Abstract:
The present teachings provide a modular articulating cement spacer mold for forming a temporary implant. The modular spacer mold includes a head component mold defining a first opening, a head connector positioned within the first opening of the head component mold, a stem component mold defining a second opening, and a stem connector to fit within the second opening of the stem component mold to mateably engage the head connector. Related kits and methods of forming a temporary implant are provided.

Description:
FIELD 
     The present disclosure relates to a hip spacer mold, and more particularly, to a modular articulating two-stage cement hip spacer mold. 
     BACKGROUND 
     A natural joint may undergo degenerative changes due to a variety of etiologies. When these degenerative changes become so far advanced and irreversible, it may ultimately become necessary to replace the natural joint with a joint prosthesis. However, due to any number of reasons, a small portion of patients that undergo such orthopedic surgical procedures suffer from infections at the surgical site and generally around the implanted joint prosthesis. In order to cure such an infection in a two-stage re-implantation, the implanted joint prosthesis is generally removed, the site is thoroughly debrided and washed, antibiotics are applied to the infected site via a temporary implant until the infection is eliminated, and a new revision type joint prosthesis is then implanted during a subsequent orthopedic surgical procedure. 
     Accordingly, there is a need for apparatus and methods to facilitate two-stage re-implantation which expedite healing at the site, provide a better fitting implant, reduce the amount of time a patient is bedridden, increase the efficiency of the surgical procedure while reducing the surgical time and cost, eliminate any re-cleaning or re-sterilizing steps, and create a customizable procedure. 
     SUMMARY 
     In various embodiments, the present teachings relate to a modular articulating cement spacer mold for forming a temporary implant. The modular spacer mold includes a head component mold defining a first opening, a head connector positioned within the first opening of the head component mold, a stem component mold defining a second opening, and a stem connector to fit within the second opening of the stem component mold to mateably engage the head connector. 
     In other embodiments, the present teachings provide kits for forming modular articulating cement spacer molds for temporary implants. The kits include at least one head component mold and at least one stem component mold. 
     The present teachings further provide methods for forming a temporary implant. A bone cement is mixed during a surgical procedure. The appropriately sized head component mold, head component connector, stem component mold, and stem connector are selected. The head component mold and the stem component mold are filled with the cement to form the temporary implant which is implanted into the patient. 
     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. 
    
    
     
       DRAWINGS 
       The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
         FIG. 1  depicts a modular cement mold according to various embodiments; 
         FIG. 2  depicts a series of neck adapters according to various embodiments; 
         FIG. 3  depicts an exploded view of the head component mold; 
         FIG. 4  depicts an exploded view of the stem component mold; 
         FIG. 5  depicts injection of a material into the stem component mold according to various embodiments; 
         FIG. 6  depicts injection of a material into the head component mold according to various embodiments; 
         FIG. 7  depicts a kit according to various embodiments; 
         FIG. 8  depicts a head component having a reinforcing head connector therein; 
         FIG. 9  depicts a series of bridges; 
         FIG. 10  depicts a head component having a stepped and tapered reinforcing head connector therein; 
         FIG. 11  depicts a stem component having a reinforcing stem connector therein; and 
         FIG. 12  depicts a head component having a reinforcing head connector therein. 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. Although certain examples and surgical methods disclosed herein are in conjunction with a temporary hip implant, it is understood that the molds and surgical methods disclosed herein can be used in any orthopedic revision surgery for any area in the patient. 
       FIG. 1  depicts a modular cement mold  10  according to the present teachings. The modular cement mold  10  is used to form a temporary femoral hip implant or prosthesis to replace a right of left portion of a femoral hip joint for a temporary healing period. The modular cement mold  10  can be formed from any biocompatible material including various polymers. In various embodiments, the polymeric material can be readily tearable and/or translucent, such as a thermoplastic elastomer. In various embodiments, the thermoplastic elastomer is silicone. In such embodiments, the silicone selected can have a sufficiently high stiffness such that the modular cement mold  10  will not sag or be deformed upon handling. An exemplary silicone that achieves these characteristics is Dow Q7-4780 or any other 80 durometer silicone. Moreover, it should be noted that the material selected should generally not adversely react with the bone cement and antibiotic selected. The modular cement mold  10  can also be made of any other appropriate materials, including, but not limited to rubber. 
     The modular cement mold  10  includes a head component mold  12  having a head connector  14  therein and a stem component mold  16  having an opening  17  for a stem connector  18 . It is understood that various features from the head component mold  12  and the stem component mold  16  can be interchanged within the scope of the present teachings. The modularity of the present teachings allows the surgeon to create a highly customized implant based on both the head and the stem size needs of the patient. This is beneficial in revision surgery where the condition of either the acetabulum or the femur may differ to the extent where a monolithic temporary implant may not best meet the needs of the patient. By providing the head connector and the stem connector, and/or the various reinforcements as detailed later herein, embodiments of the present temporary implant are optimized for strength and reinforce the high stress areas along the neck of the implant. 
     As shown in  FIG. 3 , the femoral head component mold  12  includes a first half  20  and a second half  22  which provide the articulating head of the temporary implant. The femoral head component first half  20  and second half  22  can be joined along center line  26  which corresponds to the coronal plane of the subsequently formed temporary hip implant. The halves  20  and  22  are essentially mirror images of one another and like reference numerals will be used to identify like structures for each half. 
     The halves  20  and  22  include an outer hemispherical sidewall  28  and an inner hemispherical sidewall  30  which define the entire shape of the substantially spherical articulating head. The substantially spherical articulating head and thus, the mold halves  20  and  22  can include a flattened region  31  as shown in  FIGS. 1 and 3 . The flattened region  31  can be placed opposite the articulating portion of the head so as to not hinder articulation of the final implant. A variation of the substantially spherical head is also shown in  FIGS. 8 ,  10 , and  12 . The inner hemispherical sidewall  30  can include surface area increasing features  32 . Upon filling the head component mold  12 , recess portions or depressions are left in the articulating head of the final implant which are the negative impression of the surface area increasing features  32 . The depressions increase the surface area of the resultant articulating head. Suitable depressions include, but are not limited to grooves, dimples, hemispheres, cones, stars, ridges, notches, and the like. The depressions can also include individual letters or combinations of letters and designs, such as a logo. Certain shapes, such as multi-point stars or deep cones, provide the greatest increase in surface area. As shown in  FIG. 3 , the surface area increasing feature  32  can include rounded projections to define dimples in the temporary implant. Further, referring to  FIG. 7 , a variety of different surface area increasing features  32  are shown. 
     The same surface feature  32  can be included on each of the inner hemispherical side walls  30  or the surface features can be varied in size and/or shape within the same hemispherical side wall  30  or on both hemispherical sidewalls  30 . The surface area of the temporary implant can be increased by from about 1% up to 50% or more depending on the combination of surface area increasing features  32 . An exemplary, but non-limiting, benefit of the increased surface area is the increased amount of antibiotic or other therapeutic material (i.e.: drugs, vitamins, etc.) from the surface of the temporary implant to the defect site. The increased delivery of the antibiotic or other therapeutic material expedites healing and minimizes the recovery time of the patient. The head component mold  12  further includes a trapezoidal shaped foot  34  by which to grasp the head component mold  12 . 
     The head connector  14  is used to connect the articulating head component of the finished product with the femoral stem component of the finished product. The head connector  14  can define a hollow cylindrical or tapered chamber formed by a metal insert contained within the head component mold  12 . Exemplary metals for the head connector  14  include stainless steel, titanium, cobalt, and the like and various alloys thereof. The head connector  14  can mate with the femoral stem component using a taper fit, such as a Morse taper, as a non-limiting example. The head connector  14  can also include surface roughening features or a surface texture to facilitate placement and fit of the stem connector  18  with the head connector  14 . 
     In various embodiments, the head connector  14  is a female connector and is contained within the head component mold  12  such that upon filling the head component mold  12  with a material, such as a bone cement, a void volume will be defined in the articulating head portion of the temporary implant having a volume that is roughly equivalent to the void volume defined by the head connector  14 . In still other embodiments, the head connector  14  can be a male connector and is contained at a region of the head component and does not define a hollow region within the head component mold  12  upon filling the head mold with the material. In either embodiment, the head connector  14  is fixed in the head component mold  12  so that it is not inadvertently displaced. 
     The head connector  14  is retained in the head component mold  12  by a lip or ring about the lower region of the head connector  14  which has at least one dimension greater than the opening for the head connector  14 . Any other suitable retention technique can also be employed in accords with the present teachings. For example, the head connector  14  can be retained in groove defined by the head component mold  12 . Moreover, inclusion of the head connector  14  in the head component mold  12  maintains a material-tight integrity of the head component mold  12  and prevents leakage of a filling material therefrom. In various embodiments, the head component mold  12  and the head connector  14  are provided as a single unit where the head connector  14  is embedded in the material of the head component mold  12 , as shown in  FIG. 3 . 
     As best shown in  FIG. 6 , the head component mold  12  can further include an access port  36  through which to deliver a material to fill the head component mold  12 . In various embodiments, the access port  36  can be defined at any region of the head component mold  12 . The head access port  36  is implemented into the head component mold  12  as to maintain the material-tight integrity of the head component mold  12  and does not facilitate inadvertent removal of material from within the head component mold  12 . As detailed later herein, the head access port  36  is mated with a nozzle  38  of a delivery device  40  through which a material is delivered to the head component mold  12 . 
     Turning to  FIGS. 4 and 5 , the femoral stem component mold  16  includes a first half  42  and a second half  44 . The halves  42  and  44  include an enlarged neck portion  46  and an elongated stem portion  48 . As stated above herein, the halves  42  and  44  are essentially mirror images of one another, respectively, and like reference numerals will be used to identify like structures for each half. The neck portion  46  is enlarged to provide additional strength for the temporary implant. 
     The stem component mold  16  includes outer sidewalls  50  and inner sidewalls  52 . As detailed above with respect to the head component mold  12 , the stem component mold  16  can also include surface features  32  on the sidewalls  50  and  52 . The surface area increasing features  32  can be continuous throughout the length of the stem component mold  16  or the surface area increasing features  32  can be varied in direction, size, or shape long the length of the stem component mold  16 , such as the varied direction surface area increasing features  32  comprising grooves depicted in  FIG. 4 . In still other embodiments, the surface area increasing features  32  can be placed at only discrete regions along the stem component mold  16 . It is understood that the surface area increasing features  32  on the stem component mold  16  can either match or be different from the surface area increasing features  32  on the head component mold  12 . 
     Referring to  FIGS. 1 and 2 , the stem connector  18  is adapted to fit into the opening  17  as defined by the stem component mold  16 . The stem connector  18  can have a slight taper, such as a Morse taper, as to provide the quick and tight fit with the head connector  14 . The stem connector  18  can be made of any of the biocompatible metal materials detailed above herein for use with the head connector  14 . As shown by the phantom lines, the stem connector  18  can also include a reinforcing rod  19  to extend the length of the stem component mold  16 . Further description of the reinforcing feature is provided later herein. 
     The stem connector  18  can also include surface roughening features or a surface texture to facilitate placement and fit of the stem connector  18  with the head connector  14 . As shown in  FIG. 2 , the stem connector  18  can be made in differing lengths and widths to provide further customization of the temporary implant depending on the patient&#39;s needs. 
     The halves  20  and  22  of the head component mold  12  and the halves  42  and  44  of the stem component mold  16  can be separately molded by various conventional molding techniques such as injection molding, compression molding, blow molding, spin casting, etc. In various embodiments, the head component mold  12  or the stem component mold  16  can also be molded as single pieces. 
     The halves  20  and  22  and halves  42  and  44 , respectively, can be joined substantially along the center line  26  matching the coronal plane by means of a connecting or coupling mechanism  54  on each respective part. In various embodiments, the coupling mechanism  54  can be a tongue and groove coupling mechanism  56  having a substantially rounded tongue  58  running about the outer circumference along the center line or coronal plane  26  of the first half  20  and  42 . A rectangular groove  60  can be positioned also substantially around the outer circumference of the second halves  22  and  44  along the coronal plane  26 . The tongue  56  can be rounded to provide a self centering mechanism and also to assist in engaging the rounded tongue  56  within the rectangular shaped groove  60  since engaged silicone does not slide readily with respect to one another. In various embodiments, the tongue  58  can be adhered to the groove  60  by use of a silicone adhesive. 
     The tongue  58  and groove  60  are an exemplary removal mechanism through which separation and tearing of the first half  20  or  42  from the respective second half  22  or  44  is achieved. It should also be noted that any other type of coupling mechanism could also be employed such as two planar surfaces adhered together, differently shaped mating surfaces, etc. Other removal mechanisms can include a pull string or a pull tab as are known in the art. For example, a pull string made of suture, thin metal wire, or the like can be embedded in the thermoplastic mold such that upon pulling or engaging the string, the thermoplastic stretches and tears to expose the implant. 
     Turning to  FIGS. 8 through 12 , a modular system having reinforced head molds  112  and reinforced stem molds  116  is provided. The modular systems of such embodiments share similarities with the above-described embodiments and like features are referenced by similar numerals (i.e.: head mold  12  and head mold  112 ). It is also understood that the components of all embodiments disclosed herein can be interchanged. 
     The head mold  112  is made of halves  120  and  122  and contains a head connector  114  and a reinforcing core  115 . Upon dispensing the cement into the nozzle  136 , the reinforcing core  115  is surrounded by the cement. The reinforcing core  115  provides additional support for the cement and increases the strength of the temporary implant. The reinforcing core  115  can be made of a metal or any other suitable material, as is described above. As shown in  FIGS. 8 and 10 , the core  115  can be formed to include several dimensions and tapered regions or, as shown in  FIG. 12 , the core  115  can consist of a generally uniformly tapered dimension. 
     The stem component  116  is made of halves  142  and  144  and includes a stem connector  118  and a reinforcing core  119 . The reinforcing core  119  similarly adds further support for the cement and increases the strength of the temporary implant. The reinforcing core  119  can extend the length of the stem component mold  116  as shown in  FIG. 10 , or the reinforcing core  119  can partly extend along a region of the length of the stem component mold  116 . The reinforcing core  119  can be made of a metal or any other suitable material and provides additional support for the cement and increase the strength of the temporary implant. 
     As shown in  FIG. 9 , a neck adapter or bridge  125  can be connected to either of the head component  112  or the stem component  116 . The bridge  125  can be of differing lengths to provide a neck length suitable to the individual needs of the patient. The proximal end  121  of the bridge  125  mates with the head connector  114 . The distal end  123  of the bridge  125  mates with the stem connector  118 . By varying the length of the bridge  125 , the neck length is adapted to provide a highly customized implant to the patient. The use of the bridge  125  is optional as certain patient&#39;s may not need the additional neck length. 
     Referring to  FIG. 7 , a kit  1000  is provided. The kit  1000  can include at least one head component mold  12 , at least one stem component mold  16 , and at least one stem connector  18 . In various embodiments, the kit  1000  can include a plurality of any of the head component mold  12 , stem component mold  16 , and stem connector  18 . The kit  1000  contents can be provided in differing sizes to allow for implant customization. As shown in the kit  1000 , a variety of stem connectors  18  are provided being predisposed in the stem component molds  16 . Any combination of features and parts as detailed herein can be included in the kit  1000 , such as, for example, an inclusion of a variety of differing surface area increasing features  32  being included on the different components or a deliver device(s)  40 . The components of the kit  1000  can be individually seated with the outer container. Minor modifications and inclusions in the kit  1000  which are incidental to surgical methods, such as scalpels, antibiotics, cement, gauze, etc. are also included within the scope of the present teachings. 
     In embodiments using the reinforced molds as detailed above, an exemplary kit  1000  can include at least one of the reinforced head component molds  112 , at least one reinforced stem component mold  116 , and at least one bridge  125 . The contents of the kit  1000  can also include a mixture of components, for example, a plurality of bridges  125  included with at least one reinforced head component molds  112 , at least one head component mold  12 , and at least one stem component mold  16 . 
     The present teachings further provide methods of using the modular cement mold. Although the methods are disclosed as used with certain embodiments of the present teachings, it is understood that the methods disclosed can be used with any of the mold embodiments detailed above herein. 
     First, a surgeon or assistant will mix the appropriate antibiotic loaded cement or add an antibiotic to the particular cement. It is understood that the preparation of the cement is performed according to the label instructions of the particular cement. For example, about two grams of antibiotic are mixed with each 40 gram packet of bone cement powder which is then mixed with a corresponding number of 20 milliliter ampoules of a liquid monomer. The bone cement can be a poly-methyl-methacrylate (PMMA) cement such as those produced under the trade names Generation 4(TM), CMW1, CMW2, CMW3, Zimmer Dough Type, or Zimmer LVC, or a MMA-styrene copolymer cement such as that produced under the trade names Howmedia Simplex P or Zimmer Osteobond, or an MMA-methyl acrylate copolymer such as that produced under trade names Cobalt (TM) G-HV or Cobalt (TM) HV. Once the appropriate antibiotic loaded bone cement is mixed, the bone cement is put within the delivery device  40  shown as a cement gun. 
     As shown in  FIG. 6 , with the delivery device  40  loaded with the bone cement, the appropriately sized modular components  12  and  14  are selected to form a customized fit for both the articulating head and femoral component of the final implant. For example, the appropriately sized modular components  12  and  14  along with the stem connector  18  can be selected from the kit  1000  as shown in  FIG. 7  to meet the patient&#39;s needs. Once the appropriately sized modular components  12 ,  14 , and  18  are selected, a surgeon will generally grasp the head component mold  12  and slidably and sealably insert the nozzle  38  of the delivery device  40  into the access port  36 . With the nozzle  38  substantially sealing the access port  36 , the surgeon will engage the delivery device  40  to dispense out the bone cement within the inner spherical walls  30  of the head component mold  12 . 
     As the bone cement is delivered within the head component mold  12 , air trapped within the head component mold  12  can be released using optional vent holes  62 . The vent holes  62  can be located along the center line  26 , opposite the access port  36 , or at an offset of 15° to 30° from the center line  26 , as non-limiting examples. The vent holes  62  are positioned so that any trapped air can be evacuated from the system. The vent holes  62  are sized to allow passage of air but to restrict or block passage of bone cement out of the mold. In various embodiments, the access port  36  can be somewhat flexible to allow the surgeon to angle or direct the nozzle  38  within the head component mold  12  to insure that the head component mold  12  is fully filled with the bone cement. 
     Using a translucent or transparent material to form the mold allows the surgeon to assess whether the head component mold  12  has been adequately filled without substantially any air pockets or voids. This also allows the surgeon to verify that the surface features  32  have been adequately navigated by the cement to provide the proper surface area. 
     Turning to  FIG. 5 , with respect to the stem component mold  16 , the stem connector  18  can be selected to provide the appropriate neck extension on the stem portion of the implant. The surgeon then places the stem connector  18  into the stem component mold  16  by angling the stem connector  18  in the opening  17  defined by the stem component mold  16 . As shown in  FIG. 1 , the stem connector  18  can be backed into the stem component mold  16 . The surgeon then manipulates the stem connector  18  such that the system becomes material-tight or is a closed system except for inlet of the cement into the access port  36 . Similar to the technique to fill the head component mold  12 , the surgeon inserts the delivery device  40  into the access port  36  and fills the stem component mold  16  with the cement. In embodiments where the access port  36  is placed at point along the stem component mold  16  which is distal to the stem connector  18 , deposition of the cement further presses the stem connector  18  against the opening  17  in the stem component mold  16 . 
     Once the modules of the cement mold  10  are filled by the delivery device  40 , the modules  12  and  14  can be placed on a nearby surface, such as a surgical table, to allow the cement to cure and cool while the surgeon moves on to another task, thereby substantially increasing the efficiency and reducing the time for the surgical procedure. In various embodiments, the modules  12  and  14  can be placed on the surgical table such that the foot  34  engages the table. Once the bone cement has sufficiently cured, the surgeon can grasp the modules via the foot  34  and then slips his thumbs within a cut-out region  64  to disengage the tongue and groove coupling. In embodiments using silicone, the tear characteristics of the silicone material allow the modules to be torn from the formed cement. The combined cement and the respective head connector  14  and stem connector  18  form composite implants of the combined materials. 
     The stem component of the temporary hip implant can then be simply engaged in the intramedullary canal of the host femur. The stem connector  18  is then disposed in the head connector  14  of the articulating head using the taper fit. This allows for quick and easy placement and enables the distended joint to be subsequently re-engaged with the temporary implant to enable limited non-load bearing movement by the patient. The temporary implant allows the patient to generally sit up or be transported out of a hospital during the temporary recovery stage prior to having a revision type prosthesis subsequently implanted. During this time the antibiotic in the bone cement leaches out over time to the infected area and soft-tissue tension is maintained. 
     The description of the present teachings is merely exemplary in nature and, thus, variations that do not depart from the gist of the present teachings are intended to be within the scope of the present teachings. Such variations are not to be regarded as a departure from the spirit and scope of the present teachings.