Abstract:
A low profile orthopedic device is used to fix and stabilize bones to correct anomalies in skeletal structure occurring naturally or by trauma. Bone screws are screwed into bones by application of torque. Clamps are movably attached to the screws. Each clamp includes a compression ring. A connecting rod connects several screws through slots in the clamps. The clamps are tightened to hold the rod and the heads in a pre-selected position by linear movement of the compression rings.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to orthopedic surgery and, in particular, to devices and prosthesis for stabilizing and fixing bones and joints of the body. 
     2. Description of the Prior Art 
     Published U.S. Application, US 2003/0149487 A1, published Aug. 7, 2003, teaches the use of a linear movement to apply compressive forces to connect components of an artificial hip joint. 
     U.S. Pat. No. 6,626,906 issued Sep. 30, 2003 to Young teaches a spinal rod attached to a spinal anchor by a clamp. The clamp is tightened about the anchor by a collet screwed into the clamp. The rod is held in the clamp by a split ring that is reduced in size by the collet. The anchor is placed in the bone by torque and the collet is tightened by additional torque. 
     U.S. Pat. No. 6,610,063 issued Aug. 26, 2003 to Kumar et al, U.S. Pat. No. 6,610,062 issued Aug. 26, 2003 to Bailey et al, U.S. Pat. No. 6,565,565 issued May 20, 2003 to Yuan et al, U.S. Pat. No. RE 37,665 issued Apr. 16, 2002 to Ralph et al, U.S. Pat. No. 6,478,798 issued Nov. 12, 2002 to Howland and U.S. Pat. No. 5,584,834 issued Dec. 17, 1996 to Errico et al teach a spinal rod coupled to several bone anchors by clamps that require additional torque to be applied to the assembly after the bone screw has been seated in the bone. 
     In normal practice, the bone screws are each anchored in the bone with a specific amount of torque that approaches the ultimate sustainable force between the screw threads and the bone. The bone screws are then connected together by a rod having sufficient stiffness to maintain the desired skeletal orientation. The connection between the rod and the bone screws must be strong enough to be immobile. 
     All these prior art spinal fixation devices result in additional torque applied to the assembly, and thereby to the bone screw, to tighten and lock the rod to each of the bone screws. The additional load may strip the purchase between the bone and the threads of the bone screw. To prevent such a result, some tool must be used to counter the torque of locking the rod and the screws. The use of an anti-torqueing tool requires additional coordination by the surgeon or surgeons to prevent slippage. 
     What is needed in the art is a system for connecting a rod and an embedded bone screw using compressive forces rather than torque. 
     SUMMARY OF THE PRESENT INVENTION 
     There are many instances in which it is necessary to stabilize and fix bones and bone fragments in a particular spatial relationship to correct the location of skeletal components due to injury or disease. One group of devices employ a number of bone pins, anchors, or screws placed in bones across a discontinuity in the bone or bone fragments, such as a fracture, or adjacent vertebrae, or a joint, connected by a rod to maintain a predetermined spatial location of the bones. In some cases these devices may be temporary, with subsequent removal, or permanent, in the form of a prosthesis. The devices may be internal or external of the body. The instant device may be used in these applications. However, the preferred embodiment is related to spinal fixation and the description is directed thereto by way of example and not limitation. 
    
    
     
       SHORT DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective of a portion of the spine with the orthopedic device of this invention in place; 
         FIG. 2  is a perspective of one embodiment of the orthopedic device of this invention; 
         FIG. 3  is an end view, partially in section, of the orthopedic device of this invention with the compression ring in the open position; 
         FIG. 4  is an end view, partially in section, of the orthopedic device of this invention with the compression ring in the closed position; 
         FIG. 5  is a cross section of  FIG. 3 ; 
         FIG. 6  is a cross section of  FIG. 4 ; 
         FIG. 7  is a top plan view of the clamp body of this invention; 
         FIG. 8  is a side view, partially in section, of the clamp body of this invention; 
         FIG. 9  is a perspective of the clamp body of this invention; 
         FIG. 10  is a perspective of the compression ring of this invnetion invention; 
         FIG. 11  is a top view of the compression ring of this invention; 
         FIG. 12  is a cross section of the compression ring of this invention; 
         FIG. 13  is a perspective of another embodiment of this invention; 
         FIG. 14  is a perspective of another embodiment of this invention; 
         FIG. 15  is a perspective of another embodiment of this invention; 
         FIG. 16  is a cross section of  FIG. 15  showing the compression ring in the open position; 
         FIG. 17  is a cross section of  FIG. 15  showing the compression ring in the closed position; 
         FIG. 18  is a perspective of another embodiment of this invention with the compression ring in the open position; 
         FIG. 19  is a side view of  FIG. 18  with the compression ring in the closed position; 
         FIG. 20  is a perspective of another embodiment of this invention with the compression ring in the open position; 
         FIG. 21  is a side view of  FIG. 20  with the compression ring in the closed position; 
         FIG. 22  is a perspective of another embodiment of this invention; and 
         FIG. 23  is a cross section of  FIG. 22 . 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates a portion of the lumbar spine S with a unilateral orthopedic fixation device  10  in place to stabilize and fix the vertebra in relation to each other and the sacrum in order to maintain a more natural curvature. A bilateral installation can be used, if deemed necessary. As shown in more detail in  FIG. 2 , an elongated connector bar  11  spans the discontinuity between the vertebra and bone screws  13 . As shown, the bar has a circular cross section however, other shapes may be used, such as shown for the link  29  in  FIG. 13 . The bone anchors have an exterior helical thread  60 , shown in  FIGS. 5-6 , by which the bone screws  13  gain purchase in the cancellous bone through application of torque. 
     The torque is applied to the screws by the surgeon using a tool (not shown) that engages the recess  61  in the head  15  of the screw and rotates the screw about its longitudinal axis. The amount of torque is critical to installation and the long life of the prosthesis in that too little does not secure the screw from loosening or backing out and too much causes the stripping of the thread path in the bone and loss of purchase. The surgeon attempts to apply the optimum torque when placing the screws in the bone and additional torque on the bone screw is to be avoided. As shown in  FIGS. 5 and 6 , the recess  61  is accessible through the clamp body  12  which permits pre-assembly of the screw and clamp, if desired, before placement in the bone. 
     During the spinal fixation, the several bone screws are threaded into the different vertebrae according to the anatomy of each vertebrae. This results in a series of screws without uniformity in angle or alignment. To compensate for these anomalies, the connection between the head of the screws and the clamp bodies pivots or swivels to capture the connector rod. In some instances, the rod must be bent because the screws are so far out of line or the intended correction is so severe. In other cases, a link may be used to secure the rod relative to the bone screw. To avoid application of any more torque to the bone screw, the connector rod  11  is secured to the bone screw by a linear motion which applies compressive force through clamp  12  to the rod  11  and the head  15  of the screw. 
     The exterior walls  24  of the clamp body  12  are illustrated as generally tubular with a receptacle  25 , shown in  FIG. 8 , at one end and a slot  23  at the other end. The receptacle is of a size to accommodate the head  15  of the bone screw. The slot  23  has upper and lower longitudinal ridges  17  and  18 , respectively, to grip the connector rod  11 . As shown in  FIGS. 5 and 6 , the head  15  is spherical and the inside surface  16  of the receptacle is complementary to permit a universal or swivel connection. The orthopedic device has a low profile because the connector rod is recessed in the slot  23  of clamp  12 . 
     The exterior walls  24  of clamp  12  may be tapered or otherwise shaped to provide a change in external diameter along the length. The walls  24  also are relieved with circumferential slots  27  and  28 , shown in  FIGS. 8-9 , to increase the radial flexibility of the clamp. A compression ring  14  is force fit on the exterior walls  24  of the clamp  12  by flexing the tubular walls. The compression ring  14  is moveable along the exterior walls from an open position to a closed position. The open position, as shown in  FIGS. 5 ,  18 , and  20 , allows swiveling movement of the screw head and sliding movement of the connector rod within the clamp  12 . In the closed position, shown in  FIGS. 6 ,  19  and  21 , the compression ring  14  applies compressive forces between the clamp  12  and the rod  11  and screw  13  that immobilizes the connections. The compression ring  12  14 has a skirt  26  with spaced inner annular ridges  19  and  22  which engage annular bulges  19  20 and  21 , respectively, on the exterior walls  24  of clamp  12  in the closed position. 
     The application of the compressive force that immobilizes the components of the orthopedic device is generated by a linear movement of the compression ring relative to the exterior walls of the clamp. This movement to the closed position is accomplished using a simple telescoping instrument (not shown) engaging the clamp and the compression ring so that equal and opposite forces moves the ring without imparting stress to the screw. In the event of remedial surgery, the clamp may be moved to the open position in the same manner. 
     The link  29 , shown in  FIG. 13 , extends the range of the orthopedic device in situations where the connector rod cannot directly contact the slot  23  in the clamp  12 . The link may come in different lengths or be customized to the size necessary for a particular patient. The link  29  has an arm similar to the dimensions of a connector rod but of a trapezoidal shape though other shapes may be used. The arm has a journal  30  on one end. The journal  30  is shown as a closed ring however, it may be discontinuous. The journal has a threaded bore with a set screw  31  to secure the link to the connector rod. The other end of the link is secured to the bone screw by the clamp  12  and compression ring  14 . In  FIG. 14 , the link  29 ′ arm is the same or similar in shape to a connector rod. The link has a journal  30 ′ with a set screw  31 ′ to fix the connection with the connector rod  11 . 
     In  FIGS. 15 ,  16 , and  17  another link  29 ″ is illustrated with a journal  30 ″ at one end. The link is similar to a connector rod. The journal  30 ″ is a split sleeve with a compression ring  14 ′ encircling the split sleeve. The compression ring  14 ′ has an open position, shown in  FIG. 17 , and a closed position, shown in  FIG. 16 . After adjusting the connection between the link and the connector rod  11 , the compression ring is moved to the closed position to secure the link to the connector rod. The other end of the link  29 ″ is secured in the slot of the clamp  12  to complete the tightening of the orthopedic device. 
       FIGS. 18-23  illustrate embodiments of the orthopedic device  10  in which the clamp  12  includes a retainer preventing the inadvertent separation of the connector rod  11  from the clamp. The use of these clamps and retainers is discretionary with the surgeon. In  FIGS. 18 and 19 , the exterior walls of the clamp  12  extend above the slot  23  as opposing semi-circular projections. An exterior groove  41  is formed in the semi-circular projections resulting in a terminal lip  42 . A retainer ring  40  is snapped into and held in place by the groove  41 . 
       FIGS. 20 and 21  illustrate another retainer in the form of a clip  50  which extends across and covers the open slot  23 . The ends  53  of the clip are reverse folded to snap over the lip  52  and seat into the groove  51 . 
       FIGS. 22 and 23  illustrate a clamp  12 ′ with a bore  23 ′ for passage of the connector rod  11 . The bore  23 ′ is intersected by a threaded passage  60  with a set screw retainer  61  for holding the connector rod  11  and the clamp  12 ′ together. After the rod  11  is passed through the clamps of an orthopedic device, the compression rings would be moved to the closed position locking the orientation of the rods and screws. The set screws would then be tightened to fix the rod to the clamp. In this way, the torque of tightening the set screw would be absorbed by the rod. The clamp  12 ′ is locked to the screw  13  by compression ring  14 , shown in the closed position. 
     A number of embodiments of the present invention have been described. Nevertheless, it will be understood that various modifications may be made without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the invention is not to be limited by the specific illustrated embodiment but only by the scope of the appended claims.