Abstract:
A dynamometric tool for medical use includes: a hollow grip ( 10 ), an instrument holder ( 30 ) designed to be secured in rotation to an instrument configured to co-operate with an object to be screwed, the instrument holder being extended by a shaft ( 18 ) pivoting inside the grip, the instrument holder ( 30 ) being frictionally connected to the grip via a spring member ( 34 ) arranged between the shaft ( 18 ) and the grip ( 10 ). According to the invention, the spring member ( 34 ) includes plural blades ( 36 ) elastically deformable in a substantially radial direction.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to the field of tools for medical use. It more particularly concerns a dynamometric tool intended to tighten or loosen screws or various objects comprising a screw pitch, during a surgical procedure. 
         [0002]    It is, in fact, particularly important to avoid applying uncontrolled tightening torques, for example in the case where a plate is fixed on a bone to repair a fracture. If the tightening applied is excessive, this may lead to crushing the bone and further damaging it. 
       PRIOR ART 
       [0003]    Known in the prior art are dynamometric tools for screwing, and sometimes unscrewing, various objects, in particular screws for fixing reconstructive elements in reparative surgery. As an example of application, plates can be screwed into fractured bones in order to facilitate their repair. A tool of this type comprises:
       a grip so that the surgeon can manipulate it, and   an instrument holder designed to be secured in rotation to an instrument configured to cooperate with the object to be screwed.       
 
         [0006]    In certain tools of this type, the holder is extended by a shaft pivoting inside the grip. It is frictionally connected to the grip via a spring member arranged between the shaft and the grip. The friction is provided by two Breguet toothings, i.e. saw-shaped serrated toothings, one being integral with the holder and the other being secured in rotation with the grip. Springs press the two Breguet toothings against each other so as to secure the holder and the grip in rotation. When the tightening torque is greater than the friction imposed between the two Breguet toothings by the springs, these rub against each other and escape each other. The instrument holder is then no longer driven in rotation by the grip. The maximal applicable tightening torque can be adjusted by modulating the pressure exerted by the springs. 
         [0007]    The friction created between the toothings is particularly significant and it is necessary, in order to obtain acceptable precision and longevity of the tool, for the Breguet toothings to be metallic. They, as well as the springs, are made in stainless steel, allowing surgical use which is as hygienic as possible. It is, however, necessary to grease the metallic parts in friction, which is not very satisfactory from a sanitary perspective, since a risk of grease flow outside the tool exists during sterilization operations. Moreover, the precision of such a tool is not very satisfactory (+/−10%) and it is necessary to perform calibrations regularly. 
         [0008]    Furthermore, when the maximal tightening torque is reached and the toothings escape each other, this causes jumps in the longitudinal direction of the tool, which is not pleasant for the surgeon and can cause him to make a clumsy gestures. 
         [0009]    Moreover, the materials used to produce this tool make it heavy and not very practical. 
         [0010]    The present invention therefore aims to propose a dynamometric tool free of the abovementioned drawbacks and which, in particular, is precise, light, and easy to manipulate. Particularly, when the maximal tightening torque is reached, no parasitic jumps are felt by the user. 
       BRIEF DESCRIPTION OF THE INVENTION 
       [0011]    More precisely, the invention concerns a dynamometric tool for medical use comprising:
       a hollow grip,   an instrument holder designed to be secured in rotation to an instrument configured to cooperate with an object to be screwed, said instrument holder being extended by a shaft pivoting inside the grip.       
 
         [0014]    The instrument holder is frictionally connected to the grip via a spring member arranged between the shaft and the grip. 
         [0015]    According to the invention, the spring member comprises a plurality of blades elastically deformable in a substantially radial direction. 
         [0016]    According to one advantageous embodiment, the spring member comprises a plurality of blades arranged primarily in non-radial directions. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0017]    Other details will appear more clearly upon reading the following description, done in regard to the appended drawings, in which: 
           [0018]      FIG. 1  is a longitudinal cross-sectional view of the device according to the invention; 
           [0019]      FIG. 2  is a transverse cross-sectional view of the grip, comprising a close-up plane of one area of this part, 
           [0020]      FIG. 3  particularly illustrates one embodiment of a spring member particularly adapted for implementation of the tool according to the invention, and 
           [0021]      FIGS. 4   a  and  4   b  show, in cross-section and top view, respectively, a second embodiment of a spring member. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]      FIG. 1  shows a grip  10 , with a longitudinal axis AA. Along this axis, the body  10  is passed through by a cylindrical channel  12 . A first end of the grip is provided with a screw pitch  10   a  to cooperate with a first stopper  14 . The latter part comprises a hole  16  intended to allow the passage of a shaft  18  which will be described in more detail below. 
         [0023]    The second end of the grip is also provided with a screw thread  10   b  to cooperate with a second stopper  22 . In the illustrated embodiment, this is extended by a rod  24  which can be connected to an apparatus not shown, provided with an engine to cause the rod to rotate. In variation, a sleeve can be fixed around the rod  24  to extend the grip  10  and facilitate manipulation of the tool. 
         [0024]    From the inside of the body  10 , the walls of the second stopper  22  form a housing  26  whereof the bottom has a cylindrical orifice  28  intended to receive the end of the shaft  18 . 
         [0025]      FIG. 2  is a detailed illustration of an embodiment of the structure of the channel  12  whereof the inner wall has a succession of hollows  29 , typically with a generally cylindrical shape, oriented along the axis AA. The hollows  19  occupy the entire length of the channel between the two thread pitches  10   a  and  10   b.    
         [0026]    In  FIG. 1  is also illustrated a holder  30  of the type known by one skilled in the art, of a nature to be secured in rotation to an instrument configured to cooperate with an object to be screwed. The part of the holder providing the connection with the instrument is not in itself part of the invention and will not be described in detail. 
         [0027]    The instrument holder  30  is extended by the previously mentioned shaft  18 . This is sized so as to be able to go through the hole  16 , take a position inside the channel  12  of the grip  10 , while its free end takes a position in the housing  26  and in the orifice  28 . More precisely, the shaft  18  comprises a first portion  18   a  adjusted to the dimension of the hole  16 . Then, going away from the part of the instrument holder intended to receive an instrument, a second portion  18   b  intended to be housed in the channel  12 . The second portion  18   b  is structured so as to have a typically star-shaped section, and thus forms a male member able to be connected in rotation with a female member having a corresponding shape. Lastly, the shaft ends with a third portion  18   c  intended to assume a position in the housing  26  and by a fourth portion  18   d  adjusted to the dimensions of the orifice  28 . These last two portions are separated by an annular groove  32  orthogonal to the longitudinal axis of the shaft. 
         [0028]    The instrument holder  30  is intended to be mounted pivoting, frictionally, in the channel  12 . According to one important aspect of the invention, the friction is provided by at least one spring member  34 , an example of which is illustrated in  FIG. 3 . 
         [0029]    This spring member  34  is generally cylindrically shaped and has, in its center, an opening  35  structured so as to have a typically star-shaped section, and thus forms a female member configured to be mounted without play and secured in rotation on the portion  18   b  of the shaft  18 . The proposed star shape is only an example, and other types of slots, structures or lugs can be used, the essential being that these elements are secured in rotation. 
         [0030]    The spring member  34  comprises a plurality of blades  36  elastically deformable in a substantially radial direction. These blades  36  are oriented outwardly, primarily along non-radial directions, and end, in one preferred embodiment, with a cylindrical portion  36   a  substantially orthogonal to the general plane of the spring member. 
         [0031]    The spring member  34  is intended to be mounted on the shaft  18 , inserted between the latter part and the wall of the channel  12 . The cylindrical portions  36   a  are therefore defined so as to cooperate with the hollows  29  of the channel. Other shapes may be chosen as long as the ends of the blades  36  are able to cooperate with the structures of the wall of the channel  12  to create friction. 
         [0032]    In terms of dimensions, one skilled in the art can choose the length, orientation, number and thickness (along a direction perpendicular to the general plane of the spring member) of the blades  36  of the spring member  34  so as to define the friction exerted between the spring member  34  and the grip  10 . These different parameters make it possible to determine the value of the maximal applicable tightening torque. 
         [0033]    The number of springs  34  arranged on the shaft  18  can also be modulated to adjust the maximal tightening torque. However, one will understand below, in describing the assembly of the tool, that nearly all of the length of the second portion  18   b  of the shaft must be occupied by the spring members. Thus, to vary the number of spring members arranged on the shaft, it is possible to provide for instrument holders and grips with adapted lengths. 
         [0034]    Another advantageous solution consists of replacing one spring member with a wedging device, having a similar structure, but not comprising a contact point with the grip. This device can consist of a spring member from which the cylindrical portions have been removed. A simple bush can also replace a spring member to decrease the maximal tightening torque. Preferably, the spring members are centered on the portion  18   b,  i.e. the wedging devices are also distributed on both sides of the spring members. One skilled in the art can also provide for spring members  34  having different thicknesses in order to provide other possibilities for adjustment. Any operations to adjust the maximal tightening torque are done in the factory. Preferably, the user cannot, for safety and traceability reasons, modulate the maximal tightening torque value himself. 
         [0035]    The spring member is advantageously made in a self-lubricating plastic material resistant to typical sterilization, thermal and radiation treatments. Different tests have made it possible to demonstrate that polymers of the polyether-ether-cetone type (known under the name PEEK) had all of the required characteristics. One may more particularly choose PEEK 151G. 
         [0036]    Typically, spring members as described above and made in PEEK make it possible to obtain tightening torque values in the vicinity of several N.m, typically between 1 and 10 N.m. 
         [0037]    Thus, in order to assemble the tool as illustrated in  FIG. 1 , the following operations are performed, preferably in a factory by an operator. The first stopper  14  is first firmly fixed on the grip and the shaft of the instrument holder is introduced into the hole  16 . Then, a ring  38  is assembled on the shaft  18  so as to define a precise support surface for the spring members  34 , the chosen number of which is inserted between the shaft  18  and the channel  12 . The spring members are therefore secured in rotation with the shaft  18  and in contact with the wall of the channel  12 . 
         [0038]    Then, a wedge  40  is arranged on the shaft  18 , at the level of the third portion  18   c . This wedge  40  must be supported on the last spring member arranged in the channel  12  and not on any threshold located between the second and third portions. The wedge  40  is dimensioned to occupy exactly the space between the last spring and the groove  32 . A blocking member  42  is then arranged in this groove  32  to axially position the elements already put into place. Lastly, the second stopper  22  and the rod  24  are screwed to the end of the grip  10  to ensure the maintenance of the assembly thus formed. 
         [0039]    The ring  36  on one hand, the wedge  40  and the blocking member  42  on the other, make it possible to longitudinally position the grip in relation to the instrument holder and to greatly limit the friction between the stoppers and the spring members in order to be able to perfectly control the adjustment of the maximal tightening torque. 
         [0040]    One will note that the tightening torque for the stoppers must be greater than the determined maximal tightening torque. Preferably, the stoppers can be welded to the grip  10 . 
         [0041]    Thus is obtained a tool whereof the adjustment of the maximal tightening torque can be particularly precise, with an improved lifespan. Tests have made it possible to show that the precision achieved was in the vicinity of 3% for 10,000 releases. A release is defined as being the moment when the grip is separated from the instrument holder, going from a first to a second relative position of one of these elements in relation to the other. Moreover, thanks to the radial deformation of the spring members, there is no parasitic movement to lament when the maximal tightening torque is achieved. The tool does not need to be lubricated and can be sealed, avoiding any risk of contaminating the patient. 
         [0042]    Moreover, thanks to the orientation of the blades, the maximal friction exerted between the spring members and the wall of the channel is different in the direction of screwing and the unscrewing direction. The orientation of the blades is chosen such that a same tool can be used, without modifying the adjustment of the maximal tightening torque, to immediately unscrew the object which has just been screwed. 
         [0043]    For significant torques, a spring member according to a second embodiment is proposed. In order to improve the connection with the shaft, the spring member as illustrated in  FIG. 4  comprises a hub  44  made in a material not elastically deformable, for example of the metallic type, such as a stainless steel. As above, the hub has an opening  35  structured so as to form a female member configured to be mounted without play and secured in rotation on the portion  18   b  of the shaft  18 . 
         [0044]    The spring member also comprises a ring  46  supporting the blades  36 . This ring is made in one of the materials proposed above for the spring member. The ring is arranged around the hub, securely. 
         [0045]    The ring can be molded by casting on the hub. To do this, the hub advantageously has channels going through it transversely and leading into the opening  35 . These channels are used to inject the plastic material making it possible to realize the ring. As a result of this production method, the ring has rods  46   a  housed without play in the channels and which provide an excellent, particularly rigid connection, between the hub and the ring. Moreover, the injection step thus done does not leave any trace on the upper and lower parts of the spring members, which avoids any retouching operation. 
         [0046]    The description above was provided solely as an illustration of the invention and does not limit it. Thus, without going outside the scope of the invention, one skilled in the art could also choose to arrange spring members still on the shaft of the instrument holder, but such that the spring members are secured in rotation with the grip and rub on the structures comprised by the shaft. Thus, in such an alternative, the channel can typically have a polygonal section with which the spring members cooperate. The latter parts have blades which are oriented inwardly and which cooperate with structures having an adapted shape arranged in the shaft. A spring member in two parts could be very well adapted to this embodiment.