Abstract:
A bone-engaging attachment device including a shaft threaded or otherwise adapted to mate with or to accept a fastener, and having a head extending radially at one end of the shaft. A method of attachment of the device to a bone includes preparing a hole in the bone large enough to receive the head and a channel extending from the hole, inserting the head into the hole, and moving the device to a location where the shaft extends outward through the channel while the head is engaged with the bone.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The present invention relates to bone-engaging fixation devices used in orthopedic surgery, and particularly to devices and a method for their use for positioning, immobilization, or reattachment of bones and attachment of other tissues to bones.  
         [0002]     Orthopedic surgeons use bone-engaging fixation devices for a wide variety of purposes. Soft tissue repairs often require reattachment of the soft tissue to a bone. In particular, when surgically repairing an injured joint, damaged soft tissues such as ligaments and tendons are often reattached to bone.  
         [0003]     When surgeons reduce fractures or reposition bones, rods or cables are often attached to fixation devices implanted in different bones or regions of a bone. During spinal repair surgery, rods or wires are often used to interconnect vertebrae in order to accomplish spinal fusions.  
         [0004]     Fixation devices are often implanted into holes drilled into a bone. A small hole is typically drilled through the outer, cortex, layer of the bone and into the inner, cancellous, part of the bone, and various types of securing features such as resilient barbs on pins, screw threads, or grooved surfaces on pins or staples, are used to secure such fixation devices to the bone.  
         [0005]     As a fixation device performs its function, bodily tissues or devices attached to the fixation device exert stress and the fixation device must be implanted securely enough to resist such stress and remain attached to the bone. If the fixation device does not have enough pull-out resistance to remain adequately securely attached to the bone, especially in the case of weakened or osteoporotic bone, a surgical repair may be compromised or fail. In certain bones, such as the occipital portion of the skull, it may be desired to attach an appliance securely in a location where stress may be applied in an outward direction, tending to withdraw the fixation device, and with great enough force to present a risk of withdrawing a fixation device of previous known designs.  
         [0006]     What is desired, then, is a bone-engaging fixation device with ample pull-out resistance, and that can reliably withstand greater forces in at least some directions than previously available fixation devices can bear, and a method for attachment to bone utilizing such a device.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention answers the needs mentioned above, by providing a bone-engaging fixation device for use in orthopedic surgery that includes a shaft and a radially extending head at one end of the shaft. The fixation device may be implanted in a bone by forming a generally keyhole-shaped opening through the cortex layer of the bone, and thereafter inserting the head of the fixation device inward through the larger part of the hole. The device is then pushed laterally, with its head adjacent the inner boundary of the cortex layer, so that the shaft of the device is in a narrow channel part of the keyhole-shaped opening, extending outward from within the bone. The shaft thus is available outside the bone to receive attachment of a wire or a nut or other fastener used to attach a rod, wire, another appliance, or tissue such as a ligament or tendon to the bone at the location of the fixation device.  
         [0008]     The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the preferred embodiments, taken in conjunction with the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0009]      FIG. 1  is an isometric view of a bone-engaging attachment device that is one exemplary embodiment of an aspect of the invention.  
         [0010]      FIG. 2  is an isometric view of a portion of an exterior surface of a bone, with a unicortical drill being used to prepare a hole in the bone to receive the attachment device shown in  FIG. 1 .  
         [0011]      FIG. 3  is an isometric view of the portion of an exterior surface of a bone shown in  FIG. 2 , and showing a lateral channel.  
         [0012]      FIG. 4  is an isometric view of an attachment device such as the one shown in  FIG. 1  being placed into the hole shown in  FIG. 2 .  
         [0013]      FIG. 5  is an isometric view of the attachment device shown in  FIGS. 1 and 4  being moved into the lateral channel.  
         [0014]      FIG. 6  is an isometric view showing the attachment device in place in the bone shown in  FIGS. 2-5  with a nut mated with the threads on the shaft of the device to secure a wire to the bone in which the device is implanted.  
         [0015]      FIG. 7  is a sectional view taken along line  7 - 7  of  FIG. 6 , showing a wire captured in a grooved washer.  
         [0016]      FIG. 7A  is a view similar to  FIG. 7 , showing a plate secured to a bone by the attachment device shown in  FIGS. 1 and 5 - 7 .  
         [0017]      FIG. 7B  is a view similar to  FIG. 7 , showing a rod fastened to a bone by the attachment device.  
         [0018]      FIG. 8  is a sectional side elevational view of a human skull, showing an attachment device such as that shown in  FIG. 1  implanted in the occipital region of the skull.  
         [0019]      FIG. 9  is a posterior view of a portion of the skull shown in  FIG. 8 , showing two attachment devices such as that shown in  FIG. 1  implanted in the occipital region.  
         [0020]      FIG. 10  is a sectional, partially cut-away, and simplified view of a human shoulder joint, with an attachment device that is another exemplary embodiment of the present invention implanted in the shoulder joint. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0021]     Referring now to  FIGS. 1-9  of the drawings which form a part of the disclosure herein, a bone-engaging surgical fixation or attachment device  12  has a shaft  14  and a radially extending head  16  attached to one end of the shaft  14  with an engaging face  18  facing toward the shaft  14 .  
         [0022]     The shaft  14  of the device  12  may be threaded, as shown in  FIG. 1 , and a hole  22  may be provided, extending transversely through the shaft  6  and spaced apart from the engaging face  18  by a suitable distance, to make the shaft suitable to receive a connector, for example, a wire  24  to be fastened to a bone by use of the attachment device  12 . Alternatively, the shaft might define a slot  23 , shown in broken line, extending over at least a portion of its length, to receive a rod or wire that can be captured by a nut threaded onto the shaft  14 .  
         [0023]     Protruding from the engaging face  18  are several retainers  20 , preferably evenly spaced, which, as shown in  FIG. 1 , may be inclined, wedge-shaped projecting bodies oriented around the shaft  14  where they can engage adjacent tissue so as to resist rotation of the device  12  in a direction which would tend to unscrew the shaft  14  from a threaded nut, as will be explained more fully presently.  
         [0024]     The bone-engaging attachment device  12  may be made in any of a variety of sizes depending on the particular application, considering, for example, the size of the patient, the particular bone where its use is intended, and what wire, rod, or appliance is intended to be fastened to a bone. For example, for use in the occipital region of a human skull, the shaft  14  may have a length  26  of 8 mm, and a diameter  28  of 3 mm. The head  16  may have a diameter or maximum width  30  of 10 mm and a thickness  32  of 0.80 mm, and the device  12  may be manufactured of a suitable biologically compatible metal, such as titanium or surgical stainless steel.  
         [0025]     The attachment device  12  is used by preparing a suitable hole in a bone where it is to be mounted. In the device  12 , shown in  FIG. 1  the head  16  is circular, and a corresponding circular hole may be prepared in a bone  34  by using a unicortical drill  36  to cut a circular hole to a depth  38  through the cortex  40  of the bone  34 . A preferred unicortical drill  36  has a depth stop  42  projecting radially from its cutting portion  44  to limit the depth  38  of a hole  46  to a distance of, for example, 5 mm, no more than slightly deeper than the thickness of the cortex  40 , although other drills or cutters could be used, taking care to limit the depth of the hole prepared.  
         [0026]     Once the hole  46  is prepared using the unicortical drill  36 , a relatively small side-cutting unicortical drill  48  is used to cut a channel  50 , preferably extending radially outward from the hole  46 , as indicated by the arrow  52 . The side-cutting unicortical drill  48  also has a radially extending depth stop  54 , so that the drill  48  can be used to cut the channel  50  with a depth  56  similar to the depth of the hole  46 . The side-cutting unicortical drill  48  preferably has a diameter appropriate to cut the channel  50  with a width  58  equal to the diameter  28  of the shaft  14  of the attachment device  12  intended to be attached to the bone  34 .  
         [0027]     While the head  16  is shown herein as circular, other shapes could also be used, as where an elongated oval shape might be able to fit better within a bone at a particular location. A correspondingly shaped hole  46  of an appropriate size could then be prepared by use of an appropriate drill, perhaps drilling overlapping holes.  
         [0028]     Referring next to  FIGS. 4 and 5 , the attachment device  12  is installed in the bone  34  by pressing it into the hole  46  as indicated by the arrow  60  in  FIG. 4 , so that the engaging face  18  of the head  16  is aligned slightly inward of the interior boundary of the cortex  40 , resting in the cancellous tissue of the bone  34 . The entire attachment device  12  is then moved laterally from the hole  46  into the channel  50 . The length  62  of the channel  50 , shown in  FIG. 4 , is great enough so that portions of the cortex  40  are adjacent the engaging face  18  except in the portion of the channel  50  between the shaft  14  and the hole  46 , when the attachment device  12  is moved entirely into the channel  50 , as shown in  FIG. 5 . The length  62  is thus preferably at least equal to the diameter  30  of the head  16 , so that when the attachment device  12  has been moved the engagement face  18  is adjacent an interior boundary of the cortex  40  and the head  16  is prevented from being pulled outward from the bone  34  by its engagement with the cortex  40 .  
         [0029]     A tool  64 , including a handle  66  shown partially cut away and a fork  68  of a size to fit the shaft  14 , may be used conveniently to push the attachment device  12  in the direction of the arrow  70  shown in  FIG. 5 , from its initial position within the hole  46  to its desired final position in the channel  50 . The thickness  32  of the head  16  is preferably no greater than is required for suitable strength, in order to minimize the force necessary to be exerted to push the head  16  through the cancellous tissue beneath the cortex  40  on either side of and at the end of the channel  50 .  
         [0030]     As shown in  FIGS. 6, 7 ,  7 A, and  7 B, once the attachment device  12  has been placed in the channel  50  as shown in  FIG. 5 , various options are available, such as the installation of a nut  72  by threading it onto the shaft  14 . The nut  72  may define a through-bore  74  useful to accept a spanner to tighten the nut  74  onto the shaft  14 , and the through-bore  74  may thereafter be used to receive and hold a wire or other appliance to be attached to the bone  34  by means of the device  12 . A washer  76  of the appropriate thickness is preferably installed on the shaft  14 , between the nut  72  and the outer surface of the bone  34 .  
         [0031]     As the nut  72  is tightened onto the shaft  14  the head  16  is pulled upward against the inner face of the cortex layer  40 , driving the retainers  20  into the tissue of the cortex  40 , where they engage the relatively hard bone tissue of the cortex  40  to resist rotation of the head  16  as the nut  72  is tightened onto the shaft  14 , as may be understood better with reference to  FIG. 7 . The retainers  20  may have other forms, but are preferably oriented so as to favor movement that would tend to tighten a threaded attachment and resist rotation in a loosening direction.  
         [0032]     A similar but slightly different use of the attachment device  12  is shown in  FIG. 7 , wherein a special washer  78  is located between the nut  72  and the surface of the bone  34 . The washer  78  includes a groove  80  in which a wire  82  is received and captured by the nut  72  as the nut  72  is tightened down upon the shaft  14  of the attachment device  12 .  
         [0033]     As shown in  FIG. 7A , the nut  72  may be tightened onto the shaft  14  of the attachment device  12  to attach a plate  83  to a bone, as may be desired in rigidly connecting one bone to another by the plate  83 .  
         [0034]     As shown in  FIG. 7B , a saddle nut  84  is threaded onto the shaft  14  above a washer  85  of a desired thickness to leave a saddle or slot  86  defined by the saddle nut available to receive a rod  87  which is captured in the slot  86  by a cap nut  88  threaded onto external threads on the saddle nut  84 .  
         [0035]     In  FIGS. 8 and 9  one particular application of the attachment device  12  is illustrated. In connection with stabilization of fractured cervical vertebrae C 1  and C 2 , it is desired in some cases to fuse vertebrae C 1  and C 2  together with each other and to the occipital portion  90  of the skull  89 . To accomplish satisfactory stabilization of the skull  89  a pair of attachment devices  12  may be inserted in respective holes  46  and channels  50  in the occipital portion  90  of the skull  89 , where the thickness  92  of the bone is ample for use of the device  12  and there is a great need for resistance to withdrawal of a fixation device because of the anticipated stresses related to the use of rods  91 , shown in broken line in  FIG. 9 , for example, to stabilize the skull and the adjacent vertebrae C 1  and C 2 .  
         [0036]     Depending upon the location of the required attachment to a bone, the head  16  of an attachment device  12  may be flat, as shown in  FIGS. 1-7 , or the head  16  may be arcuately curved with an appropriate radius of curvature as to form a portion of a sphere, cylinder or cone, so that the engaging face  18  may be seated more fully in contact with the interior surface of the cortex of the bone where it is to be used.  
         [0037]     Thus, as shown in  FIG. 10 , an attachment device  12 ′ is shown mounted in the head  94  of a humerus  96  to provide a point of attachment of the supra-spinatus muscle M to the humerus  96  to repair a shoulder joint injury. The head  98  of the attachment device  12 ′ is curved to fit against the interior face of the cortex  99  of the head  98  of the humerus  96 . The torn tendon  100  is attached to the attachment device  12 ′ by a tendon nut  102 , whose surface facing toward the head  98  of the humerus is preferably equipped with slanted spikes or teeth  104  in order to more securely hold the tendon and resist loosening rotation of the nut  102  on the shaft  14  of the attachment device  12 ′ while the tendon  100  heals and reattaches itself to the bone tissue.  
         [0038]     The terms and expressions which have been employed in the foregoing specification are used therein as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding equivalents of the features shown and described or portions thereof, it being recognized that the scope of the invention is defined and limited only by the claims which follow.