Abstract:
An anchoring member and packer for use in spinal osteosynthesis systems. The anchoring member can accept a connecting element such as a spinal rod, and is adapted for insertion into bone. The packer provides stability to the anchoring member particularly when the anchoring member is not fully engaged to bone. The anchoring member has a head, anchoring means for engagement to bone, and retaining means for retaining the packer against the head. The packer has a through-orifice for receiving the anchoring member and complimentary retaining means for engagement to the head of the anchoring member.

Description:
This application claims priority benefits under Title 35i United States Code, § 119 (a)-(d) of a foreign application filed in France. The application number is 01 03514 and was filed on Mar. 15, 2001. 
    
    
     BACKGROUND OF THE INVENTION 
     The invention relates to spinal osteosynthesis systems. 
     Spinal osteosynthesis systems generally comprise bone screws, such as pedicle screws. Sometimes, during the surgical operation, one or more screws are not screwed fully home, that is, the cortical thread is not fully engaged in the bone of the vertebra. This occurs for various reasons. One reason may be because the screw is too long and because, if it were screwed fully home, the distal end of the thread would re-emerge from the bone on the opposite side to the side via which the screw entered, digging into the tissues located on that side. Another reason may be an anatomical defect leading to the fact that, if the screw were screwed fully home, it would be screwed in further than the other screws of the osteosynthesis system. This leading to exaggerated and difficult-to-achieve bowing of the connecting member. To avoid this, the surgeon does not screw the screw fully into the bone, leaving the proximal part of the cortical thread disengaged from the bone. However, this has the disadvantage of making the screw unstable in the bone because this screw is not tight, as well as the disadvantage of leaving bone threads outside the bone in which the member is anchored, which leads to damage to the surrounding tissue because of the presence of the sharp corners of the screw thread. 
     One object of the invention is to provide a system which makes it possible to better stabilize an anchoring member while at the same time better isolating the non-engaged anchoring part from the adjacent environment. 
     SUMMARY OF THE INVENTION 
     This and other objects are achieved by the present invention, which is a spinal osteosynthesis assembly comprising an anchoring member having a head with a bone engaging portion, and at least one packer that contacts bone, and is able to be coupled to the anchoring member. 
     Advantageously, the part of the bone engaging portion of the anchoring member which is not engaged in the bone finds itself at least partially surrounded by the packer which isolates it from the adjacent environment. Additionally, since the packer contacts the bone, this provides better stability. In consequence, the anchoring member is stabilized and the non-engaged part of the bone engaging portion can no longer damage the tissue surrounding the anchoring member. 
     Advantageously, the packer has a slot such that the packer forms a non-closed annulus. 
     Advantageously, the packer is elastically deformable to facilitate movement of the bone engaging portion through the slot. Thus, the packer can be fitted over the anchoring member when the latter is already anchored in the bone. 
     Advantageously, the packer is in the shape of an annulus and the packer has a lip, while the anchoring member has a groove such that engagement of the lip with the groove facilitates coupling the packer to the anchoring member. Thus, the packer may be clipped onto the anchoring member in a simple movement. Also advantageously, the lip may be discontinuous. 
     Advantageously, in addition to the lip, the packer has a recess and is stackable to another packer via engagement of the lip of one packer to the recess of another packer. 
     There is also provided, according to the invention, a surgical method exhibiting the steps of fitting the packer onto the anchoring member, and inserting the anchoring member into the bone. 
     Advantageously, the method exhibits the steps of fitting the anchoring member into the bone, and then fitting the packer to the anchoring member. 
     Advantageously, the method exhibits an additional step of anchoring the anchoring member to the extent that the packer contacts the bone. 
    
    
     Other features and advantages of the invention will become apparent from reading the description herein below of one preferred embodiment and of some alternative forms. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a three-dimensional view of a first embodiment of the invention. 
     FIG. 2 is a three-dimensional view of the packer of the first embodiment. 
     FIG. 3 is a view along section III—III of FIG.  1 . 
     FIG. 4 is a view along section IV—IV of FIG.  2 . 
     FIG. 5 is a three-dimensional view of a second embodiment of the invention. 
     FIG. 6 is a three-dimensional view of the second embodiment during fitting. 
     FIG. 7 is a three-dimensional view of the packer of the second embodiment. 
     FIG. 8 is a three-dimensional view of a packer of a third embodiment of the invention. 
     FIG. 9 is a three-dimensional view of a fourth embodiment of the packer of the invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     For all the embodiments which are going to be described, just one anchoring member  2  is depicted, the remainder of the osteosynthesis system not being depicted. 
     In a way which is common to all the embodiments, an osteosynthesis system comprises a number of anchoring members  2 , in this instance monoaxial bone screws, at least one connecting element (not depicted), in this instance connecting rods of circular cross section, and locking means (not depicted) for locking the connecting elements to the anchoring members, in this instance bolts. Each anchoring member  2 , of the osteosynthesis system consists of two main parts. One is a lower part  21 , in this instance of cylindrical shape with a circular cross section having a bone thread, that is able to engage and anchor in the bone. Another is an upper part  22  of the anchoring member, which is known as the “screw head”. The upper part  22  comprises two parallel branches extending opposite each other and delimiting a U-shaped opening capable of accommodating the connecting element. The interior faces facing each other of the branches forming the U have a screw thread capable of collaborating with a complementary screw thread belonging to the locking means. Such anchoring members are described in patents FR 2,642,643 and FR 2,659,546 to which reference will be made for further details. The upper part  22  and the lower part  21  of each anchoring member  2  are connected to one another forming a surface  24  which has a circular cut  23  of roughly V-shaped cross section extending around the entire circumference of the surface  24 . 
     With reference to FIGS. 1 to  4 , a first embodiment of the invention will be described. The packer  1  has an annular shape and exhibits a lateral external surface  12  and a lateral internal surface  15 , the lateral internal surface  15  delimiting a central through-opening  14 . The upper end of the internal surface  15  comprises a lip  12  on its entire circumference. The external lateral surface  12  comprises, in its lower part, a circular cut  13  of roughly V-shaped cross section running around the entire circumference of the annulus. The internal lateral surface  15  more or less complements the part of the face  24  of the anchoring member  2  that lies between the cut  23  and the lower part  21  of the anchoring member  2 . Furthermore, the part of the external lateral surface  12  that lies below the circular cut  13  of the packer  1  more or less complements the upper part of the internal lateral surface  15 . The packer  1  has a working thickness e measures parallel to an axis A perpendicular to the overall plane of the packer. 
     The use of the first embodiment of the invention will now be described. The surgeon, before fitting the anchoring member into the bone at the desired location, fits the anchoring member  2  and the packer  1  together. To do that, part  21  exhibiting the bone thread is slipped through the orifice  14  of the packer  1  until the lip  11  comes into contact with the surface  24  of the anchoring member. At that moment, the lip  11  lies near the cut  23 . The surgeon applies additional force to the packer so that the lip  11  engages in the cut  23 . To obtain that result, the surgeon has made use of the elasticity of the material of which the packer  1  is made. This material is biocompatible, so that it can be tolerated by the human body. This may be stainless steel, such as 316L, titanium, or alternatively a titanium alloy such as TA6V4, or alternatively a polymer such as PEEK (polyetheretherketone). Once this assembly has been achieved, the surgeon fits the anchoring member into the patient in such a way that, for preference, the packer contacts the bone  5 , as illustrated in FIG.  3 . The surgeon then continues the surgical operation. 
     With reference to FIGS. 5 to  7 , a second embodiment of the invention will be described. The packer  101  is very similar to the packer  1  of the previous embodiment. This packer is formed of an annulus of a cross section identical to the cross section of the annulus that forms the packer  1 . The surface  115  is identical to the surface  15 . Likewise, the surface  112  is identical to the surface  12 . The upper end of the surface  115  has a lip  111  identical to the lip  11 . Likewise, the surface  112  has a cut  113  identical to the cut  13 . The lateral internal surface  115  delimits an orifice  114 . The difference lies in the fact that the packer  101  has a slot  116 , thus forming a non-closed annulus. This slot  116  has an opening, the width of which is roughly equivalent to the diameter of the lower part  21  of the anchoring member  2 . 
     In use, the surgeon can fit the packer  101  over the anchoring member  2  before fitting the anchoring member  2  into the patient, or alternatively he may install the packer  101  after he has positioned the anchoring member  2  in the patient. In the former instance, fitting together is done in the same way as in the previous embodiment of the invention. In the latter instance, the surgeon has fitted the anchoring member  2  while an anchoring portion of the lower part  21  of the anchoring member  2  is not engaged in the bone and projects out from the bone. To protect the surrounding tissues and organs on the one hand, and on the other hand to better stabilize the anchoring member, the surgeon will insert a packer between the head  22  of the anchoring member  2  and the surface of the bone. To do that, the surgeon clips the packer  101  under the head  22  of the anchoring member  2  as follows. As indicated in FIG. 5 by the arrow F, the part  21  is inserted into the orifice  114  and through slot  116 . As the part  21  is passing through the slot  116 , the slot  116  opens up slightly because of the elasticity of the material of the packer, to allow the part  21  to pass. Once this part  21  is in the orifice  114 , the slot  116  returns to its previous configuration, closing up on itself through the elasticity of the material of which the packer  101  is made. The surgeon then has merely to exert a force similar to the force that he would have exerted in the previous embodiment in order to insert the lip  111  of the packer  101  into the cut  23  of the anchoring member  2 . The packer  101  is fitted onto the anchoring member  2  as illustrated in FIG.  8 . Next, the surgeon continues his surgical operation in the normal way. 
     With reference to FIG. 8, a third embodiment of the invention will be described. The packer  301  differs from the packer  1  in that grooves  317  distributed uniformly around the entire circumference of an upper part of the packer  301  split the lip  311  into roughly identical angular sectors. In this instance, there are four grooves  317 . Thus, on fitting, elastic deformation of the packer  301  is easier when inserting the lip  311  into the cut  23  of the anchoring member  2 . In consequence, the surgeon supplies a force which is weaker than the force supplied to the packer  1  of the first embodiment for clipping the packer  301  onto the anchoring member  2 . 
     The use of the packer  301  is identical to the use of the packer  1  in the first embodiment. 
     With reference to FIG. 9, according to a fourth embodiment of the invention, the packer  201  is identical to the packer  101  except that the opening of the slot  216  is far smaller. This slot  216  does not allow the part  21  of the anchoring member  2  to be introduced sideways into the orifice  214 . This packer  201  is fitted in the same way as the packer  1  described earlier. Just like with the third embodiment of the invention, the deformation of the ring  201  is made easier by the presence of the slot  216  during clipping to introduce the lip  211  into the cut  23 . In consequence, the surgeon supplies a force which is weaker than the force he supplies for the packer  1  of the first embodiment for fitting the packer  201  onto the anchoring member  2 . 
     For all the embodiments, as the packers comprise on their exterior surface a cut identical to the cut made on the anchoring member, these packers can be stacked up as the surgeon sees fit, the lip of the packer below clipping into the cut of the packer above. It is thus possible for two or more packers to be slipped over and fitted onto the anchoring member. 
     Of course it is possible to make numerous modifications to the present invention without in any way departing from its scope. For example, the lips and the cut could be replaced by complementing conical surfaces delimiting what are known as “Morse tapers”. The lips may also be replaced by a screw thread while the cut may be replaced by a groove surmounting a screw thread that complements the thread. Thus, the packer will be fixed to the screw thread until the thread enters the groove where it will be held captive. 
     Still further, the lips may be replaced by a number of studs projecting toward the central orifice of the packer and distributed uniformly around the circumference of the packer, while the cut may be replaced by housings, of which there would be the same number as there are studs, which housings could accommodate and retain the studs. 
     The anchoring member could be any type of bone screw, of the polyaxial or monoaxial type. The connection between the anchoring member and the packer could lie at the head, or alternatively at the anchoring part of the member. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.