Patent Publication Number: US-2019167433-A1

Title: Orthopedic implant for sustained drug release

Description:
RELATED APPLICATIONS 
     This application is a continuation-in-part of U.S. patent application Ser. No. 15/973,820, filed May 8, 2018, which is a continuation-in-part of U.S. patent application Ser. No. 15/830,561, filed Dec. 4, 2017, both of which are incorporated by reference. 
    
    
     TECHNICAL FIELD 
     This technology relates to an implantable orthopedic device that provides for elution of a therapeutic agent. 
     BACKGROUND 
     An implantable orthopedic device, such as a component of a bone or joint replacement system, may contain an antibiotic or other therapeutic agent for elution from the device while the device is implanted. 
     SUMMARY 
     An orthopedic implant device includes an implant body with a reservoir configured store a therapeutic agent. A wall of the implant body has opposite side surfaces, including a side surface facing into the reservoir. An elution channel reaches from the reservoir through the body wall. The elution channel reaches fully through a thickness of the body wall between the opposite side surfaces, and may have a length that is greater than twice the thickness. 
     In some examples the elution channel has a length portion reaching within the body wall in a configuration parallel to the opposite side surfaces. Such a length portion may be provided in an arcuate configuration and/or a series of linear sections to define a convoluted elution path through the channel. 
     The body wall may also have multiple elution channels with a common inlet portion at the side surface facing into the reservoir. The multiple channels may reach from the common inlet portion to different respective outlet portions at the opposite side surface. 
     In another example, the implant body further has a reinforcement structure, such as a buttress, projecting from the body wall into the reservoir. The channel reaches from the body wall to the reservoir through and within the reinforcement structure. 
     The reinforcement structure may include as a truss such as, for example, a truss of orthogonal stiffener elements or a diamond cubic truss. Another reinforcement structure may include a minimal surface structure such as a gyroid. The truss or other reinforcement structure may reach across the reservoir fully between opposed portions of the body wall structure that face inward of the reservoir. 
     In another example, an elution pipe projects from an inner side surface of the body wall into the reservoir. The elution pipe and the body wall together define an elution channel communicating the reservoir with an elution pore in the body wall. The body wall may have a plurality of elution pores, and the elution pipe may be one of a plurality of elution pipes, each of which projects from the inner side surface of the body wall into the reservoir to communicate the reservoir with a respective elution pore. 
     The implant body wall may further include an adapter for a luer lock fitting to engage a syringe for injecting the therapeutic agent into the reservoir. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a perspective view of an implantable orthopedic device. 
         FIG. 2  is a sectional perspective view of a part of the device of  FIG. 1 . 
         FIG. 3  is a cross sectional view of the part shown in  FIG. 2 . 
         FIG. 4  is a perspective view of another implantable orthopedic device. 
         FIG. 5  is an opposite perspective view of the device shown in  FIG. 4 . 
         FIG. 6  is a perspective view of parts of the device shown in  FIGS. 4 and 5 . 
         FIG. 7  is a sectional view of the parts shown in  FIG. 6 . 
         FIG. 8  is a partial view of a porous body wall of an implantable orthopedic device. 
         FIG. 9  is sectional view taken on line  9 - 9  of  FIG. 8 . 
         FIG. 10  is view similar to  FIG. 9 , shown an alternative porous body wall. 
         FIG. 11  is a partial view, similar to  FIG. 9 , of another alternative porous body wall. 
         FIG. 12  is partial perspective view of an alternative implantable orthopedic device. 
         FIG. 13  is a side view of the device shown in  FIG. 12 . 
         FIGS. 14-16  are partial perspective views of additional alternative devices. 
         FIG. 17  is a perspective view of part of another alternative device. 
         FIG. 18  is a sectional view of the part shown in  FIG. 17 . 
         FIG. 19  is a view taken on line  19 - 19  of  FIG. 18 . 
         FIG. 20  is a sectional perspective view of another alternative device. 
     
    
    
     DETAILED DESCRIPTION 
     The embodiments illustrated in the drawings have components that are examples of the elements recited in the claims. The illustrated embodiments thus include examples of how a person of ordinary skill in the art can make and use the claimed apparatus. They are described here to meet the enablement and best mode requirements of the patent statute without imposing limitations that are not recited in the claims. One or more elements of one embodiment may be used in combination with, or in substitution for, one or more elements of another embodiment as needed for any particular implementation of the claimed apparatus. 
     An orthopedic implant device  10  is shown in  FIG. 1 . This example of an implant device  10  is a tibial component of a total knee replacement system. The device  10  thus includes an implant body  20  including a platform  22  and a stem  24 . The platform  22  and the stem  24  are configured to provide elution of a therapeutic agent from within the body  20  over an extended period of time while the device  10  is implanted. 
     The platform  20  has a peripheral edge surface  30  providing a shape and thickness appropriate for implanting the platform  20  at the proximal end of a tibia. A proximal side surface  32  of the platform  20  serves as a bone-replacement surface, and in this example has a contour configured to replicate a proximal surface contour of a healthy tibial plateau. A distal side surface  34  has a contour configured to mate with the opposed contour of a tibial bone surface that has been surgically prepared to receive the device  10 . 
     The stem  24  is configured for insertion into the medullary canal of the tibia to anchor the implanted device  10  in place. As best shown in  FIG. 2 , the stem  24  in the illustrated example has an elongated cylindrical shape with a longitudinal central axis  39 , an open proximal end  40 , and a closed distal end  42 . 
     A major length section  44  of the stem  24  has a uniform outer diameter. The major length section  44  includes the distal end  42  of the stem  24 . A minor length section  46  defines a cylindrical interior space  47 , and includes the proximal end  40  of the stem  24 . The minor length section  46  also has a reduced outer diameter above a shoulder surface  48 . In this manner the minor length section  46  is shaped for fitting into a bore  49  that reaches through the platform  22  to support the stem  24  in the assembled position projecting distally from the platform  22 , as shown in  FIG. 1 . 
     The major length section  44  of the stem  24  has an exterior surface  50  with pores  51 . The major length section  44  further has interior surfaces defining reservoirs and channels in fluid flow communication with the pores  51 . These include an innermost cylindrical surface  52  that is centered on the axis  39 . The innermost surface  52  defines the length and diameter of a first reservoir  55  having a cylindrical shape reaching along the axis  39  between a closed distal end  56  and an open proximal end  58 . A pair of radially opposed cylindrical inner surfaces  60  and  62  also are centered on the axis  39 . These inner surfaces  60  and  62  together define the length and width of a second reservoir  65  having an annular shape that is spaced radially outward from, and surrounds, the first reservoir  55 . The second reservoir  65  also has a closed distal end  70  and an open proximal end  72 . Stiffeners  74  may reach radially across the second reservoir  65  for structural reinforcement. 
     Additional cylindrical inner surfaces define first and second channels  75  and  77 . The first channels  75  reach radially outward from the first reservoir  55  to the second reservoir  65 . The second channels  77  reach further outward from the second reservoir  65  to the pores  51 . Construction of the reservoirs  55 ,  65 , the channels  75 ,  77  and the pores  51  is preferably accomplished by an additive manufacturing process that forms the stem  24  as a single unitary body of agglomerated additive manufacturing material. 
     When the stem  24  is assembled with the platform  22  as shown in  FIG. 1 , the open proximal ends  58  and  72  of the reservoirs  55 ,  65  communicate with the bore  49  through the interior space  47  and the open proximal end  40  of the stem  24 . Internal channels in the platform  22  may provide fluid flow paths from the bore  49  to additional openings  83 . 
     Before being implanted, the device  10  is charged with a solid therapeutic agent delivery medium. The delivery medium is impregnated with a drug or other therapeutic agent. This can be accomplished by forming a paste-like mixture of the therapeutic agent and a solid binder, and injecting the mixture into the reservoirs  55 ,  65  through the bore  49  and into the stem  24  through open proximal end  40 . 
     For example, the therapeutic agent may comprise an antibiotic, such as gentamicin, and the solid binder may comprise a powdered material, such as calcium sulfate powder. A paste may be formed by mixing those ingredients with water. As shown partially in  FIG. 1 , the pores  51  at the exterior surface  50  may be covered with parafilm  86  to contain the injected paste as it solidifies within the reservoirs  55 ,  65 . When the paste has solidified, the parafilm is removed, and the solidified material will then permit gradual elution of the gentamicin outward through the channels  75 ,  77  from the reservoirs  55 ,  65 , and further outward through the pores  51 , as the calcium sulfate delivery medium biodegrades gradually under the influence of the patient&#39;s synovial fluid. This sustains the elution over a more extended period of time compared to the more rapid elution of a liquid in the absence of a solid binder. 
     In addition to the use of a solid binder, the arrangement of reservoirs  55 ,  65  and channels  75 ,  77  also contributes to the extended period of time taken for complete elution of the therapeutic agent. Specifically, the channels  75 ,  77  provide fluid flow communication between the reservoirs  55 ,  65  in series so that elution from the reservoirs  55 ,  66  proceeds sequentially rather than simultaneously. Elution is thus sustained as the therapeutic agent in the first reservoir  55  is preserved until the therapeutic agent is depleted or nearly depleted from the second reservoir  65 . 
     Another example of an orthopedic implant device  100  is shown in  FIGS. 4 and 5 . In this example, the device  100  is a femoral component of a total knee replacement system. Like the device  10  described above, the device  100  is configured to provide elution of a therapeutic agent over an extended period of time. 
     The device  100  comprises an implant body  110  with medial and lateral legs  112  and  114  that are shaped as medial and lateral condyles. Accordingly, the medial leg  112  has an arcuate shape with a distal end portion  120 . The exterior surface  122  at the distal end portion  120  serves as a bone-replacement surface with a contour configured to replicate a healthy medial condyle bone surface contour. The lateral leg  114  similarly has an arcuate shape with a distal end  124  portion at which the exterior surface  126  has a contour replicating a healthy lateral condyle bone surface contour. The distal end portions  120  and  124  are separated across a trochlear gap  125 . 
     An intermediate section  140  of the body  110  reaches across the gap  125  between the medial and lateral legs  112  and  114 . The intermediate body section  140  has planar opposite side surfaces  142 . Each opposite side surface  142  has an arcuate anterior edge  144  adjoining the adjacent leg  112  or  114 . A posterior surface  146  ( FIG. 4 ) has a planar contour reaching across the intermediate body section  140  between the opposite side surfaces  142 . An anterior surface  148  ( FIG. 5 ) has an arcuate contour reaching along and across the gap  125  between the legs  112 ,  114 . The posterior and anterior surfaces  146  and  148  each have an array of elution pores  149 . In the illustrated example, the all of the elution pores  149  in the body  110  are remote from the bone replacement surface portions  122  and  126 . 
     As shown separately in  FIGS. 6 and 7 , an internal wall structure  160  is located at the interior of the intermediate body portion  140 . The internal wall structure  160  divides the interior of into first and second reservoirs  165  and  167 . Stiffeners  168  may be provided for structural reinforcement, and the implant body  110  also may be defined by a single unitary body of agglomerated additive manufacturing material. 
     In use, each reservoir  165  and  167  in the implant body  110  stores a solid therapeutic agent delivery medium impregnated with a therapeutic agent, such as the solidified paste described above. One or more passages for injecting the paste into the reservoirs  165  and  167  can be provided in any suitable manner known in the art of additive manufacturing. Channels  169  reaching through the inner wall structure  160  communicate the first reservoir  165  with the second reservoir  167 . Additional channels  171  communicate the second reservoir  167  with the pores  149  at the posterior and anterior external surfaces  146  and  148 . The channels  169  and  171  connect the reservoirs  165  and  167  in series so that elution from the reservoirs  165  and  167  to the pores  149  proceeds sequentially rather than simultaneously, whereby elution is sustained as the therapeutic agent in the first reservoir  165  is preserved until the therapeutic agent is depleted or nearly depleted from the second reservoir  167 . 
     As shown partially in  FIGS. 8 and 9 , another example of an orthopedic implant device includes an implant body  200  with a body wall  202 . The body wall  202  has opposite side surfaces  204  and  206 . One side surface  204  faces into a reservoir  209  for storing a solid therapeutic agent delivery medium as described above. The other side surface  206  has elution pores  215  that are spaced apart in an array on that surface  206 . Multiple elution channels  217  reach through the body wall  202  to communicate the reservoir  209  with the elution pores  215 . 
     The elution channels  217  in this example have a common inlet portion  229  ( FIG. 9 ) at the reservoir  209 . The elution channels  217  also have different respective outlet portions  231  at the elution pores  215 . Intermediate portions  235  of the elution channels  217  communicate the inlet portion  229  with the outlet portions  231  in parallel. In this example, the intermediate portions  235  of the elution channels  217  extend fully from the inlet portion  229  to the outlet portions  231  within the thickness of the body wall  202  in linear configurations parallel to the opposite side surfaces  204  and  206 . 
     With the outlet portions  231  of the elution channels  217  spaced apart from the common inlet portion  229 , as shown for example in  FIGS. 8 and 9 , each elution channel  217  has a length that reaches fully through the thickness of the body wall  202  between the opposite side surfaces  204  and  206 . Those lengths in the illustrated example are equal, but could alternatively include one or more unequal lengths. The illustrated lengths are also substantially greater than the body wall thickness. Preferably, the length of each elution channel  217  is greater than twice the thickness of the body wall  202 , and may be a greater multiple of the thickness, as shown by way of example in  FIGS. 8 and 9 . This helps to prolong elution from the reservoir  209  to the elution pores  215  for a correspondingly greater period of time. 
     Additionally, each elution pore  215  in this example has an outlet flow area Al that is substantially less than the common inlet flow area A 2 . This helps sustain elution by limiting access of the patient&#39;s synovial fluid to the solid delivery medium in the reservoir  209 . The spaced-apart array of multiple elution pores  215  with a common inlet  229  helps to distribute the therapeutic agent throughout the area of the outer side surface  206 , whereas a single outlet would provide a more concentrated delivery of the therapeutic agent. 
     Further regarding the example of  FIGS. 8 and 9 , the arrangement of elution channels is configured for a flat body wall  200 . Such an arrangement could thus be applied to either or both of the flat body walls shown in  FIGS. 6 and 7 . In another example, a similar arrangement of elution channels on an arcuate body wall  250 , as shown in  FIG. 10 , could be applied to either or both of the arcuate body walls of  FIGS. 6 and 7 . With a more circular curvature, the arrangement of  FIG. 10  could be applied to either or both of the circular body walls shown in  FIGS. 2 and 3 . In either case, the body wall  250  of  FIG. 10  has elution channels  255  with a common inlet portion  259  at a side surface  260  facing into a reservoir  263 . The elution channels  225  further have different respective outlet portions  265  that are open at elution pores  267  on an opposite side surface  270 . These elution channels  255  extend within the thickness of the body wall  250  fully from the common inlet portion  259  to the outlet portions  255  in arcuate configurations parallel to the opposite side surfaces  260  and  270 . 
     In the example of  FIG. 11 , an elongated elution channel  281  has an inlet portion  283  and an outlet portion  285 . The inlet portion  283  of the channel  281  is located on a porous body wall  286  where an inner side surface of the body wall  286  faces into a reservoir. The outlet portion  285  of the channel  281  is open at an opposite side surface  288  of the body wall  286 . As in the examples of  FIGS. 8-10 , the overall length of the channel  281  in  FIG. 11  is greater than twice the thickness of the associated body wall  286  to promote sustained elution. Additionally, the intermediate portion of the channel  281  has a series of linear sections  288  in a non-parallel orientations that provide a convoluted elution flow path between the inlet portion  283  and the outlet portion  285 . This further contributes to prolong elution. A similar arrangement can be provided in a spiral or other curvilinear configuration. 
     Another example of an implant body  300  with elongated elution channels  303  is shown partially in  FIGS. 12 and 13 . In this example, each elution channel  303  has a linear configuration with two sections  307  and  309  ( FIG. 13 ). The first section  307  reaches through the associated body wall  310  with a length equal to the surrounding thickness of the body wall  310 . The second section  309  provides the channel  303  with a total length  303  that is greater than the body wall thickness by a multiple of two or more. The greater length is provided by configuring the second section  309  of the channel  303  to reach through a buttress  312  that projects from the body wall  310  into the associated reservoir  315 . Specifically, the buttress  312  has an edge  316  adjoining the body wall  310 , and reaches from the adjoined edge  316  to a free edge  320  within the reservoir  315 . The second section  308  of the channel  303  reaches along and through an enlarged-width portion  322  of the buttress  312 . The enlarged width portion  322  in the illustrated example is configured as a pipe. 
     In the example of  FIGS. 12 and 13 , the buttresses  312  provide structural reinforcement to the body wall portions that are rendered porous by the elution channels  303 . This can enable the body walls  310  to have decreased wall thickness and/or increased porosity. 
     Structural reinforcement can also be provided in other configurations, as shown for example in  FIGS. 14, 15 and 16 . In the example of an implant body  400  as shown  FIG. 14 , structural reinforcement is provided by a truss of stiffener elements  402 . The stiffener elements  402  in this example are configured as beams in an orthogonal array reaching across the reservoir  405  fully from porous body wall portions  406  to opposed body wall portions  410 . In the example of  FIG. 15 , a truss  420  is provided in the configuration of a diamond cubic truss. In the example of  FIG. 16 , structural reinforcement is provided by a minimal surface structure in the configuration of a gyroid. Each of these examples of a reinforcement structure  402 ,  420  and  430  also projects across the respective reservoir fully from a porous body wall portion to an opposed body wall portion that faces inward of the reservoir. Such structures can be formed within the surrounding body wall structure by use of know additive manufacturing techniques. 
       FIG. 17  is a partial view of an implant body wall  500  similar to that shown in  FIG. 6 . The body wall  500  of  FIG. 17  also has a surface  502  with elution pores  505 . As further shown in  FIGS. 18 and 19 , elution pipes  510  project from an opposite side surface  512  of the body wall  500  into a reservoir  515  for containing a therapeutic delivery agent. The elution pipes  510  and the body wall  502  together define elution channels  517  that provide fluid communication between the reservoir  515  and the elution pores  505 . 
     The body wall  500  further includes an adapter  518  for a luer lock fitting to secure a syringe for injecting the therapeutic agent delivery medium agent into the reservoir  515  as described above. The adapter  518  defines a passage  519  into the reservoir  515  and, in the given example, has a male flange  520  for receiving and guiding an internal screw thread on a female luer fitting. A closure device  522  in the form of a plug or cap  522  is provided for closing and sealing the passage  519 . 
     The elution pipe  510  in the example of  FIGS. 17-19  are arranged in two separate sets. Each set includes a single inlet pipe  510  with an inlet  525  inside the reservoir  515 . Each set further includes multiple branch pipes  510  that reach from the inlet pipe  510  to respective elution pores  505 . The pipes  510  in each set thus share a common inlet  525  within the reservoir  515 . 
       FIG. 20  shows a variation of the example shown in  FIGS. 17-19 . As shown partially in  FIG. 20 , reinforcement structures in the form of buttresses  530  are provided to reach from the pipes  510  to the body wall  500 . These buttresses  530  are formed as inner walls with planar opposite sides, and reach lengthwise along the pipes  510  as shown. 
     This written description sets for the best mode of carrying out the invention, and describes the invention so as to enable a person of ordinary skill in the art to make and use the invention, by presenting examples of the elements recited in the claims. The detailed descriptions of those elements do not impose limitations that are not recited in the claims, either literally or under the doctrine of equivalents.