Patent Application
20080167723
1. Field of the Invention
The present invention relates to prosthetic hip implant components, which generally include a hip stem for implantation in the proximal femur and an acetabular cup for implantation in the acetabulum. In particular, the present invention relates to prosthetic hip stems and acetabular cups which include improved features designed to achieve more optimized outcomes with certain types of patient anatomy, such as the anatomy of female patients and/or patients having osteoporosis.
2. Description of the Related Art
Orthopedic implants are commonly used to replace some or all of a patient's hip joint in order to restore the use of the hip joint, or to increase the use of the hip joint, following deterioration due to aging or illness, or injury due to trauma. In a hip replacement, or hip arthroplasty procedure, a femoral component is used to replace a portion of the patient's femur, including the femoral neck and head. The femoral component is typically a hip stem, which includes a stem portion positioned within the prepared femoral canal of the patient's femur and secured via bone cement, or by a press-fit followed by bony ingrowth of the surrounding tissue into a porous coating of the stem portion. The hip stem also includes a neck portion adapted to receive a prosthetic femoral head. The femoral head is received within a prosthetic acetabular component, such as an acetabular cup received within the prepared recess of the patient's acetabulum.
One known hip stem includes a core formed of either a cobalt-chromium-molybdenum alloy or titanium, and a porous surface layer in the form of a matrix of small metallic beads or a wire mesh. Typically, the porous surface layer is sintered to the core by heating the core and the porous surface layer to a high temperature in order to cause the porous surface layer and core to fuse, melt, or bond together along their interface. U.S. Pat. Nos. 6,395,327, 6,514,288, and 6,685,987, each assigned to the assignee of the present invention and hereby incorporated by reference, disclose various methods of enhancing the fatigue strength and the connection between the core and the porous surface layer of the foregoing types of hip stems.
Some medical device manufacturers may manufacture a single custom implant prosthesis to accommodate the anatomy of a specific patient. Also, although prosthetic hip implants in a line of mass manufactured prostheses are provided in a range of varying sizes and are selected by surgeons to best fit the anatomy of a particular patient, improvements in the design of prosthetic hip implants are desired.
The present invention provides prosthetic hip stems for use in prosthetic hip joints and, in particular, provides prosthetic hip stems that are designed to achieve more optimized outcomes with certain types of patient anatomy, such as the anatomy of female patients and/or patients having osteoporosis. Each hip stem in a family or set of hip stems has diaphyseal width, metaphyseal width, offset, and head height dimensions. In a set of hip stems of increasing nominal size, the diaphyseal width dimension increases substantially non-proportionally to the corresponding increase of the metaphyseal width, offset, and head height dimensions, thereby providing a family or set of hip stems that is particularly adapted for patients having osteoporosis, in which the cortical bone of the diaphysis of the femur becomes thinner with progression of the osteoporosis.
In one form thereof, the present invention provides a set of prosthetic hip stems, including a plurality of hip stems of increasing nominal size, each hip stem having a distal width dimension x between 12 and 21 mm; the hip stems each having a metaphyseal width dimension y1 defined as a function of x falling within a conceptual boundary defined between the following lines: y1=0.053x+19.17 and y1=0.031x+24.61; the hip stems each having an offset dimension y2 defined as a function of x falling within a conceptual boundary defined between the following lines: y2=31 and y2=1.46x+19.86; and the hip stems each having a head height dimension y3 defined as a function of x falling within a conceptual boundary defined between the following lines: y3=0.57x+10.54 and y3=1.21x+11.82.
In another form thereof, the present invention provides a set of prosthetic hip stems, including a plurality of hip stems of increasing nominal size, each hip stem having a distal width dimension x between 13 and 18 mm, the hip stems each having a metaphyseal width dimension y1 defined as a function of x falling within a conceptual boundary defined between the following lines: y1=0.053x+19.17 and y1=0.031x+24.61; the hip stems each having an offset dimension y2 defined as a function of x falling within a conceptual boundary defined between the following lines: y2=31 and y2=1.46x+19.86; and the hip stems each having a head height dimension y3 defined as a function of x falling within a conceptual boundary defined between the following lines: y3=0.57x+10.54 and y3=1.21x+11.82.
In a further form thereof, the present invention provides a set of prosthetic hip stems, including a plurality of hip stems of increasing nominal size, each hip stem having a distal width dimension x between 13 and 18 mm; the hip stems each having an offset dimension y1 defined as a function of x falling within a conceptual boundary defined between the following lines: y1=31 and y1=1.46x+19.86.
In another form thereof, the present invention provides a set of prosthetic hip stems, each hip stem having a metaphyseal width dimension and a uniform cross section along between 35% and 65% of a distance between said metaphyseal width dimension and a distal end of said hip stem.
The above-mentioned and other features of this disclosure, and the manner of attaining them, will become more apparent and will be better understood by reference to the following description of embodiments taken in conjunction with the accompanying drawings, wherein:
Corresponding reference characters indicate corresponding parts throughout the several views. The exemplifications set out herein illustrate embodiments of the disclosure, and such exemplifications are not to be construed as limiting the scope of the invention in any manner.
Referring to
Referring particularly to
Core 36 may be made from a cobalt-chromium-molybdenum alloy or a titanium alloy, for example, via a forging or casting process, followed by machining to achieve a desired shape or profile. Polymer matrix layer 38 may be formed of an inert polyaryletherketone (“PAEK”) polymer such as, for example, polyetheretherketone (“PEEK”). Porous metal layer 40 may be a metal wire mesh of titanium fibers, or alternatively, may also comprise a metal bead matrix or other porous metal structures produced in accordance with Trabecular Metal™ technology of Zimmer, Inc. of Warsaw, Ind., for example.
Hip stem 20 may be manufactured as follows. First, core 36 is forged, followed by machining core 36 after forging to form a desired shape or profile for core 36. Core 36 is then grit blasted to sufficiently roughen its surface, and then is heat treated to facilitate polymer flow across core 36 during the injection molding process. Thereafter, core 36 is positioned within an injection molding machine with stem portion 22 of core 36 positioned within porous metal layer 40, with a gap provided therebetween. Thereafter, polymer matrix layer 38 is injected into the space between core 36 and porous metal layer 40 through suitable gates, with polymer matrix layer 38 permeating into porous metal layer 40 and into the surface of stem portion 22 of core 36 via grooves 52, dimples 56, ridges 58, and/or flats 60. Upon cooling of polymer matrix layer 38, porous metal layer 40 is firmly bonded or secured to stem portion 22 of core 36. Advantageously, core 36 is not subjected to a sintering process to apply porous metal layer 40, thereby maintaining the fatigue strength of core 36.
Referring to
Referring to
Referring to
Although version indicator feature 48 is shown herein as bump or protrusion 50, other tactile elements may be used, such as a recess, a group of recesses, or a ridge or a group of ridges, for example, in medial side 34 of neck portion 24 of hip stem 20, or at another location or locations on neck portion 24 of hip stem 20.
Referring to
Referring to
Still referring to
As discussed in further detail below, the present inventors have developed a number of improvements to hip stems and acetabular cups in order to provide more optimized results with certain types of patient anatomy, such as female anatomy.
The hip stems and acetabular cups described herein may be implanted according to surgical techniques described in U.S. Pat. No. 6,676,706, issued Jan. 13, 2004; U.S. Pat. No. 6,860,903, issued Mar. 1, 2005; U.S. Pat. No. 6,953,480, issued Oct. 11, 2005; U.S. Pat. No. 6,991,656, issued Jan. 31, 2006; abandoned U.S. patent application Ser. No. 10/929,736, filed Aug. 30, 2004; currently pending U.S. patent application Ser. No. 10/952,301, filed Sep. 28, 2004; currently pending U.S. patent application Ser. No. 11/235,286, filed Sep. 26, 2005; and currently pending U.S. patent application Ser. No. 11/105,080, filed Apr. 13, 2005, all titled METHOD AND APPARATUS FOR PERFORMING A MINIMALLY INVASIVE TOTAL HIP ARTHROPLASTY and all assigned to the assignee of the present application, the disclosures of which are hereby expressly incorporated herein by reference.
Known hip stems typically have an anteversion angle between the neck portion of the hip stem and the anatomical medial/lateral plane of from 1 to 12 degrees, for example. The present inventors have observed that for many patients, particularly certain female patients, a greater anteversion angle between the neck portion of the hip stem and the anatomical medial/lateral plane, and/or an anteversion angle between the femoral head portion and the neck portion of the hip stem, would provide more optimum anatomical benefits.
Referring to
In order to facilitate greater anteversion, hip stem 20 may include a neck portion 24 which is angled with respect to the anatomical medial/lateral plane 61. For example, hip stem 20 is shown in an anteversion alignment in solid lines in
Referring to
Each neck portion 80 is oriented in an alignment which is anteriorly angled with respect to stem portion 72 from a neutral version as defined by medial/lateral plane 76. For example, as shown in
Referring to
In particular, the recess 88 of each modular femoral head 84 defines a central axis 86 which is offset from the center of head 84 and from central axis 68 of neck portion 24 such that recess 88 of each head 84 is eccentric with respect to the center of the head 84. Central axis 86 may be angled anteriorly with respect to central longitudinal axis 68 of neck portion 24 such that each modular femoral head 84 is offset from central longitudinal axis 68 upon assembly. For example, modular femoral head 84a may be angled approximately 5° anteriorly with respect to longitudinal axis 68, i.e., central axis 86a of femoral head 84a defines a 5° angle with axis 68. In another embodiment, femoral head 84b may be angled approximately 10° anteriorly with respect to longitudinal axis 68, i.e., central axis 86b of femoral head 84b defines a 10° angle with axis 68. In yet another embodiment, femoral head 84c may be angled approximately 15° anteriorly with respect to longitudinal axis 68, i.e., central axis 86c of femoral head 84c defines a 15° angle with axis 68. In a modular system, a plurality of femoral heads 84 may be provided wherein the angle between central longitudinal axis 68 and axis 86 of same may vary from approximately 1° to 25° or more and, in particular, may be as small as 1°, 3°, 5°, and as large as 21°, 23°, or 25° or more, for example, or any angle therebetween. As discussed above, a larger anteversion angle between the femoral head and the neck portion may provide more optimum anatomical benefits in certain patient, including certain female patients.
Referring to
As shown in
Stem portion 72 defines an anatomical medial/lateral plane 91, neck portion 80 defines central longitudinal axis 79, and modular femoral head 84 defines central axis 86. Advantageously, a surgeon may choose any combination of modular components to ensure an adequate degree of anteversion is included in hip stem 90. For example, as shown in
The angle between the neck and the shaft of the femur in certain patients, including many female patients, is typically more varus than the angle between the neck and the shaft of the male femur which is relatively more valgus. Known hip stems are not shaped with a sufficiently varus neck/shaft angle which would provide optimum results in certain female patients. Also, in order to accommodate a hip stem having a more varus neck/shaft angle without the need to lengthen leg length, it is typically necessary to osteotomize a greater portion of the metaphysis of the femur in female patients than in male patients. Specifically, in certain females, the femur is osteotomized at a location near the lesser trochanter. This results in less of the metaphysis being available for hip stem fixation in many female patients as compared to male patients, thereby increasing the importance of diaphyseal fixation of the hip stem in female patients.
Referring to
Referring to
If a surgeon desires a larger neck/shaft angle, modular neck portion 120b may be chosen which defines central longitudinal axis 116b which forms an angle of approximately 120° with axis 111 and an angle of approximately 10° with central longitudinal axis 116a, i.e., a +10° change in neck/shaft angle from modular neck portion 120a. If a surgeon desires a smaller neck/shaft angle, modular neck portion 120c may be chosen which defines central longitudinal axis 116c which forms an angle of approximately 90° with axis 111 and an angle of approximately 20° with central longitudinal axis 116a, i.e., a −20° change in neck/shaft angle from modular neck portion 120a. Various values for the neck/shaft angle may be chosen depending on the varus/valgus anatomy of a particular patient. For example, the neck/shaft angle may range from approximately 90° to approximately 145°, and in particular, may be 90°, 110°, or 120°, or any increment therebetween. Hip stem 110 advantageously allows a surgeon to select from a variety of modular neck portions to vary the neck/shaft angle to optimize results in certain female patients.
The present inventors have also observed that as certain patients age, particularly females, the cortex of bone in the metaphysis and in the diaphysis of the proximal femur typically becomes thinner, particularly from the level of the lesser trochanter downwardly. The thinning cortex of the metaphysis and diaphysis results in a “stovepipe” shape of the cortex in the metaphysis and a pronounced widening of the intramedullary canal in the diaphysis, respectively. These effects are more pronounced with women who have osteoporosis, which results in further thinning of the cortex and consequent widening of the intramedullary canal, and in particular, a reduction of bone stock in the proximal diaphysis.
When cementless prostheses are used, the widened intramedullary canal of certain patients, particularly aging females, promotes a tendency for using a wider hip stem to more completely fill the intramedullary canal and achieve initial fixation. In many existing hip stems, stiffness increases with increasing width, such that use of wider hip stems of increased stiffness could result in stress shielding around the hip stem. Advantageously, the hip stems described herein which include a core, a polymer matrix intermediate layer, and porous metal outer layer, have a stiffness modulus which more closely approximates the stiffness modulus of cortical bone. This allows relative motion between the hip stem and the femur to be minimized, and allows more loading to be distributed to the cortical bone to reduce the potential for stress shielding as opposed to known, more stiff hip stems which have only a core and a porous metal coating.
Additionally, the inventors have observed that in females, the intramedullary canal tends to widen relatively more in the anterior/posterior plane, as viewed with a lateral x-ray, for example, than in the medial/lateral plane, particularly in females with osteoporosis, which commonly causes thinning of the posterior cortex of the diaphysis. Thus, when the anterior/posterior and medial/lateral diameters of the intramedullary canal are typically not equal, known hip stems which have a substantially cylindrical shape may not achieve optimal fixation in the diaphysis.
Referring to
In operation and referring to
The degree of expansion of expandable portions 138 may be controlled by the amount of rotation of shaft 134. For example, in one embodiment, a half turn, or 180° turn, of shaft 134 with the actuator device provides a limited degree of expansion of expandable portions 138 to provide initial fixation if the intramedullary canal of femur 144 is only slightly wider than hip stem 130. In one embodiment, two complete turns, or a 720° turn, of shaft 134 provides maximum expansion of expandable portions 138 to provide initial fixation if the intramedullary canal of femur 144 is substantially wider than hip stem 130, wherein shaft 134 is rotated until surface 143 of activation member 148 abuts distal end 133 of hip stem 130 to limit the travel of activation member 148. In this manner, the amount of rotation imparted to shaft 134 may advantageously allow the surgeon to provide the appropriate amount of expansion of expandable portions 138 to ensure adequate diaphyseal fixation of hip stem 130, which may be verified by X-ray or other imaging. In one embodiment, expansion points 140 may include a sliding-enhancement element, for example, a plastic sheet, to facilitate movement of porous metal layer 40 radially outward instead of a potential collapse of porous metal layer 40 in the direction of Arrow B with no radial expansion. Advantageously, portions 138 in the first, non-expanded condition define the original cross-sectional shape of the hip stem. After implantation, deformation of portions 138 advantageously allows the hip stem to have a larger cross-sectional shape in the distal portion thereof to enhance diaphyseal fixation of the hip stem in the femur.
Referring to
As shown in
In some embodiments, expandable structure 155 may be expanded non-uniformly around the circumference of hip stem 150, for example, by varying the number, relative locations, and relative cross sections of passages 153 in hip stem 150. This may allow hip stem 150 to more optimally achieve fixation in the diaphysis because hip stem 150 may expand further in the anterior/posterior plane than in the medial/lateral plane, for example, to provide optimal fixation in females with osteoporosis wherein the width of the anterior/posterior plane of the intramedullary canal may exceed that in the medial/lateral plane. As discussed above, osteoporosis in females commonly causes thinning of the posterior cortex of the diaphysis. The ability to expand in a non-uniform manner, particularly expanding further posteriorly than either medially, laterally, or anteriorly, allows hip stem 150 to achieve optimum fixation.
In a total hip arthroplasty, a prosthetic acetabular cup component is seated within a patient's acetabulum anteriorly of the medial wall of the pelvis. In certain patients, loading from the femoral prosthesis may be transmitted to the pelvis primarily around the rim of the acetabular cup, as opposed to being distributed more evenly around the hemispherical portion of the acetabular cup, which could potentially result in stress shielding around the hemispherical portion of the acetabular cup. Stress shielding of bone around the hemispherical portion of the acetabulum may cause resorption of bone in the medial wall of the pelvis posteriorly of the acetabulum, potentially resulting in migration of the acetabular cup into the medial wall of the pelvis. The present inventors have observed that in female patients, the medial wall of the pelvis is often thinner than in most men.
Referring to
Referring to
Referring to
Referring to
Referring to
Hip stem 210 generally includes a proximal, or metaphyseal, portion 212 and a distal, or diaphyseal, portion 214. Hip stem 210 may be constructed in a similar manner as hip stem 20 described above with respect to
The neck portion and the femoral head (not shown) of proximal portion 212 of hip stem 210 may be integrally formed with hip stem 210 and may be aligned in desired anteversion/retroversion and varus/valgus angles in the same manner as the other hip stems described above with reference to
Distal portion 214 of hip stem 210 may have a circular or trapezoidal cross section, and is elongated with respect to known hip stems to allow the distal portion 214 to engage the cortex of the diaphyseal isthmus, having a length dimension D2 measured from the from the mid lesser trochanter line 221 to the distal end 230 of the hip stem 210 which may be as small as 100 mm, 105 mm, or 110 mm and as large as 125 mm, 130 mm, or 135 mm, for example, or any length therebetween. Near the distal end 230, the width of hip stem 210 at dimension D3 measured laterally-medially may vary from 10 mm to 18 mm and, as shown in
Additionally, distal portion 214 of hip stem 210 may have a substantially hollow construction, including an elongated blind cavity 232 extending inwardly from distal end 230 toward proximal portion 212 of hip stem 210, optionally extending to line 220 at the base of the lesser trochanter. Cavity 232 allows distal portion 214 of hip stem 210 to flex, such that the stiffness modulus of distal portion 214 of hip stem 210 more closely approximates the stiffness modulus of the femoral bone surrounding hip stem 210 to aid in prevention of stress shielding around distal portion 214 of hip stem 210. Alternatively, distal portion 214 of hip stem 210 may be formed to include a core/polymer matrix/porous outer layer construction similar to the other hip stems disclosed herein to provide a stiffness modulus which more closely approximates the stiffness modulus of the femoral bone around distal portion 214 of hip stem 210. In a still further embodiment, distal portion 214 of hip stem 210 may include a plurality of grooves, slopes, or other enervations or weakenings therein to reduce the stiffness modulus thereof.
As described in detail below, the present invention provides prosthetic hip stems for use in prosthetic hip joints and, in particular, provides prosthetic hip stems that are designed to achieve more optimized outcomes with certain types of patient anatomy, such as the anatomy of female patients and/or patients having osteoporosis. Each hip stem in a family or set of hip stems has diaphyseal width, metaphyseal width, offset, and head height dimensions. In a set of hip stems of increasing nominal size, the diaphyseal width dimension increases substantially non-proportionally to the corresponding increase of the metaphyseal width, offset, and head height dimensions, thereby providing a family or set of hip stems that is particularly adapted for patients having osteoporosis, in which the cortical bone of the diaphysis of the femur becomes thinner with progression of the osteoporosis.
As humans and, in particular females, age, osteoporosis may be of concern. Osteoporosis may effect the femur and, in particular, the intramedullary (IM) canal of the femur. The present inventors have observed that as certain patients age, particularly females, the cortex of bone in the metaphysis and in the diaphysis of the proximal femur typically becomes thinner, particularly from the level of the lesser trochanter downwardly. The thinning cortex of the metaphysis and diaphysis results in a “stovepipe” shape of the cortex in the metaphysis, and a pronounced widening of the intramedullary canal in the diaphysis, respectively. These effects are more pronounced with women who have osteoporosis, which results in further thinning of the cortex and consequent widening of the intramedullary canal and, in particular, a reduction of bone stock in the proximal diaphysis.
When cementless hip stem prostheses are used, the widened intramedullary canal of certain patients, particularly aging females, promotes a tendency for using a wider hip stem to more completely fill the intramedullary canal and achieve initial fixation. In many existing hip stems, stiffness increases with increasing width, such that use of wider hip stems of increased stiffness could potentially result in stress shielding around the hip stem. Advantageously, the hip stems described herein which include a core, a polymer matrix intermediate layer, and porous metal outer layer, have a stiffness modulus which more closely approximates the stiffness modulus of cortical bone. This allows relative motion between the hip stem and the femur to be minimized, and allows more loading to be distributed to the cortical bone to reduce the potential for stress shielding as opposed to known, more stiff hip stems which have only a core and a porous metal coating.
Referring to
Referring to
Head portion 252 has a metaphyseal width dimension MW defined with respect to central axis CA generally at a location on head portion 252 where the relatively smooth medial curve of stem portion 254 begins to transition to neck portion 256, though the exact location of metaphyseal width dimension MW may vary slightly across hip stems of different design. In many hip stems, metaphyseal width dimension (MW) will be located at the “osteotomy line”, for example, referring to
Neck portion 256 defines both offset and head or neck height dimensions OF and HH, respectively. The offset dimension OF is the horizontal or medial/lateral distance between central axis CA and the central point CP which corresponds to the center of the femoral head component (not shown) that is attached to the neck taper. The head height dimension HH is the vertical or anterior/posterior distance between the metaphyseal width dimension MW and the central point CP. The neck angle NA is the angle between central axis CA and the neck portion axis NPA of neck portion 256.
In hip stems 250, as the diaphyseal width dimension DW increases with greater nominal size of the hip stems, the increase in the metaphyseal width, offset, and head height dimensions MW, OF, and HH is substantially proportional to the increase in the diaphyseal width dimension DW. In other words, these four dimensions increase substantially proportionally to one another in a given set of hip stems of increasing nominal size.
Referring to
Each hip stem 300 includes a proximal, metaphyseal or head portion 302, a distal, diaphyseal or stem portion 304 having a central axis CA, and a neck portion 306. Further, distal stem portion 304 has diaphyseal or distal width dimension DW, and head portion 302 has a metaphyseal width dimension MW defined with respect to central axis CA. Neck portion 306 defines both offset and head or neck height dimensions OF and HH as described above, and neck angle NA is the angle between central axis CA and the neck portion axis NPA or central axis of neck portion 306, which may be as little as 120° or 125°, or as great as 130°, 135°, 140°, or 145°.
In addition, referring to
Thus, in the specific embodiments set forth above, D2/D1 ranges from 50.4% to 57.3%, and D3/D1 ranges from 42.7% to 49.6%. However, in other embodiments, the foregoing percentages may be as little as 35%, 40%, or 45%, or as great as 55%, 60%, or 65%, indicating that hip stems 300 have a uniform or substantially uniform cross section along a substantial extent of the stem portions 304 thereof.
As described in detail below with respect to the data presented in Tables 1-5 and
For example, the femur of a patient into which a hip stem is to be placed may require a nominal “size 14” stem (i.e., a hip stem having a diaphyseal width dimension DW of 14 mm) if no osteoporosis were present. However, in various stages of osteoporosis, the intramedullary canal width increases at a greater rate than the metaphyseal region, as discussed above. Thus, in hip stems 300, the diaphyseal width dimension DW may be sized at a dimension equivalent to a greater sized conventional stem, while the metaphyseal width MW, offset OF, and head height HH dimensions are sized at dimensions equivalent to a lesser sized conventional stem. In this manner, the distal portion of a hip stem 300 can fully occupy the canal of Type B or Type C bone at advanced stages of osteoporosis, for example, while the metaphyseal portion 302 and neck 306 of the hip stems is still dimensioned substantially equivalent to a non-osteoporotic bone. Thus, hip stem 300 maintains sufficient contact with the bone, such that bony ingrowth is facilitated after implantation, and hip stem 300 substantially fills the femoral canal while preventing “hangup” of the hip stem in the metaphyseal region of the femur during insertion of the hip stem. Moreover, the offset OF and head height HH of the hip stem 300 remain properly sized for the anatomy.
As described herein, as normal, i.e., non-osteoporotic femurs or femurs with Type A bone increase in size across a given patient population, the metaphyseal and diaphyseal regions of the femur typically increase proportionately and sets of hip stems 250, for example, have a corresponding proportional rate of increase with respect to the dimensions of diaphyseal width, DW, metaphyseal width MW, offset OF and head height HH across a range of prostheses of increasing nominal size. However, due to osteoporosis, the canal of the diaphyseal region of the femur may have a width which does not correspond to a normal bone, while the metaphyseal region may have a width which does correspond to a normal bone. Thus, sets of hip stems 300 of the present invention have distal or diaphyseal widths DW that increase at a non-proportional rate, sometimes a greater rate, than their corresponding metaphyseal width MW, offset OF, and head height HH to accommodate osteoporotic bone.
In order to provide hip stems 300 in accordance with the above, the inventors have designed hip stems 300 having the dimensions discussed below. Tables 2-4 below and their corresponding charts in
The relationship between the distal width dimension DW and the metaphyseal width dimension MW is shown in Table 2 below and in
The relationship between the distal width dimension DW and the offset dimension OF is shown in Table 3 below and in
The relationship between the distal width dimension DW and the head height dimension HH is shown in Table 4 below and in
The relationship between the distal width dimension DW and each of the metaphyseal width, offset, and head height dimensions MW, OF, and HH, respectively, for a number of exemplary sets of hip stems 300 of increasing nominal size has been set forth separately in Tables 2-4 above and in
In alternate embodiments, the dimensions of metaphyseal or head portion 302 and diaphyseal or distal portion 304 of hip stems 300 may be determined with reference to any anterior/posterior, medial/lateral, or other suitable dimensions of the metaphyseal or head portion 302 and diaphyseal or distal portion 304 of hip stems 300 other than the particular dimensions set forth and described above. Thus, the hip stems of the present invention are progressively dimensioned across a range of increasing nominal sizes to fill the diaphyseal region of the femur while properly filling, i.e., not impinging or being obstructed by, the metaphyseal region of the femur. Thus, the diaphyseal regions of the present hip stems have widths which increase at a rate greater than the metaphyseal regions/widths to provide sufficient contact and fill of the diaphyseal region of the femur while simultaneously providing a good fit in the metaphyseal region of the femur.
The present hip stems may also be designed to accommodate for variation in medial/lateral (M/L) width of the canal and anterior/posterior (A/P) width of the canal during progression of osteoporosis. In this connection, the inventors have observed that in females, the intramedullary canal tends to widen relatively more in the anterior/posterior plane, as viewed with a lateral x-ray, for example, than in the medial/lateral plane, particularly in females with osteoporosis, which commonly causes thinning of the posterior cortex of the diaphysis. Thus, the anterior/posterior and medial/lateral diameters of the intramedullary canal may not be equal. Generally, the canal begins as circular, then becomes somewhat oval-shaped during middle stages of osteoporosis, and then returns to a substantially circular shape at advanced stages of osteoporosis. Thus, during middle stages of osteoporosis, the A/P dimension of the canal loses bone first to create the oval shape of the canal and the M/L dimension loses bone at later stages of osteoporosis to return the canal to substantially the same original circular cross-sectional shape. Thus, the present hip stems may be designed to have greater A/P dimensions than M/L dimensions to accommodate for this variation in the canal during progression of osteoporosis.
While this disclosure has been described as having exemplary designs, the present disclosure can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the disclosure using its general principles. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this disclosure pertains and which fall within the limits of the appended claims.
This application is a continuation-in-part of U.S. patent application Ser. No. 11/687,862, entitled PROSTHETIC HIP IMPLANTS, filed on Mar. 19, 2007, which claims the benefit under Title 35, U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 60/783,880, entitled PROSTHETIC HIP IMPLANTS, filed on Mar. 20, 2006, and this application also claims the benefit under Title 35, U.S.C. §119(e) of U.S. Provisional Patent Application Ser. No. 60/900,667, entitled PROSTHETIC HIP IMPLANTS, filed on Feb. 9, 2007, and the disclosures of each of the foregoing references are expressly incorporated by reference herein.
| Number | Date | Country | |
|---|---|---|---|
| 60783880 | Mar 2006 | US | |
| 60900667 | Feb 2007 | US |
| Number | Date | Country | |
|---|---|---|---|
| Parent | 11687862 | Mar 2007 | US |
| Child | 12028377 | US |
