Patent Publication Number: US-2005143748-A1

Title: Pressurizer

Description:
RELATED APPLICATIONS  
      This application claims the benefit of U.S. provisional patent application Ser. No. 60/520,232, filed Nov. 14, 2003, the advantages and disclosure of which are herein incorporated by reference. 
    
    
     FIELD OF THE INVENTION  
      The present invention generally relates to a pressurizer for use with a bone cement injection device to inject bone cement into a bone canal or other anatomical site under pressure.  
     BACKGROUND OF THE INVENTION  
      Total hip arthroplasty (THA) is a procedure that relieves pain and increases mobility of patients having discomfort and partial immobility caused by degenerated natural hip joints. In the THA procedure, an artificial hip joint replaces the natural hip joint. In particular, a spherical end of the patient&#39;s femur is removed and replaced with a metallic implant. The metallic implant comprises a stem and a ball fixed to the stem. The stem fits down the center of the femur in a surgically prepared bone canal, i.e., a medullary canal, and is fixed in place by bone cement. The bone cement provides a rigid structure to lock the stem of the metallic implant in the medullary canal. The ball of the metallic implant fits into a socket of an acetabular component to complete the artificial hip joint.  
      Several factors affect the success of the THA procedure with respect to the preparation and injection of the bone cement into the medullary canal. One of the most important factors is the pressure at which the bone cement is supplied into the medullary canal. Typically, the bone cement is injected into the medullary canal through a nozzle of a bone cement injection device. Once the medullary canal is filled with bone cement, the metallic implant is inserted into the bone cement. The bone cement hardens between the bone and the metallic implant. Fixation of the metallic implant relies upon the interlocking of the bone cement between cancellous bone, which forms an inner surface of the medullary canal, and keyed features or projections on the metallic implant.  
      In the THA procedure, problems can occur with inadequate penetration of the bone cement into the cancellous bone of the inner surface. As a result, the metallic implant loosens prematurely, resulting in failure of the artificial hip joint. This penetration can be improved by pressurizing the bone cement within the medullary canal. Pressurization can be improved by using a pressurizer such as those shown in U.S. Pat. Nos. 4,896,662 to Noble; 5,741,265 to Chan; and 6,017,350 to Long. Each of the pressurizers shown in these patents includes a body defining an inlet for receiving the nozzle of the bone cement injection device and an outlet in direct communication with the medullary canal. The body seals the medullary canal to pressurize the bone cement in the medullary canal. However, each of these pressurizers requires the nozzle to be positioned generally in line with the medullary canal to inject the bone cement into the medullary canal. Thus, these pressurizers require relatively straight-line access to the medullary canal.  
     BRIEF SUMMARY OF THE INVENTION  
      The present invention provides a pressurizer for use with a bone cement injection device to inject bone cement into an anatomical site under pressure. The pressurizer includes a body having a proximal end and a distal end. The distal end is formed of a resilient material to seal against the anatomical site. An inlet is defined at the proximal end and an outlet is defined at the distal end. A channel interconnects the inlet and the outlet to convey the bone cement to the anatomical site. The channel defines a cement flow path that directionally varies between the inlet and the outlet such that the bone cement can be injected inline with the anatomical site while the bone cement injection device is positioned at an angle to the anatomical site.  
      One advantage of this configuration is a reduction in congestion of equipment near the anatomical site. With the configuration of the present invention, the bone cement injection device can be kept out of the way of the anatomical site, such as a medullary canal, during the procedure.  
      In another aspect of the present invention, the body includes a support member formed of rigid material and a wall of resilient material surrounds the rigid support member. The support member is preferably formed from a polycarbonate or like material and the wall is preferably formed from silicone.  
      In yet another aspect of the present invention, a handle is fixed to the body to manipulate the body during use, e.g., to facilitate placement of the body in the medullary canal. The handle may be fixed to the support member or to the wall or the handle may be a separate component.  
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS  
      Advantages of the present invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:  
       FIG. 1  is a perspective view of a pressurizer of the present invention being used with a bone cement injection device to inject bone cement into an anatomical site under pressure;  
       FIG. 2  is a cross-sectional perspective view of the pressurizer of  FIG. 1  taken along the line  2 - 2  in  FIG. 1 ;  
       FIG. 3  is an exploded view of an alternative embodiment of the pressurizer illustrating a support member and a wall of resilient material that is formed about the support member;  
       FIG. 4  is a perspective view of the pressurizer of the alternative embodiment of  FIG. 4 ;  
       FIG. 5  is a perspective view of another alternative embodiment of the pressurizer in which a handle is fixed to a body of the pressurizer to facilitate manipulation of the body during use; and  
       FIG. 6  is a perspective view of another alternative embodiment of the pressurizer with the handle fixed to the support member of the body. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION  
      Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a pressurizer is generally shown at  14 . The pressurizer  14  is preferably used in combination with a bone cement injection device  30  to form a bone cement injection system. The injection system provides for the injection of bone cement BC into an anatomical site  12 , such as a bone canal  12 , under pressure.  
      Referring to  FIG. 1 , the pressurizer  14  comprises a body  16  extending between a proximal end  18  and a distal end  20 . The proximal end  18  of the body  16  is defined by a first planar surface  42  having a generally elliptical shape. The distal end  20  of the body  16  is defined by a second planar surface  44  having a generally elliptical shape. The planar surfaces  42 ,  44  are disposed in planes that are transverse to one another. The body  16  defines an inlet  28  in the first planar surface  42  and an outlet  32  in the second planar surface. The inlet  28  is adapted to receive a nozzle  29  of the bone cement injection device  30 . The outlet  32  is adapted for operatively communicating with the bone canal  12 . A generally circular channel  33  extends through the body  16  between the inlet  28  and the outlet  32 .  
      Referring to  FIG. 2 , the channel  33  comprises first  36  and second  38  segments. The first segment  36  is disposed about a first axis A and extends from the inlet  28  to the second segment  38 . The second segment  38  is disposed about a second axis B and extends from the first segment  36  to the outlet  32 . The first A and second B axes intersect one another inside the body  16  at an acute angle α relative to one another. As a result, the first  36  and second  38  segments are arranged at the acute angle α to one another, i.e., are nonlinear relative to one another, such that the bone cement is redirected inside the body  16  as the bone cement travels from the first segment  36  into the second segment  38  during injection. In other words, still referring to  FIG. 2 , the channel  33  defines a cement flow path C that directionally varies between the inlet  28  and the outlet  32 . The cement flow path C begins at an angle to the bone canal  12  in the first segment  36  and finishes in line with the bone canal  12  in the second segment  38 . Preferably, the channel  33  maintains a substantially uniform diameter along the first  36  and second  38  segments between the inlet  28  and the outlet  32 . The inlet  28  and outlet  32  and the first  36  and second  38  segments are preferably circular in shape.  
      The body  16  includes a wall  40  of resilient material, preferably elastomeric material, formed about the channel  33 . The wall  40  is more preferably formed from silicone, and most preferably formed from silicone having a durometer of at least 40 Shore A. In alternative embodiments, the silicone may have an alternative stiffness or be replaced with a like material. As seen in the cross-sectional view of  FIG. 2 , the wall  40  varies in thickness between the proximal  18  and distal  20  ends. An annular seal  31  is integrally formed with the wall  40  in the first segment  36  of the channel  33  to seal the nozzle  29  in the first segment  36 . In alternative embodiments, the annular seal  31  may be a separate o-ring that fits into a groove formed in the wall  40  in the first segment  36 .  
      The wall  40  gives the body  16  a boot-shaped appearance with a front surface  39  extending in a curvilinear shape from the proximal end  18  to the distal end  20 , a rear surface  41  extending from the proximal end  18  to a heel section  22 , and a bottom surface  43  extending from the heel section  22  to the distal end  20 .  
      Referring specifically to  FIG. 2 , the body  16  includes a first portion  24  lying generally along the first axis A from the proximal end  18  to the heel section  22  and a second portion  26  lying generally along the second axis B from the heel section  22  to the distal end  20 . The first  24  and second  26  portions share the front surface  39 . The rear surface  41  extends along the first portion  24  from the proximal end  18  to the heel section  22  and the bottom surface  43  extends along the second portion  26  from the heel section  22  to the distal end  20 . The rear surface  41  has a length L 1  that is from 20 to 100 percent longer than a length L 2  of the bottom surface  43 , more preferably, 30 to 70 percent longer than the length L 2  of the bottom surface  43 , and most preferably 30 to 50 percent longer than the length L 2  of the bottom surface  43 . Of course, in other embodiments, the lengths could vary outside of this range, or they could be equal. The first portion  24  gradually increases in size along the first axis A from the proximal end  18  to the heel section  22 . Likewise, the second portion  26  gradually decreases in size along the second axis B from the heel section  22  to the distal end  20 .  
      Referring to  FIGS. 3 and 4 , an alternative embodiment of the pressurizer  114  is shown. In this embodiment, the body  116  includes a rigid support member  150  to provide additional support and structural rigidity to the body  116  during use. This additional support is helpful in transferring additional axial pressure into the body  116  to help seal the pliable silicon wall  140  against the inner surface  47  of the bone canal  12 . Hence, the rigid support member  150  further assists in transferring a force exerted by the user on the bone cement injection device  30  into the body  116  to increase the strength of the seal between the wall  140  and the inner surface  47 . This further pressurizes the bone cement BC in the bone canal  12 .  FIG. 3  illustrates the rigid support member  150  separated out from the rest of the body  116 . This is for illustrative purposes only. In practice, the wall  140  of resilient material is formed about the rigid support member  150 . Preferably, the wall  140  is overmolded onto the resilient body  150 .  
      Referring to  FIG. 4 , the rigid support member  150  includes a tubular member  152  extending between first and second ends to further define said channel  133 . The tubular member  152  has a first tubular section  154  to further define the first segment  136  of the channel  133  and a second tubular section  156  angled at the acute angle α relative to the first first tubular section  154  to further define a portion of the second segment  138 . A groove may be formed inside the first tubular section  154  to seat the annular seal  131 . A first rigid flange  160  is fixed about the tubular member  152  and perpendicular to the tubular member  152  at the first end to further define the inlet  128  of the body  116 .  
      Wings  158  are fixed on opposite sides of the tubular member  152  from the first rigid flange  160  distally along the first tubular section  154 . The wings  158  extend radially outwardly from the first tubular section  154  into the wall  140  relative to the first axis A. The first rigid flange  160  perpendicularly intersects the wings  158 . In this embodiment, the first rigid flange  160  presents the first planar surface  142  in which the inlet  128  is defined. A second rigid flange  162  is fixed about the tubular member  152  and perpendicular to the tubular member  152  at the second end.  
      The second rigid flange  162  is positioned within the body  116  between the heel section  122  and the distal end  120  of the body  116 . Preferably, the second rigid flange  162  terminates distal of the heel section  122  and proximal to the distal end  120 . Thus, the wall  140  of resilient material extends distally past the second end of the rigid support member  150  in an unsupported manner to define a flexible portion  161  for sealing against the inner surface  47  of the bone canal  12  as the bone cement BC is injected into the bone canal  12  through the pressurizer  114 . Preferably, the wall  140  completely surrounds the rigid support member  150 , except at the first flange  160 . Thus, these two components are inseparable. The rigid support member  150  is preferably formed from a rigid material such as polycarbonate or like material, including stainless steel.  
       FIG. 5  illustrates yet another embodiment of the pressurizer  214 . In this embodiment, a handle  266  is fixed to the body  216  to maneuver the body  216  during use. The handle  266  is preferably fixed to the rear surface  241  of the first portion  224 . The handle  266  includes a base plate  268  having an arcuate shovel-like shape to match the shape of the rear surface  241  of the first portion  224 . The base plate  268  is preferably mounted to the rear surface  241  of the first portion  224  by an adhesive, ultrasonic welding, interdigitation of prongs in the base plate  268 , or by other methods well known in the art such that the base plate  268  is fixed to the body  216 . An arm  270  extends from the base plate  268  in a cantilevered manner and includes a first section  272  and a second section  274  extending at an obtuse angle to the first section  272 . The second section  274  lies generally in the same plane as the first planar surface  242 . In a further embodiment  314  shown in  FIG. 6 , the handle  366  may be fixed to the rigid support member  350  at the first rigid flange  360 . In other embodiments, the handle  266 ,  366  could also be a selectively removable component of the pressurizer  214 ,  314 .  
      These handle arrangements provide additional mechanical advantage to the user when placing the body  216 ,  316  in the bone canal  12  and injecting the bone cement BC into the bone canal  12 . This additional mechanical advantage can replace some of the force required from the user on the bone cement injection device  30  to ensure an adequate seal between the body  216  at the distal end  220 ,  320  and the inner surface  47  of the bone canal  12 . Thus, the handle  266 ,  366  provides better maneuverability of the pressurizer  214 ,  314  and the bone cement injection device  30  in surgical procedures. In some instances in which the user can exert a majority of the required force using the handle  266 ,  366 , a flexible nozzle (not shown) can replace the rigid nozzle  29 , shown in  FIG. 1 .  
      During use, referring back to  FIG. 1 , the nozzle  29  of the bone cement injection device  30  is positioned within the first segment  36  and is sealed therein by the annular seal  31 . The pressurizer  14 , with nozzle  29  sealed thereto, is inserted into the bone canal  12 . In particular, the distal end  20  is positioned within the bone canal  12  such that the front surface  39  and the bottom surface  43  adjacent to the distal end  20  creates a seal with an inner surface  47  of the bone canal  12 . The distal end  20  is configured to provide a suitable sealing interface between the pressurizer  14  and the inner surface  47 . This interface is critical in pressurizing the bone cement BC within the bone canal  12 .  
      Once in sealed engagement, the bone cement BC is injected through the nozzle  30  into the first segment  36 . The bone cement BC travels along the cement flow path C, where the bone cement BC is redirected in the second segment  38  toward the outlet  32  to be ultimately discharged from the outlet  32  into the bone canal  12 . This configuration allows a user to inject the bone cement BC into the pressurizer  14  at an angle, while the bone cement BC is redirected to be discharged from the outlet  32  inline with the bone canal  12 . Once the bone canal  12  is close to being filled, as shown in  FIG. 1 , the bone cement BC is injected under pressure. The pressurizer  14  maintains the seal within the bone canal  12  to facilitate pressurization of the bone cement BC during injection. The pressure in the bone canal  12  results from a combination of a force produced by the user on the bone cement injection device  30  and the seal of the pressurizer  14  within the bone canal  12 . The pressure assists in reducing air pockets within the bone cement BC. The pressure also increases contact with cancellous bone and penetration into the cancellous bone along the inner surface  47  of the bone canal  12 , thus increasing the structural integrity of the bone cement BC in THA or like procedures. A plug  46  is preferably used to seal a distal end of the bone canal  12  and prevent the distal migration of the bone cement BC during injection.  
      The embodiments described herein allow the surgeon in a THA or like procedure to inject the bone cement BC into the bone canal  12  at an angle to the bone canal  12 . Often, this is necessary given the constraints of the anatomical site in which the procedure is being performed. Furthermore, these embodiments provide added flexibility and maneuverability in total hip arthroscopy and total knee arthroscopy procedures. These procedures are minimally invasive. The pressurizer  14 ,  114 ,  214 ,  314  of the present invention can be used in such procedures given its flexibility. For instance, in a muscle-sparing procedure, the maneuverability of the pressurizer  14 ,  114 ,  214 ,  314  and the bone cement injection device  30  allows the user to access the anatomical site at varying angles in between muscle layers. The pressurizer  14 ,  114 ,  214 ,  314  can similarly be used in a lateral approach to total knee arthroscopy.  
      Obviously, many modifications and variations of the present invention are possible in light of the above teachings.