ORTHOPEDIC IMPLANT FOR SUSTAINED DRUG RELEASE

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. Elution channels reach from the reservoir through the body wall. The elution channels include an elongated channel traversing a thickness of the body wall between the opposite side surfaces. The elongated channel may have a length greater than twice the thickness.

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.

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 device10is shown inFIG. 1. This example of an implant device10is a tibial component of a total knee replacement system. The device10thus includes an implant body20including a platform22and a stem24. The platform22and the stem24are configured to provide elution of a therapeutic agent from within the body20over an extended period of time while the device10is implanted.

The platform20has a peripheral edge surface30providing a shape and thickness appropriate for implanting the platform20at the proximal end of a tibia. A proximal side surface32of the platform20serves 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 surface34has a contour configured to mate with the opposed contour of a tibial bone surface that has been surgically prepared to receive the device10.

The stem24is configured for insertion into the medullary canal of the tibia to anchor the implanted device10in place. As best shown inFIG. 2, the stem24in the illustrated example has an elongated cylindrical shape with a longitudinal central axis39, an open proximal end40, and a closed distal end42.

A major length section44of the stem24has a uniform outer diameter. The major length section44includes the distal end42of the stem24. A minor length section46defines a cylindrical interior space47, and includes the proximal end40of the stem24. The minor length section46also has a reduced outer diameter above a shoulder surface48. In this manner the minor length section46is shaped for fitting into a bore49that reaches through the platform22to support the stem24in the assembled position projecting distally from the platform22, as shown inFIG. 1.

The major length section44of the stem24has an exterior surface50with pores51. The major length section44further has interior surfaces defining reservoirs and channels in fluid flow communication with the pores51. These include an innermost cylindrical surface52that is centered on the axis39. The innermost surface52defines the length and diameter of a first reservoir55having a cylindrical shape reaching along the axis39between a closed distal end56and an open proximal end58. A pair of radially opposed cylindrical inner surfaces60and62also are centered on the axis39. These inner surfaces60and62together define the length and width of a second reservoir65having an annular shape that is spaced radially outward from, and surrounds, the first reservoir55. The second reservoir65also has a closed distal end70and an open proximal end72. Stiffeners74may reach radially across the second reservoir65for structural reinforcement.

Additional cylindrical inner surfaces define first and second channels75and77. The first channels75reach radially outward from the first reservoir55to the second reservoir65. The second channels77reach further outward from the second reservoir65to the pores51. Construction of the reservoirs55,65, the channels75,77and the pores51is preferably accomplished by an additive manufacturing process that forms the stem24as a single unitary body of agglomerated additive manufacturing material.

When the stem24is assembled with the platform22as shown inFIG. 1, the open proximal ends58and72of the reservoirs55,65communicate with the bore49through the interior space47and the open proximal end40of the stem24. Internal channels in the platform22may provide fluid flow paths from the bore49to additional openings83.

Before being implanted, the device10is 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 reservoirs55,65through the bore49and into the stem24through open proximal end40.

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 inFIG. 1, the pores51at the exterior surface50may be covered with parafilm86to contain the injected paste as it solidifies within the reservoirs55,65. When the paste has solidified, the parafilm is removed, and the solidified material will then permit gradual elution of the gentamicin outward through the channels75,77from the reservoirs55,65, and further outward through the pores51, as the calcium sulfate delivery medium biodegrades gradually under the influence of the patient'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 reservoirs55,65and channels75,77also contributes to the extended period of time taken for complete elution of the therapeutic agent. Specifically, the channels75,77provide fluid flow communication between the reservoirs55,65in series so that elution from the reservoirs55,66proceeds sequentially rather than simultaneously. Elution is thus sustained as the therapeutic agent in the first reservoir55is preserved until the therapeutic agent is depleted or nearly depleted from the second reservoir65.

Another example of an orthopedic implant device100is shown inFIGS. 4 and 5. In this example, the device100is a femoral component of a total knee replacement system. Like the device10described above, the device100is configured to provide elution of a therapeutic agent over an extended period of time.

The device100comprises an implant body110with medial and lateral legs112and114that are shaped as medial and lateral condyles. Accordingly, the medial leg112has an arcuate shape with a distal end portion120. The exterior surface122at the distal end portion120serves as a bone-replacement surface with a contour configured to replicate a healthy medial condyle bone surface contour. The lateral leg114similarly has an arcuate shape with a distal end124portion at which the exterior surface126has a contour replicating a healthy lateral condyle bone surface contour. The distal end portions120and124are separated across a trochlear gap125.

An intermediate section140of the body110reaches across the gap125between the medial and lateral legs112and114. The intermediate body section140has planar opposite side surfaces142. Each opposite side surface142has an arcuate anterior edge144adjoining the adjacent leg112or114. A posterior surface146(FIG. 4) has a planar contour reaching across the intermediate body section140between the opposite side surfaces142. An anterior surface148(FIG. 5) has an arcuate contour reaching along and across the gap125between the legs112,114. The posterior and anterior surfaces146and148each have an array of elution pores149. In the illustrated example, the all of the elution pores149in the body110are remote from the bone replacement surface portions122and126.

As shown separately inFIGS. 6 and 7, an internal wall structure160is located at the interior of the intermediate body portion140. The internal wall structure160divides the interior of into first and second reservoirs165and167. Stiffeners168may be provided for structural reinforcement, and the implant body110also may be defined by a single unitary body of agglomerated additive manufacturing material.

In use, each reservoir165and167in the implant body110stores 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 reservoirs165and167can be provided in any suitable manner known in the art of additive manufacturing. Channels169reaching through the inner wall structure160communicate the first reservoir165with the second reservoir167. Additional channels171communicate the second reservoir167with the pores149at the posterior and anterior external surfaces146and148. The channels169and171connect the reservoirs165and167in series so that elution from the reservoirs165and167to the pores149proceeds sequentially rather than simultaneously, whereby elution is sustained as the therapeutic agent in the first reservoir165is preserved until the therapeutic agent is depleted or nearly depleted from the second reservoir167.

As shown partially inFIGS. 8 and 9, another example of an orthopedic implant device includes an implant body200with a body wall202. The body wall202has opposite side surfaces204and206. One side surface204faces into a reservoir209for storing a solid therapeutic agent delivery medium as described above. The other side surface206has elution pores215that are spaced apart in an array on that surface206. Multiple elution channels217reach through the body wall202to communicate the reservoir209with the elution pores215.

The elution channels217in this example have a common inlet portion229(FIG. 9) at the reservoir209. The elution channels217also have different respective outlet portions231at the elution pores215. Intermediate portions235of the elution channels217communicate the inlet portion229with the outlet portions231in parallel. In this example, the intermediate portions235of the elution channels217extend fully from the inlet portion229to the outlet portions231within the thickness of the body wall202in linear configurations parallel to the opposite side surfaces204and206.

With the outlet portions231of the elution channels217spaced apart from the common inlet portion229, as shown for example inFIGS. 8 and 9, each elution channel217has a length that reaches fully through the thickness of the body wall202between the opposite side surfaces204and206. 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 channel217is greater than twice the thickness of the body wall202, and may be a greater multiple of the thickness, as shown by way of example inFIGS. 8 and 9. This helps to prolong elution from the reservoir209to the elution pores215for a correspondingly greater period of time.

Additionally, each elution pore215in this example has an outlet flow area Al that is substantially less than the common inlet flow area A2. This helps sustain elution by limiting access of the patient's synovial fluid to the solid delivery medium in the reservoir209. The spaced-apart array of multiple elution pores215with a common inlet229helps to distribute the therapeutic agent throughout the area of the outer side surface206, whereas a single outlet would provide a more concentrated delivery of the therapeutic agent.

Further regarding the example ofFIGS. 8 and 9, the arrangement of elution channels is configured for a flat body wall200. Such an arrangement could thus be applied to either or both of the flat body walls shown inFIGS. 6 and 7. In another example, a similar arrangement of elution channels on an arcuate body wall250, as shown inFIG. 10, could be applied to either or both of the arcuate body walls ofFIGS. 6 and 7. With a more circular curvature, the arrangement ofFIG. 10could be applied to either or both of the circular body walls shown inFIGS. 2 and 3. In either case, the body wall250ofFIG. 10has elution channels255with a common inlet portion259at a side surface260facing into a reservoir263. The elution channels225further have different respective outlet portions265that are open at elution pores267on an opposite side surface270. These elution channels255extend within the thickness of the body wall250fully from the common inlet portion259to the outlet portions255in arcuate configurations parallel to the opposite side surfaces260and270.

In the example ofFIG. 11, an elongated elution channel281has an inlet portion283and an outlet portion285. The inlet portion283of the channel281is located on a porous body wall286where an inner side surface of the body wall286faces into a reservoir. The outlet portion285of the channel281is open at an opposite side surface288of the body wall286. As in the examples ofFIGS. 8-10, the overall length of the channel281inFIG. 11is greater than twice the thickness of the associated body wall286to promote sustained elution. Additionally, the intermediate portion of the channel281has a series of linear sections288in a non-parallel orientations that provide a convoluted elution flow path between the inlet portion283and the outlet portion285. This further contributes to prolong elution. A similar arrangement can be provided in a spiral or other curvilinear configuration.

Another example of an implant body300with elongated elution channels303is shown partially inFIGS. 12 and 13. In this example, each elution channel303has a linear configuration with two sections307and309(FIG. 13). The first section307reaches through the associated body wall310with a length equal to the surrounding thickness of the body wall310. The second section309provides the channel303with a total length303that is greater than the body wall thickness by a multiple of two or more. The greater length is provided by configuring the second section309of the channel303to reach through a buttress312that projects from the body wall310into the associated reservoir315. Specifically, the buttress312has an edge316adjoining the body wall310, and reaches from the adjoined edge316to a free edge320within the reservoir315. The second section308of the channel303reaches along and through an enlarged-width portion322of the buttress312. The enlarged width portion322in the illustrated example is configured as a pipe.

In the example ofFIGS. 12 and 13, the buttresses312provide structural reinforcement to the body wall portions that are rendered porous by the elution channels303. This can enable the body walls310to have decreased wall thickness and/or increased porosity.

Structural reinforcement can also be provided in other configurations, as shown for example inFIGS. 14, 15 and 16. In the example of an implant body400as shownFIG. 14, structural reinforcement is provided by a truss of stiffener elements402. The stiffener elements402in this example are configured as beams in an orthogonal array reaching across the reservoir405fully from porous body wall portions406to opposed body wall portions410. In the example ofFIG. 15, a truss420is provided in the configuration of a diamond cubic truss. In the example ofFIG. 16, structural reinforcement is provided by a minimal surface structure in the configuration of a gyroid. Each of these examples of a reinforcement structure402,420and430also 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. 17is a partial view of an implant body wall500similar to that shown inFIG. 6. The body wall500ofFIG. 17also has a surface502with elution pores505. As further shown inFIGS. 18 and 19, elution pipes510project from an opposite side surface512of the body wall500into a reservoir515for containing a therapeutic delivery agent. The elution pipes510and the body wall502together define elution channels517that provide fluid communication between the reservoir515and the elution pores505.

The body wall500further includes an adapter518for a luer lock fitting to secure a syringe for injecting the therapeutic agent delivery medium agent into the reservoir515as described above. The adapter518defines a passage519into the reservoir515and, in the given example, has a male flange520for receiving and guiding an internal screw thread on a female luer fitting. A closure device522in the form of a plug or cap522is provided for closing and sealing the passage519.

The elution pipe510in the example ofFIGS. 17-19are arranged in two separate sets. Each set includes a single inlet pipe510with an inlet525inside the reservoir515. Each set further includes multiple branch pipes510that reach from the inlet pipe510to respective elution pores505. The pipes510in each set thus share a common inlet525within the reservoir515.

FIG. 20shows a variation of the example shown inFIGS. 17-19. As shown partially inFIG. 20, reinforcement structures in the form of buttresses530are provided to reach from the pipes510to the body wall500. These buttresses530are formed as inner walls with planar opposite sides, and reach lengthwise along the pipes510as 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.