Patent Application
20070043448
Not Applicable.
1. The Field of the Invention.
The present invention relates generally to prosthetic implants, and more particularly, but not necessarily entirely, to a prosthetic hip system for increasing the intrinsic stability between the prosthetic implant and at least one bone.
2. Description of Related Art
It is known in the art to replace the natural hip joint with an artificial hip replacement. Numerous artificial implants are available that can be used to replace the natural hip joint with an artificial ball and socket combination. Although there are many techniques used in a hip replacement surgery to replace the natural femoral components of the hip joint, each technique essentially requires resection of the femoral head, exposing the medullary canal of the femur, and creating an enlarged medullary cavity and an enlarged medullary canal in the distal portion of the proximal femur using a reamer, such that a prosthetic femoral implant may be implanted therein.
Generally, after the proximal femur has been surgically prepared, a distal stem portion of the prosthetic femoral implant may be inserted into the reamed section of the medullary canal, and a proximal stem portion of the prosthetic femoral implant may be inserted into the enlarged cavity of the proximal femur in a secure, seated position. It will be appreciated that typical prosthetic femoral implants include at least the following: a neck member that extends medially and proximally away from the proximal stem portion of the implant and terminates in a substantially spherical head member, and a stem component. The head member is configured for being inserted into an artificial acetabular implant that is configured for being located within the acetabulum of the hip. The head member may be further configured for rotational contact with the acetabular component about the three major orthogonal axes.
There are two major systems to secure the femoral component of the implant within the medullary canal of the femur. The first system, sometimes referred to as a cementless system, utilizes the natural tendencies of the bone to grow into porous sections of the femoral implant without the aid of cement. The cementless system requires the removal of a majority, if not all, of the softer, cancellous bone and uses the natural tendencies of the bone to grow into the implant, forming a tight, secure fit between the implant and the bone, to thereby maintain the implant within said bone. This system was first introduced nearly forty years ago and has become the preferred method of installation in recent years due, at least in part, to the strength of the connection between the implant and the bone ingrowth.
The second system, sometimes referred to as a cemented system, utilizes bone cement to maintain the implant within the bone. The use of cement requires the removal of bone tissue while leaving a layer of cancellous bone tissue to anchor the implant to the bone with the aid of cement. This process was used extensively during the 1970's and 1980's, and is still commonly used today on a more limited basis in comparison with the cementless system.
Both systems may be advantageously used in appropriate circumstances depending upon a patient's needs. For example, recovery from an operation using the cementless system takes an average of about three months before the patient may return to any activity so that new bone may be permitted to grow into the pores of the implant. The result is a connection that has the potential to endure in the patient for a long period of time, for some patients that may be as long as 20 years or more. The cementless system is recommended for patients who lead active lives, and is typically used in relatively young patients.
Conversely, the cemented system results in a decrease in post-operative pain, compared to the cementless system, and an increase in joint mobility. However, the interface between the bone, the cement and the implant may not be as strong as the cementless system and may result in premature loosening as compared to the cementless system. Therefore, the cemented system is typically used in less active, older patients.
It is a fairly common occurrence for femoral implants to loosen from the bone or cement over time due, at least in part, to the high stresses placed on the hip joint. Specifically in cementless total hip arthroplasty, dislocation of the hip joint has been and continues to be a problem. In recent years a trend has developed in the orthopedic industry to increase the femoral offset of the implant between the head of the implant and a long axis of the femur to help reduce dislocation. As the femoral offset increases, the potential for increased torsional forces placed on the stem-bone interface likewise increases, and the potential for the stem loosening increases, resulting in increased post-operative pain, disability and an increased risk that additional revision surgery may be necessary. Attempts have been made in the prior art to increase the efficiency of the bond between the implant and either bone or cement, such that the loosening of the implant from the bone (or from the cement in cemented systems) over time is decreased.
One such attempt to improve the adhesion of the stem of the implant to the bone, or cement is found in U.S. Pat. No. 5,480,452 (granted Jan. 2, 1996 to Hofmann et al.). Hofmann et al. discloses a femoral prosthesis having a proximal portion formed as a wedge for thrusting into the medullary canal and achieving fixation to the bone, ribs for securing the prosthesis against medial-lateral motion, while providing a degree of flexibility in the anterior-posterior direction, and a slot formed in the distal stem, which is flared for enhancing fixation distally. However, this device is disadvantageous in that the device is unable to withstand the increased torsional loads that may be placed on the device due to an increase in the lateral offset and to the frictional forces acting tangentially on the bone-implant interface. Torsional forces are disadvantageous in that over time they may cause loosening of the implant from the bone.
U.S. Pat. No. 5,935,172 (Ochoa et al.) discloses a joint prosthesis having a plurality of negative surface features and comprises a first, body portion and a second, cap portion for the distal end of the body to fit into. The body further has a metaphyseal fitting region to contact the surrounding bone to initiate bone ingrowth. However, this device is disadvantageous because it lacks the structure necessary to contact the posterior calcar wall and the anterior cortex of the femur permitting solid contact with cortical bone. Thus, torsional forces may not be resisted.
The prior art is thus characterized by several disadvantages that are addressed by the present invention. The present invention minimizes, and in some aspects eliminates, the above-mentioned failures, and other problems, by utilizing the methods and structural features described herein.
The features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by the practice of the invention without undue experimentation. The features and advantages of the invention may be realized and obtained by means of the instruments and combinations particularly pointed out in the appended claims.
The features and advantages of the invention will become apparent from a consideration of the subsequent detailed description presented in connection with the accompanying drawings in which:
For the purposes of promoting an understanding of the principles in accordance with the invention, reference will now be made to the embodiments illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Any alterations and further modifications of the inventive features illustrated herein, and any additional applications of the principles of the invention as illustrated herein, which would normally occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention claimed.
Before the present device and methods are disclosed and described, it is to be understood that this invention is not limited to the particular configurations, process steps, and materials disclosed herein as such configurations, process steps, and materials may vary somewhat. It is also to be understood that the terminology employed herein is used for the purpose of describing particular embodiments only and is not intended to be limiting since the scope of the present invention will be limited only by the appended claims and equivalents thereof.
The publications and other reference materials referred to herein to describe the background of the invention and to provide additional detail regarding its practice are hereby incorporated by reference herein. The references discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as a suggestion or admission that the inventors are not entitled to antedate such disclosure by virtue of prior invention.
Designers of hip stem prostheses may choose to increase the lateral offset between a femoral head of an implant and the longitudinal axis, or mid-line, of a femur in order to restore, at least partially, the biomechanics of the natural hip joint. An increased lateral offset operates to increase the torsional forces that are exerted on the femoral implant, and such forces may be applied to the bone-implant interface specifically between a stem portion of the implant and the medullary canal of the femur. Additionally, torsional forces may be derived from the sum of the interface surface friction forces acting parallel to the interface surface, and the torque created by the forces normal to the interface surface acting to resist the offset force applied to the femoral head. There is, therefore, an increased need for torsional stability to prevent the implant from loosening from the bone.
Applicants have discovered that torsional forces may more effectively be opposed by utilizing a prosthetic device having a variety of intrinsic stabilization features, some of which may contact the cortical bone surfaces of the femur to aid in resisting torsional forces.
Applicants have further discovered that by interchanging and combining several of the intrinsic stabilization features, different results may be achieved, thus allowing a surgeon to adjust the device to the needs of a particular patient by combining several of the intrinsic stabilization features.
Referring now to
It will be appreciated that the femoral prosthetic device 10 of the present invention may generally be separated into two distinct portions, parts or components. Namely, a stem component 11, and a head/neck component 12. The stem component 11 may further be separated into a proximal portion 14, also referred to herein as a proximal body portion or a proximal stem portion, and a distal portion 16, also referred to herein a distal stem portion. It will be appreciated that the proximal portion 14 may comprise approximately twenty-five to fifty percent of the entire stem component 11, while the corresponding distal portion may comprise approximately fifty to seventy-five percent of the entire stem component 11, as illustrated in the FIGS. The head/neck component 12 of the femoral prosthetic device 10 may generally comprise a femoral head component 20, and a neck component 30.
It will be appreciated that the device 10 may have a longitudinal axis, designated by the line A-A, that may be centered with respect to the distal portion 16 of the stem component 11. The axis A-A may also extend centrally between a proximal end 11a and a distal end 11b of the stem component 11. A plane may run through the longitudinal axis A-A and may separate the stem component 11 into an anterior side 18 and a posterior side 19. Accordingly, the axis A-A may delineate the stem component 11 into distinct anterior 18 and posterior sides 19. It will be appreciated that the anterior side 18 and the posterior side 19 of the device 10 may be distinguished by the features of the present invention. Therefore, the device 10 may be manufactured such that each device 10 may be particularly made for being implanted into a left or right femur, to be used as part of a hip replacement.
The femoral head component 20 may act as the ball portion of the ball and socket joint and may be configured and dimensioned to attach to an acetabular bearing surface of an acetabular device, such as an acetabular cup (not illustrated in the figures), which may be used as the socket of the ball and socket joint. The femoral head component 20 may be substantially spherical, as shown, or may be any other suitable shape that is either presently known, or which may become known in the future, in the art for attaching the femoral component to the acetabular bearing surface, and that functions as the ball portion of a ball and socket joint.
It will be appreciated that the femoral head component 20 may be attached to the neck component 30 in a manner known in the art. For example, a distal end 21 of the head component 20 may include an aperture 22, illustrated as dashed lines in
It should be noted that the neck component 30 may be configured as a modular neck 30 or as an integral neck 30 without departing from the scope of the present invention. The modularity of the neck component 30 advantageously creates an ability for the surgeon to fine tune and adjust the femoral prosthetic device 10 by increasing or decreasing the lateral offset relative to the patient's needs. Additionally, the modularity of the neck component 30 may aid the surgeon during a revision surgery without removing the entire stem component 11.
As used herein, the phrase “lateral offset” refers to the horizontal distance relative to a patient in a standing position from the center of the pelvis to the center of the femoral canal in the natural hip joint. In the prosthetic implant 10, “lateral offset” refers to the horizontal distance between a central reference 24 of the femoral head component 20 and the longitudinal axis A-A of the femoral stem component 11 of the implant 10. It will be appreciated that the lateral offset may be increased or decreased by replacing the modular neck 30 with another differently sized modular neck 30, which may be longer or shorter than the modular neck 30 being replaced. Thus, the length of the neck 30 may function to increase or decrease the lateral offset.
Referring now to
It will be appreciated that the double taper may advantageously provide a primary lock, and a secondary lock, should the primary lock fail. Additionally, the features associated with the indexable portion 131 may also provide the surgeon with the added flexibility of assembling and disassembling the device 10 during surgery without removing the stem component 11 from the bone.
As illustrated particularly in
As illustrated in
It will be appreciated that the angle of anteversion θ may be adjusted. For example, as illustrated in
Referring now to
The embodiments of
It should be noted that the outer tapered portion 138 may be modified by one of skill in the art to be of any length, either larger or smaller than illustrated in
As illustrated in
Each of the inner tapered portion 139 and the outer tapered portion 138 may utilize a taper angle relative to the reference axis A′-A′, wherein the taper angle that may be within a range of self-locking tapers, and the self-locking taper of the inner tapered portion 139 and the outer tapered portion 138 may be utilized together or individually without departing from the scope of the present invention. It should be noted that the length of the inner tapered portion 139 may be such that the taper does not bottom out such that a secure connection between the neck component 30 and the stem component 11 may occur. It will be appreciated that the term “bottom out,” as used herein, refers to the condition where the tapered portion 131 of the modular neck component 30, particularly a distal end 139b of the inner tapered portion 139, descends to the lowest point possible in the recess 120 of the stem component 11, which recess 120 may be formed within the proximal portion 14 of the stem component 11, before being fully seated within the recess 120, such that the primary locking fit and the self-locking taper fit does not fully occur. Therefore, it will be appreciated that the best possible connection will not occur when the tapered portion 131 bottoms out in the recess 120.
The inner tapered portion 139 may function to provide a connection with the recess 120 that acts as a primary self-locking taper for locking and securing the neck component 30 to the stem component 11. Whereas, the outer tapered portion 138 may function as a secondary locking taper to secure the neck component 30 to the stem component 11, and may act as an emergency backup to maintain the stem component 11 as part of the femoral prosthetic device 10 such that the stem component 11 does not separate from the rest of the femoral prosthetic device 10, should the primary locking taper fail for any number of reasons. It should be noted that the primary and secondary locks may be modified such that the outer tapered portion 138 provides the primary locking function, while the inner tapered portion 139 provides the secondary locking function without departing from the scope of the present invention. It will be appreciated that the outer tapered potion 138 and the inner tapered portion 139 may each be modified by one of skill in the art to be of any length, either larger or smaller than illustrated in
As illustrated in
It will be appreciated that the recess 120 may be present when the femoral prosthetic device 10 utilizes the modular neck 30, but may not be present when the device 10 utilizes the integral neck 30.
It will likewise be appreciated that the number of first splines 124 of the outer tapered portion 138 and the number of corresponding second splines 122 may also be modified to include more or less first splines 124 and corresponding second splines 122 than illustrated. It will be appreciated that as the number of splines increases or decreases in either the outer tapered portion 138 or the first portion 141 of the recess 120, the opposite and corresponding component's splines will be modified in number accordingly. It will further be appreciated that the outer tapered portion 138 may be modified to remove the first splines 124 such that the outer tapered portion 138 may be substantially smooth, and the first splines 124 may be located on the inner tapered portion 139, for example, without departing from the scope of the present invention. Accordingly, the first sidewall 140 of the recess 120 may also be modified by one of skill in the art by removing the corresponding second splines 122 such that the first sidewall 140 may be a smooth sidewall to matingly engage the smooth outer tapered portion 138. The corresponding second splines 122 may be located, for example, on the second sidewall 142 of the recess 120, and the above and similar modifications are intended to fall within the scope of the present invention.
As stated previously, the corresponding second splines 122 may function as gear teeth having twelve different positions or orientations, denoted by numerals 0-11 situated in a similar position as a standard clock. The differing positions may be established by the first splines 124 of the outer tapered portion 138 and the corresponding second splines 122 of the first sidewall 140. The first splines 124 and the corresponding second splines 122 may matingly engage one another in any one of the twelve positions or orientations, which permits the modular neck 30 to be arranged in a specific orientation such that differing version angles may be achieved. The version angle may be adjusted by removing the modular neck 30 from the recess 120 and rotating the modular neck 30 to the desired orientation creating the desired version angle. It should be noted that the splines and corresponding second splines 122 may be modified by one of skill in the art such that more or less than twelve different positions or orientations, by which the modular neck 30 may be attached to the recess 120, may be achieved and such modifications are contemplated by the present invention.
As mentioned previously, the second sidewall 142 formed within the recess 120 may define a cavity or depression, and may further define the second portion 143. It should be noted that both the first portion 141 and the second portion 143 may be tapered at an angle relative to the neck axis B-B, wherein the taper angle may match the corresponding taper of outer tapered portion 138 and the inner tapered portion 139, respectively, of the modular neck 30, such that the recess 120 and the modular neck 30 may be locked together. Accordingly, the taper angle of the first portion 141 and the second portion 143 may be within a range of taper angles of the self-locking type, and the second portion 143 may provide for the primary fixation of the recess 120 to the modular neck 30, thus connecting the proximal portion 14 to the head/neck component 12 of the device 10.
It will be appreciated that the depth of the second portion 143 of the recess 120 may be dimensioned to be deep enough so as to avoid “bottoming out” of the taper, ensuring that the self-locking taper may fully occur. Whereas, the outer tapered portion 138 of the modular neck 30 may be configured for matingly engaging the first portion 141 of the recess 120 forming a secondary lock or fixation, should the primary lock or fixation fail.
It will be appreciated that the structure and apparatus disclosed herein is merely one example of a positioning means for positioning the modular neck component in multiple selectable orientations within the recess of the stem component, and it should be appreciated that any structure, apparatus or system for positioning the modular neck component in multiple selectable orientations, which performs functions the same as, or equivalent to, those disclosed herein are intended to fall within the scope of a positioning means for positioning the modular neck component in multiple selectable orientations, including those structures, apparatus or systems for positioning the modular neck component in multiple selectable orientations, which are presently known, or which may become available in the future. Anything which functions the same as, or equivalently to, a means for positioning the modular neck component in multiple selectable orientations falls within the scope of this element.
Referring back to
The proximal portion 14 of the present invention may comprise the proximal conical flare 50 and an enlarged proximal body portion 70 configured for filling, at least partly, the metaphyseal cavity in the femur. As illustrated, the proximal conical flare 50 may be located proximally on the proximal portion 14 of the stem component 11. Specifically, the proximal conical flare 50 may be formed near the proximal end 11a of the stem component 11, as illustrated in
As illustrated in
The proximal conical flare 50 may further have a surface 56 that tapers at an angle relative to a line C-C (the line C-C being parallel to the longitudinal axis A-A) forming a posterior flare 57 that may be located proximally on the posterior side 19 of the stem component 11 such that the proximal conical flare 50 may fill at least a portion of a cavity in the bone. It will be appreciated that the posterior flare 57 may be formed from about one to about twenty percent of the entire stem component 11 on the upper most portion of the proximal portion 14. For example, applicants have found that the posterior flare 57 that comprises about four to ten percent of the entire stem component 11 to be useful, and particularly about four to six percent. The surface 56 of the posterior flare 57 may have a flare angle relative to the line C-C that is parallel to the longitudinal axis A-A, represented by γ, that may be between the range of about fifteen degrees to about forty-five degrees. For example, applicants have found that the surface 56 having a flare angle γ between the range of about twenty degrees to about forty degrees to be advantageous, and more specifically, applicants have found that a flare angle γ of thirty degrees to be advantageous.
In addition to the above range of angles for surface 56, the flare angle γ may, for example, be about fifteen degrees, or about sixteen degrees, or about eighteen degrees, or about twenty degrees, or about twenty-two degrees, or about twenty-four degrees, or about twenty-six degrees, or about twenty-eight degrees, or about thirty degrees, or about thirty-two degrees, or about thirty-four degrees, or about thirty-six degrees, or about thirty-eight degrees, or about forty degrees, or about forty-two degrees, or about forty-four degrees, or about forty-five degrees.
The posterior flare 57 may be configured and dimensioned to maintain the necessary wall thickness for increased fatigue value of the proximal conical flare 50. It will be appreciated that as the size of the stem component 11 increases, the angle of surface 56 may decrease to maintain the desired wall thickness. Likewise, as the size of the stem component 11 decreases, the angle of surface 56 may increase to maintain the desired wall thickness.
It will be appreciated that the femur comprises isoelastic properties, such that it will readily expand and contract. Accordingly, the proximal conical flare 50 may be configured to micro settle or micro subside into a position of stability as expansion and contraction of the femur occurs. As the proximal conical flare micro settles or subsides it will produce a compression load such that the proximal conical flare 50 may aid in transferring unnatural hoop stresses exerted on the device 10 into more natural compressive loads. It will further be appreciated that the conical features of the present invention, whether a conical proximal portion 14, or the rounded contour or rounded shape of the proximal conical flare 50, may provide a mechanism that may fit and fill the proximal cavity of the femur and that will not “hang up” on any portion of the cortical bone, or will not prematurely stabilize on a portion of the conical bone. Premature stabilization may result in aseptic loosening of the device 10, which may cause the device 10 to fail. Therefore, the conical features of the present invention may avoid aseptic loosening and provide for a device 10 that will not prematurely stabilize within the cavity of the bone by being hung up on the cortical bone. Accordingly, the conical proximal flare 50 may stabilize into a position of stability within the cavity.
It will be appreciated that the proximal conical flare 50 may further be comprised of a top surface 52 as illustrated. The proximal conical flare 50 may be tapered and have a symmetrical taper ratio per each side of the proximal conical flare 50. It will be appreciated that the taper ratio may be calculated by one of skill in the art having possession of this disclosure without undue experimentation.
As the stem component 11 micro subsides into its position of stability over time, it is possible that the entire stem 11 may settle several millimeters within the cavity. In such a case, the modular neck component 30 of the present invention advantageously permits a surgeon the opportunity to go back to the surgical site and replace one modular neck component 30 with another longer modular neck component 30 without interrupting the interface between the femur and the stem component 11, such that joint laxative and potential dislocation may be avoided. Therefore, the modularity of the neck component 30 allows for some potential correction in the hip joint of the device 10 with minimal disruption to the device 10.
It will be appreciated that in a natural femur stress is loaded from the outside in, whereas in a prosthetic femoral component stress is loaded from the inside out. One aspect of the device 10 of the present invention may be to transmit the forces to the outer, harder cortical bone as opposed to the inner, softer cancellous bone. The conical or bowl shaped contour of the proximal conical flare 50 of the present invention advantageously provides compressive loads, as opposed to hoop loads, and allows finite subsidence of the proximal conical flare 50 to a more stable position, as well as stabilizing the stem component 11 of the device 10 within the prepared medullary cavity. Therefore, as stresses are placed on the device 10, the proximal conical flare 50 may direct and transmit the forces to the outer cortical bone, such that the forces may be evenly distributed through the entire bone. As the proximal conical flare 50 subsides into the more stable position, the lateral offset of the device 10 may change. Advantageously, the modularity of the neck 30 allows for the adjustment of the lateral offset as described above by changing the length of the modular neck 30, thus restoring the lateral offset to more accurately simulate the biomechanics of the natural femur.
As mentioned previously, the proximal portion 14 may also include the anterior metaphyseal tapering flare 80 (illustrated best in
The anterior metaphyseal tapering flare 80 may also comprise an enlarged portion 81 that protrudes from the anterior side 18 of the proximal portion 14, and configured as an anatomical body to engage the cortical bone to thereby transfer stress from the device to the bone. The anterior metaphyseal tapering flare 80 may further comprise a surface 82. The surface 82 may taper at an angle relative to a line D-D parallel to the longitudinal axis A-A, designated as α, the taper angle α being within a range of about ten degrees to about twenty degrees. For example, applicants have found a taper angle α of about twelve to about eighteen degrees to be a useful taper angle for the surface 82, and more specifically a range of about fourteen degrees to about sixteen degrees. In addition to the above range of angles for surface 82, the taper angle α may, for example, be about ten degrees, or about twelve degrees, or about fourteen degrees, or about sixteen degrees, or about eighteen degrees, or about twenty degrees.
It will be appreciated that the surface 82 may begin tapering, at the taper angle α listed above, from the proximal end 11a of the stem component 11 distally toward the distal end 11b of the stem component 11 for approximately one-half the length of the entire proximal portion 14 of the stem component 11. It will be appreciated that the length of the surface 82 may be modified to be greater than or less than one-half the length of the proximal portion 14, without departing from the scope of the present invention.
As illustrated best in
It will be appreciated that the anterior metaphyseal tapering flare 80 may be configured for contacting and filling, at least a portion of, the proximal metaphyseal cavity of the proximal femur such that the anatomical features found on the proximal femur may be contacted by the anterior metaphyseal tapering flare 80. Thus, the anterior metaphyseal tapering flare 80 may contact at least a portion of the anterior cortex of the femur providing solid contact with the harder cortical bone to aid in distributing stresses placed on the device 10, and to increase resistance to torsional loads. It will be appreciated that the contact between the cortical bone and the anterior metaphyseal tapering flare 80 may also increase the stability of the entire device 10.
It should be noted that the anterior metaphyseal tapering flare 80 may be used in conjunction with the other aspects of the invention described herein, or the anterior metaphyseal tapering flare 80 may be used alone. For example, the anterior metaphyseal tapering flare 80 may be used in conjunction with the proximal conical flare 50 to provide maximum torsional load resistance and to provide increased intrinsic stability to the device 10. It will be appreciated that the anterior metaphyseal tapering flare 80 may be used in conjunction with any of the features of the present invention, and is not limited to being used with only the proximal conical flare 50.
The proximal portion 14 of the stem component 11 may also comprise a tapered exterior surface 75 (illustrated best in
As mentioned previously, the tapered exterior surface 75 of the proximal portion 14, in one embodiment, may lead into a tapered exterior surface 76 of the distal portion 16 of the stem component 11 (illustrated best in
As illustrated in
As illustrated in
Additionally, the distal portion 16 of the stem component 11 may comprise at least one flute 43 for increasing torsional resistance. It will be appreciated that the at least one flute 43 may extend along the entire length of the distal portion 16, or the at least one flute 43 may extend along only part of the distal portion 16 without departing from the scope of the present invention. The at least one flute may be utilized to contact an inner surface of the medullary canal of the femur to thereby anchor the distal portion 16 of the stem component and to stabilize the device 10, thus resisting torsional forces that act on the femur.
It will be appreciated that one of the many challenges facing the surgeon in a hip replacement procedure is inhibiting what is referred to in the field as thigh pain. The everyday, repetitive movements that cause the leg to bend and twist introduce a substantial amount of stress in the femur, a large portion of which is transmitted through the inner core of the soft, cancellous bone, which has a larger degree of flexibility than the harder, cortical bone. It will be appreciated that if the stem component 11, and particularly the distal portion, is less flexible than the portion of the inner core of cancellous bone that it replaces, less stress will be distributed through the normal stress paths of the femur. Instead, the stress finds alternative, abnormal distribution paths though the thigh, thereby causing thigh pain.
The challenge in reducing thigh pain is heightened by the fact that the stem component 11 must have enough strength to withstand the normal torsional, bending and tension forces introduced thereto by the hip joint. Although materials have been developed in an attempt to accommodate all of these forces and stress transfers, the problem of thigh pain still remains. The coronal slot 60 was introduced to impart a limited degree of flexibility to the distal portion 16 of the stem component 11. As force is applied to the femur, the coronal slot 60 may allow the distal portion of the stem component 11 to compress somewhat to decrease some of the alternative stress distribution, thereby reducing thigh pain somewhat. Therefore, the coronal slot 60 may function to impart a limited degree of flexibility to the distal portion 16 of the stem component 11 and to the device 10 as a whole.
The coronal slot 60 is illustrated in
Referring now to
Referring now to
The stem component 11 may comprise, whether a hybrid stem or not, a rough surface 116 located on the proximal portion 14 of the stem component 11 for increasing the interdigitation between bone or bone cement and the proximal portion 14, to thereby increase the strength of the fixation. It will be appreciated that the rough surface 116 may be created using different materials depending upon the application, whether a cementless application is used or a hybrid cemented application is used. Examples of the materials that may be used to create the rough surface finish on the proximal portion 14 include matte, porous, HA, porous HA, combinations thereof, or beads, or other finishes.
In the hybrid cemented application, a coating of beads, for example 0.5 mm in size, that have been bead blasted onto the surface of the proximal portion 14 may be used to increase the surface area of the proximal portion 14, thereby increasing the interdigitation between the bone, the bone cement, and the proximal portion 14 of the stem component 1, such that a more secure proximal fixation of the stem component 11 to the bone may be achieved.
It should be noted that the roughness and method of applying the surficial roughness to the proximal portion 14 may be as described above, or the rough surface 116 may be corrugated or any other mechanism for producing a roughened surface to provide increased surface area. The method for manufacturing the surficial roughness may include any method presently known, or which may become known in the future, in the art for adding a surficial roughness to the proximal portion 14 of the stem component 11. Additionally, the material, design and shape used to create the roughness may be modified by one of skill in the art using any suitable material, design and shape presently known, or which may become known, in the art for increasing the surface area and interdigitation of the proximal portion 14 of the stem component 11. It will be appreciated that other components or parts of components may also have the rough surface finish, such as the neck component 30. Further, the area that the roughness comprises on the stem component 11 or neck component 30 may vary depending upon the desired outcome, which can be determined by one of skill in the art.
Additionally,
In the hybrid stem component 11 of
In the hybrid stem component 11 of the present invention, the basic concept may comprise a custom fit and fill in the proximal portion 14 of the stem component 11 in the proximal metaphyseal cavity of the femur, such that the proximal portion 14 of the stem component 11 and the bone cement may fill the variable proximal metaphyseal shape of the proximal femur. Conversely, the distal portion 16 of the stem component 111 may be press-fit, and not cemented, into the distal portion of the cavity or canal in the proximal femur such that the stem component 11 may be removed during a revision surgery with minimal bone disruption distally, should removal become necessary.
Referring now to
As illustrated in
Practically, the process of implanting the hybrid stem component 11 may include the following. First, insert the stem component 11 about half-way into the metaphyseal cavity so that the distal portion 16 sits essentially within the metaphyseal cavity with the top of the restrictor 115 being readily accessible. Second, add a viscous bone cement to the metaphyseal cavity to fill the cavity. Last, continue to insert the stem component 11 into the cavity until the proximal portion 14 of the stem component 11 may be securely seated therein. Thus, the proximal portion 14 may be seated within the cavity and surrounded by bone cement, whereas the distal portion 16 may be press-fit into the cavity securing the stem component 11 to the bone.
Regarding the hybrid stem component 11, applicants have found that the stem component 11 manufactured from cobalt-chromium alloy material, because of its stiffness, will not put the same amount of stress on the interface between the stem component 11 and the cement mantle as a titanium alloy stem component 11. Accordingly, the hybrid stem component 11 utilizes the advantages of cobalt-chromium alloy, which is the material of choice in cemented applications, to interface with the bone cement on the proximal portion 14 to thereby reduce the stress placed on the cement mantle interface. Accordingly, the hybrid stem component 11 may be manufactured from cobalt-chromium alloy to increase the chances of clinical success.
Referring now to
Referring now to
It will be appreciated that the type of material used to manufacture the device 10 as a whole, and each of the component parts may affect the interface between the device 10 and the bone, or bone cement in some embodiments. Accordingly, several different materials may be utilized by the present invention, including metal, such as titanium, stainless steel, cobalt-chromium-molybdenum alloy, titanium-aluminum vanadium alloy, or other alloys thereof. It will further be appreciated that the properties of various metals differ with respect to their relative hardness, tensile strength, and yield strength. For example, according to ASTM designation: F136-98, forged titanium-6aluminum-4vanadium alloy has a tensile strength of 125.000 psi and a minimum yield strength of 115.000 psi (hereinafter referred to as “forged titanium”). While forged cobalt-28chromium-6 molybdenum alloy has a tensile strength of 170.000 psi, and a yield strength of 120.000 psi, according to ASTM designation: F799-99 (hereinafter referred to as “forged cobalt-chromium”). Additionally, cast cobalt-28chromium-6 molybdenum alloy has a tensile strength of 95.000 psi and a yield strength of 65.000 psi, according to ASTM designation: F75-98.
It will be appreciated that one of the many factors in choosing a material to design an artificial hip device is the tendency for the device to corrode, particularly at modular taper fitting sites, where crevice corrosion may occur. According to an article by M. Viceconti et al., “Design-related fretting wear in modular neck hip prosthesis,” Journal of Biomedical Materials Research, Vol. 30, 181-186 (1996), traditionally, forged titanium has been used in the industry to combat the results of corrosion with relative success. The success of forged titanium is due, at least in part, to the very thin layer of titanium oxide that covers the whole surface of the implant, under normal conditions. The titanium oxide layer's chemical properties protects the forged titanium even in very harsh conditions, such as those found in a human body. However, even with forged titanium, modular sites and taper fitting sites may be subject to corrosion due to: (1) the abrasion of the forged titanium causing damage to the protective layer causing fretting corrosion, and (2) the small volumes of fluid that may be trapped causing crevice corrosion.
Additionally, “notch sensitivity” may also induce undesirable corrosion and cracking, as the minor nicks, and cracks in the implant may induce further corrosion, cracking and wear as the harsh conditions of the human body act on the implant. As modular forged titanium prostheses have become standard in the orthopedic industry, the occurrence of corrosion of forged titanium implants has increased. Accordingly, to minimize or reduce corrosion, applicants have used forged cobalt-chromium, which stress shields the bone more effectively than forged titanium due to its stiffer properties, in prosthetic components, including modular neck components 30 and stem components 11, to aid in the reduction of corrosion and other problems associated with modular junctions using forged titanium.
Forged cobalt-chromium is a metal that has a higher tensile strength and higher yield than forged titanium. As such, forged cobalt-chromium is stiffer than forged titanium, and therefore absorbs more load and is able to distribute the stress placed on the device 10 over a larger area than forged titanium. Accordingly, the device 10, made of forged cobalt-chromium, may not impose as much stress on the cement implant interface than a device 10 made of forged titanium thereby reducing aseptic loosening of the stem.
However, it has been demonstrated that forged titanium has significant biocompatible properties that permits bone to grow around and even into the forged titanium. Accordingly, forged titanium has been used extensively in the orthopedic industry not only for cementless stem applications, but also in cemented stem applications.
Reference will now to made to
As illustrated in
It will be appreciated that the busing insert 200 may comprise the structural features present in the recess 120 as described in connection with earlier embodiments, leaving the recess 120 essentially free of those components. For example, the bushing insert 200 may comprise its own recess 210, which may comprise a first portion 241 defined by a first sidewall 241a, and a second portion 243 defined by a second sidewall 243a, which are similar to the first portion 141 and the second portion 143 of the recess 120. Accordingly, the first portion 241 may include a corresponding second splines 222 for matingly engaging the first splines 124 of the outer tapered portion 138 of the modular neck component 30 so that the modular neck component 30 may be indexed within the bushing insert 200, which indexing is described more fully above in connection with
It will be appreciated that the bushing insert 200 and the recess 120 may both be shaped similarly. In each of the embodiments containing the bushing insert 200 and the recess 120, the shape of the bushing insert 200 and recess 120 may be any suitable shape known in the art. For example, the bushing insert 200 and corresponding recess 120 may be circular or oval; or triangular, square, hexagonal or any other polygonal shape, which may be utilized as the shape for the bushing insert 200 and recess 120.
The bushing insert 200 may be configured and dimensioned to seat within the recess 120, and the bushing insert 200 may be attached to the recess 120 by any one of the following locking mechanisms: (1) a taper lock, or taper press-fit; (2) a mechanical interlock; or (3) a press-fit lock.
Referring particularly to
Additionally, the taper angle A of the outer wall 202 and the inner sidewall 120a may taper at an angle between a range of about one degree to about three degrees per side for forming a taper press-fit. For example, the taper angle A may be between one and two degrees. The outer wall 202 and the inner sidewall 120a may matingly engage one another by way of a taper press-fit, wherein the bushing insert 200 may be slightly larger than the recess 120. Accordingly, the outer wall 202 may contact the inner sidewall 120a creating an intimate taper press-fit.
Referring now to
It will be appreciated that the key 220, keyway 205, and notch 221 may all be modified to include various shapes and designs known to those of ordinary skill in the art for forming a mechanical interlock between two components, and such shapes and designs are intended to fall within the scope of the present invention. Additionally, it will be appreciated that other mechanical interlocks may be utilized by the present invention. For example, the bushing insert 200 may be mechanically interlocked with the recess 120 by twisting the bushing insert 200 a quarter twist within the recess 120 mechanically engaging portions from the bushing insert 200 and recess 120 forming an interference fit.
Referring now to
It will be appreciated that the outer wall 202 and the upper wall surface 202a of the bushing insert 200 of
It will be appreciated that the friction press-fit and associated contact between surfaces may occur along a majority of those surfaces, forming a very strong connection. Thus, the press-fit may occur between two corresponding surfaces, namely between: (1) the upper wall surface 202a and the second inner sidewall 120b, and (2) the outer wall 202 and the first inner sidewall 120a. It will be appreciated that the press-fit lock designed to lock the bushing insert 200 to the recess 120 may also be formed between only one of the corresponding surfaces listed above (either (1) or (2)), and a press-fit occurring in two separate locations is not required. Accordingly, either press-fit taken alone may function to lock the bushing insert 200 to the recess 120, without departing from the scope of the present invention.
Applicants have conceived of a device 10 that may minimize the problems associated with forged titanium at the modular junctions, i.e. between the neck component 30 and the recess 120 in the stem component 11, by taking advantage of the mechanical properties of both forged titanium and forged cobalt-chromium. It will be appreciated that the head component, the neck component 30, the stem component 11, and the bushing insert 200 may each be manufactured from either forged cobalt-chromium, cast cobalt-chromium, or forged titanium, or any combination thereof without departing from the scope of the present invention. However, applicants have discovered that loads placed on the neck/stem junction may be effectively distributed and the results of fatigue, and problems associated with the fatigue of forged titanium and cast cobalt-chromium, may be minimized by using a stem component 11 manufactured from either forged titanium or cast cobalt-chromium, and a modular neck component 30 and bushing insert 200 manufactured from forged cobalt-chromium.
It will be appreciated that because of the forged cobalt-chromium material, the forces acting on the modular neck component 30 may be effectively and evenly distributed to the bushing insert 200. The bushing insert 200, having a greater surface area than the neck component 30, may further distribute the forces through the forged titanium stem component 11. The stem component 11 comprises a large surface area and thereby distributes the remaining stress through to the bone. Therefore, the bushing insert 200 may protect the forged titanium stem component 11 at the junction of the stem/neck from stress, such that the forged titanium will not encounter the same level of stress. Accordingly, the forged titanium stem component 11 may be subject to less force, such that there is less of a chance the stem component 11 will experience damage.
The forged cobalt-chromium bushing insert 200 may also reinforce the junction between the neck component 30 and the recess 120 of the stem component 11 such that there is a junction comprising forged cobalt-chromium on forged cobalt-chromium, which is a stronger connection than an all forged titanium connection. Therefore, the bushing insert 200 may effectively act as a fatigue reinforcer and as a load distributor to protect the stem component 11 from damage.
Referring now to
As illustrated in
It should be noted that each of the above-described components may be used in conjunction with one another or in a combination with other specific features to create a device 10 that may be specifically tailored to the anatomical needs of each patient. For example, referring to
In accordance with the features and combinations described above, a useful method of implanting a femoral prosthetic implant into a patient's hip joint by a surgeon includes the steps of:
(a); reaming a hole in a femur to expose the medullary canal of said femur;
(b) ascertaining the anatomy of the patient;
(c) determining the combination of intrinsic features to be used to simulate the anatomy of the femur and to resist torsional loads increasing the intrinsic stability of the device, including the following features: (i) a modular, indexable neck; (ii) an appropriate angle of anteversion; (iii) a proximal conical flare having a rounded bottom contour; (iv) an anterior metaphyseal tapering flare; (v) a straight stem; (vi) a curved stem; (vii) a straight coronal slot; and (viii) a helical slot;
(d) selecting an appropriate device having the appropriate combination of features; and
(e) implanting said device into the medullary canal.
In accordance with the features and combinations described above, another useful method of implanting a femoral prosthetic implant into a patient's hip joint includes the steps of:
(a) exposing an opening in a patient's medullary canal of a femur;
(b) selecting a device having a combination of intrinsic stabilizing features including: (i) a modular, indexable neck; (ii) an appropriate angle of anteversion; (iii) a proximal conical flare having a rounded bottom contour; (iv) an anterior metaphyseal tapering flare; (v) a straight stem; (vi) a curved stem; (vii) a straight coronal slot; and (viii) a helical slot, said device further having a head portion, a proximal portion and a stem component; and
(c) positioning the stem component within the medullary canal such that the proximal portion substantially fills the opening of the medullary canal.
Those having ordinary skill in the relevant art will appreciate the advantages provide by the features of the present invention. For example, it is a potential feature of the present invention to provide a femoral prosthetic device which is simple in design and manufacture. Another potential feature of the present invention is to provide such a femoral prosthetic device that is capable of increasing the resistance to the torsional loads that are placed upon the prosthetic device in the femur. It is another potential feature to provide optimum solid contact with the anterior cortical bone, while at the same time substantially filling the metaphyseal area of the femur. It is a further potential feature of the present invention to provide solid cortical contact in the femur without removing cortical bone in the posterior wall region of the femur.
It is yet another potential feature of the present invention to provide a bushing insert that may be located within the recess of the stem component, thereby acting as a stress distributor and a fatigue reinforcer. Is another potential feature of the present invention to provide a modular neck component having indexable capability and that further provides a double taper lock. It a potential feature to provide a stem component having one or more of the following features: a proximal conical flare, an anterior metaphyseal tapering flare, a coronal slot, a sagittal slot, a helical slot, a tapering distal stem portion, a straight distal stem portion, and a curved distal stem portion.
In the foregoing Detailed Description, various features of the present disclosure are grouped together in a single embodiment for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the following claims are hereby incorporated into this Detailed Description by this reference, with each claim standing on its own as a separate embodiment of the present disclosure.
It is to be understood that the above-described arrangements are only illustrative of the application of the principles of the present invention. Numerous modifications and alternative arrangements may be devised by those skilled in the art without departing from the spirit and scope of the present invention. Thus, while the present invention has been shown in the drawings and described above with particularity and detail, it will be apparent to those of ordinary skill in the art that numerous modifications, including, but not limited to, variations in size, materials, shape, form, function and manner of operation, assembly and use may be made without departing from the principles and concepts set forth herein.
This application is a continuation of co-pending U.S. patent application Ser. No. 10/405,065, filed Mar. 31, 2003, entitled “INTRINSIC STABILITY IN A TOTAL HIP STEM,” which claims the benefit of U.S. Provisional Application No. 60/442,188, filed Jan. 22, 2003. Co-pending U.S. patent application Ser. No. 10/405,065 is a continuation-in-part application of U.S. patent application Ser. No. 10/244,149, filed Sep. 13, 2002, entitled “DIFFERENTIAL POROSITY PROSTHETIC HIP SYSTEM,” which claims the benefit of U.S. Provisional Application No. 60/372,390, filed Apr. 12, 2002. U.S. patent application Ser. No. 10/405,065, is a continuation-in-part application of U.S. patent application Ser. No. 09/505,876, filed Feb. 17, 2000, entitled “MODULAR NECK FOR FEMUR REPLACEMENT SURGERY,” now U.S. Pat. No. 6,464,728, which is a continuation-in-part application of U.S. patent application Ser. No. 09/059,698, filed Apr. 14, 1998, now abandoned. All of the above mentioned applications are hereby incorporated by this reference herein in their entireties, including but not limited to those portions that specifically appear hereinafter, the incorporation by reference of all applications being made with the following exception: In the event that any portion of the above-referenced applications is inconsistent with this application, this application supercedes said portion of said above-referenced applications.
| Number | Date | Country | |
|---|---|---|---|
| 60442188 | Jan 2003 | US | |
| 60372390 | Apr 2002 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10405065 | Mar 2003 | US |
| Child | 11589037 | Oct 2006 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 10244149 | Sep 2002 | US |
| Child | 11589037 | Oct 2006 | US |
| Parent | 09505876 | Feb 2000 | US |
| Child | 10405065 | US | |
| Parent | 09059698 | Apr 1998 | US |
| Child | 09505876 | Feb 2000 | US |
