Abstract:
A device and method for joint replacement surgery, such as total hip replacement surgery, including a bone cement plug which is adaptable to any size bone canal, an insertion tool for deploying the plug in the canal, and a cradle for storing the plug and insertion tool, The bone cement plug comprises a body defined by a series of separable units, each with a flange. The flanges decrease in diameter from the proximal end of the body to the distal end of the body. For smaller canals that cannot receive the large flanges, appropriate units of the plug may be removed, thus eliminating the oversized flanges in favor of the more appropriately sized flanges.

Description:
FIELD OF THE INVENTION 
     This invention relates to surgical devices and procedures in general. More particularly, this invention relates to bone cement plugs of the sort used in conjunction with bone cement dispensers to compact bone cement into bone canals during joint replacement surgeries. 
     BACKGROUND OF THE INVENTION 
     Bone cement plugs are well known in the art. Such devices are generally used in conjunction with bone cement dispensers to compact bone cement into a bone canal before fixing a prosthetic device in that bone canal. By way of example, bone cement plugs are commonly used in conjunction with bone cement dispensers to compact bone cement into the medullary canal of a femur before fixing the femoral stem of an artificial hip in that canal. 
     More particularly, in joint replacement surgeries, such as total hip and shoulder replacements, bone cement is commonly used to fix the stem of a prosthetic device in the medullary canal of a bone of the joint. In this respect, it has generally been found that a prosthetic device will be more securely fixed in a bone canal if the bone cement is well packed into the bone canal before the stem of the prosthetic device is positioned in the bone canal. 
     To this end, after initial preparation and cleaning of the bone canal, the distal portion of the canal is generally occluded with a bone cement plug. The bone cement plug limits uncontrolled flow of bone cement into the distal portion of the bone canal. Ideally, the bone cement plug limits the column of bone cement to about 1 to 2 cm beyond the distal tip of the stem of the prosthesis. After the bone cement plug has been set at the distal portion of the bone canal, bone cement is injected into the distal-most part of the occluded bone canal, adjacent to the plug, using a bone cement dispenser having a long nozzle. The bone canal is then filled with bone cement in a retrograde fashion, by withdrawing the nozzle of the bone cement dispenser from the distal end of the bone canal toward the proximal end of the bone canal as the cement issues from the nozzle. Retrograde filling helps to avoid trapping air in the distal-most part of the bone canal. 
     After the bone canal has been filled with bone cement, a bone canal pressurizer is connected to the bone cement dispenser. The pressurizer is pressed against the open end of the bone so as to occlude the proximal end of the bone canal. Then more cement is injected into the bone canal, through the pressurizer, under pressure. Under such pressurization, the cement in the bone canal intrudes into the interstices of the inner surface of the bone wall defining the bone canal. When the bone cement sets, a micro-interlock is established between the cement and the irregularities of the inner surface of the bone wall. This significantly enhances fixation of the prosthetic device in the bone canal. 
     A variety of bone cement plugs are known in the art. 
     See, for example, the bone cement plugs described and illustrated in U.S. Pat. Nos. 4,245,359; 4,276,659; 4,293,962; 4,302,855; 4,344,190; 4,447,915; 4,627,434; 4,686,973; 4,697,584; 4,745,914; 4,936,859; 4,950,295; 4,994,085; 5,061,287; 5,078,746; 5,092,891; 5,376,120; and 5,383,932. 
     See also, for example, the bone cement plug described and illustrated in British Patent Document No. 2,253,564A. 
     See also, for example, the publication entitled “Polyethylene medullary plug according to Stuhmer/Weber” distributed by ALLO PRO AG of Switzerland. 
     See also related apparatus described and illustrated in U.S. Pat. Nos. 4,011,602; 4,523,587; and 4,904,267. 
     See also related apparatus described and illustrated in European Patent Document No. 0,006,408 B1; and PCT Patent Document No. WO 94/15544. 
     Unfortunately, all of the bone cement plugs developed to date tend to suffer from one or more significant disadvantages. For example, in general, fixation of the bone cement plug depends on the friction established between the wall of the bone canal and the bone cement plug. Currently, the most common surgical technique is to first measure the size of the prepared bone canal. This typically involves sequentially inserting a number of different “sizers” into the bone canal so as to determine the gross cross-sectional diameter of the canal at the desired depth. Having thus determined the size of the bone canal, an over-sized plug is inserted into the canal so as to occlude the bone canal at the desired depth. 
     If the bone cement plug is not sufficiently over-sized relative to the diameter of the bone canal, or if the plug is too easily deformable, the engagement of the bone cement plug with the wall of the bone canal will be less than optimal, which may lead to complications. For example, during the aforementioned pressurization phase, or during the subsequent insertion of the prosthesis, increased pressure of the bone cement can cause the insufficiently-anchored plug to migrate distally. 
     On the other hand, if the bone cement plug is too greatly over-sized, and/or if the plug is overly rigid, the bone cement plug cannot be inserted into the bone canal to the desired depth. Also, excessively forceful insertion of the bone cement plug into the bone canal can cause the wall of the bone canal to fracture in some circumstances. 
     In the past, people have traditionally attempted to address these problems by providing plugs in a variety of different sizes for the surgeon to choose from. Unfortunately, this increases the cost of manufacturing the plugs and also increases the cost of inventory. 
     The foregoing demonstrates the need for a novel bone cement plug that may be adapted to fit any size bone canal. Ideally, a bone cement plug should be easy to deploy at the desired depth in the bone canal and effective in closing off that bone canal. The bone cement plug must also be bio-compatible with the patient. Furthermore, the bone cement plug should be inexpensive to produce. 
     SUMMARY OF THE INVENTION 
     These and other objects are addressed by the present invention, which comprises a novel device and method for use during joint replacement surgery, such as total hip replacement surgery. The present invention provides a universal bone cement plug which is appropriate for use in any size bone canal. The universal bone cement plug comprises a plurality of detachable units with flanges of decreasing diameter. The invention also provides an insertion tool for deploying the bone cement plug in a bone canal, and a cradle for storing the plug and insertion tool. 
     The bone cement plug is easy to deploy and align at a desired depth in a bone canal. The rigid, but deformable, plug occludes the bone canal and retains cement in the cavity so defined. The plug is bio-compatible with the patient. 
     A bone cement plug formed in accordance with the present invention includes a body defined by a series of separable units. Each unit has one or more flexible flanges. Preferably the flanges are slit at their periphery. The flanges decrease in size from the proximal end of the body to the distal end of the body. The largest flange accommodates the largest bone canal reasonably expected to be encountered during surgery. For smaller bone canals in which the largest flange would not fit, appropriate units of the plug may be removed, thus eliminating the oversized flanges in favor of the more appropriately sized flanges. 
     A first embodiment of the bone cement plug facilitates separating of the units by cutting the body, preferably with the aid of a notch or score line in the body. 
     A second embodiment of the bone cement plug facilitates separating of the units by tearing the body, preferably with the aid of a notch or score line in the body. 
     A third embodiment of the bone cement plug facilitates separating of the units by disengaging a fastening mechanism located between adjacent separable units. 
     Whether whole or truncated, the body of the bone cement plug presents an interface which is engageable by the insertion tool, such that the bone cement plug may be releasably attached to the insertion tool. 
     The insertion tool facilitates deploying the bone cement plug at a desired depth in the bone canal. An insertion tool formed in accordance with the present invention provides a handle for grasping by the surgeon, a shaft, and a distal end that releasably engages the slug. 
     The cradle stores the bone cement plug and the insertion tool prior to use. The cradle also provides firm support for the plug should a surgeon need to cut down the plug prior to deploying it in a bone canal. A cradle formed in accordance with the present invention includes a base with an anvil mounted thereon for receiving the plug. At least one set of fingers is preferably mounted on the base for retaining the insertion tool. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other features of the present invention will be more fully disclosed or rendered obvious by the following detailed description of the invention, which is to be considered in conjunction with the accompanying drawings wherein like numbers refer to like parts and further wherein: 
     FIG. 1 is a top plan view of a bone cement plug, insertion tool and cradle, all formed in accordance with the present invention; 
     FIG. 2 is a side elevational view of the apparatus of FIG. 1; 
     FIG. 3 is a partial cross-sectional view of a human hip joint; 
     FIG. 4 is a partial front elevational view of a human femur, with a portion to be removed being shown in phantom; 
     FIG. 5 is a partial perspective view of a human femur, with a portion removed; 
     FIG. 6 is a partial cross-sectional view of a human femur, with a portion removed and with a broached medullary canal; 
     FIG. 7 is an enlarged, partial cross-sectional view taken along line  7 — 7  of FIG. 1; 
     FIG. 8 is an end view showing the proximal end of the bone cement plug shown in FIG. 7; 
     FIG. 9 is an enlarged side elevational view of the insertion tool shown in FIGS. 1 and 2; 
     FIG. 10 is a partial side elevational view, partially in section, of a bone cement plug formed in accordance with the present invention, with the plug being shown deployed in the medullary canal of a bone; 
     FIG. 11 is a schematic perspective view of a portion of the structure shown in FIG. 10; 
     FIG. 12 is a side elevational view of an alternative form of bone cement plug formed in accordance with the present invention; 
     FIG. 13 is an end view showing the proximal end of the bone cement plug shown in FIG. 12; and 
     FIG. 14 is a side elevational view, in section, of the bone cement plug of FIG. 12, with the plug&#39;s separable units being shown in exploded view, and adjacent to the distal end of the insertion tool. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring first to FIGS. 1 and 2, the present invention provides a bone cement plug  100 , an insertion tool  200  and a cradle  300 , which together define an overall kit  400 . In general, in use, the surgeon first determines what size bone cement plug should be used to occlude the subject bone canal. If necessary, the surgeon may modify the size of plug  100 , e.g., by cutting it down. After any such re-sizing of the bone cement plug, the surgeon attaches the plug to insertion tool  200 . With the insertion tool  200 , the surgeon deploys plug  100  in the subject bone canal so that the plug becomes lodged in the canal. The insertion tool  200  is then disengaged from plug  100  and removed. The occluded portion of the bone canal is then filled with bone cement and fitted with a prosthesis. 
     More particularly, and referring now to FIGS. 3-6, a human hip joint  500  is shown. The hip joint  500  includes a femur  502  and a pelvis  504 . Femur  502  has a head  506 . Head  506  is received in a socket  508  of pelvis  504 . When head  506  and socket  508  do not function properly, such as in the case where a patient suffers from serious joint deterioration, head  506  and/or socket  508  may be replaced. Where head  506  is to be replaced, head  506  of femur  502  is exposed and removed. Once head  506  is removed, a medullary canal  510  is broached into femur  502 . Prior to introducing cement into medullary canal  510 , a bone cement plug  100  is introduced into the canal and positioned in the distal end  512  thereof. The bone cement plug  100  must be sized to fit securely in canal  510  and occlude the canal. 
     A surgeon ascertains the size of the distal end  512  of bone canal  510  by introducing any number of sizing tools (not shown) into canal  510 . After the surgeon has ascertained the size of the distal end  512  of canal  510 , the surgeon must determine an appropriate size for the bone cement plug which is to occlude the canal  510 . Prior to the present invention, the surgeon would typically have to select one particular bone plug from a number of different bone cement plugs, each having different sizes. The present invention eliminates this situation, by providing a universal bone cement plug which can be properly sized by the surgeon for any size bone canal. 
     Referring next to FIGS. 7 and 8, bone cement plug  100  is shown in greater detail. Bone cement plug  100  comprises a singular, substantially rigid body  102 . 
     Body  102  consists of a plurality of different segments or units  104 , i.e.,  104 A,  104 B,  104 C, etc. A particular unit  104  may be separated from the remaining units  104  by severing the body  102  along a surface  106  between the units  104 , e.g., with a knife or scalpel. Body  102  also may be torn or broken so as to separate the units  104  from one another. To facilitate separation, body  102  may also include necked-down regions  108 , or score lines (not shown), which may be aligned with surfaces  106 . The invention also may rely on other mechanisms for introducing local material weakness at desired locations along the body  102 , such as a notch (not shown), so as to facilitate separating one unit  104  from another unit  104 . 
     Body  102  is releasably engageable with insertion tool  200  (FIG.  9 ). This is so regardless of whether one or more of the units  104  have been removed from body  102 . To that end, body  102  may employ any satisfactory fastening mechanism for connecting bone cement plug  100  to insertion tool  200 . With the embodiment shown in FIGS. 1,  2 ,  7  and  8 , body  102  is shown as having female threads  110  extending from the proximal end  112  toward the distal end  114  thereof. The removal of a unit  104  does not detrimentally impact the fastening mechanism (in this case, the threads  110 ) or the orientation thereof relative to body  102 . Regardless of how many units  104  are removed from body  102 , the threads  110  remain engageable by the insertion tool. For this embodiment, the insertion tool  200  has male threads  202  (FIG. 9) that are engageable with the female threads  110  of body  102 , as discussed in more detail below. 
     Referring again to FIG. 7, each unit  104  has at least one flexible flange  116 . As shown in FIG. 8, the flanges  116  preferably include slits  118  which define flaps  120  therebetween. Although shown extending radially in FIG. 8, the slits  116  may extend along any direction which permits the flaps  120  to overlap one another when bone cement plug  100  is deployed in a bone canal. Furthermore, as seen in FIG. 7, slits  118  are preferably angled relative to the longitudinal axis of the bone cement plug. This angulation helps flaps  120  slide over one another when the bone cement plug is deployed in a bone canal and the flanges  120  are compressed radially. In addition, such angulation also provides sharp edges which can catch on the side wall of the bone canal, so as to help stabilize the plug as the insertion tool  200  is unthreaded from the deployed bone cement plug. Referring now to FIGS. 10 and 11, it will be seen that as the cross-sectional area in which a plug  100  is positioned decreases, the flanges  116  bend. Often, when a slit-less flange is forced to bend, the generally radial surface buckles and causes gaps to occur along the periphery of a flange  116 . This is especially true when symmetrical flanges mate with irregularly-shaped cross sections, such as when a generally round flange mates with a typically oval-shaped medullary canal. As seen in FIG. 11, because flanges  116  are provided with the slits  118 , the flaps  120  may overlap one another so as to provide a good seal with the walls of the bone canal. 
     Referring again to FIG. 7, the present plug  100  is shown with multiple flanges  116 . Multiple flanges allow seating of the plug  100  so that it resists movement and tilting relative to the bone, especially under torsional stresses. As shown in FIGS. 10 and 11, the larger flanges  116 C and  116 B are positioned so that they bend and wedge into place in the medullary canal  510 . The smaller flange  116 A may, but does not have to, be wedged into place and bent against the sides of the medullary canal  510 . In some cases, the smaller flange  116 A may not even touch the sides of medullary canal  510 . In any case, the smaller flange  116 A generally pilots the plug  100  through the typically tapering medullary canal  510  and keeps the plug  100  centered and aligned therein. 
     The size of a medullary canal varies greatly from patient to patient. Accordingly, no one size flange, or set of flanges, is appropriate for all canals. The present bone cement plug  100  is adaptable to any size canal because the body  102  of plug  100  is defined by multiple, detachable units  104 . In the case where one or more flanges  116  are too large for a particular medullary canal  510 , the unit or units  104  from which an inappropriately large flange or flanges  116  extend may be separated from the remainder of body  102 , leaving one or more unit or units  104  having smaller flanges  116 . For example, referring to FIG. 7, if flange  116 D is too large for insertion in a medullary canal  510 , the unit  104 C is detached from the remaining units  104 B and  104 A, which remain attached to one another. 
     Referring again to FIGS. 1,  2  and  9 , insertion tool  200  has a handle  204  which a surgeon grips. Tool  200  also has a shaft  206  which extends from handle  204  to a distal end  208 . The distal end  208  of tool  200  is configured so as to be releasably engageable with the proximal end of any unit of the body  102 . For example, as shown, the distal end  208  of insertion tool  200  may have male threads  202  thereon that mate with the female threads  110  of the plug body  102 . It will be appreciated that this threaded connection between bone cement plug  100  and insertion tool  200  will permit the plug and insertion tool to be quickly and easily attached together prior to deployment of the plug in a bone canal; and once the plug has been lodged in the distal end of the bone canal, whereby the plug will be prevented from rotating within the bone canal, the threaded connection will permit plug  100  and insertion tool  200  to be quickly and easily detached from one another so as to leave plug  100  deployed within the bone canal. 
     The present invention also provides a cradle  300  (FIG. 2) including a base  302 . An anvil  304  (FIGS. 2 and 7) is mounted on the base  302 . The anvil  304  is configured to receive a bone cement plug  100 . Additionally, the anvil  304  holds the plug  100  securely so that a surgeon may inspect, size or otherwise prepare the plug  100  for use. For example, in the event that a unit  104  of the plug  100  must be removed so as to achieve a better fit in a medullary canal, and in the event that a cutting tool is to be used to separate a unit  104  from the body  102  of the plug, the anvil  304  maintains the plug  100  in position so that it does not move during cutting, and provides an excellent cutting surface for the cutting tool to contact. At least one set of fingers  306  (FIG. 2) is mounted on the base  302  for retaining the insertion tool  200  in a lateral direction. A second set of fingers  308  (FIG. 2) may also be mounted on the base  302  for retaining the insertion tool  200  in a lateral and axial direction. Additionally, a stop  310  (FIG. 2) may be mounted on the base  302  for retaining the insertion tool  200  in an axial direction. 
     Referring next to FIGS. 12-14, there is shown a bone cement plug  1000  which is also formed in accordance with the present invention. Bone cement plug  1000  is similar to the aforementioned bone cement plug  100 , except that the body  1002  of bone cement plug  1000  is formed from a plurality of separate, interengageable units  1004 , i.e.,  1004 A,  1004 B,  1004 C, etc. Units  1004  together form a substantially rigid body  1002 . Any fastening convention that permits the units  1004  to releasably interengage one another, and insertion tool  200 , may be used. For example, other than the distal-most unit  1004 A, the units  1004  may have male threads  1005  formed on a distal end  1007  thereof; and all of the units  1004  may have female threads  1010  formed in the proximal ends  1011  thereof. When assembled to define a body  1002 , for example, male threads  1005  of unit  1004 C threadingly engage female threads  1010  of unit  1004 B. Female threads  1010  of the proximal-most unit  1004  are engaged by the male threads  202  of insertion tool  200 . 
     Each unit  1004  also has at least one flexible flange  1016 . As shown in FIG. 13, the flanges  1016  preferably have slits  1018  which define flaps  1020  therebetween. 
     In one preferred method of use, bone cement plug  1000  is packaged in kit  400  in its fully assembled state, i.e., with all of the units  1004  connected together so as to form the complete body  1002 , and with bone cement plug  1000  received by the cradle&#39;s anvil  304 . Thereafter, during use, the surgeon removes bone cement plug  1000  from anvil  304 , re-sizes it if necessary by removing one or more units  1004 , and then mounts the remaining assembly to insertion tool  200  for insertion in a bone canal. 
     In yet another method of use, a bone cement plug  100 , or a fully assembled bone cement plug  1000 , is sterilely packaged in a disposable kit  400 , which also includes a disposable insertion tool  200  made of injection molded plastic. Alternately, the bone cement plug  100 , or the bone cement plug  1000 , can be packaged sterilely, with or without the anvil. In this latter case, the surgeon is provided with a resterilizable insertion tool  200  at the time of surgery. 
     Bone cement plug  100  and bone cement plug  1000  are formed out of a bio-compatible material. In one form of the invention, they are formed out of a non-absorbable plastic material such as polyethylene. In another form of the invention, they are formed out of a biodegradable material of the sort well known in the art. 
     The invention provides many features. One feature is that the present bone cement plug is universal and adaptable for any size medullary canal. Since only one universal plug needs to be provided, the cost of manufacturing and of inventory is lower than with conventional plugs. Another feature is that, regardless of how the plug is sized, it is engageable with the insertion tool so that the plug may be deployed in a medullary canal. A further feature is the cradle for storing the plug and insertion tool, which also provides an anvil for modifying the size of the plug. An additional feature is that the present bone cement plug is easy to deploy and align at a desired depth in a medullary canal. Yet another feature of the present invention is that the rigid, but deformable, plug occludes a medullary canal and retains bone cement in the occluded cavity prior to insertion of a prosthetic appliance. Yet a further feature of the invention is that the plug is bio-compatible with the patient. 
     The present invention is not limited to the foregoing specific embodiments, but also encompasses all improvements and substitutions within the scope of the appended claims.