Abstract:
Methods and devices for treatment of osteonecrosis of the femoral head with core decompression include a dowel adapted for placement into a core decompression channel of a femoral head. A cathode at the distal end of the dowel provides electrical stimulation of bone growth in the femoral head. A method of treating osteonecrosis of the femoral head involves placing a dowel having a cathode thereon into a core decompression channel of a femoral head in a state of osteonecrosis. Electrical current is supplied to the cathode for electrical stimulation of bone growth in the femoral head.

Description:
BACKGROUND OF THE INVENTION 
     This invention relates to stimulation of bone growth in the femoral head, and particularly to devices and methods used to treat osteonecrosis of the femoral head. 
     Osteonecrosis, or avascular necrosis (AVN), of the femoral head is a serious medical condition which afflicts about 20,000 people per year. Due to poor blood circulation to the head of the femur, bone necrosis occurs. As the body tries to remove the necrotic bone by osteoclastic resorption, the head of the femur weakens and eventually collapses, leading to total hip replacement. 
     Core decompression is a common procedure used to treat and retard progression of osteonecrosis of the femoral head that involves cutting a channel from the lateral cortex, just beneath the flare of the trochanter, into the necrotic bone of the femoral head. Various trials have been conducted to determine the effectiveness of core decompression on the treatment of osteonecrosis of the femoral head, with some including the use of bone grafting and electrical stimulation to study their effects on treatment. 
     In core decompression procedures utilizing electrical stimulation in addition to bone grafting to treat osteonecrosis of the femoral head, direct current bone growth stimulators have been used in conjunction with normal cancellous bone material removed from the trochanteric region and distal neck to improve the effectiveness of the treatment. In these procedures, the cathode electrodes of the stimulators have been wrapped around bone chips removed from the core decompression channel and sutured into place for placement into the core decompression channel. 
     Cathode placement devices are known to be used with direct current electrical stimulators to provide control of placement of the direct current electrical stimulator cathode and to alleviate migration of the cathode. An example of a cathode placement device is the EBI OsteoStim® CorticalLok bone dowel. The OsteoStim CorticalLok bone dowel is designed for placement across bone fractures to stimulate bone fusion, having distal and proximal portions designed to hold the intermediate shaft portion in position across a bone fracture. 
     There remains a need for a cathode placement device for the treatment of osteonecrosis of the femoral head that is adapted for use in conjunction with core decompression surgical procedures. 
     SUMMARY OF THE INVENTION 
     The present invention provides new methods and devices for treatment of osteonecrosis of the femoral head. According to one aspect of the invention, a dowel adapted for placement into a core decompression channel of a femoral head has a cathode at the distal end thereof for electrical stimulation of bone growth in the femoral head. 
     A new method according to the present invention involves placing a dowel having a cathode thereon into a core decompression channel of a femoral head in a state of osteonecrosis, and supplying electrical current to the cathode for electrical stimulation of bone growth in the femoral head. 
     According to a further aspect of the present invention, a device for treatment of osteonecrosis of the femoral head includes a resorbable dowel adapted for placement into a core decompression channel of a femoral head to provide an osteogenic environment. 
     In broad terms, the invention provides a new indication for a dowel with a cathode for electrical bone growth stimulation: The method comprises providing such a dowel and indicating its use for treatment of the osteonecrosis of the femoral head. 
     The objects and advantages of the present invention will be more apparent upon reading the following detailed description in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of one embodiment of a dowel for treatment of osteonecrosis of the femoral head according to the present invention. 
         FIG. 2  is a perspective view of another embodiment of a dowel for treatment of osteonecrosis of the femoral head according to the present invention. 
         FIG. 3  shows an implantable bone growth stimulator with the dowel of  FIG. 1 . 
         FIG. 4  illustrates placement of the device of  FIG. 4  in a core decompression channel of a subject&#39;s femoral head. 
     
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
     For the purpose of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, such alterations and further modifications in the illustrated device and such further applications of the principles of the invention as illustrated therein being contemplated as would normally occur to one skilled in the art to which the invention relates. 
       FIG. 1  shows an embodiment of a dowel  10  according to the present invention, typically having a length in the range of about 4-8 centimeters (cm), preferably about 6 cm. The dowel  10  has a proximal end  12 , preferably having an outer diameter in the range of about 6-12 millimeters (mm), preferably about 8-10 mm, and has a reduced-diameter distal portion  14 , preferably about 2 mm smaller in diameter, to maintain substantially the same outer diameter of the dowel  10  when a cathode electrode of a bone growth stimulator is wrapped around the distal portion  14 . One suitable cathode is titanium wire having a diameter of about 1 mm, insulated through the dowel, with an un-insulated exposed length of about 12 cm wrapped around the distal portion. A bore  16 , preferably oriented along the longitudinal axis of the dowel  10 , is provided as a path for the cathode wire. The bore  16  may be sized slightly larger than a cathode wire to provide a snug fit for the cathode wire and to maintain overall dowel strength, or, alternatively, may be larger, as shown in  FIG. 2 , reducing the overall mass of the dowel  22  to promote faster resorption and facilitate bone ingrowth. 
     In other alternative embodiments, the dowel may have an external longitudinal groove for carrying a cathode wire from the proximal end of the dowel to the distal end of the dowel, or the dowel may have an external threaded portion in place of the reduced-diameter distal portion  14 , with the major diameter of the threads equal to the outer diameter of the proximal end  12  and with the cathode wire in the roots of the threads. Alternatively, the cathode electrode may be internally concentrated within the dowel at the distal end. Further, the dowel could have a concentration of carbon embedded in a spiral or helical pattern about the dowel that could be used as an electrically conductive path in place of using a cathode wire. 
     The dowel  10 ,  22  may be made of allograft bone, such as cortical bone, or, more preferably may be made of a resorbable material such as commercially available Lactosorb from Biomet, Inc. or Bioplex from Interpore Cross International, Inc, or from calcium phosphate (CaPO 4 ) or calcium sulphate (CaSO 4 ), for example. Utilizing resorbable materials such as Lactosorb or Bioplex allows manufacture of the dowel  10 ,  22  without need of allograft bone and avoids the cost and complications associated with the use of allograft bone. 
     Referring to  FIG. 3 , there is illustrated an example of an implantable bone growth stimulator  24 , such as OsteoGen™ surgically implanted bone growth stimulator from EBI, contemplated for use with dowels  10 ,  22  comprising a current generator  26  having a housing  28  that is electrically conductive and comprises an anode, an insulated lead  30 , and a cathode electrode  32 . A battery and control circuitry are disposed within the housing and serve to deliver an electrical current through bone tissue between the anode of the housing and the cathode. Such electrical current is effective in stimulating the growth of bone at a site in the vicinity of the cathode, according to well-known principles. 
       FIG. 3  illustrates how the cathode electrode  32  of the bone growth stimulator  24  is used with the dowel  10  of  FIG. 1 . The cathode electrode  32  is preferably introduced into bore  16  by way of the proximal opening  34 , where it may be advanced through the dowel  10  to the distal opening  36  of the shaft  16 . The cathode electrode  32  is then wrapped about the reduced-diameter distal portion  14  of the dowel  10  so that the cathode electrode  32  is concentrated at the distal end  18  of the dowel  10 . The dowel  10  may then be used as a placement device to place the cathode electrode  32  of the bone growth stimulator  24  in the core decompression channel of a subject&#39;s femur, and to hold the cathode electrode  32  adjacent to necrotic bone of the femoral head. 
     In one preferred method of treating osteonecrosis of the femoral head, the dowels  10 ,  22  of the present invention may be used in conjunction with a core decompression procedure to provide an osteogenic environment within the femoral head and to partially bear weight placed upon the femoral head. The method involves placing a dowel adapted to fit into a core decompression channel, such as dowels  10  and  22 , into a core decompression channel, in place of, or in conjunction with bone material removed during cutting of the core decompression channel, to promote bone growth. 
     Another preferred method of treating osteonecrosis of the femoral head involves utilizing the dowels  10 ,  22  of the present invention as a cathode placement device to improve efficacy of the treatment. The cathode electrode  32  of a bone growth stimulator  24  may be wrapped about dowels  10 ,  22 , as previously described, so that the cathode electrode  32  is concentrated at the distal end  18  of the dowel  10 . The dowel  10  may then be inserted into a core decompression channel  34  of a subject&#39;s femoral head  36 , as shown in  FIG. 4 , oriented so that the distal end  18  of the dowel  10  is adjacent the distal end  38  of the core decompression channel  34 . The bone growth stimulator  24  may then be used to supply direct current in the range of 20-200 microamperes (μA) to the cathode electrode  32 , with 100 μA being a more preferred current level to stimulate bone growth within femoral head  36 . 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only preferred embodiments have been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected.