Abstract:
The device for conditioning an organic ligament to be implanted, in particular a ligament as a cruciate ligament replacement, is equipped with a first and with a second receiving element for receiving and tensioning the ligament at two distanced locations, wherein the first receiving element is connected to means for the periodic, and with respect to the ligament, translatoric adjustment of the first receiving element.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The invention relates to a device for conditioning an organic ligament to be implanted, in particular a ligament as a cruciate ligament replacement.  
           [0002]    In cruciate ligament plasty as a rule organic ligaments from the body of the patient are applied. These ligaments with a re-loading after operation often experience a length change. This may lead to renewed instabilities of the knee joint. Therefore one strives to condition the ligament before implantation, i.e. the ligament is preoperatively stretched to a permanent length so that a later length change may not occur.  
           [0003]    It is known that the ligament to be implanted directly before or during the operation is stretched by the operator by the application of force, wherein one assumes that the ligament loses the property of extending later. With this the ligament is for example tied together to a loop and received between both hands or index fingers and stretched.  
           [0004]    With this there is the disadvantage that the manual stretching amongst other things depends individually on the condition of the operator so that inasmuch as this is concerned there are to be expected no reproducable and exact stretching results, not least because these also depend on the nature of the respective ligament itself.  
         BRIEF SUMMARY OF THE INVENTION  
         [0005]    It is therefore the object of the invention to provide a device with which it is possible to simulate the procedure of the manual stretching and to carry out a permanent extension of the ligament which can be estimated in its extent, so that the intensity of the conditioning may also be carried out with differently stable ligaments in a reproducable manner.  
           [0006]    For achieving this object the device for conditioning a ligament according to the invention comprises a first and a second receiving element for receiving and for tensioning the ligament at two distanced points, wherein the first receiving element is connected to means for the periodic, and with respect to the ligament, translatoric adjustment of the first receiving element.  
           [0007]    The strip is thus accommodated at the receiving elements in the device and subjected mechanically to a preferably adjustable periodic alternating load for so long until one finally from experience values may assume that the ligament is sufficiently stretched and after the implantation, e.g. as a cruciate ligament replacement, is no longer extended.  
           [0008]    The means for the periodic adjustment of the receiving element comprise a disk which is driven by a motor and onto which eccentrically and linkedly a crank is arranged with one of its ends. At the other end of the crank there is fastened the receiving element. With this conception there is thus effected the periodic stretching of the ligament with an eccentric drive.  
           [0009]    The two receiving elements are usefully formed as a hook into which the ligament in the form of a loop may be loosely hung. The one hook which forms the second receiving element is arranged on a linearly displaceable unit. This unit comprises an axially displaceably mounted rod which is connected to an elastic element which is rigidly arranged on it and which may be a helical spring. With this it is the case of a compression spring which holds the ligament tensioned, wherein the rod in operation of the device is adjusted against or with the action of the spring according to the position of the eccentric.  
           [0010]    For the reproducability of the conditioning it is important that the force which the device exerts on the tensioned ligament is measured and where appropriate may also be adjusted. It is therefore further envisaged that the mentioned displaceable unit comprises means for measuring the maximum force exerted by the elastic element onto the rod. These force measuring means in a simple embodiment form consist of a sliding ring placed on a cylindrical part as well as an abutment for the sliding ring.  
           [0011]    Furthermore the device for the purpose of adjustability to varyingly long ligaments or ligament loops comprises further adjusting means for adjusting the distance between the two receiving elements or hooks.  
           [0012]    For an exact adjusting of the ligament loading the linearly displaceable unit has tensioning means for setting and fixing the axial position of the mentioned rod relative to this unit. A simple embodiment with regard to this results with the use of a screw and a nut as a tensioning means.  
           [0013]    With the suggested device it is possible, in contrast to a conditioning by hand, to be able to achieve a reproducable and, according to demand, an exact and sufficient conditioning of the ligament. In particular it may be ensured that on account of the previous alternating loadings the ligament has experienced its largest possible length change before the implantation so that damaging length changes later after implantation on account of natural loading may be ruled out. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWING  
       [0014]    One embodiment example of the invention is hereinafter described by way of the drawing which schematically shows a lateral view of a conditioning device according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0015]    The device  1  is assembled on a base plate  19  on which a motor is stationarily arranged which drives a vertically mounted disk  8 . On this disk there is linkedly arranged a crank  9  with its one end  9   a.  The other end  9   b  of the crank is connected to an open hook  3  which represents the first receiving element for the ligament  2  to be conditioned.  
         [0016]    According to the representation the ligament is tied to a loop and knotted at the ends. The one end of the loop is hung in the hook  3 , whilst the other loop end is carried or accommodated by a hook  4  as a second receiving element. The two hooks  3  and  4  are located at two points or locations  5  and  6  at a distance a to one another.  
         [0017]    The hook  4  is arranged on a fixable unit  10  linearly displaceable on the base plate  19 . This unit and thus also the hook  4  are displaceable relative to the motor  7 . A T-groove guide  20  permits with this the guiding and fixing of the unit  10  on the base plate  19  with adjusting and fixing means  16 , wherein the unit  10  is fastened on the base plate  19  when it is located at its required distance to the motor  7 , thus when the two hooks  3  and  4  have the required distance A to one another, this distance depending on the length of the ligament loop.  
         [0018]    The unit  10  comprises a nut  18  in which a screw  17  is screwed. The screw  17  and the nut  18  represent tensioning means with which relative to the unit  10  an axially displaceably mounted rod  11  may be adjusted with respect to its axial position. The rod  11  carries the second hook  4 . A helical spring  12  acts between the unit  10  and the rod  11  such that the rod  11  via the spring  12  is elastically mounted with respect to the unit  10 .  
         [0019]    The rod  11  comprises a cylindrical part  13  on which a sliding ring  14  is pushed. An abutment  15  on the screw  17  ensures that the sliding ring  14  with an axial displacement of the rod  11  on the cylindrical part  13  may only reach up to a certain position. At a scale  13   a  calibrated with respect to the spring force, on the cylindrical part  13  then at the position of the sliding ring  14  the force of the spring  12  which is maximally exerted onto the hook  4  and thus onto the ligament  2  may be measured or read off.  
         [0020]    The conditioning of the ligament  2  is effected such that it firstly is formed into a loop and is knotted at the ends and then with the loop ends is hung into the two hooks  3  and  4 . Via the adjusting means  16  the unit  19  is moved to the position at which the hooks have a distance a which the hooks have to one another between the two hook positions  5  and  6  and at which the ligament is not tensioned or only a little. Thereafter the unit  10  with the help of the adjusting means  16  is fastened on the base plate  19 .  
         [0021]    In operation of the motor  7  via the then rotating disk  8  and the crank  9  there arises a periodic and essentially translatoric adjusting of the hook  3  relative to the unit  10 . By rotating the tensioning screw  17  the intensity and the maximum of the forces acting onto the ligament  2  may be set. As has already been mentioned from the scale  13   a  one may read off how large the alternating load acting on the ligament  2  is, wherein of course there also exists the possibility of changing the maximum of the force according to requirement in the previously described manner by rotating the tensioning screw  17  in the one or the other direction in the context of a fine adjustment.  
         [0022]    By way of the dynamic load the ligament  2  is periodically alternately loaded and stretched, wherein by way of the selection of the treatment time and the intensity of the load change one may assume an influence on the result of the conditioning. This time and the intensity are professionally selected according to experience values such that the ligament  2  after the conditioning procedure is maximally stretched without damage so that one may assume that after the implantation no further length change is given.  
         [0023]    Otherwise the device according to the invention by way of a suitable positioning of the unit  10  relative to the motor  7  and adjusting of the tensioning screw  17  relative to the unit  10  may be set such that the ligament  2  to be stretched is periodically stretched with a force which lies between zero and a selected maximal value, by which means there results a particularly efficient conditioning.