US20100249943A1 - Modular necks for orthopaedic devices - Google Patents

Abstract

There is provided a system of modular orthopaedic devices. The system comprises one or more hip implants or trials, each hip implant or trial having a femoral stem and one of at least two neck segments having different geometries. Each neck segment comprises a proximal end configured to receive a femoral head portion and a distal end configured to be operably received by a proximal portion of the femoral stem. Each proximal end comprises a central portion generally representative of a femoral head center. When each of the at least two neck segments are joined with the femoral stem, the central portion is displaced a predetermined distance in a single direction relative to the femoral stem. The neck segments provided, therefore, advantageously allow a user to independently adjust any one of a height, an offset, or a version angle of an orthopaedic device for best performance and fit.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• This application claims the benefit of U.S. Provisional Application No. 60/976,717, filed Oct. 1, 2007 and U.S. Provisional Application No. 60/976,697, filed Oct. 1, 2007. The disclosure of each application is incorporated by reference in its entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
• N/A
BACKGROUND OF THE INVENTION
• 1. Field of the Invention
• The present invention relates generally to orthopaedic implants, and more particularly to modular femoral implants for use in hip arthroplasty.
• 2. Related Art
• In some instances, an implant may sit higher or lower than anticipated after its insertion into a medullary canal of a bone. For example, in hip arthroplasty, a femoral stem portion of a hip prosthesis may seat proximally proud, or might otherwise seat more distally than expected after it is inserted into a prepared femoral canal. This problem may cause the patient to have too short or too long of a leg.
• If the femoral stem portion sits too proud proximally, it can be removed, and the medullary canal can be re-reamed with a larger reamer to allow the stem to seat more distally. This increases the risk of fracture and is more invasive, because precious cortical bone is removed to make room for the prosthesis. If the hip prosthesis seats too far distally in the femoral canal, it can be removed, and re-reamed to make room for a larger prosthesis.
• In order to avoid these problems, prior implants have incorporated modular designs. For example, some prior designs use proximal bodies of varying height. Each of the proximal bodies are configured to join to a distal stem of the implant at a middle portion of the implant. Overall implant height adjustments are made by selecting a proximal body that provides the desired implant height, and then securing it to the distal stem segment. However, there are several problems with these prior designs. For example, the junction between the proximal body and the distal stem forms a stress riser at a central portion of the implant, making the implant more vulnerable to fatigue and shear under loading. Many of these modular prior art devices are susceptible to fatigue failure. Moreover, these prior implants can be difficult to assemble because the junction is usually located inside the femoral canal and cannot be easily seen. Lastly, each junction is subject to contamination by bone debris, blood, or other biological matter that could potentially prevent or interfere with establishing a good taper lock at the junction, further increasing the risk of implant failure.
• Modular necks have also been used in the past to adjust implant height. However, such conventional Cremascoli-type modular necks (such as those used in PROFEMUR® implants by Wright Medical Technology, Inc.) adjust implant height by changing the overall neck length or the neck angle as shown inFIGS. 9a-9c. This method disadvantageously changes offset and/or version angle simultaneously with height, because of the way the sine and cosine components of the neck change with changes in neck length (i.e., the hypotenuse) and angle. In an operating room, it can become quite tedious and confusing to keep track of what geometries are changing between neck segment selections during trial reduction.
• For example, the geometric changes between modular necks (910,920) of the prior art create spherical spatial paths (950) of the femoral head center (912,922) as they are interchangeably assembled to a femoral stem (900). The spherical spatial paths (950) cause some change in at least offset or version angle in order to achieve a desired height. This is clearly shown inFIG. 9a. Therefore, to this end, if a surgeon wants to change the height of an implant using prior art modular necks, he or she must make compromises between leg length discrepancy and joint stability/range-of-motion. Due to the complex and iterative nature of changing more than one input variable at a time, it is difficult for a surgeon to re-establish the proper joint stability when using modular necks of the prior art, if leg length needs to be adjusted.
• Another way the prior art aims to address leg length is by providing kits of non-modular implants have different proximal geometries in order to adjust overall implant height. In hip arthroplasty, these non-modular implants are sometimes referred to as calcar-replacing femoral stems. The problem with using such monolithic stems is that a surgeon needs to extract the entire implant from the medullary canal and replace it with another implant in order to change the overall implant height. Each time an implant is inserted and extracted from a medullary canal, there is trauma to the bone and surrounding soft tissues (e.g., increased risk of fat embolism and/or fracture). Moreover, each time an implant is inserted and extracted from a medullary canal, there may be a loss of bone fixation or stability. Furthermore, each time an implant is inserted and extracted from a medullary canal, rotation needs to be re-set and there is no guarantee that the height will be optimal when the implant is fully re-seated in the canal.
• There remains a need in the art to provide an easy, reliable, minimally-invasive method of adjusting the height of an implant without unnecessary steps. There also remains a need in the art to provide an easy, reliable method of adjusting the height of an implant without compromising soft tissue and bone integrity. There is also a need to reduce the number of trialing steps needed to optimize performance and fit for a patient. There is also a financial need to reduce the amount of time required for a hip arthroplasty procedure. Moreover, there is a need to provide a means for adjusting implant height without compromising the structural integrity of said implant.
SUMMARY OF THE INVENTION
• The aforementioned needs are satisfied by several aspects of the present invention.
• According to one aspect of the invention, there is provided a system of modular orthopaedic devices. The system comprises one or more hip implants or trials, each hip implant or trial having a femoral stem and one of at least two neck segments having different geometries. Each neck segment comprises a proximal end configured to receive a femoral head portion and a distal end configured to be operably received by a proximal portion of the femoral stem. Each proximal end comprises a central portion generally representative of a femoral head center. When each of the at least two neck segments are joined with the femoral stem, the central portion is displaced a predetermined distance in a single direction relative to the femoral stem. The neck segments provided, therefore, advantageously allow a user to independently adjust any one of a height, an offset, or a version angle of an orthopaedic device for best performance and fit.
• According to yet another aspect of the invention, there is provided a kit of modular neck segments. The kit allows a surgeon to fine-tune leg length independently of offset and/or version angle.
• According to yet even another aspect of the invention, there is provided a kit of modular neck segments. The kit allows a surgeon to fine-tune implant offset independently of overall implant height and/or version angle.
• According to another aspect of the invention, there is provided a kit of modular neck segments. The kit allows a surgeon to fine-tune version angle independently of implant offset and/or overall implant height.
• According to yet another aspect of the invention, there is provided a method of using the system of modular orthopaedic devices discussed above. The method generally includes steps of: 1) implanting a femoral stem of a hip implant or trial for best cortical fixation, 2) selecting a first neck segment with a first geometry, 3) assembling the first neck segment with the implanted femoral stem, 4) assessing leg length, 5) if needed, removing the first neck segment from the femoral stem and replacing it with one or more second neck segments having one or more second geometries, each of the one or more second geometries being configured to move a femoral head center a predetermined distance in a superior-inferior direction independently of offset and version angle, 6) determining an optimum neck segment geometry which provides the best overall height of the hip implant and leg length, 8) selecting, from a kit of neck segments having said optimum neck segment geometry, a final neck segment having the proper offset or version angle to obtain joint stability and acceptable range of motion, 9) implanting a neck segment having the same geometry as said final neck segment and finishing the surgical procedure as conventionally done.
• Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating certain embodiments of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.
BRIEF DESCRIPTION OF THE DRAWINGS
• The accompanying drawings, which are incorporated in and form a part of the specification, illustrate the embodiments of the present invention and together with the written description serve to explain the principles, characteristics, and features of the invention. In accordance with the invention there will be shown in the drawings and described herein, more than one preferred embodiment. These preferred embodiments are merely representative of the invention and should not be construed as a limitation on the scope of the present invention.
• It will also be understood that like or analogous elements and/or components, referred to herein, are identified throughout the drawings by like reference characters. In addition, it will be understood that the drawings are merely representations, and some of the components may have been distorted from actual scale for purposes of pictoral clarity. In the drawings:
• FIGS. 1aand1bare coronal views of a hip implant comprising a femoral stem (100) and two superimposed neck segments (200,210) that allow independent adjustment of offset (510) in the medial-lateral direction (500).
• FIGS. 2aand2bare sagittal views of the hip implant shown inFIGS. 1aand1b.
• FIGS. 3aand3bare coronal views of a hip implant comprising a femoral stem (100) and two superimposed neck segments (200,220) that allow independent adjustment of offset (410) in the superior-inferior direction (400).
• FIGS. 4aand4bare sagittal views of the hip implant shown inFIGS. 3aand3b.
• FIGS. 5aand5bare coronal views of a hip implant comprising a femoral stem (100) and two superimposed neck segments (200,230) that allow independent adjustment of version (610) in the anterior-posterior direction (600).
• FIGS. 6aand6bare sagittal views of the hip implant shown inFIGS. 3aand3b.
• FIG. 7 shows one embodiment of the present invention which comprises a kit (700) of modular neck segments for a femoral stem, the kit allowing a surgeon to independently control height, offset, and version angle of a hip implant.
• FIG. 8 is a schematic illustrating a method of using the kit (700) shown inFIG. 7 according to some embodiments.
• FIGS. 9a-9care examples of prior art modular neck segments (910,920) which do not allow independent adjustments of height, offset, and version angle.
DETAILED DESCRIPTION OF THE EMBODIMENTS
• The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses.
• Referring to the accompanying drawings,FIGS. 1a-2billustrate a system of modular orthopaedic devices according to some embodiments. The system comprises a femoral stem (100) and one of at least two neck segments (200,210). The neck segments (200,210) generally have a proximal end configured to receive a femoral head implant (not shown), and a distal end configured to be operably received by the femoral stem (100). The junction between the neck segments (200,210) may be any known in the art, but is preferably a Morse taper lock. The proximal end of each neck comprises a central portion (202,212) which is representative of the femoral head center when each of a femoral stem (100), neck (200), and femoral head implant (not shown) are assembled together.
• One of said at least two neck segments may be a standard neck segment (200) having a neutral referencing orientation. The neutral referencing orientation may comprise, for instance, an origin defined by a neutral height (410) in the superior-inferior direction (400), a neutral offset (510) in the medial-lateral direction (500), and a neutral version angle (610) in an anterior-posterior direction (600). The other of said at least two neck segments may be a high offset neck segment (210) having its central portion (212) positioned with a higher offset (510) in a medial-lateral direction (500) than the standard neck segment (200). However, the high offset neck segment (210) generally maintains the same neutral version angle (610) and height (410) as the standard neck segment (200). The system of neck segments (200,210) shown inFIGS. 1a-2ballows the surgeon to laterally or medially displace a hip prosthesis for greater hip abduction and motion without affecting leg length and anteversion/retroversion.
• It should be noted that in addition to the increased offset neck segment (210) shown, multiple other neck segments yielding different overall implant offsets may be included in the system. For instance, a system of neck segments may comprise without limitation, very high offset (high abduction), high offset (abducted), very low offset (high adduction), and low offset (adducted) neck segments, each having the same version angle (610) and height (410), but each producing a different overall implant offset (510) in the medial-lateral direction (500).
• FIGS. 3a-4billustrate a system of modular orthopaedic devices according to some embodiments. The system comprises a femoral stem (100) and one of at least two neck segments (200,220). The neck segments (200,220) generally have a proximal end configured to receive a femoral head implant (not shown), and a distal end configured to be operably received by the femoral stem (100). The junction between the neck segments (200,220) may be any known in the art, but is preferably a Morse taper lock. The proximal end of each neck comprises a central portion (202,222) which is representative of the femoral head center when each of a femoral stem (100), neck (200), and femoral head implant (not shown) are assembled together.
• One of said at least two neck segments may be a standard neck segment (200) having a neutral referencing orientation. The neutral referencing orientation may comprise, for instance, an origin defined by a neutral height (410) in the superior-inferior direction (400), a neutral offset (510) in the medial-lateral direction (500), and a neutral version angle (610) in an anterior-posterior direction (600). The other of said at least two neck segments may be an increased height neck segment (220) having its central portion (222) positioned at a greater height (410) in a superior-inferior direction (400) than the standard neck segment (200). However, the increased height neck segment (220) generally maintains the same neutral version angle (610) and offset (510) as the standard neck segment (200). The system of neck segments (200,220) shown inFIGS. 3a-4ballows the surgeon to superiorly or inferiorly displace a hip prosthesis for proper leg length without affecting abduction and anteversion/retroversion.
• It should be noted that in addition to the increased height neck segment (220) shown, multiple other neck segments yielding different overall implant heights may be included in the system. For instance, a system of neck segments may comprise without limitation, very short (more distal), short (distal), very long (more proximal), and long (proximal) neck segments, each having the same version angle (610) and offset (510), but each producing a different overall implant height (410) in the superior-inferior direction (400).
• FIGS. 5a-6billustrate a system of modular orthopaedic devices according to some embodiments. The system comprises a femoral stem (100) and one of at least two neck segments (200,230). The neck segments (200,230) generally have a proximal end configured to receive a femoral head implant (not shown), and a distal end configured to be operably received by the femoral stem (100). The junction between the neck segments (200,230) may be any known in the art, but is preferably a Morse taper lock. The proximal end of each neck comprises a central portion (202,232) which is representative of the femoral head center when each of a femoral stem (100), neck (200), and femoral head implant (not shown) are assembled together.
• One of said at least two neck segments may be a standard neck segment (200) having a neutral referencing orientation. The neutral referencing orientation may comprise, for instance, an origin defined by a neutral height (410) in the superior-inferior direction (400), a neutral offset (510) in the medial-lateral direction (500), and a neutral version angle (610) in an anterior-posterior direction (600). The other of said at least two neck segments may be an anteverted neck segment (230) having its central portion (232) positioned with a greater displacement (610) in an anterior-posterior direction (600) than the standard neck segment (200). However, the anteverted neck segment (230) generally maintains the same neutral height (410) and offset (510) as the standard neck segment (200). The system of neck segments (200,230) shown inFIGS. 5a-6ballows the surgeon to anteriorly or posteriorly displace a hip prosthesis for proper anteversion/retroversion without affecting abduction/adduction and leg length.
• It should be noted that in addition to the anteverted neck segment (230) shown, multiple other neck segments yielding different overall implant version angles may be included in the system. For instance, a system of neck segments may comprise without limitation, highly retroverted (more posterior), slightly retroverted (posterior), highly anteverted (more anterior), and slightly anteverted (anterior) neck segments, each having the same height (410) and offset (510), but each producing a different overall implant version angle (610) in the anterior-posterior direction (600).
• One of ordinary skill in the art would appreciate that the abovementioned systems may be combined in any fashion to provide numerous intra-operative options for a surgeon. For example,FIG. 7 illustrates a kit (700) which may be provided according to the teachings disclosed herein. The kit (700) comprises a first group (710) of at least two neck segments having different lengths. When assembled with a femoral stem (not shown), each of said at least two neck segments in said first group (710) yields a different overall implant height. During trial reduction, a surgeon may use the first group (710) of neck segments to assess and “lock-in” leg length for the remainder of trial reduction. For instance, a surgeon may determine that for a particular patient, a first optimum neck segment geometry (712) will ensure a proper leg length. Next, the surgeon will obtain a second group (720) of neck segments from a series of groups (720,730,740). Each neck segment contained in the second group (720) will posses the same first optimum neck segment geometry (712), and thereby, ensure a proper leg length. Finally, the surgeon will select a neck having a version angle (722) and offset (724) that provides the best stability and range of motion for a given first optimum neck segment geometry (712). The order in which version angle (722) and offset (724) are decided may vary according to surgeon preference.
• FIG. 8 is a schematic illustrating a method of using the systems of modular orthopaedic devices discussed above. The method may include steps of: implanting a femoral stem of a hip implant or trial for best cortical fixation (802); selecting a first neck segment with a first geometry (804); assembling the first neck segment with the implanted femoral stem (806); assessing leg length (808); if needed, removing the first neck segment from the femoral stem and replacing it with one or more second neck segments having one or more second geometries, each of the one or more second geometries being configured to move a femoral head center a predetermined distance in a superior-inferior direction independently of offset and version angle (810); determining an optimum neck segment geometry which provides the best overall height of the hip implant and leg length (812); selecting, from a kit of neck segments having said optimum neck segment geometry, a final neck segment having the proper offset or version angle to obtain joint stability and acceptable range of motion (814); and implanting a neck segment having the same geometry as said final neck segment and finishing the surgical procedure as conventionally done (816).
• Adjustment for intra-operative leg length discrepancies without changing the offset and version of an implant is desirable, because it may reduce the number of joint dislocations and the number of revision surgeries due to leg length discrepancies. Moreover, the ability to change implant height independently of offset and version may reduce trial reduction time, thereby decreasing hospital overhead and risks associated with extended patient exposure (e.g., bacteria, anesthesia).
• The present invention may advantageously utilized in prostheses for other joints, such as shoulders. For example, the femoral stems and femoral heads mentioned throughout this disclosure may alternatively be humeral stems and humeral heads, respectively. The present invention may be used selectively within a particular product system, or universally across different orthopedic product lines.
• In some instances, the neck segments provided may be labeled with indicia to indicate a geometric configuration. Such indicia may be, for example, textual in form (e.g., “STANDARD” or “STD” or “OFFSET” or “HIGH OFFSET”). Similarly, numbers may be provided on the neck segments to indicate actual geometric displacements of the femoral head center (e.g., the number “+10” near the word “OFFSET” may indicate an increase in offset of 10 millimeters, whereas the number “0” may indicate a neutral position). Indicia on neck segments may specify any one of a height, an offset, or a version angle, and may be formed by laser etching, printing, colorization, engraving, molding, or rapid prototyping.
• In some embodiments, all high offset neck segments within a system may share a common symbol or color or both. In another embodiment, all neck segments having the same height within a system may share a common symbol or color or both. In yet another embodiment, each standard offset neck segment within a system may share a common symbol or color, or both. A banding system such as ones used for resistors in the electronic arts may be employed so as to provide easy recognition of values for height, offset, and version. Indicia may be placed on the distal and/or proximal ends of the modular neck segments to indicate proper or incorrect orientation. For example, to ensure that a neck segment is not inserted upside-down, indicia may be oriented in a way such that a user can only properly read it when the neck segment is installed in its correct orientation relative to the femoral stem. In some instances, indicia may be in the form of a separate piece that permanently connects with a modular neck segment, or in the form of a sticker that may be removed from the neck segment and disposed of.
• Preferably, the distal portion of each neck segment of the present invention comprises a Morse taper having an oval-tapered cross section which mates with a corresponding oval-tapered hole in a proximal stem portion. However, any alternative means for connecting the modular neck segment may be used. Preferably, the proximal end of each neck segment of the present invention comprises a frustoconically-tapered surface that mates with a corresponding frustoconically-tapered hole in a femoral head component (not shown).
• The proximal and distal end portions of each neck segment within the system may be tapered or non-tapered and may be configured for a press-fit. A transverse cross-section of the proximal and distal ends of the neck segments may comprise conical, square, elliptical, trapezoidal, or other polygonal shapes. The proximal and distal end portions of each neck segment within the system may also comprise splines, keys, registration elements, or orientation features. The proximal and distal end portions of each neck segment within the system may or may not be identical in shape or size. In some embodiments, it may be favorable to make a femoral head completely integral and/or monolithic with the neck segments described herein.
• The portion of the neck segments extending between the proximal and distal end portions may have different shapes and may be optimized for increased range of motion and decreased impingement. The surface texture of the portion between the first and second connection portions is preferably smooth, but may have a textured or grit-blasted surface when provided as a trial for easy handling. Trial neck segments described herein may be provided as re-usable or disposable devices.
• The neck segments of the present invention may connect directly to a monolithic stem or to a modular stem. The present invention may comprise as few or as many neck segments in a selection as is needed to provide a user with the number of configuration options desired. The neck segments may be custom-made or custom-packaged for a pre-templated patient, so that fewer neck segments are needed for trial reduction during a surgery for said pre-templated patient. Any of the neck segments described herein can be made of any material suitable for permanent or temporary implantation into a human or animal including, but not limited to, cobalt chrome, titanium, stainless steel, oxidized zirconium, PEEK, and polyethylene.
• In view of the foregoing, it will be seen that the several advantages of the invention are achieved and attained.
• The embodiments were chosen and described in order to best explain the principles of the invention and its practical application to thereby enable others skilled in the art to best utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It must be noted that as used herein and in the appended claims, the singular forms “a” “and,” and “the” include plural references unless the context clearly dictates otherwise.
• As various modifications could be made in the constructions and methods herein described and illustrated without departing from the scope of the invention, it is intended that all matter contained in the foregoing description or shown in the accompanying drawings shall be interpreted as illustrative rather than limiting. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims appended hereto and their equivalents.

Claims (14)

1. A system of modular orthopaedic devices comprises: at least one hip implant, the hip implant having a femoral stem; a head portion; and at least two neck segments having different geometries, each neck segment comprising a proximal end configured to receive the femoral head portion and a distal end configured to be operably received by a proximal portion of the femoral stem; wherein each proximal end of each neck segment comprises a central portion generally representative of a femoral head center such that when each of the at least two neck segments are interchangeably joined with the femoral stem, the central portion is displaced a predetermined distance in a single direction relative to the femoral stem.

2. The system ofclaim 1 wherein the single direction is any one of a height, an offset, or a version angle of an orthopaedic device.

3. The system ofclaim 1, wherein the at least one hip implant, the head portion and the at least two neck segments are temporary trials.

4. The system ofclaim 1, wherein the at least one hip implant, the head portion and the at least two neck segments are modular neck segments.

5. The system ofclaim 1, wherein the at least two neck segments comprise a kit of neck segments configured to adjust leg length independently of offset and/or version angle.

6. The system ofclaim 1, wherein the at least two neck segments comprise a kit of neck segments configured to adjust implant offset independently of overall implant height and version angle.

7. The system ofclaim 1, wherein the at least two neck segments comprise a kit of neck segments configured to adjust version angle independently of implant offset and overall implant height.

8. A method of using a modular orthopaedic device, comprising the steps of: a. implanting a femoral stem of a hip implant for cortical fixation; b. selecting a first neck segment with a first geometry; c. assembling the first neck segment with the implanted femoral stem; d. assessing an orientation of the first neck segment in a first direction; e. removing the first neck segment from the femoral stem; and f. replacing it with a second neck segment having a second geometry, the second geometry being configured to move a femoral head center a predetermined distance independently in the first direction.

9. The method ofclaim 8 wherein the single direction is any one of a height, an offset, or a version angle of an orthopaedic device.

10. The method ofclaim 8, wherein the hip implant, and the first and second neck segments are temporary trials.

11. The method ofclaim 8, wherein the wherein the hip implant; and the first and second neck segments are modular neck segments.

12. The method ofclaim 8, wherein the replacing step further comprises the step of choosing a second neck segment from a kit of neck segments configured to adjust leg length independently of offset and/or version angle.

13. The method ofclaim 8, wherein the replacing step further comprises the step of choosing a second neck segment from a kit of neck segments configured to adjust implant offset independently of overall implant height and version angle.

14. The method ofclaim 8, wherein the replacing step further comprises the step of choosing a second neck segment from a kit of neck segments configured to adjust version angle independently of implant offset and overall implant height.

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