Abstract:
A spinal osteosynthesis device comprising a bone anchorage element, a vertebral rod, a connector for interconnecting the rod and the anchorage element so that the anchorage element is capable of being angularly oriented in a polyaxial manner relative to the rod. A fixation element is provided for fixing the position of the connector in translation and in rotation relative to the rod. A clamp element is provided for clamping the bone anchorage element to the connector in a predetermined angular position independent of the fixation element.

Description:
TECHNICAL FIELD BACKGROUND 
     The present invention relates to a bone implant apparatus, and more specifically but not exclusively a spinal osteosynthesis device of the type including a bone anchorage element, a vertebral rod, and a connector for interconnecting the rod and the anchorage element such that the anchorage element is capable of being angularly oriented in a polyaxial manner relative to the rod. 
     BACKGROUND 
     U.S. Pat. No. 5,486,174 and EP-A-0612507 describe such devices in which the connector is constituted by two jaws which define a lateral recess for the rod and in which conical openings are provided for the passage of the bone anchorage element. The latter comprises a shank having a double screw thread, one end part of which constitutes a bone anchorage screw. The opposite threaded end part projects from the upper jaw to permit the clamping of the assembly of the parts by a nut which comes to bear against the upper jaw. 
     Provided between the two threaded parts of the anchorage element shank is a spherical shoulder which comes to bear against the conical wall of the opening of the connector. 
     In this device, as in other known spinal osteosynthesis systems, a single nut is used to clamp the anchorage element, the connector and the rod in a chosen position. Consequently, if it is desired to increase the spacing between two consecutive anchorage elements, for example in the treatment of spondylolisthesis or for restoring a discal height or recreating a lordosis it is in fact only possible to slightly incline the anchorage element, without obtaining the desired increase in the spacing. 
     SUMMARY OF INVENTION 
     One object of the invention is to provide a spinal osteosynthesis device so arranged as to easily permit such an adjustment of the spacing between two successive anchorage elements. 
     One form of the present invention is a unique bone implant device. A further form is a unique spinal implant apparatus. Still a further form is a unique spinal osteosynthesis method. 
     According to another form of the invention, the spinal osteosynthesis device comprises separate means, on one hand means for fixing the position of the connector in translation and in rotation on the rod and, on the other hand, means for independently clamping the bone anchorage element to the connector in the chosen angular position. Such a separation of the clamping means permits easily adjusting the position of the connector, and consequently of the bone anchorage element, in translation on the rod, relative to the neighboring bone anchorage element and therefore obtaining an improved correction. 
     Further objects, forms, embodiments, aspects, features, benefits and advantages of the present invention will be apparent to one of ordinary skill in the art from the following description and drawings. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     The invention will now be described with the reference to the accompanying drawings which illustrate an embodiment thereof by way of a non-limitative example. 
     FIG. 1 is a partial half cross-sectional view, half elevational view to an enlarged scale of an embodiment of the spinal osteosynthesis device according to the invention. 
     FIG. 2 is an elevational view to a smaller scale, in the direction of arrow K, of the device of FIG.  1 . 
     FIG. 3 is a diagrammatic elevational view illustrating the application of the device of FIGS. 1 and 2 to the treatment of spondylolisthesis. 
    
    
     DESCRIPTION OF PREFERRED EMBODIMENT 
     The spinal osteosynthesis device illustrated in FIGS. 1 and 2 comprises a vertebral rod  1 , a bone anchorage element  2  constituted in this embodiment by a pedicle screw, and a connector  3  for interconnecting rod  1  and anchorage element  2 . This embodiment includes a nut  4  for clamping the assembly of the parts  1 ,  2 , and  3 , which is adapted to be screwed on a threaded end part  5  of bone anchorage element  2 . 
     Bone anchorage part  7  is in the illustrated embodiment a screw which is extended by a cylindrical head  8  itself followed by a convex and preferably spherical bearing surface  9  which has the same center of curvature as surface  6  and is connected to end part  5  by a smooth shank  11 . 
     Head  8 , bearing surface  9  and shank  11  are disposed in an opening  12  extending throughout connector  3  in a direction substantially perpendicular to the longitudinal axis XX of the rod  1 . Rod  1  is itself disposed in a cylindrical channel  13  formed in connector  3  to one side of opening  12 . Opening  12  has a first conical part  12   a  which receives head  8  and bearing surface  9 , and a second conical part  12   b  through which extends shank  11  and at the end of which a washer  14  fixed to the nut  4  bears against the bearing surface  6  when the nut  4  is screwed on the threaded end part  5 . 
     Shank  11  is spaced from wall  12   b,  and walls  12   a,    12   b  and shank  11  are shaped and have a size for allowing a polyaxial orientation of the anchorage element  2 . 
     The connector  3  includes a body portion or a first member that is integral in the illustrated embodiment, i.e. made in one piece, and there is provided transversely of the channel  13  a tapped hole  15  which opens onto channel  13  and in which a screw or a second member  16  is engageable. Screw  16  has a bearing surface  17  to enable screw  16  to be screwed down and applied against rod  1  at the end of the screwing. A recess  20  provided in screw  16  is so shaped as to receive a corresponding screwing tool. 
     The combination of the walls  12   a,    12   b  and the bearing surface  9  which is applied against the end  22  of wall  12   a,  renders anchorage element  2  polyorientable in multiple directions within limits defined by walls  12   a,    12   b.  This polyorientability helps the surgeon to achieve a close adaptation of the osteosynthesis device of the present invention to the anatomy of the considered vertebral segment while limiting as far as possible the extent to which rod  1  must be bent. Whatever be the orientation imparted to anchorage element  2 , washer  14  fixed to nut  4  bears against bearing surface  6 , and to this end washer  14  is provided with a concave internal bearing surface  23 . 
     In one embodiment of the invention, opening  12  has a longitudinal axis A, which may correspond to a longitudinal axis of bone anchorage element  2 , as illustrated in FIG.  1 . The size and shape of walls  12   a,    12   b  permit bone anchorage element  2  to be selectively oriented at any of a number of angles in three dimensions with respect to axis A. For example, bone anchorage element  2  can be placed so that its longitudinal axis substantially coincides with one of axes A′ or A″, or at any position within the cone formed by rotation of axis A′ and/or A″ about axis A. Bone anchorage element  2  therefore enjoys at least two degrees of freedom in its orientability. Walls  12   a,    12   b  of connector  3  could be configured to allow bone anchorage element  2  to be positioned at any angle between about 0 and 45 degrees with respect to axis A. In the specific embodiment shown in FIG. 1, bone anchorage element  2  can be oriented at any angle between about 0 and 8 degrees with respect to axis A. 
     The present invention therefore permits separating the operations of adjusting, on one hand, the position in translation and rotation of connector  3  on rod  1 , and, on the other hand, the clamping of the angular position of connector  3  on anchorage element  2 , thereby enabling the surgeon to effect these two adjustments separately. 
     In the case, for example, of an application of the apparatus of the present invention to the correction of a spondylolisthesis (FIG.  3 ), a first bone anchorage element  18  is anchored in the sacrum S and a second bone anchorage element  19  is anchored in the vertebra L 5  having the spondylolisthesis to be corrected. Rod  1  extends through the two connectors  3 , respectively associated with the anchorage elements  18  and  19  and capable of being clamped in position by respective nuts  4 , each connector  3  being provided with a screw  16 . 
     The surgeon uses as a support anchorage element  18 , which constitutes a fixed point. He tightens nut  4  on connector  3  associated with anchorage element  19  of the vertebra L 5  to be corrected. This tightening has a taking up effect (arrow F 1 ) by the rearward pull on anchorage element  19  toward connector  3  (while rod  1  remains fixed). This displacement, substantially a simple translation along rod  1 , may be advantageously completed, owing to the invention, by an adjustment of the position of connector  3  of anchorage element  19 , its set screw  16  being unscrewed to permit this adjustment. Thus, the position of the vertebra L 5  to be corrected may be adjusted not only in accordance with the above described method by a simple pivoting of its anchorage element  19  about the fixed bearing point on the sacrum S but also by an adjustment (arrow F 2 ) along rod  1 , by separate means, namely nut  4  and screw  16  provided by the invention. This permits in this case restoring a discal height or restoring a local lordosis. The threaded part  21  of anchorage element  19  projects from the nut  4 , which has a fracture-initiating region  4   a  defining a part  4   b  remote from connector  3  and a part  4   c  close to connector  3 . 
     After nut  4  has been clamped on connector  3 , threaded part  21  that projects beyond the upper part  4   b  of nut  4 , together with said upper part  4   b,  is broken off and removed. Nonetheless, in other embodiments a break-off operation may not be desired. Accordingly the present invention also contemplates a non-frangible nut that does not include a fracture-initiating region. Such a non-frangible nut is threaded onto threaded part  21  of anchorage element  19  into contact with bearing surface  6  of connector  3  in one embodiment and tightened with an appropriate tool. 
     Thus, one embodiment of the present invention contemplates a bone implant apparatus including a rod, a bone anchorage element with a distal anchoring portion, a proximal threaded shank portion, and a head portion, and a connector that connects the rod and the bone anchorage element. The connector defines an opening that receives the bone anchorage element, a channel adapted to receive the rod and offset from the opening, and a threaded hole in communication with the channel. The opening is bounded by one or more walls with a portion that engages the head of the bone anchorage element and that is shaped and sized to permit multi-axial orientation of the bone anchorage element with respect to the opening. A set screw is threaded into the threaded hole and bears against the rod when the rod is within the channel of the connector, and a nut is provided for threading on the proximal portion of the bone anchorage element to lock the bone anchorage element in a desired orientation. 
     Another embodiment of the present invention contemplates a connector for connecting a bone anchorage element to a rod in a bone implant apparatus. Connector includes a first member having an opening configured to receive the bone anchorage element, a channel offset from said opening and configured to receive the rod, and an internally threaded hole communicating with the channel. The opening is bounded by at least one wall configured to allow the bone anchorage element to be oriented polyaxially with at least two degrees of freedom. A second member, such as a set screw, is threaded within the internally threaded hole and can be threaded down against the rod to lock the first member with respect to the rod. 
     Other variations and alternatives in the above-described structures are contemplated to be a part of the present invention. For example, connector  3  can be assembled or fashioned from multiple pieces interlocked or otherwise fastened together. As another example, the connector of the present invention could permit polyaxial positioning of a bone anchorage element while being incapable of translation or rotation with respect to a rod, such as where the connector is permanently fixed to the rod. Such a connector includes an opening identical or similar to opening  12  of connector  3  (FIG.  1 ). As a further example, the constructs of the present invention can be used on other portions of the spine above the lower lumbar vertebrae, or on other portions of the body, such as the long bones. 
     The invention is applicable to other corrections such as those mentioned before and various variants thereof may be envisaged.