Abstract:
A prosthetic trial for a joint prosthesis includes a stem having a proximal section and a distal section for implantation in a bone. A body includes a channel receiving at least the proximal section of the stem. A locking mechanism is at least partially disposed within the body. The locking mechanism is biased into a locking position in which the mechanism locks the stem within the first channel of the body. The locking mechanism is accessible outside said body to be pulled into a releasing position to unlock the stem from the body.

Description:
TECHNICAL FIELD OF THE INVENTION 
     The present invention relates generally to a surgical trial instrument assembly and, more particularly, to a surgical trial instrument assembly for determining the required dimensions of a prosthetic femoral component. 
     BACKGROUND OF THE INVENTION 
     During the lifetime of a patient, it may be necessary to perform a joint replacement procedure or arthroplasty on the patient as a result of, for example, disease or trauma. One such type of joint replacement procedure is a hip replacement procedure in which a diseased and/or damaged hip joint is replaced with a prosthetic hip joint. A typical hip replacement procedure utilizes a prosthesis that generally includes a femoral stem component, a proximal body component, and a neck segment. The femoral stem is implanted in a prepared medullary canal of the patient&#39;s femur. 
     During performance of such a hip replacement procedure, the surgeon must evaluate the size and condition of the patient&#39;s bones (e.g. the patient&#39;s femur) in order to determine the proper type and configuration of each of the various types of prosthetic components that are to be implanted. One or more provisional components are temporarily fixed to a bone prior to permanent fixation of the prosthetic joint. The provisional components are intended to mimic certain aspects of the permanent prosthetic joint in order for a surgeon to validate measurements and to test several different possible component sizes and shapes. Hence, provisional components are aptly known as “trials”, and the procedure is known as “trialing.” 
     Currently, in a majority of revision total hip arthroplasties, the bone has little or no supportive metaphysis or diaphyseal areas. This makes it difficult for surgeons to reproduce the proper anatomy. To do this, the surgeon may use a distally fixed implant. This facilitates trialing from the distal femoral cortex and subsequent proximal anatomy. Many trials are used in surgery having one basic anterior/posterior proximal anatomical body with altering characteristics (i.e., stem lengths, bow, offsets, neck lengths, neck anteversion). Each instance requires a single monolithic trial that duplicates the implant, which is therein made from casting substrate. Some trialing techniques utilize the broach as the stem and then attach a proximal trial onto the broach. 
     Other techniques require that the broach be removed from the medullary canal to allow the use of a trial having a stem portion, a head and a neck. For example, some have disclosed a system including a group of variously sized trial neck/body portions and a group of differing length trial stem portions which are mixed and matched to create a suitable trial. The trials are held together using a ball and spring detent system. Such ball and spring systems do not create a tight, wiggle-free connection. Because the trial pieces are not held tightly together, there can be errors in the use of the actual implant. 
     Because many variations in sizes and shapes of trials are required to be available to the surgeon, it is necessary to maintain a large inventory of trials. Such a large inventory is costly, occupies valuable operating room space, and is difficult to manage. If the trial is a singular piece, then there must be upwards of 50 full trials. These full trials take up large amounts of space in instrument sets. 
     In some modular trials, the different parts of the trial are assembled using threads. However, this makes connection and disconnection lengthy and cumbersome. In other modular trial designs, the different parts are held together by nothing more than a ball plunger of balseal. These features are not suitable for a solid, wiggle-free connection which resists tensile forces as well as rotational ones. Others use the reamer as the trial stem. However, not all distal reamers are suitable for working as trials. 
     SUMMARY OF THE INVENTION 
     According to one embodiment of the present invention, a modular prosthetic trial for a joint prosthesis. The trial includes a first piece having a proximal section and a distal section configured for implantation in a bone. The proximal section includes a non-threaded proximally extending protrusion. The trial also includes a second piece having a proximal section and a distal section, the distal section including a recess for receiving the non-threaded proximally extending protrusion. A locking mechanism is at least partially disposed within the recess of the second piece. The locking mechanism is sized and shaped to engage the protrusion such that the locking mechanism locks the first piece to the second piece. 
     According to another embodiment of the present invention, a method for assembling a modular trial is provided. The method includes inserting a non-threaded proximally extending protrusion from a first piece into a corresponding recess in a distal portion of a second piece. The proximally extending protrusion engages a locking mechanism disposed in the second piece. The method further includes activating the locking mechanism to lock the first piece to the second piece. 
     According to yet another embodiment of the present invention, a kit for use in performing joint arthroplasty is provided. The includes a plurality of first trial pieces having a proximal section and a distal section configured for implantation in a bone. The proximal section has a non-threaded proximally extending protrusion. The kit also includes a plurality of second trial pieces having a proximal section and a distal section. The distal section includes a recess for receiving the non-threaded proximally extending protrusion and the proximal section includes a non-threaded proximally extending protrusion. Each of the plurality of second trial pieces includes a locking mechanism at least partially disposed within the recess of the second trial piece. The locking mechanism is sized and shaped to engage the protrusion such that the locking mechanism locks the first trial piece to the second trial piece. The kit also includes a third trial piece that includes a proximal end and a distal end. The distal end includes a recess for receiving the non-threaded proximally extending protrusion of one of the plurality of second trial pieces, and the distal end includes a locking mechanism at least partially disposed within the recess of the third trial piece. The locking mechanism is sized and shaped to engage the protrusion such that the locking mechanism locks the second trial piece to the third trial piece. 
     The above and other features and advantages of the present invention will become apparent from the following description and the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a perspective view of a modular trial assembly according to one aspect of the present invention. 
         FIG. 2  illustrates a partially cut-away view of the modular trial assembly of  FIG. 1 . 
         FIG. 3  is a perspective view of a locking mechanism according to one embodiment of the present invention. 
         FIG. 4  is a close-up view of the modular trial assembly of  FIG. 1 . 
         FIG. 5  illustrates a kit of a plurality of modular trial assembly parts according to one embodiment of the present invention. 
         FIG. 6  is a flow chart illustrating the method of assembling a modular trial assembly according to one embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While the invention is susceptible to various modifications and alternative forms, a specific embodiment thereof has been shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular form disclosed, but on the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     It should initially be appreciated that the present invention can be used after proper resection of a patient&#39;s proximal femur for evaluating the size and shape of an implant therefor prior to committing to the final preparation of the proximal femur. The proximal end portion of the patient&#39;s femur can be resected by use of, for example, a bone saw (not shown). Proper resection of the proximal femur is beyond the scope of the present disclosure. Reference should be made to an appropriate surgical manual for such resection. 
     Referring now to  FIG. 1 , there is shown a modular trial assembly  10  according to one embodiment of the invention, including a first piece or distal body  12 , a second piece or middle body  14 , and a third piece or proximal body  16 . In this embodiment, each of the pieces makes up part of a distal stem. However, it should be appreciated that in other embodiments, the pieces may make up different parts of a different implant or trial. 
     As shown in  FIG. 1 , the middle body  14  includes a distal section  18  and a proximal section  20 . The distal section  18  includes a locking mechanism  22 . The proximal body  16  also includes a distal section  24  and a proximal section  26 . The distal section  24  of the proximal body  16  also includes a locking mechanism  28 . 
       FIG. 2  shows a cross-sectional view of the modular trial  10 . As shown, the distal body  12  has a distal section  30  that is configured for implantation into a bone. The distal body  12  also has a proximal section  32 . The proximal section  32  includes a non-threaded proximally extending protrusion  34 , which in the illustrated embodiment is a pin. In this embodiment, the pin includes a lip  36 . In other embodiments, other types of protrusions may be used. Also, other types of shapes other than lips may be used. 
     As shown in  FIG. 2 , the pin  34  extends into a recess  38  of the middle body  14 . The locking mechanism  22  of the middle body  14  is also at least partially disposed in the recess  38 . As shown, the locking mechanism  22  engages the lip  36  of the pin  34 . 
     Turning now to  FIG. 3 , a perspective view of the locking mechanism  22  is shown. The locking mechanism  22  includes a first wall  40  and a second wall  42  opposite the first wall  40 . The first and second wall  40 ,  42 , each define an interior groove or recess  44  that is sized and shaped to receive the pin  34 . At an end of the groove  44 , the wall  40 ,  42  forms a spiral-shaped edge  46 . The spiral shaped edge  46  gradually spirals toward an edge of the wall  40 ,  42 . Although in  FIG. 3 , only one edge  46  is shown, it should be understood that the edge  46  may be formed in both walls  40 ,  42 . Although in other embodiments, the edge  46  may only be formed in one of the two walls  40 ,  42 . In other embodiments, the edge  46  may be cam-shaped. Alternatively, the edge  46  may be ramp-shaped. 
     As shown in  FIG. 4 , the edge  46  engages the lip  36 . The wall  40  includes a hex-shaped recess  48  for engaging a tool (not shown). The tool engages the recess  48  and works to turn the locking mechanism  22  from an unlocked to a locked position. When the locking mechanism  22  is in the unlocked position, the pin  34  fits within the groove  44 . As the locking mechanism  22  is turned, the lip  36  of the pin  34  engages the spiral edge  46 . Because the edge  46  is spiral-shaped, the lip  36  rides along the edge  46  and is pulled closer to the edge of the wall  40 ,  42 , pulling the pin  34  further into the recess  38 . Once the locking mechanism  22  has been fully turned (in this case, ¼ turn) the pin  34  is locked into the recess  38 . 
     In some embodiments, the pin  34  has two lips  36 , opposing one another (not shown). In those embodiments, the locking mechanism  22  has two spiral-shaped edges  46 , one for engaging each lip. As the locking mechanism  22  is turned, the lips  36  ride along the spiral edges  46 , both toward the opposite edges of the walls  40 ,  42 . This effectively locks the pin  34  in place. 
     As shown in  FIG. 1 , the distal section  18  of the middle body  14  includes at least one anti-rotation protrusion (or device)  49   a . The anti-rotation protrusion  49   a  couples with an anti-rotation recess  49   b  on the proximal section of the distal body  12 . The anti-rotation device and recess  49   a ,  49   b , keep the distal body  12  and middle body  14  from rotating relative to one another. In some embodiments, there are two anti-rotation devices and recesses  49   a ,  49   b —one on each side of the respective body  14 ,  12 . The anti-rotation devices  49   a  may be of different sizes (as will be the anti-rotation recesses  49   b ) as this ensures that the distal body  12  will be inserted into the middle body  14  in the proper orientation. In some cases, the distal body  12  may be so slightly bowed that it is difficult to recognize. The different sized anti-rotation devices and recesses  49   a ,  49   b  ensure that the bow is correctly positioned. In the described embodiment, the middle body  14  includes a protrusion and the distal body includes a recess. Other anti-rotation devices may be used. Also, the middle body  14  may include a recess and the distal body  12  the protrusion. The connection between the proximal body  16  and the middle body  14  may also include anti-rotation devices  49   a ,  49   b  as illustrated. Other anti-rotation devices may also be used. 
     Returning now to  FIG. 3 , the wall  42  is shown with indicia  51 . The indicia  51  are used to indicate when the locking mechanism is locked. In this embodiment, the indicium  51  is an arrow. When the arrow  51  points one way, the locking mechanism  22  is unlocked. When it points in a different direction, the locking mechanism  22  is locked. In some embodiments, the walls  40 ,  42  may also have an irregularly curved outer shape. Thus, when the locking mechanism  22  is unlocked, the outer portion of the walls  40 ,  42  extend out past a side of the middle body  14 . When the locking mechanism  22  is in a locked position, the outer portions of the walls  40 ,  42  are flush with the side of the middle body  14 , allowing the trial  10  to replicate an implant. In some embodiments, both indicia  51  and a curved shape may be used. In other embodiments, other indicating methods or no indicating methods may be used. 
     Returning now to  FIGS. 1 and 2 , it is shown that the proximal section  20  of the middle body  14  includes a non-threaded proximally extending protrusion  52 . In this embodiment, the non-threaded proximally extending protrusion  52  of the middle body  14  is a pin—in fact, the same as the pin  34  of the distal body. The distal section  24  of the proximal body  16  includes a recess  54  and a locking mechanism  56 . The recess  54  and locking mechanism  56  are the same as the recess  38  and locking mechanism  22  of the middle body  14 . 
     Turning now to  FIG. 5 , a trial system kit  60  is shown according to one embodiment of the present invention. The trial system kit  60  can include multiple sizes of each of the distal body  12 , the middle body  14 , and the proximal body  16 . In some embodiments, there may be only one proximal body  16 . As shown, the multiple sizes of the distal body  12  can include different lengths and different shapes. Some of the distal bodies  12 , middle bodies  14 , and proximal bodies  16  include straight distal portions while others have curved or bowed distal portions. Thus, different sizes and shapes of the distal body  12 , middle body  14 , and proximal body  16  can be mixed and matched with one another to produce a modular trial assembly  10  ( FIG. 1 ) that matches the size and shape of the patient&#39;s joint anatomy. Various trial assemblies may be tried in order to ascertain which final implant will work best, in the surgeon&#39;s judgment. Regardless of which combination of distal body  12 , middle body  14 , and proximal body  16  is used to assemble the modular trial  10 , the manner of assembly, which will be discussed in detail herein, is substantially the same. 
     Turning now to  FIG. 6 , a method for assembling the trial  10  will be described. At step s 70 , a distal body  12 , a middle body  14 , and a proximal body  16  will be selected from the kit  60 . The distal body  12 , middle body  14 , and proximal body  16  selected will be sized and shaped such that when they are connected, the trial will match the patient&#39;s anatomy. At step s 72 , the pin  34  of the distal body  12  will be inserted into the recess  38  of the middle body  14  and locking mechanism  22 . The locking mechanism  22  will be turned to lock the pin  34  into place (step s 74 ). The user may decide to check using the indicia or other features (such as the shape of the locking mechanism  22 ) that the locking mechanism is fully locked. At step s 76 , the pin  52  of the middle body is inserted into the recess  54  of the proximal body  16  and locking mechanism  56 . The locking mechanism  56  is then turned to lock the pin  52  in place (step s 78 ). As before with the locking mechanism  22 , the user may wish to check the indicia or other features to ensure that the locking mechanism  56  is locked. The trial  10  is then assembled. Steps s 72  through s 78  may be performed in any order. It does not matter which pieces are coupled to one another first or if the pieces are locked prior to the next piece being added. 
     In some embodiments, the patient&#39;s anatomy may be such that the patient does not need all three bodies  12 ,  14 ,  16 . In those cases, two of the bodies  12 ,  14 ,  16  may be used in any combination that best fits the patient&#39;s anatomy. In other embodiments, the patient&#39;s anatomy may require multiple middle bodies  14 . In such cases, more than one middle body  14  may be used. 
     In one embodiment, the bodies  12 ,  14 ,  16  are made of a lightweight sterilizable material such as aluminum and the locking mechanisms  22 ,  56  are made using stainless steel. In other embodiments, the locking mechanisms may also be made of aluminum or other sterilizable material. In other embodiments, the bodies  12 ,  14 ,  16  may be made of other sterilizable material. In some embodiments, the trial  10  may be made entirely of plastic. 
     Although the embodiments above have all been described as forming a distal stem, it should be understood that the invention may include other trials. For example, the same type of locking mechanism could be used with a distal stem connecting to a neck portion of a hip prosthesis. In other embodiments, the distal body  12  could be a broach or other instrument that is attached to a middle body  14  or proximal body  16 . Alternatively, the broach could be attached via the locking mechanism described to a neck portion. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such an illustration and description is to be considered as exemplary and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention are desired to be protected. 
     There are a plurality of advantages of the present invention arising from the various features of the present invention and associated method described herein. It will be noted that alternative embodiments of the modular trial assembly and associated method of the present invention may not include all of the features described yet still benefit from at least some of the advantages of such features. Those of ordinary skill in the art may readily devise their own implementations of a modular trial assembly and associated method that incorporate one or more of the features of the present invention and fall within the spirit and scope of the present invention as defined by the appended claims.