oils or greases, which cannot be sterilized or which degrade under high temperatures. The preferred embodiment also uses a plurality of spring washers, instead of a coil spring, as the elastic element. The elasticity of the spring washers changes very little after initial exposure to the high temperatures required for autoclaving. Although a coil spring or other elastic element might be used in the alternative, the elasticity of a coil spring may continually change with repeated autoclaving, thereby impeding the ability to adjust accurately the maximum torque setting of the device. Accurate adjustment of the device over a wide range of torque settings is also made possible by the feature of screwing the base unit into and out of the housing.

Other features of the invention are set forth below.

Brief Description of Drawings

Preferred features of the present invention are disclosed in the accompanying drawings, wherein similar reference characters denote similar elements throughout the several views, and wherein:

  • FIG. 1 shows an exploded view of an embodiment of the torque limiting device;
  • FIG. 2 shows an assembled sectional side view of the present invention according to FIG. 1;
  • FIG. 3 shows an external view of the assembled invention according to FIG. 2;
  • FIG. 4 is a cross-sectional view of the output shaft and flange on line I - I of FIG 1, with the housing and transmission balls removed; and
  • FIG. 5 is a cross-sectional view of the inner surface of the base unit on line II - II of FIG. 1, with the output shaft, transmission balls, and housing removed.

Detailed Description of the Preferred Embodiments

Referring to FIGS. 1-5, the preferred embodiment of the present invention comprises five main components:

  • (a) the base unit 3, which is formed of one piece comprising input stem 4 and hub 5;
  • (b) the shaft 9, comprising the interior shaft portion 10, flange 11, and output shaft portion 13;
  • (c) the external housing 24;
  • (d) a drive connection 30, comprising transmission balls 16 occupying divots 29 in hub 5 and through holes 12 in flange 11; and
  • (e) an elastic element 18, comprising a plurality of spring washers 19.

The invention is assembled in the following manner:

Base unit 3 is constructed of a single unit comprising the input stem 4 and the hub 5. The input stem 4 is designed such that it may be secured in the chuck of a drill, rotary tool, or other such instrument. The outer surface of the hub 5 is threaded (not shown) so that it may be screwed into the large threaded opening 25 at one end of the housing 24. The set screw 23 is screwed into the small threaded opening 26 in the surface of the housing 24 to engage one of the grooves 28 in the side of hub 5, thereby preventing the base unit 3 from turning relative to the housing 24. The base unit 3 is further secured in place by means of the snap ring 2 and the rear housing plate 1. The base unit 3 and housing 24 will therefore rotate as a single unit, either with or about the shaft 9, in the manner described in a later paragraph.

The shaft 9, partially located within the housing 24, is constructed of a single piece comprising the small interior shaft portion 10, the flange 11, and the output shaft portion 13. The interior shaft portion 10 rotates within the recess 6 in the hub 5. The ball bearings 7 and dowel pin 8 also fit in the recess 6 to facilitate rotation of the interior shaft portion 10. The interior shaft portion 10 is joined to the flange 11, which is joined to the output shaft portion 13, which extends from the flange 11 through the small opening 27 in the housing 24 opposite the large threaded opening 25. At the end of the output shaft portion 13 is an opening 14, in which is inserted a standard coupling device 32 for holding the drill bit, screwdriver bit, or like object (not shown). The coupling device 32 is secured in the opening 14 by means of a dowel pin 31, which passes through the hole 15 in the output shaft portion 13 and a hole (not shown) in the coupling device 32. The input stem 4, hub 5, interior shaft portion 10, flange 11, output shaft portion 13, housing 24, and the coupling device 32 all share a common axis of rotation.

The drive connection 30 between the hub 5 and the output shaft portion 10 is established by means of a plurality of transmission balls 16. In the preferred embodiment, the transmission balls 16 are located in the through holes 12 of the flange 11, said through holes 12 being shown in FIG. 4. The transmission balls 16 are maintained in the through holes 12 by the flat bearing washer 17, which is disposed about the output shaft 13 to cover the face of the flange 11 opposite the hub 5. The surface of the flat bearing washer 17 is hardened to reduce wear and abrasion, thereby reducing the amount of dust, grit or rust that may accumulate in the device. In the alternative, the transmission balls 16 could be located in recesses (not shown), ratherthan through holes, in the surface of the flange 11, although this would require the more complicated process of hardening the surface of the flange 11 instead of the separate flat bearing washer 17. The use of through holes instead of recesses in the flange 11 offers the additional advantage that there is no axial motion of the shaft 9 and correspondingly no hammering or impact on the drill bit or screw. In either embodiment, the diameter of each transmission ball 16 is somewhat larger than the depth of the through hole 12 or recess in flange 11, such that a small portion of each transmission ball 16 extends beyond the flange 11 to engage the divots 29 in the inner surface of the hub 5. The number and placement of the divots 29 correspond to the number and placement of the through holes 12 in flange 11, such that each transmission ball 16 can simultaneously engage both a divot 29 and a through hole 12.

The drive connection 30 between the base unit 3 and shaft 9 is maintained by means of an elastic element 18, which in the preferred embodiment comprises a plurality of spring washers 19. Spring washers 19 are preferred because their elasticity will not be affected by the high temperatures required for repeated autoclaving, although a coil spring or other elastic element might be used as well. The spring washers 19 exert a force against the flat bearing washer 17 at one end and the thrust bearing washer 20 at the other end. The thrust bearing washer 20 has an opening 21, through which passes the output shaft portion 13. A plurality of ball bearings 22 is disposed about the output shaft portion 13 in the opening 21 in order to facilitate the rotation of the output shaft portion 13 in the housing 24.

The force of the spring washers 19 against the flat bearing washer 17 maintains the transmission balls 16 in the divots 29 in the hub 5, thereby establishing a drive connection between the base unit 3 and the shaft 9. Rotation of the stem 4 by a rotary or other device thereby results in rotation of the drill bit in output shaft 13. As the screw (not shown) tightens in the bone, the screw will exert a counter-torque on the output shaft portion 13, which will be transmitted to the transmission balls 16 by flange 11. Once the counter-torque on the transmission balls 16 exceeds the torque from spring washers 19, the counter-torque will cause the transmission balls 16 to disengage from the divots 29, thus severing the drive connection 30 between the input stem 4 and the shaft 9 and thereby preventing overtightening of the screw. In the preferred embodiment, the divots 29, shown in FIG. 5, are shaped by using a ball end mill to form the indentations as the base unit 3 is rotated about its axis. The resultant shape of the divots 29, which might be called a curved ellipse, eases the rolling action of the transmission balls 16 into and out of such divots 29, thereby reducing the abrasion of the moving parts and hence the amount of dirt, grit, or rust that may accumulate as a result of repeated use and autoclaving. This shape also eliminates the need for heavy lubricating oils or greases, which cannot be sterilized or which degrade with autoclaving. The curved ellipse shape is also symmetrical, in that the transmission balls 16 encounter the same shape regardless of whether the transmission balls 16 are moving about the axis of rotation of the device in a clockwise or counterclockwise direction. This symmetrical feature permits the device to be used for either right-handed or left-handed screws, or for either the insertion or removal of such screws.

The maximum torque that may be exerted on the screw is a function of the force exerted by the spring washers 19 against the transmission balls 16. Thus, the maximum torque exerted on the screw can be adjusted by increasing or decreasing the force exerted by the spring washers 19, which can be accomplished by decreasing or increasing the effective length occupied by the spring washers 19 within the housing 24. In the preferred embodiment, the length occupied by the spring washers 19, and thus the maximum torque exerted on the screw, is adjusted by loosening the set screw 23; screwing base unit 3 into or out of the housing 24 until the desired torque setting is reached; and then retightening the set screw 23 to engage one of the grooves 28 in the hub 5 to secure the base unit 3 in the housing 24. The screwing feature of base unit 3 and the presence of multiple grooves 28 to engage set screw 23 permit the accurate adjustment of the maximum torque of the invention over a wide range of torque settings.

All of the components of the preferred embodiment described above are constructed of stainless steel or other material that will reduce wear and abrasion, can be sterilized, and can endure repeated autoclaving. Although other materials might be used as well, there may be a resultant degradation in performance, accuracy, or endurance.

Further, it should be understood that variations and modifications within the scope of the invention may occur to those skilled in the art to which the invention pertains. The scope of the present invention is defined by the appended claims.


Anspruch[de]
  1. Drehmomentbegrenzendes Gerät zur Anwendung in der operativen Medizin, umfassend:
    • ein drehbares Gehäuse (24) mit einem ersten und einem zweiten Ende;
    • eine Grundeinheit (3), die mit dem ersten Ende des Gehäuses (24) in Eingriff steht, wobei die Grundeinheit (3) einen Eingangsstiel (4) aufweist, der mit einer Drehvorrichtung in Eingriff steht;
    • eine Abtriebswelle (13), die sich durch das zweite Ende des Gehäuses (24) erstreckt, wobei die Abtriebswelle (13) mit einem Flansch (11) versehen ist, der um die Welle (13) angeordnet ist, wobei der Flansch (11) und die Grundeinheit (3) nebeneinanderliegende Flächen haben;
    • mehrere Ausnehmungen in den Flächen der Grundeinheit (3) und des Flansches (11), wobei die Ausnehmungen gegenseitig ausgerichtet angeordnet werden können;
    • eine Kugel (16), die in und zwischen jedem Paar der gegenüberstehenden Ausnehmungen angeordnet ist, und
    • ein elastisches Element (18), das um die Abtriebswelle (13) zwischen dem Flansch (11) und dem zweiten gegenüberstehenden Ende des Gehäuses (24) angeordnet ist, wobei das elastische Element (18) einen Druck aufbringt, um eine Antriebsverbindung zwischen den Kugeln (16) und den gegenüberstehenden Flächen herzustellen, wobei die Antriebsverbindung verstärkt wird, wenn das von dem biegsamen Element (24) auf die Kugeln (16) aufgebrachte Drehmoment von dem Gegendrehmoment überschritten wird, das von dem Flansch (11) auf die Kugeln (16) aufgebracht wird,
    dadurch gekennzeichnet, dass

    die Ausnehmungen in der Fläche der Grundeinheit (3) in Form gebogener Ellipsen (29) ausgebildet sind, wobei die Enden der gebogenen Ellipsen auf einem durch die Drehung der Grundeinheit (3) um ihre Achse gebildeten Kreis liegen, um das Rollen der Kugeln (16) in die Ausnehmungen in der Grundeinheit (3) hinein und aus ihnen heraus zu erleichtern.
  2. Drehmomentbegrenzendes Gerät nach Anspruch 1, wobei die Grundeinheit (3) durch Schrauben mit dem ersten Ende des Gehäuses (24) in Eingriff gebracht wird und das Drehmoment durch Schrauben der Grundeinheit (3) in das Gehäuse (24) hinein oder aus ihm heraus verstellbar ist, wodurch das elastische Element (18) zusammengedrückt oder auseinandergezogen wird.
  3. Drehmomentbegrenzendes Gerät nach Anspruch 1 oder 2, wobei sich die Ausnehmungen in der Fläche des Flansches (11) durch den Flansch (11) erstrecken und weiter ein Scheibenelement umfassen, das um das Wellenelement zwischen dem Flansch (11) und dem elastischen Element (18) angeordnet ist, um die Kugeln (16) in den Ausnehmungen in dem Flansch (11) zu halten.
  4. Drehmomentbegrenzendes Gerät nach einem der Ansprüche 1 bis 3, wobei die Ausnehmungen in der Fläche der Grundeinheit (3) symmetrisch sind, so dass die Kugeln (16) unabhängig davon, ob sich die Kugeln (16) im Uhrzeigersinn oder entgegen dem Uhrzeigersinn um die Drehachse des Gerätes drehen, auf dieselbe Form der Ausnehmung treffen.
  5. Drehmomentbegrenzendes Gerät nach einem der Ansprüche 1 bis 4, wobei das biegsame Element (18) mehrere Federringe (19) umfasst.
  6. Drehmomentbegrenzendes Gerät nach einem der Ansprüche 1 bis 5, wobei das Gehäuse (24), die Grundeinheit (3), der Eingangsstiel (4), die Abtriebswelle (13), der Flansch (11), die Kugeln (16), das Scheibenelement und das elastische Element (18) aus Edelstahl hergestellt sind.
  7. Drehmomentbegrenzendes Gerät nach einem der Ansprüche 1 bis 6, wobei alle Bauteile der Vorrichtung im Autoklaven sterilisierbar sind, ohne die Funktion der Vorrichtung zu beeinträchtigen.
Anspruch[en]
  1. A torque-limiting device for surgical use, comprising:
    • a rotatable housing (24) having first and second ends;
    • a base unit (3) engaged within the first end of said housing (24), said base unit (3) having an input stem (4) for engagement with a rotary device;
    • an output shaft (13) extending through the second end of said housing (24), said output shaft (13) having a flange (11) disposed about said shaft (13), said flange (11) and said base unit (3) having adjacent faces;
    • a plurality of recesses in said faces of said base unit (3) and said flange (11), said recesses being positionable for mutual alignment;
    • a ball (16) located in and between each pair of said opposing recesses; and
    • an elastic element (18) disposed about said output shaft (13) between said flange (11) and said second opposing end of said housing (24), said elastic element (18) exerting a force to maintain a drive connection between said balls (16) and said opposing faces, said drive connection being severed when the torque exerted on said balls (16) by said elastic element (24) is exceeded by the counter-torque exerted on said balls (16) by said flange (11),
    characterized in that

    said recesses in the face of said base unit (3) are formed in the shape of curved ellipses (29), in which the ends of said curved ellipses lie on a circle formed by the rotation of said base unit (3) about its axis, to facilitate the rolling action of said balls (16) into and out of said recesses in said base unit (3).
  2. The torque-limiting device of claim 1, wherein the base unit (3) is threadably engaged in the first end of said housing (24), and the torque is adjustable by screwing said base unit (3) into or out of said housing (24), thereby causing said elastic element (18) to compress or expand.
  3. The torque-limiting device of claim 1 or 2, wherein said recesses in the face of said flange (11) extend through said flange (11), and further comprising a disc unit disposed about said shaft unit between said flange (11) and said elastic element (18) to maintain said balls (16) in said recesses in said flange (11).
  4. The torque-limiting device according to one of the claims 1 to 3, wherein said recesses in the face of said base unit (3) are symmetrical, such that said balls (16) encounter the same shape of said recess regardless of whether said balls (16) are moving about the axis of rotation of said device in a clockwise or counterclockwise direction.
  5. The torque-limiting device according to one of the claims 1 to 4, wherein the elastic element (18) comprises a plurality of spring washers (19).
  6. A torque-limiting device according to one of the claims 1 to 5, wherein said housing (24), said base unit (3), said input stem (4), said output shaft (13), said flange (11), said balls (16), said disc unit, and said elastic element (18) are constructed of stainless steel.
  7. A torque-limiting device according to one of the claims 1 to 6, wherein all components of said device are sterilisable by autoclaving without affecting the operation of the device.
Anspruch[fr]
  1. Dispositif de limitation du couple destiné à utilisation en chirurgie, qui comprend :
    • un boîtier rotatif (24) qui présente une première et une deuxième extrémité;
    • une unité de base (3) engagée dans la première extrémité dudit boîtier (24), ladite unité de base (3) présentant une tige d'entrée (4) destinée à être engagée sur un dispositif rotatif;
    • un arbre de sortie (13) qui traverse la deuxième extrémité dudit boîtier (24), ledit arbre de sortie (13) présentant une bride (11) disposée autour dudit arbre (13), ladite bride (11) et ladite unité de base (3) présentant des surfaces adjacentes;
    • une pluralité de creux ménagés dans lesdites faces de ladite unité de base (3) et de ladite bride (11), lesdits creux pouvant être positionnés de manière à être mutuellement alignés;
    • une bille (16) située dans et entre lesdits creux opposés de chaque paire; et
    • un élément élastique (18) disposé autour dudit arbre de sortie (13) entre ladite bride (11) et ladite deuxième extrémité opposée dudit boîtier (24), ledit élément élastique (18) exerçant une force pour maintenir une liaison d'entraînement entre lesdites billes (16) et lesdites surfaces opposées, ladite liaison d'entraînement étant interrompue lorsque le couple exercé sur lesdites billes (16) par ledit élément élastique (24) est déplacé par le contre-couple exercé sur lesdites billes (16) par ladite bride (11),
    caractérisé en ce que

       lesdits creux ménagés dans la surface de ladite unité de base (3) ont la forme d'ellipses incurvées (29), les extrémités desdites ellipses incurvées étant situées sur un cercle formé par la rotation de ladite unité de base (3) autour de son axe, pour faciliter l'action de roulement desdites billes (16) dans et hors desdits creux de ladite unité de base (3).
  2. Dispositif de limitation du couple selon la revendication 1, dans lequel l'unité de base (3) est engagée par filetage dans la première extrémité dudit boîtier (24), le couple pouvant être ajusté en vissant ou en dévissant ladite unité de base (3) dans ledit boîtier (24) pour ainsi amener ledit élément élastique (18) à se comprimer ou à se détendre.
  3. Dispositif de limitation du couple selon la revendication 1 ou 2, dans lequel lesdits creux ménagés dans la surface de ladite bride (11) traversent ladite bride (11), et comprenant en outre une unité de disque disposée autour de ladite unité d'arbre entre ladite bride (11) et ledit élément élastique (18) pour maintenir lesdites billes (16) dans lesdits creux de ladite bride (11).
  4. Dispositif de limitation du couple selon l'une des revendications 1 à 3, dans lequel lesdits creux ménagés dans la surface de ladite unité de base (3) sont symétriques de telle sorte que lesdites billes (16) rencontrent la même forme desdits creux que lesdites billes (16) se déplacent autour de l'axe de rotation dudit dispositif dans le sens des aiguilles d'une montre ou dans le sens contraire des aiguilles d'une montre.
  5. Dispositif de limitation du couple selon l'une des revendications 1 à 4, dans lequel l'élément élastique (18) comprend une pluralité de rondelles de ressort (19).
  6. Dispositif de limitation du couple selon l'une des revendications 1 à 5, dans lequel ledit boîtier (24), ladite unité de base (3), ladite tige d'entrée (4), ledit arbre de sortie (13), ladite bride (11), lesdites billes (16), ladite unité de disque et ledit élément élastique (18) sont réalisés en acier inoxydable.
  7. Dispositif de limitation du couple selon l'une des revendications 1 à 6, dans lequel tous les composants dudit dispositif peuvent être stérilisés à l'autoclave sans affecter le bon fonctionnement du dispositif.






IPC
A Täglicher Lebensbedarf
B Arbeitsverfahren; Transportieren
C Chemie; Hüttenwesen
D Textilien; Papier
E Bauwesen; Erdbohren; Bergbau
F Maschinenbau; Beleuchtung; Heizung; Waffen; Sprengen
G Physik
H Elektrotechnik

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