US20100137996A1 - Femoral and tibial base components - Google Patents

Abstract

Various embodiments are directed to base components that are usable with implantable mechanical energy absorbing systems. According to one embodiment, the base component includes a low-profile body having a elongate, straight portion at a first end and a curved body portion at a second end. The second end is elevated as compared to the first end. An inner surface of the low-profile body has a raised portion extending along the elongate, straight portion of the low-profile body. The base component also includes a plurality of openings positioned along the low-profile body for alignment and purposes of affixation to body anatomy.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application is a continuation-in-part of U.S. application Ser. No. 11/743,097, filed May 1, 2007, a continuation-in-part of U.S. application Ser. No. 11/743,605, filed May 2, 2007, a continuation-in-part of U.S. application Ser. No. 11/775,139, filed Jul. 9, 2007, a continuation-in-part of U.S. application Ser. No. 11/775,149, filed Jul. 9, 2007 and a continuation-in-part of U.S. application Ser. No. 11/775,145, filed Jul. 9, 2007, the entire disclosures of which are expressly incorporated herein by reference.
FIELD OF EMBODIMENTS
• Various embodiments disclosed herein are directed to structure for attachment to body anatomy, and more particularly, towards approaches for providing mounting members for extra-articular implantable mechanical energy absorbing systems.
BACKGROUND
• Joint replacement is one of the most common and successful operations in modern orthopaedic surgery. It consists of replacing painful, arthritic, worn or diseased parts of a joint with artificial surfaces shaped in such a way as to allow joint movement. Osteoarthritis is a common diagnosis leading to joint replacement. Such procedures are a last resort treatment as they are highly invasive and require substantial periods of recovery. Total joint replacement, also known as total joint arthroplasty, is a procedure in which all articular surfaces at a joint are replaced. This contrasts with hemiarthroplasty (half arthroplasty) in which only one bone's articular surface at a joint is replaced and unincompartmental arthroplasty in which the articular surfaces of only one of multiple compartments at a joint (such as the surfaces of the thigh and shin bones on just the inner side or just the outer side at the knee) are replaced. Arthroplasty as a general term, is an orthopaedic procedure which surgically alters the natural joint in some way. This includes procedures in which the arthritic or dysfunctional joint surface is replaced with something else, procedures which are undertaken to reshape or realigning the joint by osteotomy or some other procedure. As with joint replacement, these other arthroplasty procedures are also characterized by relatively long recovery times and their highly invasive procedures. A previously popular form of arthroplasty was interpositional arthroplasty in which the joint was surgically altered by insertion of some other tissue like skin, muscle or tendon within the articular space to keep inflammatory surfaces apart. Another previously done arthroplasty was excisional arthroplasty in which articular surfaces were removed leaving scar tissue to fill in the gap. Among other types of arthroplasty are resection(al) arthroplasty, resurfacing arthroplasty, mold arthroplasty, cup arthroplasty, silicone replacement arthroplasty, and osteotomy to affect joint alignment or restore or modify joint congruity. When it is successful, arthroplasty results in new joint surfaces which serve the same function in the joint as did the surfaces that were removed. Any chodrocytes (cells that control the creation and maintenance of articular joint surfaces), however, are either removed as part of the arthroplasty, or left to contend with the resulting joint anatomy. Because of this, none of these currently available therapies are chondro-protective.
• A widely-applied type of osteotomy is one in which bones are surgically cut to improve alignment. A misalignment due to injury or disease in a joint relative to the direction of load can result in an imbalance of forces and pain in the affected joint. The goal of osteotomy is to surgically re-align the bones at a joint and thereby relieve pain by equalizing forces across the joint. This can also increase the lifespan of the joint. When addressing osteoarthritis in the knee joint, this procedure involves surgical re-alignment of the joint by cutting and reattaching part of one of the bones at the knee to change the joint alignment, and this procedure is often used in younger, more active or heavier patients. Most often, high tibial osteotomy (HTO) (the surgical re-alignment of the upper end of the shin bone (tibia) to address knee malalignment) is the osteotomy procedure done to address osteoarthritis and it often results in a decrease in pain and improved function. However, HTO does not address ligamentous instability—only mechanical alignment. HTO is associated with good early results, but results deteriorate over time.
• Other approaches to treating osteoarthritis involve an analysis of loads which exist at a joint. Both cartilage and bone are living tissues that respond and adapt to the loads they experience. Within a nominal range of loading, bone and cartilage remain healthy and viable. If the load falls below the nominal range for extended periods of time, bone and cartilage can become softer and weaker (atrophy). If the load rises above the nominal level for extended periods of time, bone can become stiffer and stronger (hypertrophy). Finally, if the load rises too high, then abrupt failure of bone, cartilage and other tissues can result. Accordingly, it has been concluded that the treatment of osteoarthritis and other bone and cartilage conditions is severely hampered when a surgeon is not able to precisely control and prescribe the levels of joint load. Furthermore, bone healing research has shown that some mechanical stimulation can enhance the healing response and it is likely that the optimum regime for a cartilage/bone graft or construct will involve different levels of load over time, e.g. during a particular treatment schedule. Thus, there is a need for devices which facilitate the control of load on a joint undergoing treatment or therapy, to thereby enable use of the joint within a healthy loading zone.
• Certain other approaches to treating osteoarthritis contemplate external devices such as braces or fixators which attempt to control the motion of the bones at a joint or apply cross-loads at a joint to shift load from one side of the joint to the other. A number of these approaches have had some success in alleviating pain but have ultimately been unsuccessful due to lack of patient compliance or the inability of the devices to facilitate and support the natural motion and function of the diseased joint. The loads acting at any given joint and the motions of the bones at that joint are unique to the body that the joint is a part of. For this reason, any proposed treatment based on those loads and motions must account for this variability to be universally successful. The mechanical approaches to treating osteoarthritis have not taken this into account and have consequently had limited success.
• Prior approaches to treating osteoarthritis have also failed to account for all of the basic functions of the various structures of a joint in combination with its unique movement. In addition to addressing the loads and motions at a joint, an ultimately successful approach must also acknowledge the dampening and energy absorption functions of the anatomy, and be implantable via a minimally invasive technique. Prior devices designed to reduce the load transferred by the natural joint typically incorporate relatively rigid constructs that are incompressible. Mechanical energy (E) is the action of a force (F) through a distance (s) (i.e., E=F^xs). Device constructs which are relatively rigid do not allow substantial energy storage as the forces acting on them do not produce substantial deformations—do not act through substantial distances—within them. For these relatively rigid constructs, energy is transferred rather than stored or absorbed relative to a joint. By contrast, the natural joint is a construct comprised of elements of different compliance characteristics such as bone, cartilage, synovial fluid, muscles, tendons, ligaments, etc. as described above. These dynamic elements include relatively compliant ones (ligaments, tendons, fluid, cartilage) which allow for substantial energy absorption and storage, and relatively stiffer ones (bone) that allow for efficient energy transfer. The cartilage in a joint compresses under applied force and the resultant force displacement product represents the energy absorbed by cartilage. The fluid content of cartilage also acts to stiffen its response to load applied quickly and dampen its response to loads applied slowly. In this way, cartilage acts to absorb and store, as well as to dissipate energy.
• With the foregoing applications in mind, it has been found to be necessary to develop effective structure for mounting to body anatomy. Such structure should conform to body anatomy and cooperate with body anatomy to achieve desired load reduction, energy absorption, energy storage, and energy transfer. The structure should also provide a base for attachment of complementary structure across articulating joints.
• For these implant structures to function optimally, they must not cause a disturbance to apposing tissue in the body, nor should their function be affected by anatomical tissue and structures impinging on them. Moreover, there is a need to reliably and durably transfer loads across members defining a joint. Such transfer can only be accomplished where the base structure is securely affixed to anatomy. Therefore, what is needed is an approach which addresses both joint movement and varying loads as well as complements underlying anatomy and provides an effective base for connecting an implantable extra-articular assembly.
SUMMARY
• Briefly, and in general terms, the disclosure is directed to base components that are mountable to a bone and may be used for cooperation with an implantable extra-articular system. In one approach, the base components facilitate mounting an extra-articular implantable link or mechanical energy absorbing system.
• According to one embodiment, the base components of the link or energy absorbing system are contoured to the bone surfaces of the femur and tibia and are secured with bone screws on the medial cortices of the femur and the tibia. The bases can also be attached to lateral sides of the bones of a knee joint or on either side of members defining other joints. The base components are also designed to preserve the articulating joint and capsular structures of the knee. Accordingly, various knee procedures, including uni-compartmental and total joint replacement, may be subsequently performed without requiring removal of the base components.
• In one specific embodiment, the base component includes a body having an inner surface that is contoured to mate with a bone surface. The inner surface contacts the bone surface and may be porous, roughened or etched to promote osteointegration. The inner surface can be coated with an osteointegration composition. Optionally, or additionally, the base component is secured to a bone surface with a plurality of fastening members. The base component is also shaped to avoid and preserve structures of the knee. Moreover, the base component is configured to locate a mounting member on the bone in order to position a kinematic load absorber for optimal reduction of forces on a joint. The base component is a rigid structure that may be made from titanium, cobalt chrome, or polyetheretherketones (PEEK). In an alternate approach, the base can be formed at least partially from flexible material.
• It is contemplated that the base component includes a low-profile body having an elongate, straight portion at a first end portion and a curved body portion at a second end portion. The second end portion is elevated as compared to the first end portion and occupies a plane displaced from the first end. An inner surface of the low-profile body has a raised portion extending along the elongate, straight portion of the body. The base component also includes a plurality of openings positioned along the elongate portion of the body. Additionally, the body can include two openings positioned side-by-side on the curved portion thereof.
• According to another embodiment, the base component is a generally curved body having a first end, a second end, an outer surface, and an inner surface. The curved body is non-planar such that the second end of the body is elevated as compared to the first end of the body. In an application relating to treating a knee joint, the inner surface of the body includes a raised portion that is contoured to the medial surface of the femur above the medial epicondyle. The body also includes a plurality of openings, wherein two openings are positioned side-by-side near the second end. Additionally, the openings provide differing trajectories for receiving fastening members.
• In one particular approach, the disclosed base has an osteointegration surface area greater than 39 mm². More specifically, a femoral base component can embody a surface area of 971 mm²and a tibial component can have a surface area of approximately 886 mm². The bases can further be coated with a titanium plasma spray having a thickness of 0.033 inches plus or minus 0.005 inches. Alternatively, an hydroxyapatite plasma spray resulting in a 35 μm plus or minus 10 μm thickness is contemplated.
• Moreover, it is contemplated that various sized bases be made available. In that regard, due to expected variability in anatomy, up to five or more femoral base sizes and two or more tibial base sizes can be available to a physician.
• The bases can be configured so that relative motion between a base component and a mating bone is less than 150 microns. For certain applications, the durability of the base to bone connection as well as material should be such that the structure can withstand five million cycles of functional loading.
• Other features and advantages will become apparent from the following detailed description, taken in conjunction with the accompanying drawings, which illustrate by way of example, the features of the various embodiments.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1A is a perspective view of one embodiment of a base component.
• FIG. 1B is a perspective view of the base component ofFIG. 1A mounted to a bone.
• FIG. 1C is a perspective view of another embodiment of a base component.
• FIG. 1D is a side view depicting the base component ofFIG. 1C mounted to a bone.
• FIG. 2 is side view of a femur and indicates a preferred location of a pivot point for an extra-articular mechanical energy absorbing system.
• FIG. 3 is a side view of another embodiment of a base component for mounting to a bone.
• FIG. 4 is view of an inner surface of the base component shown inFIG. 3.
• FIG. 5 is a side view of the base component shown inFIG. 3 mounted on a bone.
• FIG. 6 is a side view of an alternate embodiment of a base component for mounting to a bone.
• FIG. 7 is a side view of an inner surface of the base component shown inFIG. 6.
• FIG. 8 is a perspective view of the inner surface of the base component shown inFIG. 6.
• FIG. 9A is a cross-section view of the end of the base component that receives a mounting member.
• FIG. 9B is a cross-sectional view of the end of the base component shown inFIG. 3.
• FIG. 9C is a perspective view of the sleeve shown inFIG. 9B.
• FIG. 10A is a side view of another embodiment of an inner surface of the base component for mounting to a bone.
• FIG. 10B is a perspective view of yet another embodiment of inner surface of the base component.
• FIG. 11 is a side view of one embodiment of a base component fixed to a femur.
• FIG. 12 is a front view of one embodiment of a base component fixed to the medial surface of a femur.
• FIG. 13 is a perspective view of another embodiment of a base component for mounting to a bone.
• FIG. 14 is a perspective view of an inner surface of the base component shown inFIG. 13.
• FIG. 15A is a cross-section view of one embodiment of the base component shown inFIG. 14.
• FIG. 15B is a cross-section view of one embodiment of a portion of the base component shown inFIG. 14.
• FIG. 16 is a front view of the base component ofFIG. 13 mounted to the medial surface of a tibia.
• FIG. 17 is a side view of the base component ofFIG. 13 mounted to the medial surface of the tibia.
• FIG. 18 is a side view of a juxtapositional relationship of the base components to one embodiment of an extra-articular implantable mechanical energy absorbing system.
• FIG. 19 is a front view of the embodiment shown inFIG. 18.
• FIGS. 20A-B are side views of base components having flexible regions.
• FIGS. 21A-B are perspective views of an adjustable base assembly.
• FIG. 22 is a perspective view of another embodiment of a base.
• FIG. 23 is a perspective view of a first approach to a base assembly with mounting structure extending laterally on a bone.
• FIG. 24 is a perspective view of a second approach to a base assembly with mounting structure extending laterally.
• FIG. 25 is a perspective view of a third approach to a base assembly with mounting structure extending laterally.
• FIG. 26 is a perspective view illustrating a base component with structure supported by anatomy.
• FIG. 27 is a perspective view depicting a base including multiple components.
• FIG. 28 is a perspective view depicting yet another approach to a supported base assembly.
• FIG. 29 is a perspective view of a base including tissue in-growth promoting substructure.
• FIG. 30 is a perspective view of another base including in-growth promoting substructure.
• FIG. 31 is a perspective view of yet another approach to a base component.
• FIG. 32 is a perspective view of yet a further approach to a base component.
• FIG. 33 is a perspective view of a base component including a slotted portion.
• FIG. 34 is a perspective view depicting a base component with coded holes.
DETAILED DESCRIPTION
• Various embodiments are disclosed which are directed to base components for attachment to body anatomy. In a preferred approach, femoral and tibial base components are provided for attachment to extra-articular implantable link or mechanical energy absorbing systems.
• In a specific embodiment, the femoral and tibial base components are contoured to the medial surfaces of the femur and tibia, respectively. The base components have a low-profile design and contoured surfaces thereby minimizing the profile of the base components when mounted to the bone surface and enabling atraumatic soft tissue motions over the bone components. The base component is secured to a bone surface with one or more fastening members. Optionally, or additionally, the inner surface of the base components may be modified to promote osteointegration of the base component into bone. Osteointegration is a process of bone growth onto and about an implanted device that results in integrating the implant to the bone, thereby facilitating the transfer of load and stress from the implant directly to the bone. After osteointegration, fasteners used to initially attach the base component to bone no longer are needed to carry the load and stress from the implant.
• The base component can be configured to be an anchor for the extra-articular implantable link or mechanical energy absorbing system used to reduce forces on the knee or other joints (e.g., finger, toe, elbow). The base component can be also designed to distribute loads onto the bone from an extra-articular implantable link or mechanical energy absorbing system while avoiding articulating joint and capsular structures.
• Various shapes of bases are contemplated and described. Moreover, it is contemplated that various sized and similar shaped bases be made available to a physician so that a proper fit to variably sized and shaped bones can be accomplished. In that regard, it is contemplated that up to five or more different femoral bases and two or more different tibial bases can be available to a physician.
• The base components disclosed herein are structures that are different and distinct from bone plates. As defined by the American Academy of Orthopedic Surgeons, bone plates are internal splints that hold fractured ends of bone together. In contrast, the base components disclosed herein are designed to couple to and transfer loads from a link of an implanted extra-articular system to the bones of the joint. Furthermore, the loading conditions of a bone plate system are directly proportional to the physiological loads of the bone it is attached to, by contrast the loading conditions of a base is not directly proportional to the physiological loading conditions of the bone but is directly proportional to the loading conditions of the link to which it is coupled. In various embodiments, the base component is configured to transfer the load through a combination of the fastening members used to secure the base component to the bone and/or one or more osteointegration areas on the base component.
• Further, previous approaches and studies on osteointegration surfaces have not considered cyclic loading. Thus, the approaches to the bases disclosed herein address needs in this area and in particular, provides an approach which achieves extra-cortical boney in-growth under cyclic loading. In certain disclosed applications, a shear strength of about 3 MPa or more can be expected.
• Referring now to the drawings, wherein like reference numerals denote like or corresponding parts throughout the drawings and, more particularly toFIGS. 1-20B, there are shown various embodiments of a base component that may be fixed to a bone. In one specific application, the base components are configured to be affixed to members defining a joint. Moreover, in one particularly specific approach, the base can be configured to include a surface contacting periosteum.
• Turning now toFIGS. 1A-1B, abase component1 fixable to the medial surface of a femur is illustrated. It is to be recognized, however, that thebase component1 can be configured to be fixed to a lateral side of the femur, on the tibia, or other anatomy of the body. Thebase component1 includes anouter surface3 and aninner surface5. Theouter surface3 of the base component has a low-profile and is curved to eliminate any edges or surfaces that may damage surrounding tissue when the base component is affixed to bone. Thebase component1 includes alocking hole2 that locates acoupling structure15 adjacent point17 (FIG. 2). Thefemoral base component1 is intended to be positioned about thecenter19 of knee rotation inFIG. 2. According to one embodiment, thebase component1 is mounted to the femur so that thecoupling structure15 is located approximately 6 mm anterior and approximately 1 mm superior to thecenter19 of rotation of the knee on the medial epicondyle. Such spacing is relevant to each of the disclosed embodiments. Mounting the energy absorbing components at this location allows the extra-articular mechanical energy absorbing system to reduce forces during the heal strike to toe-off phase of a person's gait. Alternatively, the base component may be mounted at different positions on the femur to reduce forces during different phases of a person's gait.
• FIGS. 1C-D illustrate another embodiment of abase component1 mountable on the medial surface of the femur. Again, it is noted that this embodiment of thebase component1 can be positioned laterally as well as on other anatomy. Thebase component1 includes a raisedsurface9 to suspend thetaper locking opening2 higher off the bone surface to avoid the knee capsule and associated structures of the knee joint. It is contemplated that thetaper locking opening2 be offset approximately10 mm or less from the surface of the joint capsule. In one specific embodiment, thetaper locking opening2 is offset approximately 3 mm from the capsular structure. In another approach, thetaper locking opening2 is offset approximately 6 mm from the capsular structure. Accordingly, thebase component1 allows for positioning of an extra-articular device on the knee joint while preserving the knee for procedures such as ACL or PCL repair or replacement, Pes replacement, or total knee replacement.
• It is contemplated that the inner surface of thebase component1 be contoured to directly contact the bone surface. The inner surface may be curved in an anterior to posterior direction as well as superior to inferior directions. According to one embodiment, the inner surface includes one or more compositions that induce osteointegration to the cortex of long bones in the body. The inner surface represents thebase component1 to bone surface area required to support expected shear forces resulting from 40 lbs. of load carrying. Alternatively, theinner surface5 is roughened or etched to improve osteointegration.
• The surface area of the osteointegration area is proportional to the forces being carried at a joint by the extra-articular mechanical energy absorbing system. For example, the surface area of the inner surface is at least 39 mm²for a secure fixation to the femur and in order to carry 40 pounds in 4 mm of compression of a kinematic load absorber. A safety factor may be built into base component as larger surfaces may be used in other embodiments. For example, a femoral base component can include an osteointegration surface area of approximately 971 mm². Alternatively, a tibial base component includes an osteointegration surface area of approximately 886 mm².
• In certain embodiments, the load transferred from the absorber to the base component can change over time. For example, when the base component is initially fixed to the bone, the fastening members carry all the load. Over time, as the base component osteointegrates with the underlying bone, both the fastening members and the osteointegrated surface carry the load from the implanted system. Once the base component is completely osteointegrated with the underlying bone, the osteointegration area carries most (if not all) the load. Due to the same, the energy absorbing system may be configured in an inactive state, only later activating the device once sufficient osteointegration has occurred.
• Alternatively, the implant may be intended for temporary use and so removability of the components is important. In these instances boney in-growth is not desirable. To prevent boney in-growth no porous coating is applied and alternative surface geometry and/or material may be used that does not encourage bone growth, additionally the fasteners are designed to carry 100% of link loads for duration of implantation.
• The base component also includes a plurality ofopenings7 that are sized to receive fastening members used to permanently secure the base component to the bone. Theopenings7 define through-holes that may receive fastening members such as compression screws and/or locking screws. As shown inFIGS. 1A-D, theopenings7 are spaced about theouter surface3 of thebase component1. In one embodiment, the openings can be positioned on theouter surface3 such that they are located as close as possible to thetaper locking opening2. Theopenings7 may also have divergent bore trajectories to further maximize the pull forces required to remove the base component from the bone. The number and trajectories of the openings may be varied in alternate embodiments.
• FIGS. 3-4 illustrate another embodiment of abase component10. The base component includes a body that is configured to position a mounting member (not shown) at apoint17 superior and anterior to thecenter19 of knee rotation on the medial epicondyle as shown inFIG. 2. Thebase component10 also includesosteointegration rods25 that extend along the surface of the bone. It is contemplated that theosteointegration rods25 follow the contours of the bone surface. Accordingly, theosteointegration rods25 can be made of malleable materials. In another embodiment, theosteointegration rods25 can be configures to penetrate the bone surface as shown inFIGS. 3-4. Theosteointegration rods25 have a sufficient surface area to allow for the transfer of the forces of the implanted system onto the bone. According to one embodiment, all of the surfaces of theosteointegration rods25 include materials or is treated to promote bone growth.
• As shown inFIGS. 3-4, thebase component10 includes a plurality ofopenings11,19,22,24.Opening11 has a diameter sized to receive standard K-wires that are used to temporarily locate thebase component10 on the bone.Openings19,22,24 are sized to receive fastening members used to permanently secure the base component to the bone.Openings19 define through holes for compression screws andopening22,24 are configured to receive locking screws. In one embodiment, the lockingscrew openings22,24 are threaded. As shown inFIGS. 3-4, theopenings22,24 are located near the mountingend15 of the base component in order to receive fasteners which securely fix the base component to the bone and maximize pull-out forces. Theopenings22,24 may also have divergent bores trajectories to further maximize the pull forces required to remove the base component from the bone. The number and trajectories of the openings may be varied in alternate embodiments. Apost access port13 is provided near the mountingend15 of the base component10 (see for exampleFIG. 5). Thepost access port13 is sized to receive a tool that allows for disassembly of a mount member (not shown) from thebase component10 by pushing thepost23 of the mount member out of the base component.Openings26 additionally alter the stress distribution on cortical bone surface that can stimulate boney remodelling. Bone can grow up into these holes further adding shear strength to the bone implant interface.
• Turning now toFIG. 6, a presently preferred embodiment of abase component10 that is mountable to a femur is shown. Thebase component10 includes a body having anelongated portion12 and acurved portion14. The body is generally narrow having a roundedfirst end16 and a squared-offsecond end18. In various embodiments, thesecond end18 is configured to attach to mounts and/or devices for absorbing energy at a joint. As shown inFIG. 6, the upper surface of the body is a generally curved such that a center of the body is thicker than the edges of the body. Thebase component10 also includes rounded edges in order to minimize sharp edges that may otherwise cause damage to surrounding tissues when the component is coupled to body anatomy such as the femur.
• As shown inFIG. 7, the body also includes a plurality ofopenings20 and21 configured to receive fastening members. Theopenings20 and21 are generally aligned along the center of the elongate portion of the body. Theopenings20 and21 on the elongated portion of thebody12 are positioned such that the fastening members contact the osteointegration area of the femur. According to one embodiment, theopenings20 and21 are configured to accept compression screws that compress thebase component10 onto the bone surface. The compression screws may be cancellous screws of either uni-cortical or bicortical design. Theopenings20 are sized to accommodate a particular screw size.
• Additionally, twoopenings22,24 are provided on thecurved portion14 of the body. Theopenings22,24 are positioned such that fastening members inserted there through (as shown inFIGS. 11-12) will be configured closer to the center of rotation of the femur. In one embodiment, thefastening members22,24 are locking screws and theopenings22,24 include threads for engaging like structure of the locking screws. It is to be recognized that locking screws securely anchor the base to the bone such that the relative motion between thebase component10 and the mating bone is less than 150 microns. The locking screws function to stabilize the base component as micro-motions of the base component prevent osteointegration of the base component.
• Additionally, theopenings20,21,22,24 can be oriented to provide fastening member trajectories that maximize pull out forces thereby minimizing the possibility that the base component is separated from the bone. According to one embodiment, the trajectories of the openings are oriented such that the opening trajectories are normal or approximately normal to the shear loading forces on thebase component10. For example, the twoopenings22,24 on thecurved portion14 of the body have differing fastening member trajectories as theposterior opening22 orients a fastening member at a downward trajectory (SeeFIG. 18), and theanterior opening24 orients a fastening member at an upward trajectory (SeeFIG. 19).
• Theopenings20,21,22,24 can be countersunk to allow the fastening members to sit below the surface of the base body as shown inFIG. 10. In one specific approach, theopenings20 are sized to accommodate 4.0 mm screws. In other approaches, theopenings20 may be sized to accommodate 3.5 mm, 4.5 mm, 5.0 mm, or 6.5 screws.
• In a preferred embodiment, twoopenings20 on the elongated portion of thebase component10 are sized and threaded to accommodate3.5 mm bicortical compression screws. The mostinferior opening21 on the elongated portion of the base component is sized to accommodate a 6.5 mm unicortical compression screw. Theopenings22,24 on thecurved portion14 of the body are sized and threaded to accommodate 4.5 mm locking screws.
• While screws are used to fix thebase component10 to the bone, those skilled in the art will appreciate that any fastening members known or previously developed may be used to secure a base component to a bone. For example, in other embodiments, a fastening device similar to a moly bolt or a toggle bolt is used to secure the base component to a bone. Additionally,FIGS. 1-11 illustrate abase component10 having fivefastener openings20,21,22,24; however, it is contemplated that other embodiments of the base component may be have any number of openings having various screw trajectories.
• Referring back toFIG. 6, thebase component10 also includes a plurality ofholes26 that may be used for aligning the base component on the bone. Optionally, thebase component10 may include a plurality of holes (not shown) to promote bone in-growth thereby improving base component stability. In this regard, K-wires can be configured through theholes26 to maintain alignment of a base to bone during its affixation thereto by fastening members.
• FIG. 7 illustrates a view of theinner surface28 of thebase component10. As shown, theinner surface28 is a roughened or etched surface to improve osteointegration. Alternatively, theinner surface28 is modified to induce bone growth. Thus, osteointegration can be obtained through mechanical interlocking or as a result of chemical loading. For example, theinner surface28 may be coated with bone morphogenic protein 2 (BMP-2), hydroxyapatite (HA), titanium, cobalt chrome beads, or any other osteo-generating substance. According to one embodiment, a titanium plasma spray having a thickness of approximately 0.033 in.±0.005 in. is applied to theinner surface28. In another embodiment, a HA plasma spray having a thickness of approximately 35 μm±10 μm is applied to facilitate osteointegration.
• As shown inFIG. 7, theinner surface28 has a first radius of curvature at theproximal end30 of thebase component10 and a second radius of curvature at thedistal end32 of the inner surface where the first radius of curvature is greater than the second radius of curvature. Alternatively, the first radius of curvature is less than the second radius of curvature. In another embodiment, the first and second radii of curvature are approximately equal.
• Additionally, as best seen inFIG. 8, theinner surface28 is generally helical in shape when moving from theproximal end30 of thebase component10 to thedistal end32 of the base component. That is, theinner surface28 twists when moving from the top of the inner surface to the bottom of the inner surface. The helical nature of theinner surface28 generally follows contours of the femur when moving distally (down the femur) and posteriorly (front to back). Accordingly, the contouring of theinner surface28 helps to reduce the overall profile of thebase component10 when affixed to the medial surface of the femur. Additionally, the contouring of theinner surface28 increases the surface area in which the base component contacts the femur thereby improving load distribution.
• Additionally, as shown inFIG. 8, theend18 of thebase component10 includes abore40. Thebore40 is sized to receive a post (SeeFIG. 9B) of a mountingmember15. According to one embodiment, thebore40 has a uniform inner diameter. Alternatively, thebore40 is tapered (e.g., inner diameter decreases when moving away from the opening of the bore). In yet another embodiment, a funnellingfeature46 is provided around the opening of thebore40 as shown inFIG. 9A. The funnellingfeature46 acts as a guide to facilitate the insertion of the mounting member into the bore. Theend18 of thebase component10 also includesalignment members42 for properly orienting the mounting member (not shown) on the base component.
• FIGS. 9B-C illustrate a cross-section view of one embodiment of thebore40 of thebase component10 including asleeve44. Thesleeve44 acts as a sacrificial piece of material that prevents damage to thebore40 while providing a good secure fit between the mounting member and the base component. In one embodiment, thesleeve44 is press fit into thebore40. The inner diameter of thesleeve44 can be uniform or alternatively, the outer diameter is variable. Additionally, one or more rings can be provided on the outer diameter of thebore40. As thesleeve44 is inserted into thebore40, therings48 on the outer diameter deform thereby providing a secure connection between thebase component10 and the mountingmember15. Additionally, thesleeve44 facilitates the removal of the mountingmember15 from thebase component10. Additionally, interpositional segments can be placed at theend18 of thebone component10 to change the length of the base component. The two part base/mounting member system provides a method for good attachment of the base to the bone and a more simple surgical technique for installing the link assembly. It also allows a sheath (not shown) and/or wear components of the link/mounting member assembly to be removeable and/or replaceable without removing or replacing the base components. It further allows the wear components of the link/mounting member assembly and the base components to be different materials. For example, the base components can be titanium or titanium alloy which promote osteo-integration and the wear components can be much harder materials such as cobalt chrome (e.g., Biodur CCM Plus), ceramic, or other durable materials that produce a minimal amount of particulate material or, if particulate material is generated, the smallest size of particulate material.
• With reference toFIG. 10A, another embodiment of theinner surface28 of a base component is shown having a plurality ofspikes34 projecting out of the inner surface. While thespikes34 shown inFIG. 10A are solid, it is contemplated that the spikes (not shown) may also include an inner bore (similar to a needle) that promotes for bone in-growth. According to one embodiment, thespikes34 may be positioned anywhere on the inner surface28 (e.g., randomly dispersed or concentrated in one or more areas) in order to preserve critical anatomy (e.g., periosteal vessels), improve pull out forces (i.e., more force required to pull component away from bone), and/or stimulate osteointegration. Thespikes34 may extend approximately 2 mm from theinner surface28 of thebase component10. As those skilled in the art will appreciate, any useful spike length is contemplated. In yet another embodiment, one or morehollow tabs36 are provided on theinner surface28 as shown inFIG. 10B. Thetabs36 may be any shape (e.g., rectangular, triangular, or any polygonal shape) having a hollow opening (i.e., the walls of the tab form the perimeter of the shape) thereby promoting osteointegration and stability to thebase component10.
• FIGS. 11-12 illustrate thebase component10 affixed to the medial surface of the femur. As best seen inFIG. 12, thebase component10 has a generally low-profile when mounted to the bone. Thebase component10 is affixed to the medial surface of the femur in order to preserve critical anatomy such as, but not limited to, medial collateral ligaments while positioning thesecond end18 of the base component as close to the center of rotation of the femur. Moreover, thecurved portion14 of thebase component10 is offset from the surface of the bone to avoid critical structure while maintaining a low profile of the device.
• Thebase component10 shown inFIGS. 1-12 is configured to be fixed to the medial surface of the left femur. It is to be appreciated that a mirror image of thebase component10 shown inFIGS. 1-12 would be fixable to the medial surface of the right femur. In an alternate embodiment, the base component may be configured to be fixed to the lateral surface of the left or right femur. In yet another approach, base components may be fixed to both the lateral and medial surfaces of the left or right femur.
• A presently preferred embodiment ofbase component60 that is mountable to the medial surface of the tibia is depicted inFIG. 13. As shown, thetibial base component60 has an overall curved shape. Thebase component60 includes amain body portion62 and anarm portion64. Thearm portion64 of thebase component60 is shaped to position a link or absorber assembly approximately perpendicular to the tibial plateau to provide desired alignment across the joint. Alternatively, thearm portion64 may be angled relative to the tibial plateau in order to provide some torque across the joint. The upper surface of the body is a curved convexly where the center of the body is thicker than the edges of the body. Thebase component60 also includes rounded edges in order to minimize sharp edges that may otherwise cause damage to surrounding tissues when the component is coupled to the tibia. Themain body portion62 is generally narrow and includes a roundedfirst end66 and a squared-offsecond end68. In various embodiments, thesecond end68 is configured to attach to mounts and devices for absorbing energy at a joint. Themain body portion62 is the portion of thebase component60 that contacts the tibia. Thearm portion64 is offset laterally from the bone (i.e., the arm portion does not contact the tibia). While thearm portion64 of thebase component60 is offset from the bone, the base component defines a low-profile when mounted to the bone.
• As shown inFIGS. 13-17, thebase component60 also includes a plurality ofopenings70. Theopenings70 are aligned along the center portion of thebase component60. Theopenings70 are positioned such that the screws contact the osteointegration area of the tibia. Additionally, twoopenings72,74 are provided on thearm portion64 of thebase component60. The twoopenings72,74 are positioned such that the screws (as shown inFIGS. 18-19) will be mounted closer to the mounting location of the mounting member (not shown) at the end of the base component.
• Additionally, theopenings70,72,74 are oriented to provide differing trajectories for fastening members that maximize pull forces thereby minimizing the possibility that thebase component60 is separated from the bone. According to one embodiment, the opening trajectories are oriented such that the hole trajectories are normal or approximately normal to the shear loading forces on thebase component10. For example, as shown inFIG. 19, the twoopenings72,74 on thearm portion64 of the base component have differing trajectories, theposterior opening72 orienting a fastening member at an upward trajectory, and theanterior opening74 orienting a fastening member at a slightly upward trajectory.
• Theopenings70,72,74 can be countersunk to allow the heads of fastening members to sit below the surface of the body as shown inFIGS. 16-17. According to one embodiment, theopenings70,72,74 are sized to accommodate 4.0 mm diameter fastening members. In other embodiments, theopenings72,74 may be sized to accommodate 3.5 mm, 4.5 mm, or 5.0 mm diameter fastening members. Additionally, the inner bores of theopenings70,72,74 may be threaded for use with locking screws (i.e., head of the screw also includes threads that engage threads in the bore of the screw hole). In preferred approaches, a combination of compression screws and locking screws are used to secure thebase component60 to a bone.
• While screws are used to fix the femoral andtibial base components10,60 to the bone, those skilled in the art will appreciate that any fastening members known or developed in the art may be used to accomplish desired affixation. Although thebase components10,60 depicted inFIGS. 6-7 and13-14 illustrate structure having five openings, it is contemplated that other embodiments of the base component may be have any number of openings. Additionally, the openings may be oriented such that fastening members will have different trajectories.
• As shown inFIG. 13-17, thetibial base component60 also includes a plurality ofholes76 that may be used during alignment of thebase component60 on the tibia and sized to receive structure such as a K-wire. Optionally, thebase component60 may include a plurality of holes (not shown) to promote bone in-growth thereby improving base component stability.
• FIG. 14 illustrates a perspective view of theinner surface78 of thetibial base component60. Theinner surface78 represents the base to bone surface arch required to support expected shear forces resulting from 60 lbs. of load carrying. As shown inFIG. 14, theinner surface78 is a roughened surface for improving osteointegration. Alternatively or additionally, theinner surface78 is coated to induce bone growth. For example, theinner surface78 may be coated with bone morphogenic protein 2 (BMP-2) or hydroxyapatite, titanium, cobalt chrome beads. As shown inFIGS. 15A-15B, theinner surface78 is a contoured surface that promotes good contact between thebase component60 and the tibia. Accordingly, the inner surface facilitates thebase component60 absorbing and transferring load forces from the base component to the tibia. Similar to the embodiments disclosed inFIGS. 10A-10B, theinner surface78 of thebase component60 may include one or more spikes or tabs.
• FIGS. 15A-B are cross-sectional views of theinner surface78 of thetibial base component60. As shown inFIG. 15A, theinner surface78 has an osteointegration coating applied to thetop surface80 and theedges82 of theinner surface78. In another approach, the osteointegration coating (not shown) is only applied to the inner surface.FIG. 15B illustrates a another embodiment where a portion of theosteointegration coating84 on theinner surface78 is over-contoured (i.e., extends above the plane of the inner surface78). Theover-contoured coating84 surface is compressed when thetibial base component60 is affixed to the bone, thereby preventing micro-motion of the base component. Theover-contoured coating84 also concentrates the compressive forces on the middle of theinner surface78.
• With reference toFIGS. 16-17, thetibial base component60 has a generally low-profile when mounted to the bone. Thebase component60 is mounted to the medial surface of the tibia in order to preserve critical anatomy such as, but not limited to, medial collateral ligaments while positioning thesecond end68 of the base component as close to the pivot point of the tibia. As best seen inFIG. 16, thearm portion64 of thebase component60 is also offset from the surface of the tibia to avoid critical structure while maintaining a low profile of the base component.
• Thetibial base component60 shown inFIGS. 13-17 is configured to be fixed to the medial surface of the left tibia. As those skilled in the art will appreciate, a mirror image of thebase component60 shown inFIGS. 13-17 would be fixable to the medial surface of the right tibia. Additionally, the base component may be configured to be fixed to the lateral surface of the left or right tibia. In another approach, the base component may be configured to be coupled to lateral surfaces of both the tibia and fibula. In yet another embodiment, base components may be fixed to both the lateral and medial surfaces of the left or right tibia.
• FIGS. 18-19 illustrate one embodiment of an extra-articular implantable mechanicalenergy absorbing system100 that is coupled to the second ends18,68 of the femoral andtibial base components10,60, respectively. Through the connections provided by thebase components10,60, the mechanicalenergy absorbing system100 can function to reduce desired forces from a knee joint. It is also to be recognized that the placement of the bases on the bones is made such that further procedures, such as a TKA, can be conducted at the joint while leaving the bases in place but after removing the absorbing system. Additionally, the absorbing system can be replaced without having to replace the base components resulting in removal of all of the wear components.
• The various embodiments of the base component may be made from a wide range of materials. According to one embodiment, the base components are made from metals and alloys such as, but not limited to, Titanium, stainless steel, Cobalt Chrome. Alternatively, the base components are made from thermo-plastic materials such as, but not limited to, polyetheretherketones (PEEK). Various embodiments of the base components are rigid structures.
• FIGS. 20A-B illustrate atibial base component110 and afemoral base component120 having partiallyflexible regions112,122 for flexing and/or twisting. As shown, eachbase component110,120 includes arigid section114,124 and theflexible region112,122. Therigid section114,124 of thebase components110,120 are mountable to the bone and can include an osteointegration surface. Theflexible region112,122 of thebase components110,120 extends from the base and provides additional load bypass capabilities. Theflexible regions112,114 of thebase components110,120 apply a linear or nonlinear spring force when the flexible region is deflected. Additionally, theflexible regions112,122 provide adjustability in positioning of the base component on the bone by minimizing some degree of precision required to find the proper mounting location on the bone. It is also contemplated that theflexible regions112,122 can also be used to absorb additional forces in an overload situation to protect thebase component110,120 stability.
• Various other embodiments of bases are contemplated. Such bases can incorporate one or more of the previously described features or can embody structure separate to itself.
• In particular, as shown inFIGS. 21A and B, one or more of the bases can include adjustment structures. Here, a base130 can include twopieces132,134 which are slideable with respect to each other. Atop piece132 can be formed of a material through which fastening members can be forceably inserted without originally including one or more through holes, whereas thebottom piece134 can include previously machined through holes. Thus, thetop piece132 can be adjusted with respect to the bottom piece and the adjusted juxtapositional relationship can be set with the fasteners employed to attach the assembly to body anatomy. Accordingly, such alterations can translate into adjusting as desired the action of absorber components of an energy absorbing assembly. It is also contemplated that the materials be selected for the bases so that they define flexible structure intended to absorb forces. Such an approach is useful where the sub-structure of an energy absorbing device includes a defined fully loaded position so that further loads are transferred to the flexible bases.
• Moreover, a base136 can be configured to attach to cortical bone as shown inFIGS. 22-25. In these approaches, the base136 can have an extension138 (SeeFIG. 22) including mounting holes so that attachment to cortical bone is possible. Additionally, the base136 can include aportion140 extending about lateral surfaces of a bone to thereby be connectible to cortical bone (SeeFIGS. 23-25). As depicted inFIGS. 22-24, certain of these approaches can also include detachablelink pin substructures142 for releasably attaching to an energy absorbing device or other structures. Moreover, as with all disclosed approaches, these embodiments can includesurfaces146 promoting boney in-growth, such as indicated inFIGS. 23 and 24. Additionally, as specifically shown inFIG. 25, theremovable pin substructure142 can be formed in anextension150 that is itself removable from thebase136.
• In yet other approaches, the base component can include structure which relies on surrounding anatomy for additional support. For example, as shown inFIG. 26, a base160 can include structure extending to and overlaying afibula162. Further, as shown inFIG. 27, abase assembly170 can include multiple pieces attached to opposite sides of a bone and can further include a restraining cross-bar172 extending from one of the multiple pieces to another.
• Similarly, as depicted inFIG. 29, support for an energy absorbing orother device180 can be obtained from opposite sides of a joint. For instance, one end of the device can be supported by a laterally placedbase182 and another supported by a medially placedbase184. To do so, arod186 can be positioned across an interior of a bone from a laterally configured implanted device to amedial side base184. In this way, where necessary, diseased or complex anatomy can be avoided so that a good fit to bone can be achieved.
• Turning now toFIGS. 29-32, yet further contemplated embodiments ofbases190 are illustrated. Such bases can have simple through holes192 (FIGS. 29 and 32) for fastening members or such holes can include countersinks194 (FIG. 31). Additionally, the fastening holes can definescrew head sockets196 as shown inFIG. 30. Moreover, the contemplated bases can embody various approaches for accomplishing connection to the bone such as by including spikes198 (FIGS. 29 and 32) or rotatable spurs200 (FIG. 30). Furthermore, thebases190 can includesmall holes202 such as those having a diameter of less than 1 mm for boney, interlocking in-growth (FIG. 29).
• Finally, as shown inFIG. 33, the base210 can include a slottedregion212 for receiving corresponding structures. Also, the holes214 formed on a base216 can be numbered or otherwise identified to assist a physician in selecting proper fastening members.
• The various embodiments described above are provided by way of illustration only and should not be construed to limit the claimed invention. Those skilled in the art will readily recognize various modifications and changes that may be made to the claimed invention without following the example embodiments and applications illustrated and described herein, and without departing from the true spirit and scope of the claimed invention, which is set forth in the following claims. In that regard, various features from certain of the disclosed embodiments can be incorporated into other of the disclosed embodiments to provide desired structure.

Claims (15)

1-9. (canceled)

10. An implantable extra-articular mechanical energy absorbing system, comprising:

an absorber, the absorber configured to absorb a predetermined load; and

a base including a low-profile body having a mounting portion configured to be operatively connected to the absorber and a bone contacting surface having a selected surface area configured to promote a bone response such as osteointegration.

11. The system ofclaim 10, wherein the mounting portion is elevated above the bone surface to position the absorber outside the joint capsule.

12. The system ofclaim 10, further comprising one or more projections extending from the bone contacting surface.

13. The system ofclaim 10, further comprising one or more through holes positioned along the low-profile body, the through holes configured to receive fastening members.

14. The system ofclaim 10, wherein osteointegration is promoted by a coating applied to the bone contacting surface.

15. The system ofclaim 10, wherein osteointegration is promoted by providing the base contacting surface with a roughened surface.

16. The system ofclaim 10, wherein the bone contacting surface is contoured for a medial portion of a femur or a tibia.

17. The system ofclaim 10, wherein the bone contacting surface is contoured for a femur or tibia.

18. The system ofclaim 10, wherein the selected surface area is about 39 mm2 or greater.

19. The system ofclaim 10, wherein the bone response is mechanical interlocking into the base.

20. The system ofclaim 10, wherein the bone response is chemical bonding onto the base.

21. The surface ofclaim 10, wherein the interface between the osteointegrated surface and bone has a shear strength of about 3 MPa or greater without support from fasteners.

22. The system ofclaim 10, wherein the shear strength of the base-bone interface is greater than the shear stress applied by the forces of the absorber.

23. An implantable extra articular system comprising a base including a periosteum contacting surface and a mounting surface, the mounting surface configured to operatively connect to a link wherein the mounting surface overlies bone and is displaced from the bone.

Images