WO2015157356A1

WO2015157356A1 - Orthopedic implant and complementary encasement for supplying a payload of beneficial agent to the implant

Info

Publication number: WO2015157356A1
Application number: PCT/US2015/024812
Authority: WO
Inventors: Carl Deirmengian
Original assignee: Carl Deirmengian
Priority date: 2014-04-08
Filing date: 2015-04-08
Publication date: 2015-10-15

Abstract

An orthopedic implant includes at least one reservoir for receiving a therapeutically-significant payload of a beneficial agent. The reservoir may be provided internally to the implant, recessed beneath a long-term fixation surface of the implant. An encasement is configured to be complementary to, and mate with, the implant. The encasement has an inner surface that fits closely with the implant, such that a portion of the inner surface abuts the outer surface of the implant, and so that a portion of the inner surface provides an air gap relative to the surface of the implant and/or its reservoir(s). The encasement acts as a three-dimensional template for applying the beneficial agent to the surface of the implant in a selective fashion, so that beneficial agent is supplied where it is needed and is prevented from being applied where it would interfere with the implant fixation process.

Description

ORTHOPEDIC IMPLANT AND COMPLEMENTARY ENCASEMENT FOR SUPPLYING A PAYLOAD OF BENEFICIAL AGENT TO THE IMPLANT

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of priority of U.S. Provisional Patent Application No. 61/976,717, filed April 8, 2014, the entire disclosure of which is hereby incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates generally to orthopedic implants for human and animal use, and more particularly to an orthopedic implant adapted for receiving a load of a beneficial agent, and a complementary encasement configured for selectively distributing the load of beneficial agent along a surface of the implant.

BACKGROUND

[0003] Orthopedic implants are used to replace damaged bones and joints and permit continued use and movement. For example, a hip implant may be used to replace a damaged hip joint. Various orthopedic implants, and methods for their manufacture and implantation through surgery, are well-known in the art.

[0004] Despite precautions taken during surgery, complications related to such implants may occur. Infection after joint replacement, called periprosthetic joint infection or PJI, is a devastating complication that may occur early or late after surgery. PJI is associated with many possible patient presentations, ranging from acute life- threatening systemic infection to occult chronic pain. Failure to treat PJI invariably results in worsening systems and failure of the joint replacement. PJI is one of the most common causes of failure after hip and knee replacement surgery. [0005] There are several accepted treatment options for PJI, all requiring a surgical intervention. One option is to simply irrigate and debride the local joint tissues while retaining the original implants. This option is the least traumatic to the patient but is also associated with the lowest rate of success due to possible bacterial persistence in the joint. Another option is to remove the implants from the joint as part of the treatment. This option is referred to as an exchange arthroplasty, and is associated with the highest rates of success in eradicating the infection.

[0006] A one-stage exchange, which is the preferred mode of care among many surgeons, involves (1 ) removal of all implants from the infected joint (2) radical debridement of all infected or necrotic tissues (3) irrigation with high volumes of sterile irrigant fluid (4) re-preparation and sterilization of the surgical field and (5)

reimplantation with new sterile implants. This mode of care is preferred by some surgeons because it only requires one surgical intervention and is associated with a relatively high rate of PJI eradication.

[0007] A two-stage exchange, which is also a preferred mode of care among many surgeons, involves (1 ) removal of all implants from the infected joint (2) debridement of all infected or necrotic tissue (3) irrigation with high volumes of sterile irrigant fluid (4) re-preparation and sterilization of the surgical field (5) insertion of a temporary spacer block using high-concentration antibiotic impregnated materials (6) closure of the wound and initiation of a waiting period of 4-12 weeks to allow for systemic and local antibiotics to fully eradicate the PJI (7) confirmation that the PJI has been eradicated using clinical and laboratory indicators and (8) reimplantation of final permanent sterile implants with or without cement through a second surgery. This mode of care is preferred by some surgeons because it provides for high local levels of antibiotics through the temporary spacer block over a period of weeks, demonstrating improved eradication of PJI in many studies. Many surgeons believe that the first stage of a two-stage exchange is responsible for eradicating the infection, due to the high levels of local antibiotic provided. This belief is due to data demonstrating that patients with unintentional long-term retention of the spacer block do not appear to have a higher rate of reinfection compared to patients undergoing the second stage.

[0008] It might seem intuitive to propose the utilization of a one-stage exchange procedure, using high levels of antibiotic in the cement to provide the benefits of a two-stage exchange. This option would marry the one procedure benefit of a one- stage exchange with the local antibiotic treatment benefits of a two-stage exchange. Unfortunately, the levels of antibiotic in the cement that are required for treatment (3-12 g/bag of cement) of PJI render the cement less mechanically suitable for long-term fixation of the implants, as required by a one-stage exchange. Furthermore, this

"married" treatment option depends on cementation as the fixation strategy, which is considered suboptimal by many surgeons, especially for a revision hip replacement. These surgeons prefer to utilize implants with surface treatments that allow for bone attachment (uncemented implants).

[0009] One option available to the surgeon is to treat PJI with a one-stage exchange using uncemented implants, and adding high concentration antibiotic cement to the articular space around the implant. This option, at first glance, appears to marry the benefits of a one-stage and two-stage exchange, however there are several concerning issues with this option. First, the cement placed into the articular space may act like a foreign body, making joint impingement or cement entrapment a likely complication. Second, the cement would occupy space in the joint, likely limiting capsular healing and inhibiting range of motion. Third, the cement placed in the joint space would not be contacting the bone previously adjoining the implant at the time of PJI, thus limiting the efficacy of the antibiotic eluting cement.

[0010] At this time there are no implants that can provide for reliable long- term fixation while simultaneously providing for high levels of antibiotic in the same anatomic interface with an antibiotic eluting material. Thus there is an urgent need in the art for compositions and methods that allow for an implant to achieve reliable long-term fixation to bone while simultaneously providing for local treatment with high levels of antibiotics.

SUMMARY

[0011] In one aspect, the present invention provides an orthopedic implant for delivering a payload of beneficial agent to a surgical site. The implant has an outer surface defining a fixation surface configured with a surface treatment for facilitating long-term fixation to bone. The implant further has a reservoir for receiving beneficial agent, the reservoir being configured such that beneficial agent received in the reservoir will not interfere with an interface of the fixation surface with bone in the surgical site.

[0012] In another aspect the present invention provides an encasement for selectively applying a payload of beneficial agent to an orthopedic implant having an outer surface. The encasement has an encasement body configured to receive at least a portion of an orthopedic implant having an outer surface. The encasement body has an inner surface defining: a first region in which the inner surface is spaced from the implant's outer surface, when mated therewith, to provide an air gap into which a flow of beneficial agent will flow when introduced between the mated orthopedic implant and encasement; and a second region in which the inner surface fits closely with the implant's outer surface, when mated therewith, to create a seal substantially preventing the flow of beneficial agent from exiting the first region and entering the second region.

[0013] According to another aspect of the present invention, an orthopedic implant system is provided for delivering a payload of beneficial agent to a surgical site. The system includes an orthopedic implant having an outer surface defining a fixation surface configured with a surface treatment for facilitating long-term fixation to bone. The system further includes an encasement configured to be selectively matable with the implant. The encasement has an inner surface defining: a first region in which the inner surface is spaced from the implant's outer surface, when mated, to provide an air gap into which a flow of beneficial agent will flow when introduced between the mated orthopedic implant and encasement; and a second region in which the inner surface fits closely with the implant's outer surface, when mated, to create a seal substantially preventing the flow of beneficial agent from exiting the first region and entering the second region.

[0014] In accordance with another aspect, the present invention provides a kit comprising an orthopedic implant and an encasement disposed within a sealed package. A cement gun and/or a supply of beneficial agent may also be disposed within the sealed package. The encasement may be constructed of one of a translucent and a transparent material, and the supply of beneficial agent may be tinted to facilitate visualization of the existence of, or flow of, beneficial agent relative to the

transparent/translucent encasement.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The present invention will now be described by way of example with reference to the following drawings in which:

[0016] Figure 1A shows a standard primary hip implant exemplary of the prior art;

[0017] Figure 1 B shows a cross-section of the implant of Figure 1A, taken along line AA' of Figure 1A;

[0018] Figure 2A show a standard revision hip implant exemplary of the prior art that includes a modular stem;

[0019] Figure 2B shows a cross-section of the implant of Figure 2A, taken along line BB' of Figure 2;

[0020] Figure 3A shows an exemplary stem in accordance with an

exemplary embodiment of the present invention; [0021] Figure 3B shows a cross-section of the implant of Figure 3A, taken along line CC of Figure 3A;

[0022] Figure 4A shows an alternative embodiment of a stem in accordance with an alternative embodiment of the present invention;

[0023] Figure 4B shows a cross-section of the implant of Figure 4A, taken along line DD' of Figure 4A;

[0024] Figure 5A-5C show an exemplary encasement complementary to the stem of Figures 3A and 3B;

[0025] Figure 6A shows the encasement of Figures 5A-5C in mated relationship with the stem of Figure 3A and 3B;

[0026] Figure 6B shows a cross section of the stem and encasement of Figure 6A, taken along line EE' of Figure 6A;

[0027] Figures 7A-7C show an exemplary encasement complementary to the stem of Figures 4A and 4B;

[0028] Figure 8A shows the encasement of Figures 7A-7C in mated relationship with the stem of Figures 4A and 4B; and

[0029] Figure 8B shows a cross section of the stem and encasement of Figure 8A, taken along line FF' of Figure 8A.

DETAILED DESCRIPTION

[0030] The present invention relates generally to a novel orthopedic implant, particularly an implant that is suitable for long-term fixation, and further is configured to carry a load of a beneficial agent in a manner that will not interfere with the long-term fixation. As used herein, "long-term fixation" includes both cemented and uncemented (e.g., via bony ingrowth) fixation. As used herein the term "orthopedic implant" or simply "implant" may refer to a medical device, including device used to replace or supplement damaged, diseased or missing bone or tissue. Such orthopedic implants may be used in the spine, extremities, knees, face, hips, joints or any other region of the body, as will be appreciated by those skilled in the art. By way of non-limiting example, the implant may be a spinal implant, a hip implant (femoral or acetabular), a knee implant, a facial implant, a shoulder implant, an elbow implant, a cranial implant, and ankle implant, a wrist implant, etc. Such orthopaedic implants have a variety of shapes and sizes consistent with the teachings of the prior art.

[0031] Further, the present invention provides an encasement

complementary to an orthopedic implant, a combination of the orthopedic implant and a complementary encasement, and an implant kit or kits including at least an orthopedic implant and an encasement complementary to the orthopedic implant.

[0032] In certain aspects, an orthopedic implant in accordance with the present invention may be substantially conventional in structure. For illustrative purposes only, and without limiting the scope of the present invention, the present invention is discussed below with reference to an exemplary orthopedic implant used in hip replacement procedures. Figure 1A shows a conventional standard primary hip implant exemplary of the prior art, and Figure 2A shows a conventional standard revision hip implant exemplary of the prior art. As is typical of many conventional hip implants, the exemplary hip implant 10 of Figure 1A includes a unitary stem 20 and a mated or matable acetabulum 30 for insertion in the socket of a hip joint. Figure 2A shows an alternative stem exemplary of the prior art, namely, a multi-piece stem 20 including first and second stem portions 20a, 20b. As is known in the art, the stem is inserted into the diaphysis of bone, after the bone has been prepared using

conventional instruments and techniques. [0033] As further known in the art, at least a portion of the surface of the implant is intended to become fixed to adjacent bone, with or without cement. This portion is referred to herein as the fixation surface. Within the fixation surface region, the surface 24 of the implant may be provided with a surface treatment designed to promote bony ingrowth or cemented fixation, as is typical of implants suited for long- term fixation. By way of example, the surface treatment may be a texture, polish, or coating, such as a hydroxyapatite coating and/or titanium beads that provide ongrowth, ingrowth or adhesion surfaces, as is well known in the art. In the examples of Figure 1 A and 2A, the stem 20 is configured with a fixation surface 22, 22a, 22b including a surface treatment designed to promote long-term fixation within the region of the fixation surface 22, to cause the implant (particularly the stem 20) to be fixed in a cemented or uncemented fashion to the prepared bone.

[0034] Figure 3A shows an exemplary orthopedic implant 10 for hip

replacement in accordance with the present invention. The implant 10 is somewhat conventional in structure in that it includes a stem 50 and an acetabulum 30 matable therewith, and the stem includes a fixation surface 52 having a surface 54 provided with a surface treatment designed to allow for long-term fixation to the bone (in either a cemented or uncemented fashion).

[0035] However, the exemplary stem 50 of Figure 3A is not entirely

conventional in structure. Rather, in accordance with an exemplary embodiment of the present invention, the stem 50 is specially-configured to provide on its outer surface at least one reservoir for receiving a therapeutically-significant volume (or "load") of a beneficial agent. Beneficial agents such as antibiotics, bone growth factors, antiinflammatory agents, pain killers, and other beneficial drugs may be provided to patients to enhance the healing or integration process and avoid or treat post-operative infection. The therapeutically-significant volume of a beneficial agent will vary depending upon a number of factors including, for example, the nature and identity of the beneficial agent, the nature and identify of the matrix material, the condition to be treated, the weight of the patient, the existence of absence of certain pre-existing conditions, such as an infection, and/or the tissue, bone, joint, or region to be treated. By way of example, a therapeutically significant concentration in the range of 3-12 grams of antibiotics per bag of carrier matrix is likely suitable for many implants.

[0036] The reservoir extends inwardly on the stem/implant, beneath the portion of the surface 54 intended to allow long-term fixation, to provide depth to the reservoir, as can be appreciated from Figure 3B. Accordingly, the reservoir may define a sub-"fixation surface" space for receiving the beneficial agent, so that beneficial agent received in the reservoir will not interfere with the abutting relationship and/or fit between the fixation surface 54 and the prepared bone or long-term cement mantle. The reservoir may have any suitable configuration, but preferably extends continuously in an elongated fashion along a portion of the implant, to provide length to the reservoir. For example, in certain embodiments, a reservoir extending from about 2 to about 8 inches (or any sub-range therein) along the surface of the implant is provided. The reservoir may, but need not, have a uniform cross-section. Further, the reservoir may, but need not, extend in a linear direction. Further, more than one reservoir may be provided on the implant, in which case the therapeutically-significant volume of beneficial agent may be provided in the combined volume of the individual reservoirs. One or more reservoirs may be positioned along the implant/bone interface, while others may be positioned along the articular edge of the implant, to allow for drug elution into the synovial fluid. In the example of Figures 3A and 3B, two reservoirs 60a, 60b are provided in the form of channels extending longitudinally along the length of the stem 50. Furthermore, for other shapes such as a hemispherical acetabular implant, the reservoirs may be circumferential or have other shapes. Additionally, reservoirs may be placed along the shoulder of the hip implant or along the articular edge of another implant to allow for articular elution of the drug.

[0037] Figures 4A and 4B show an alternative embodiment of a stem in accordance with an alternative embodiment of the present invention. In this

embodiment, there are a plurality of relatively small and circumferentially discontinuous surfaces that collectively make up the surface 54 for contacting the bone. Multiple longitudinally extending reservoirs 60a, 60b, 60c, 60d, 60e, 60f are defined by the stem 50. It is again emphasized however, that the reservoirs may have any desired shape or configuration, and may extend longitudinally on the implant, circumferentially on the implant, or may be placed in a more irregular or "patched" pattern. In another example, these regions extend in a spiral-like configuration down the length of the stem.

[0038] The present invention further provides an encasement complementary to a specific corresponding implant, and more particularly to the configuration of its surface(s) for long-term fixation and its reservoir(s) for receiving the beneficial agent. Figure 5A-5C show an exemplary encasement 80 complementary to the stem 50 of Figures 3A and 3B. Figures 7A-7C show an exemplary encasement 80 complementary to the stem 50 of Figures 4A and 4B. More specifically, the encasement 80 may be a single-piece or multi-piece body 81 configured to receive at least a portion of a corresponding orthopedic implant. The encasement's body 82 has an inner surface 84 designed to receive and fit closely with the implant, as will be appreciated from Figures 5B and 7B. The encasement is preferably made of a flexible materials that can be removed or peeled away from the implant. Structural modifications to the encasement may be made to facilitate removal of the encasement from the implant.

[0039] The encasement 80 is matable with a corresponding implant. Figures 6A and 6B show the encasement of Figures 5A-5C in mated relationship with the stem 50 of Figures 3A and 3B. Figures 8A and 8B show the encasement of Figures 7A-7C in mated relationship with the stem 50 of Figures 4A and 4B. Referring now to Figures 6A, 6B, 8A and 8B, the encasement 80 is configured such that, when mated with a corresponding implant, a substantial portion of its inner surface 84 abuts a substantial portion of the implant's outer surface 54, but does not abut the portion of the implant's surface forming the reservoir(s), e.g., reservoirs 60a and 60b in Figure 6B and 60a, 60b, 60c, 60d, 60e, 60f in Figure 8B. Thus, the encasement's inner surface 84 is designed to provide an air gap 90 between the implant 50 and the encasement 80 for receiving the beneficial agent therebetween, as shown in Figures 6B and 8B. In this manner, the encasement 80 acts somewhat like a three-dimensional template for applying the beneficial agent to the surface of the implant - specifically to cause application of the beneficial agent in the reservoir(s) or onto other desired areas on the surface of the implant. Further, the encasement acts somewhat like a three-dimensional template to prevent application of the beneficial agent onto other areas on the surface of the implant, some of which may be intended to provide for long-term fixation. In some embodiments, the encasement may direct the beneficial agent to areas that are more prominent, and not necessarily sub-surface reservoirs in the implant, as long as this does not interfere with the desired final positioning of the implant.

[0040] In a preferred embodiment, the encasement 80 defines a fitting 86 for mating with a delivery nozzle of a conventional injector, delivery device, or cement gun (collectively "cement gun"), and a port 88 for admitting passage of the beneficial agent from the cement gun into the encasement 80, as will be appreciated from Figures 5A, 5C, 7A and 7C. Such cement guns are widely commercially available, and are well- known in the art in the field of orthopedic surgery. Such cement guns are outside the scope of the present invention and are not discussed in detail herein. The fitting may have any suitable structure for mating with the delivery nozzle of such a cement gun, and thus may be generally formed as an opening, tube, or other input port for mating with and/or receiving such a delivery nozzle, and preferably sealingly engaging therewith. Any suitable fitting configuration may be used. Such delivery nozzles and such fittings are well known in the art of orthopedic surgery and are beyond the scope of the present invention, and thus are not discussed in detail herein.

[0041] In the embodiments shown Figures 6A and 8A, the encasement does not fully enclose the reservoirs. Accordingly, the reservoir is open to the atmosphere at a distal end of the channel opposite the fitting. This opening acts as a vent, so that as a flow of beneficial agent is introduced into the reservoirs via the fitting(s), air present in the channel is pushed along the channel by the flow and caused to exit the reservoir via the vent. In alternative embodiments, the encasement fully encloses the

reservoirs/channels, but a vent hole is provided in the encasement toward the distal end of the reservoir, so that air in the reservoir is vented through the body of the encasement 80 via the vent hole.

[0042] It should be noted that in the examples of Figures 5A-8B, the encasement covers some, but not all of the corresponding implant. In other

embodiments, the encasement is configured to fully envelop its corresponding implant. Further, it will be noted in these examples that each encasement includes a single fitting for supplying beneficial agent to multiple reservoirs. However, it should be appreciated that alternatively, the encasement is configured such that a single fitting feeds a single reservoir, and further that the encasement may be configured with multiple fittings supplying beneficial agent to respective reservoirs in a 1 -to-1 correspondence. Further still, it will be noted that in these examples the reservoirs are provided in the form of elongated channels extending generally linearly. However, the reservoirs may have any suitable configuration, and may extend in a non-linear fashion along the surface (e.g. in an arcuate or spiral configuration), or may be substantially localized any may not extend in elongated fashion (e.g., may be for example circular or square as viewed from the surface).

[0043] The encasement may be provided as opaque, translucent, or transparent. Optionally, the beneficial agent may be tinted to facilitate visualization of the existence of, or flow of, beneficial agent relative to a transparent/translucent encasement.

[0044] Thus, the present invention is applicable to any orthopedic implant having any configuration, and is most preferably used in combination with an implant having any surface treatment for the purpose of providing for long-term fixation to the bone, while still providing a volume of space to carry a load of beneficial material, such as an antibiotic-loaded material. Additionally, the present invention is further applicable to any orthopedic implant having any configuration and including any surface treatments for the purpose of providing for both long-term fixation and cemented fixation to bone. [0045] Accordingly, the system of the invention provides a new and convenient platform for the treatment of pathology. In one embodiment, the system of the invention provides a platform for inserting an implant that can achieve reliable long- term (cemented or uncemented) fixation to bone, while simultaneously having a region that stores an antibiotic-loaded material for the purpose of treating an infection, preferably a periprosthetic joint infection. In another embodiment, the system of the invention provides a platform for inserting an implant that can achieve uncemented fixation to bone, while simultaneously achieving cemented fixation to the bone.

[0046] In certain embodiments, the implant and complementary encasement are provided together in a kit. In some such embodiments, the implant and

complementary encasement are provided in a single package, e.g., within a single sterile package. In other embodiments, the implant and complementary encasement are provided in separate packaging.

[0047] In use, the implant and complementary encasement may be first separated from any packaging. The encasement may then be fitted onto the implant, for example by sliding the implant into an open end of the encasement, or fitting the implant into the encasement and then closing the encasement around the implant. This causes the inner surface 84 of the encasement to abut portions of the outer surface of the implant, and further provides an air gap at the implant's reservoirs.

[0048] Alternatively, the implant and complementary encasement may be appropriately mated before packaging. In this case, after the package is opened, the implant/encasement is immediately ready for injection of the drug-loaded or drug- unloaded material/agent.

[0049] Next, a conventional cement gun is loaded with a beneficial agent, such as an antibiotic-loaded or plain cement. Such loading may be performed in a conventional manner, e.g., by placing a prepared tube of beneficial agent into the body of the cement gun, as well known in the art. Next, a dispensing nozzle of the cement gun is mated to a fitting 86 of the encasement, e.g. by inserting the nozzle into the fitting 86 in abutting relationship thereto. The cement gun is then operated (e.g., by squeezing the trigger) to manually pump a flow of the beneficial agent from the cement gun through the port 88 in the fitting 86, and thus into the encasement. The structure of the encasement causes the beneficial agent to flow into the reservoir(s), e.g., 60a, 60b, of the implant 50. More specifically, the agent is caused by the structure of the encasement to flow where there are air gaps between the encasement and implant, those air gaps being created selectively by the complementary configuration of the implant and complementary encasement. Notably, the air gaps are configured to cause the beneficial agent to flow into the reservoirs, while substantially preventing the flow of beneficial agent from covering a surface of the implant outside of the air gaps.

Accordingly, the flow of beneficial agent is effectively limited to the intended regions on the implant, namely, in the reservoirs, by using the encasement as a template to apply the beneficial agent to the implant.

[0050] The pumping of beneficial agent may be continued while the surgeon of other medical professional visually monitors the mated implant and encasement. In certain embodiments, the encasement is made of a transparent or translucent material, and the flow of agent within the channels may be visualized directly through the body of the encasement. In any event, when the reservoir has been filled with the beneficial agent, the flow of agent will exit the vent opening or vent hole. Visualization of agent exiting the vent opening/vent hole is a visual indication that the corresponding reservoir(s) is/are full, and that it is no longer necessary to continue pumping beneficial agent into the encasement. The cement gun can then be removed from the fitting 86. As well known in the art, the beneficial agents are somewhat gel-like in viscosity or consistency, and thus tend to stay where applied, and thus there is no substantial concern of the beneficial agent exiting the reservoir(s) or otherwise draining from the encasement.

[0051] For embodiments provided with multiple fittings, the surgeon, etc. may next mate the cement gun with a next fitting and fill the corresponding reservoir with beneficial agent in a similar manner. This may be repeated for each fitting until all reservoirs have been filled.

[0052] After all reservoirs have been filled and the cement gun has been decoupled from all fittings, the surgeon may perform a visual inspection to confirm that the implant has been properly prepared with beneficial agent. The encasement may then be peeled away or removed from the prepared implant. For example, this many involve manually sliding the encasement off of the implant, or opening the encasement and lifting out the implant, etc., depending upon the configuration of the encasement. At this point, the implant is loaded with the beneficial agent. More specifically, the reservoirs of the implant are filled with a load of beneficial agent, and little or no agent is provided on the surface of the implant outside of the reservoirs. Thus, the implant is ready for mating with bone via standard cemented or uncemented fixation procedures.

[0053] The implant may then be inserted into a diaphysis of bone, after the bone has been prepared using conventional instruments and techniques. Implantation may be made using cemented or uncemented fixation techniques, in a conventional manner, as appropriate.

[0054] In accordance with the teachings described above, the implant with reservoirs and long-term fixation areas may also be utilized in the second stage of a two-stage procedure to treat infection.

[0055] In a first case example, consider that a patient with a chronic infection of a hip requires treatment. In such a case, the surgeon removes the infected implants and performs a debridement and irrigation to remove as much infected tissue as possible. After establishment of a sterile field, the bone is prepared for reimplantation with a revision hip implant that attains uncemented fixation. The hip

implant/encasement combination is then used to fill the implant reservoirs with 2 bags of methylmethacrylate cement, each bag carrying 8 grams of antibiotic. The surgeon waits for the cement to cure, then removes the encasement. The resulting implant is loaded with antibiotic carrying cement, but has more prominent surfaces that can attain uncemented fixation. This implant is impacted into the femur, providing for uncemented fixation, and simultaneously providing for high levels of local antibiotic. The acetabulum has a corresponding strategy, and is accordingly implanted.

[0056] In a second case example, consider that a patient with a chronic infection of a knee requires treatment. The surgeon removes the infected implants and performs a debridement and irrigation to remove as much infected tissue as possible. After establishment of a sterile field, the bone is prepared for reimplantation with a revision knee implant that attains cemented fixation. The knee implant/encasement combination is used to fill the implant reservoirs with 2 bags of methylmethacrylate cement, each bag carrying 8 grams of antibiotic. In this specific example, the reservoirs may be positioned along the stem, as well as along the edges of the articular surface. The surgeon waits for the cement to cure, then removes the encasement. The resulting implant is loaded with antibiotic carrying cement, but has available surfaces that can attain cemented fixation with cement that has better structural integrity. This implant is impacted into the femur, providing for cemented fixation, and simultaneously providing for high levels of local antibiotic.

[0057] While there have been described herein the principles of the invention, it is to be understood by those skilled in the art that this description is made only by way of example and not as a limitation to the scope of the invention, and that various changes in detail may be effected therein without departing from the spirit and scope of the invention as defined by the claims.

Claims

What is claimed is:

1 . An orthopedic implant for delivering a payload of beneficial agent to a surgical site, the orthopedic implant comprising:

an implant body having an outer surface, the outer surface defining:

a fixation surface configured with a surface treatment for facilitating long- term fixation to bone; and

a reservoir for receiving beneficial agent, the reservoir being configured such that beneficial agent received in the reservoir will not interfere with an interface of the fixation surface with bone in the surgical site.

2. The orthopedic implant of claim 1 , wherein said surface treatment comprises at least one of a texture, a polish and a coating.

3. The orthopedic implant of claim 1 , wherein said orthopedic implant is selected from a group consisting of: a spinal implant, a hip implant, a knee implant, a facial implant, a shoulder implant, an elbow implant, a cranial implant, an ankle implant, and a wrist implant.

4. The orthopedic implant of claim 1 , wherein said reservoir extends inwardly of said orthopedic implant relative to said fixation surface.

5. The orthopedic implant of claim 1 , wherein said reservoir is positioned internally to an area of said fixation surface.

6. The orthopedic implant of claim 1 , wherein said reservoir is positioned externally to of an area of said fixation surface.

7. The orthopedic implant of claim 1 , wherein said reservoir extends continuously in elongated fashion along a portion of said implant.

8. The orthopedic implant of claim 7, wherein said reservoir extends continuously in elongated fashion along said outer surface, said reservoir having a length falling within a range of about 2 inches to about 8 inches.

9. The orthopedic implant of claim 8, wherein said reservoir has a cross- section that is uniform along its length.

10. The orthopedic implant of claim 7, wherein said reservoir extends linearly in a linear direction.

1 1 . The orthopedic implant of claim 7, wherein said reservoir extends non- linearly.

12. The implant system of claim 1 1 , wherein said reservoir extends in a spirallike configuration.

13. The implant system of claim 1 , wherein said outer surface of said orthopedic implant is configured to define a plurality of reservoirs extending inwardly of said orthopedic implant.

14. An orthopedic implant system for delivering a payload of beneficial agent to a surgical site, the system comprising:

an orthopedic implant having an outer surface defining a fixation surface configured with a surface treatment for facilitating long-term fixation to bone; and

an encasement configured to be selectively matable with the implant, the encasement having an inner surface defining:

a first region in which the inner surface is spaced from the implant's outer surface, when mated, to provide an air gap into which a flow of beneficial agent will flow when introduced between the mated orthopedic implant and encasement; and a second region in which the inner surface fits closely with the implant's outer surface, when mated, to create a seal substantially preventing the flow of beneficial agent from exiting the first region and entering the second region.

15. The implant system of claim 14, wherein said outer surface of said orthopedic implant is configured to define a reservoir extending inwardly of said implant.

16. The implant system of claim 15, wherein said reservoir extends

continuously in elongated fashion along a portion of said implant.

17. The implant system of claim 16, wherein said reservoir extends

continuously in elongated fashion along said outer surface, said reservoir having a length failing in a range of about 2 inches to about 8 inches.

18. The implant system of claim 17, wherein said reservoir has a cross- section that is uniform along its length.

19. The implant system of claim 16, wherein said reservoir extends linearly in a linear direction.

20. The implant system of claim 16, wherein said reservoir extends non- linearly.

21 . The implant system of claim 20, wherein said reservoir extends in a spirallike configuration.

22. The implant system of claim 14, wherein said outer surface of said orthopedic implant is configured to define a plurality of reservoirs extending inwardly of the implant.

23. The implant system of claim 14, wherein said encasement is configured so that it does not fully enclose said orthopedic implant when mated thereto.

24. The implant system of claim 14, wherein said encasement is configured to fully enclose said orthopedic implant when mated thereto.

25. The implant system of claim 15, wherein said encasement defines a port for admitting a flow of beneficial agent, said portion being positioned to be disposed adjacent a proximal portion of said reservoir when mated to said orthopedic implant.

26. The implant system of claim 25, wherein said encasement defines a vent hole positioned to be disposed adjacent a distal portion of said reservoir when mated to said orthopedic implant.

27. The implant system of claim 25, wherein said encasement defines a fitting adjacent said port, said fitting being configured to receive and sealingly engage with a delivery nozzle of a cement gun for delivering a flow of beneficial agent.

28. The implant system of claim 14, wherein said orthopedic implant is selected from a group consisting of: a spinal implant, a hip implant, a knee implant, a facial implant, a shoulder implant, an elbow implant, a cranial implant, an ankle implant, and a wrist implant.

29. An encasement for selectively applying a payload of beneficial agent to an orthopedic implant having an outer surface, the encasement comprising:

an encasement body configured to receive at least a portion of an orthopedic implant having an outer surface, the encasement body having an inner surface defining:

a first region in which the inner surface is spaced from the implant's outer surface, when mated therewith, to provide an air gap into which a flow of beneficial agent will flow when introduced between the mated orthopedic implant and

encasement; and a second region in which the inner surface fits closely with the implant's outer surface, when mated therewith, to create a seal substantially preventing the flow of beneficial agent from exiting the first region and entering the second region.

30. The encasement of claim 29, wherein the encasement body is a unitary body.

31 . The encasement of claim 29, wherein the encasement body comprises multiple pieces matable to form the encasement body.

32. The encasement of claim 29, said encasement body further defining a fitting for mating with a delivery nozzle of a conventional cement gun, and a port for admitting passage of a flow of beneficial agent from the cement gun and into the encasement body.

33. The encasement of claim 29, wherein said encasement body further defines a vent hole for venting air through the encasement body.

34. The encasement of claim 29, said encasement body further defining a plurality of fittings, each fitting being configured for mating with a delivery nozzle of a conventional cement gun, and a respective plurality of ports, each port being configured for admitting passage of a flow of beneficial agent from the cement gun and into the encasement body.

35. The encasement of claim 34, wherein said encasement body further defines a plurality of vent holes for venting air through the encasement body.

36. The encasement of claim 29, wherein said encasement is configured to covers some, but not all, of the outer surface of the implant.

37. The encasement of claim 29, wherein said encasement is configured to fully envelop the outer surface of the implant.

38. The encasement of claim 29, wherein said encasement body is constructed of an opaque material.

39. The encasement of claim 30, wherein said encasement body is constructed of one of a translucent and a transparent material.

40. A kit comprising:

a sealed package;

the orthopedic implant of claim 1 disposed within the sealed package; and the encasement of claim 29 disposed within the sealed package.

41 . The kit of claim 40, further comprising:

a cement gun disposed within the sealed package.

42. The kit of claim 41 , further comprising:

a supply of beneficial agent disposed within the sealed package.

43. The kit of claim 40, wherein the encasement is constructed of one of a translucent and a transparent material.

44. The kit of claim 43, further comprising a supply of beneficial agent disposed within the sealed package, said beneficial agent being tinted to facilitate visualization of the existence of, or flow of, beneficial agent relative to the encasement.