Abstract:
Apparatus and methods of protecting modular implant connection portions are provided. A guard includes an outer sidewall and an inner sidewall defining a cavity that covers a modular implant connection portion. The modular implant connection covered with the guard can facilitate test-fitting of other modular implant components and allows reaming of the tissue around the guard.

Description:
FIELD 
     The present teachings relate to methods and apparatus for protecting a modular implant connection. 
     BACKGROUND 
     The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. 
     The need for articulating joint replacement may be due to injury, over use, trauma, or disease, for example. To repair the articulating joint, it may be necessary to implant the prosthesis into a long bone such that part of the prosthesis completely replaces the articulating end of the bone. Modular prostheses are often used in connection with long bones as they provide a customizable fit along the length of the prosthesis and are assembled intraoperatively. During the operative procedure, the surgeon may “trial” fit various components of the modular implant to accommodate the particular anatomy of the patient. Trial fitting of an implant may, however, leave regions of the implant exposed, including the connection points between the components of the modular implant. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     In various embodiments, the present teachings provide apparatus for and methods of protecting a modular implant connection portion including a guard having an outer sidewall and an inner sidewall and further defining a cavity. 
     Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. It should be further understood that while certain embodiments may illustrate an articulating joint, the apparatus and methods disclosed herein are useful for non-articulating modular implants as well. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure. 
         FIG. 1  is a side view of a modular femoral stem implant according to various embodiments; 
         FIG. 2A  is a side view of a guard according to various embodiments; 
         FIG. 2B  is a cross-section of a guard along line  2 B- 2 B of  FIG. 2A  according to various embodiments; 
         FIG. 3A  is a side view of a guard according to various embodiments; 
         FIG. 3B  is cross-section view of a guard along line  3 B- 3 B of  FIG. 3A  according to various embodiments; 
         FIG. 4  is a side view of a guard having a grasping feature according to various embodiments; 
         FIG. 5  is side view of a guard having a grasping feature according to various embodiments; and 
         FIGS. 6A-6I  depict a surgical method according to various embodiments. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. While various embodiments are shown in conjunction with a femoral implant, it is understood that the present teachings are applicable to other modular implant systems. It is further understood that the concepts disclosed herein can be used at various connection points in any suitable multiple segment medical device. 
     Referring to  FIG. 1 , in various embodiments a modular implant system  100  is provided. The modular implant system  100  includes a distal stem  10  component, a guard  12 , a proximal body  14 , a femoral head  16 , a trial  18 , and a threaded bolt  20 . The guard  12  protects at least one of the connection point  21  and proximal end  22  of the distal stem  10  component. The protection prevents any inadvertent scratching or damage to the distal stem  10  or the proximal body  14  while allowing test fitting using the trial  18  to simulate the size and fit of the proximal body  14  relative to the proximal end  22  of the distal stem  10 . The modular implant system  100  can be provided as a kit which includes multiple combinations of each of the distal stem  10  component, guard  12 , proximal body  14 , femoral head  16 , trial  18 , and bolt  20 . The combinations can include various sizes, lengths, and shapes of any of the modular implant system  100  components to facilitate ease of use and a customized fit. 
     The distal stem  10  is disposed into a long bone  200 , as best illustrated in  FIGS. 6A-6I . The distal stem  10  is shaped to accommodate insertion into the long bone  200  or repair site. Returning to  FIG. 1 , the proximal end  22  of the distal stem  10  includes a tapered outer surface  24  which mates with the guard  12 . The proximal end  22  outer surface  24  is shaped as a Morse taper  26  to facilitate the locking fit or tapered fit connection with the proximal body  14  and corresponding tapered sidewall  54 . The proximal end  22  of the distal stem  10  further defines a threaded distal stem bore  30  which extends partially through the distal stem  10  along a longitudinal axis L. As detailed later herein, the distal stem bore  30  facilitates securing of the modular implant system  100 . 
     In various embodiments, the length of the Morse tapered region  26  of the distal stem  10  along the longitudinal axis is about 0.5 inches to about 3 inches. It is understood that the length of the Morse tapered region  26  can vary as the size of the distal stem  10  and the modular implant  100  vary to accommodate the particular needs of the patient. 
     The guard  12  can be made out of a biocompatible polymer, such as polyethylene or PEEK. In various embodiments, the guard  12  can be rigid or semi-rigid. The guard  12  is maintained on the proximal end  22  of the distal stem  10  through surface tension caused by the tight fit therebetween. 
     The guard  12  includes an outer cylindrical sidewall  32  and an inner sidewall  34 . The inner sidewall  34  can be tapered as shown in  FIGS. 2A and 2B , or the inner sidewall  34  can be cylindrical as shown in  FIGS. 3A and 3B . Referring to  FIGS. 2A and 2B , in embodiments where the inner sidewall  34  is tapered, the thickness of the guard  12  varies along the length of the guard  12  such that the thickness decreases from the proximal end  36  to the distal end  38 . 
     Returning to  FIGS. 2A-3B , the inner sidewall  34  mates with the outer tapered sidewall  24  of the proximal end  22  of the distal stem  10 . The inner sidewall  34  of the guard  12  is disposed over the proximal end  22  of the distal stem  10  to provide a cap or cover over the proximal end  22  of the distal stem  10 . 
     Turning to  FIGS. 2A-5 , the guard exterior  32  is substantially cylindrical. The cylindrical shape facilitates the test fitting of the trial  18  without causing the trial  18  to lock onto the guard  12  or, in other words, provides a readily removable and temporary engagement. The cylindrical exterior  32  of the guard  12  also facilitates use with other existing modular components. 
     In various embodiments, the guard  12  has an exterior diameter of about 0.25 inches to about 1 inch. Variations in the exterior diameter measurements of the guard  12  are within the scope of the present teachings to accommodate the particular needs of the patient and the various sizes of trials  18 . Turning to  FIGS. 4 and 5 , the exterior  32  of the guard  12  can also include at least one grasping feature  42  by which the guard  12  can be grasped and manipulated. As shown in  FIG. 4 , an embodiment of the grasping feature  42  includes at least two recessed dimples  44 . The dimples  44  can be used to grasp the guard  12  to remove it from the distal stem  10 . As shown in  FIG. 5 , an embodiment of the grasping feature  42  includes a series of ridges  46  spaced about the exterior surface of the guard  12 . While the ridges  46  of the depicted embodiment are vertical ridges, it is understood that the ridges  46  can also be horizontally disposed about a body of the exterior surface  32  of the guard  12 . 
     As best shown in  FIGS. 2A and 2B , the guard cavity  40  and the interior sidewall  34  have different cross-sections than the guard exterior  32 . The guard cavity  40  and interior sidewall  34  define a Morse taper  48  cross-section along an inner diameter of the guard  12 . The guard cavity  40  is mated to the Morse taper  26  at the proximal end  22  of the distal stem  10 . The mated shape of the Morse tapers  26  and  48  provides a tight connection between the stem  10  and the guard  12 , which protects the proximal end  22  of the distal stem  10  from debris. Although the fit differs, it is understood that the embodiment of  FIGS. 3A and 3B  also protect the proximal end  22  of the distal stem  10  from debris. 
     In various embodiments, the guard cavity  40  and the length of the guard  12  are substantially the same as those of the Morse tapered region  26  of the distal stem  10 . Any difference in length may be an amount which is sufficient to provide adequate protection to the Morse tapered region  26  of the distal stem  10 . As a non-limiting example, the variation between the length of the Morse taper region  26  and the guard cavity  40  can be less than about 15% or less than about 10%. 
     Referencing  FIGS. 2A-5 , the guard  12  further defines a bore  50  at the proximal or top end  36  of the guard  12 , which in the depicted embodiment, is opposite to the guard cavity  40 . As best shown in  FIG. 1 , when the guard  12  is disposed over the proximal end  22  of the distal stem  10 , the bore  50  of the guard  12  and the bore  30  in the stem  10  are substantially aligned and concentric along longitudinal axis L. 
     Referring to  FIG. 1 , the proximal body  14  includes a cavity  52  which mates with the distal stem  10 . The proximal body cavity area  52  is defined by a tapered sidewall  54  which provides a removable and adjustable fit with the Morse taper region  26  of the distal stem  10 . The proximal body  14  further includes a bore  56  which concentrically aligns with the bore  30  of the distal stem  10 . The proximal body  14  can mate with another component, such as the articulating head  16  of a hip implant via connection point  58 . 
     Still referencing  FIG. 1 , the trial  18  includes a cavity  64  which mates with the distal stem  10 . The cavity  64  is defined by a cylindrical sidewall  66  which provides a removable and adjustable fit with the guard  12  when the guard  12  is placed on the Morse taper region  26  of the distal stem  10 . Generally, the trial  18  in the system  100  has substantially similar outer dimensions to those of the corresponding proximal body  14 . One difference between the trial  18  and the proximal body  14  is that the trial  18  utilizes the cylindrical interior sidewall  66  to prevent locking with the cylindrical exterior  32  of the guard  12 . As detailed in the surgical methods below, the trial  18  can be used to approximate which proximal body  14  will be used in the system  100  as implanted into the patient. 
     Turning to  FIGS. 6A-6I , in various embodiments, methods of using the modular implant system  100  are provided. Generally, the distal stem  10  is inserted into a long bone  200  through a bone cavity  202  formed therein, such as the bone cavity  202  prepared in the intramedullary canal  204 . The distal stem  10  is placed into the bone cavity  202  by impaction using a surgical hammer (not shown), as a non-limiting example. The area around the distal stem  10  is manipulated through reaming, contouring, or other techniques to provide clearance for the proximal body  14 , as necessary. One or several trial bodies  18  are then placed on the guard  12  in a manner similar to that described previously in order to determine an appropriate size for the proximal body  14 . For example, should a first trial body  18  not fit within the expanded bone cavity  202  or not provide a proper fit, the operator will continue to select other trial bodies  18  until an appropriate fit is achieved. After the appropriate proximal body  14  is selected, the guard  12  is removed from the distal stem  10 . The cavity  52  of the proximal body  14  is then placed on top of the distal stem  10  at the proximal end  22  so that the proximal body  14  and the distal stem  10  are in locking engagement to secure the implant  100 . 
     Referring to  FIG. 6B , in various embodiments, to insert the distal stem  10  into the bone cavity  202  or intramedullary canal  204 , a screw inserter  300  can be passed through the aligned opening defined by the distal stem  10  opening  30  and the bore  50  of the guard  12 . It is noted that the screw inserter  300  can be aligned with the distal stem  10  via the guard bore  50  and the stem opening  30 . Sufficient force is then applied to the screw inserter  300  to impact the distal stem  10  into the surrounding intramedullary canal  204  in any suitable manner. For example, a surgical hammer may be used to impact the screw inserter. 
     Referring now to  FIGS. 6C and 6D , after the distal stem  10  is fixed into the bone cavity  202 , the bone surrounding the proximal end  22  of the distal stem  10  can be reamed to accommodate the proximal body  14 . The reaming is conducted around the guard  12 , which remains in a fixed position during reaming, to protect the Morse taper  26  connection point of the distal stem  10 . A reaming device  302  is disposed over the guard  12 , and the reaming device  302  spins about the guard  12  as indicated by the arrows  306 . Leaving the guard  12  in a fixed position during reaming protects the connection point  21 . In addition, the guard  12  serves as a bearing surface for the reaming device  302 . 
     In various embodiments, the reaming is performed in the bone  200  to a depth that is equal to the length of the guard  12 . During the surgical procedure, a user can measure the height of the guard  12  and/or the size of the proximal body  14  and select a reamer  302  capable of forming an opening having an appropriate depth. This can be achieved by measuring the height of the guard  12  and selecting a reamer  302  having a bit  304  of substantially the same height as the guard  12 . In such embodiments, maintaining the depth of reaming to substantially the same depth as the guard  12  protects the distal stem  10 . In the embodiment illustrated in  FIGS. 6C and 6D , the bit  304  has a conical shape to enlarge the bone cavity  202  in the surrounding bone  200 . It is understood that a bit  304  having a non-conical shape, such as a cylinder as a non-limiting example, can also be used to enlarge the cavity  202 . In various embodiments, the reaming device  302  can form a cylindrical bore, a partial cylindrical bore, or any other suitably shaped bore that mates with the cylindrical exterior surface  32  of the guard  12 . The selected bit  304  will determine the shape of the opening about the guard  12 . For example, the conical bit  304  will provide a conical shaped opening, while a cylindrical bit will provide a cylindrical shaped opening. In various embodiments, additional contouring, over that provided by the bit  304 , of the bone  200  may be necessary to accommodate the proximal body  14 . The additional contouring can be performed in any suitable manner, such as using a scalpel or a surgical drill, for example. 
       FIG. 6E  shows a prepared bone cavity  202  in which the trial  18  can be tested for fit relative to the guard  12  on the distal stem  10 . Turning to  FIG. 6F , the cylindrical sidewall  66  of the trial cavity  64  is removably engaged with the cylindrical exterior  32  of the guard  12 . The mating cylindrical shapes  32  and  66  prevent the two bodies from being locked together and provides an adjustable and removable temporary connection therebetween as indicated by arrow  308 . Testing the trial  18  relative to the guard  12  on the distal stem  10  protects the Morse taper connection  26  of the distal stem  10 . It is understood that a similar test-fitting can be conducted with the femoral head component  16  and connection point  58  of  FIG. 1 , as a non-limiting example. 
     Turning to  FIGS. 6G and 6H , after selecting the appropriate sized trial  18 , the guard  12  can be removed from the distal stem  10  to expose the outer tapered sidewall  24  of the distal stem  10 . The guard  12  can be grasped using the grasping feature  42  illustrated as recessed dimple  44  on the guard  12  with forceps  306 , for example. It is understood that the guard  12  can also be removed using a pull-string or other implements. 
     Turning to  FIG. 6I , the proximal body  14 , which corresponds to the selected trial  18 , is then disposed over the exposed distal stem  10  and connection point  21  after the guard  12  is removed. The connection between the proximal body  14  and the exposed distal stem  10  provides a locked fit via the Morse taper interaction therebetween. In various embodiments, the system  100  can be secured using bone cement or other securing devices known in the art, and in embodiments, the proximal body  14  and distal stem  10  can be secured using some combination of bolt  20 , bone cement, or other securing devices. 
     The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the invention, and all such modifications are intended to be included within the scope of the invention.