Abstract:
A revision hip implant comprises a stem, sleeve, and neck. A proximal IM portion and a distal IM portion of the stem are generally aligned along a long axis of the stem. A body portion of the stem is proximally oriented and has a surface extending generally radially out from the long axis of the stem. The sleeve is configured to be received over the distal intramedullary canal portion of the stem and further has an inner surface configured to mate with the distally extending taper surface of the proximal intramedullary canal portion. The neck is configured to be received in the body portion of the stem. The body portion of the stem has a neck receiving surface configured to mate with a neck taper portion of the neck. The neck taper portion is oriented at an angle relative to the long axis.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/033,213, filed Mar. 3, 2008. The disclosure of the application is incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates generally to a system and methods for implanting a revision hip prosthetic and, more particularly, to a system and method for implanting a modular revision hip prosthetic. 
       SUMMARY OF THE INVENTION 
       [0003]    It is in view of the above problems that the present invention was developed. 
         [0004]    An embodiment of a revision hip implant comprises a stem, a sleeve, and a neck. The stem has a body portion, a proximal intramedullary canal portion and a distal intramedullary canal portion. The proximal intramedullary canal portion and the distal intramedullary canal portion are generally aligned along a long axis of the stem. The body portion is proximally oriented relative to the proximal intramedullary canal portion and further has a surface extending generally radially out from the long axis of the stem. The proximal intramedullary canal portion has a distally extending taper surface. The sleeve is configured to be received over the distal intramedullary canal portion of the stem and further has an inner surface configured to mate with the distally extending taper surface of the proximal intramedullary canal portion. The neck is configured to be received in the body portion of the stem. The body portion of the stem has a neck receiving surface configured to mate with a neck taper portion of the neck. The neck taper portion is oriented at an angle relative to the long axis. 
         [0005]    According to another embodiment of the invention, the distal intramedullary portion of the stem further comprises flutes extending along the length of the stem. 
         [0006]    In yet another embodiment of the revision hip implant, the sleeve further comprises a conical portion and a cylindrical portion. The conical portion is oriented proximal to the stem body and the cylindrical portion extends distally away from the conical portion. 
         [0007]    Alternatively, the surface extending generally radially out from the long axis of the stem on the body portion of the stem may be configured to rest upon a bone cut. 
         [0008]    In another embodiment, the sleeve is configured to asymmetrically extend away from the long axis of the stem. 
         [0009]    According to another embodiment, the neck is received on the stem along a first axis. A head is received on the neck along a second axis, the first and second axes being parallel to each other. 
         [0010]    Further features, aspects, and advantages of the present invention, as well as the structure and operation of various embodiments of the present invention, are described in detail below with reference to the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    The accompanying drawings, which are incorporated in and form a part of the specification, illustrate embodiments of the present invention and together with the description, serve to explain the principles of the invention. In the drawings: 
           [0012]      FIG. 1  is a view of an embodiment of a revision hip implant set including a group of stems, a group of sleeves, and a group of necks; 
           [0013]      FIG. 2  is an exploded view of an embodiment of a hip implant according to an aspect of the invention; 
           [0014]      FIG. 3  is a view of an embodiment of a revision hip implant according to an aspect of the invention; 
           [0015]      FIG. 4  is a cutaway view of a femur with distal preparation instrumentation according to an aspect of the invention; 
           [0016]      FIG. 5  is a cutaway view of the femur with trialing instrumentation according to an aspect of the invention; 
           [0017]      FIG. 6  is a cutaway view of the femur with additional trialing instrumentation according to an aspect of the invention; 
           [0018]      FIG. 7  is a cutaway view of the femur with proximal preparation instrumentation according to an aspect of the invention; 
           [0019]      FIG. 8  is a cutaway view of the femur with portions of a hip implant and implant instrumentation; and 
           [0020]      FIGS. 9 through 11  are cutaway views of the femur with portions of a hip implant and hip instrumentation according to an aspect of the invention. 
       
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
       [0021]    Referring to the accompanying drawings in which like reference numbers indicate like elements,  FIG. 1  illustrates a view of an embodiment of a revision hip implant set including a group of stems  10 , a group of sleeves  20 , and a group of necks  30 . The set includes a three piece modular implant system that may allow a surgeon to address the individual patient needs. The set may be used in revision hip arthroplasty where other treatments or devices have failed in rehabilitating hips damaged as a result of trauma or noninflamatory degenerative joint disease (NIDJD) or any of its composite diagnoses of osteoarthritis, avascular necrosis, traumatic arthritis, slipped capital epiphysis, fused hip, fracture of the pelvis and diastrophic variant. 
         [0022]    Modular hip components may also be indicated for inflammatory degenerative joint disease including rheumatoid arthritis, arthritis secondary to a variety of diseases and anomalies and congenital dysplasia. Other indications include old, remote osteomyelitis with an extended drainage-free period, in which case the patient should be warned of an above normal danger of infection postoperatively. Such a modular revision system may also be used as treatments of non-union, femoral neck fracture and trochanteric fractures of the proximal femur with head involvement that are unmanageable using other techniques, endoprosthesis, femoral osteotomy or Girdlestone resection, fracture-dislocation of the hip, and correction of deformity. The three piece implant system may provide distal fixation and secondary proximal support while allowing the surgeon intra-operative flexibility to achieve the best patient fit. Better fixation and fit may provide better implant stability and outcomes. 
         [0023]    Preoperative planning for a revision total hip arthroplasty should require a standard set of radiographs, which includes an antero-posterior (A-P) radiograph of the pelvis and a lateral radiograph of the affected hip. Depending on the length of the existing femoral component several additional radiographs may be necessary. Specifically, the A-P and lateral radiographs should include the entire femoral component. On occasion a full-length A-P radiograph of the entire femur may be necessary. As part of the preoperative work-up, the surgeon may consider other imaging modalities such as bone scans and computerized tomography (CT). However, these are not typically necessary for preoperative templating. Determine the appropriate classification for the femoral revision, for example the Paprosky Revision Classification. This will aid in determining the appropriate position and size of the revision stem you will need. As with primary THA preop planning, establishing proper leg length requires assessment of a number of clinical and radiographic parameters. Establishing the proper reference lines requires using a horizontal line between the inferior portion of the teardrop as well as a horizontal line between the inferior margin of the obtruator foramen and ischial tuberosity. Due to the often distorted anatomy in revision cases, utilizing all three reference lines may be necessary. 
         [0024]    Similarly, due to bony defects on the femoral side, a combination of anatomic landmarks such as the superior margin of the greater trochanter and inferior margin of the lesser trochanter must be utilized. These obviously need to be compared to similar points in the contralateral side using the A-P radiograph. Any pelvic obliquities and/or spinal deformity must also be taken into account based on radiographic and clinical assessments. The consideration of all relevant factors is necessary to successfully restore the patient&#39;s proper leg length. 
         [0025]    A revision hip implant according to an aspect of the invention generally includes a stem  12 ,  14 , or  16 , a sleeve  22 ,  24 , or  26 , and a neck  32 ,  34 , or  36 . The stem may be chosen from the group of stems  10  and similarly the sleeve and neck may be chosen from the group of sleeves  20  and the group of necks  30 , respectively. 
         [0026]    The stem  12 ,  14 , or  16  may be a tapered stem having a distal intramedullary portion  40 , a proximal portion  42  and a proximal intramedullary portion  44 . The distal portion  40  may include flutes  48  positioned distally for improved fixation of the implant to the diaphysis. The diameters and lengths of the distal portion  40  of the stem may vary according to patient need. The proximal portion  42  includes a body having a distal flat surface  52  and a neck interface surface  54 . The distal flat surface  52  may be oriented to rest upon a cut portion of a femur. The neck interface surface  54  mat be configured to receive a neck. The proximal intramedullary portion  44  of the stem includes a sleeve mating surface  50 . The sleeve mating surface  50  receives one of the group of sleeves  20 . 
         [0027]    The sleeves  20  in the system provide secondary proximal support to the distal fixation and enhance implant stability. The sleeves may be conical sleeves and may be coated, such as coated with Smith &amp; Nephew&#39;s STIKTITE™ coating and then coated in hydroxyapatite (HA). The sleeves  20  may include an internal mating surface  60  a proximal end portion  62 , a distal end portion  64 , a conical portion  66  and a cylindrical portion  68 . Generally, the proximal end portion  62  of the sleeve is larger than the distal end portion  64 . 
         [0028]    Different sleeves  22 ,  24 , and  26  may have different relationships between the different portions of the sleeves. For example, a first sleeve may have a smaller internal mating surface  60  (for a smaller diameter stem portion) but have a larger conical portion  66 , thus making the sleeve thicker. Alternatively, the conical and cylindrical portions may also be a single portion, either cylindrical or conical. The shape and characteristics of the sleeve are chosen based upon the bone of the patient. Where thicker sleeves are necessary to ensure proximal fixation, a thicker sleeve may be used. Where sleeves requiring more taper are necessary, a sleeve with a larger proximal end portion  62  relative to the proximal end portion  64  may be used. 
         [0029]    Alternatively, different sleeves may be asymmetric. Such a sleeve may extend more medially, more anteriorly, more laterally, or more posteriorly relative to the long axis of the stem. Such a sleeve may allow the surgeon to plan for additional asymmetric bone defects within the IM canal. 
         [0030]    Necks  32 ,  34 , and  36  for the modular stem may be modular and available in multiple offset, leg length and version options. For example, the offsets and leg lengths may include a standard offset, high offset, and a high offset+10 mm. The version may include anteverted left and anteverted right. This allows the surgeon to fine tune the offset, length and version to achieve fit and function for each patient. 
         [0031]    In order to achieve different options in the neck, the neck includes a stem mating portion  80  a neck extension  82  and a head mating portion  84 . A stem taper  88  is used to join the neck to the stem. A distal end  90  of the neck is inserted within the neck mating surface  54 . A head taper  94  aligns with a proximal end portion  96  of the neck. The proximal end portion  96  defines the most proximal portion of the neck, which is used to help determine offset, leg length and version. The head taper  94  joins the neck to a femoral head, thus setting the offset, version, and length of the prosthesis relative to an acetabulum. 
         [0032]    Each neck is preferably made of cobalt chrome and includes the circulotrapezoidal neck design for increased range of motion. The 12/14 taper of the neck accepts compatible heads. The geometries of the necks may be changed in order to achieve different implant configurations. Neutral necks (neutral 0° anteversion) may be available in standard and high offset. The standard neutral neck may have a neck shaft angle of 131°. The high offset neutral neck may have a neck shaft angle of 125° when inserted in the varus orientation and 137° when inserted in the valgus orientation. Left anteverted necks may shift the femoral head, 10 degrees, anteriorly relative to the stem on a left hip and posteriorly relative to the stem on a right hip when inserted in the varus orientation. Right anteverted necks may shift the femoral head center based on the operative leg in an equivalent manner. Anteverted necks may be available in one offset option, for example 6 mm more than the standard offset neck, and then may create a neck shaft angle of 125° when inserted in the varus orientation and a neck shaft angle of 137° when inserted in the valgus orientation. The high offset+10 neck may have a neck shaft angle similar to a high offset neck and an additional 10 mm of height. 
         [0033]    To aid in proper neck orientation, a marking such as a laser etch on top of the neck trunnion (the proximal neck portion  96 ) is provided on the high offset and anteverted neck implants and plastic neck trials. Such markings may be arrows or other indicia such that when the neck is inserted in the pocket on the neck mating surface, the arrow on top of the neck points superiorly relative to the patient&#39;s femur if the neck shaft angle is varus, 125° and inferiorly if the neck shaft angle is valgus, 137°. To reduce intraoperative confusion of left &amp; right anteverted necks, the top of the trunnion of the necks may also be laser etched with an “L” for left anteverted and an “R” for right anteverted. Additionally, color coding of the anteverted neck implant packaging and corresponding trial necks may be provided to account for neck characteristics or neck orientations. 
         [0034]    Turning now to  FIGS. 2 and 3 ,  FIG. 2  is an exploded view of an embodiment of a hip implant according to an aspect of the invention and  FIG. 3  is a view of an embodiment of a revision hip implant according to an aspect of the invention. The sleeve  26  is received over the distal end of the stem  14 . The sleeve  26  mates with the sleeve mating surface  44  proximally along the stem. The taper between the sleeve  26  and the stem  14  fits such that forces directed distally along the stem (such as patient weight) would push against the taper junction between the stem  14  and sleeve  26 . The sleeve  26  generally aligns along the long axis of the stem  14 . 
         [0035]    The stem  14  receives the neck  32  in a pocket on the head portion of the stem. In a neck neutral orientation, the taper of the neck  32  to the stem  14  may be aligned with the taper of the neck  32  to the femoral head. As the offset, version and height change, the relative direction of the tapers (and thus the forces associated with those tapers) move relative to one another. 
         [0036]    Instruments associated with the implants may provide surgical efficiency during the implantation of the stem.  FIGS. 4 through 11  show steps of a surgical procedure which may be used to prepare, trial, and implant a modular revision hip prosthetic device within a femur. With respect to  FIG. 4 ,  FIG. 4  is a cutaway view of a femur  100  with distal preparation instrumentation according to an aspect of the invention. A distal reamer  102  allows the surgeon to properly prepare and size the canal for optimal fit of the tapered, fluted distally fixed stem. The distal portion of the femur is reamed by attaching a quick connect instrument  104  to an appropriate distal reamer  102  and ream the distal femoral canal in 0.5 mm increments until desired distal fit is achieved. It is preferred to begin reaming with a distal reamer that is at least 2 mm smaller than the template size. Such a reamer would have little or no resistance to reaming as it progresses through the IM canal. Additionally, to minimize potential risk of reaming through the anterior cortex, the reamer  102  may be directed from anterior to posterior. Preferably, the size of the stem is 0.25 mm greater than the equivalently sized reamer, which may provide an automatic press fit. 
         [0037]    The depth of the reamer  102  may be determined by aligning a mark on the quick connect instrument with the greater trochanter. If the greater trochanter is not available then alternative anatomical reference may be made. For example, a ruler can be used to measure from the distal end of the osteotomy to the previous location of the greater trochanter. Upon achieving desired distal fit, the quick connect device  104  may be disengaged and the final distal reamer  102  may be left in the canal. 
         [0038]    As shown in  FIG. 5 ,  FIG. 5  is a cutaway view of the femur  100  with trialing instrumentation according to an aspect of the invention. When used in conjunction with trial bodies and necks, the distal reamer  102  may function as intramedullary trials which should provide the surgeon with more accurate assessment of implant positioning while reducing the number of instruments and trial components. 
         [0039]    In some revision cases, medial bone may need to be removed to accommodate the neck platform of the neck body. An osteotomy jig  112  may be used to address this bone removal. The osteotomy jig  112  is placed over the distal reamer  102  and proximal spacer  110  and may be fixed to reamer  112  with a screw. Arrows on the osteotomy jig  112  may indicate the location where the minimum bone must be removed for the trial neck body (and the subsequent implant) to properly seat. The location of the depth may be marked with a cautery pin. After the jig  112  is removed, an oscillating saw is used to osteotomize the bone. Once the bone is properly oriented, then a trial body may be used to position the body of the stem. 
         [0040]    With respect to  FIG. 6 ,  FIG. 6  is a cutaway view of the femur  100  with additional trialing instrumentation according to an aspect of the invention. A trial body  116  is seated on the spacer  110  on the distal reamer  102 . A trial neck component  118  is engaged with the body  116 . Indicia on the trial neck  116  may orient the neck  118  relative to the body  116 . With the trial completely formed, a range of motion (ROM) exercise may be performed to confirm proper seating of implant, assess joint tension, and ensure there is no impingement to the hip. Trial neck components  118  and trial neck pocket version (manipulated by adjusting the rotation of the body  116  on the spacer  110 ) may be adjusted as appropriate to achieve desired leg length, neck offset, and neck version. A mark can be made on the bone with a cautery pin to mark desired version for implant. 
         [0041]    Turning now to  FIG. 7 ,  FIG. 7  is a cutaway view of the femur  100  with proximal preparation instrumentation according to an aspect of the invention. A proximal reamer  120  may be used over the distal reamer  102 . These “over the top” reamers  120  allow the surgeon to leave the distal reamer  102  in the canal to maintain the relative position of the cavities for the proximal sleeve and the distal taper of the stem. By reaming “over the top” the surgeon is preparing for the proximal segment based on the location of the distal reamer. 
         [0042]    The distal reamer may be used by first removing the trial neck body, trial neck component, and proximal trial spacer. The distal reamer  102  is left in the canal. Beginning with the smallest appropriate size, the proximal cone reamer  120  is advanced over the shaft of the distal reamer  102 . The proximal cone reamer  120  will rotate, however the distal reamer  102  will act as a guide and should not advance. If an ETO is not performed or if the femoral canal is small, a starter proximal reamer may be necessary to remove bone that may impede the application of the proximal cone reamers  120 . The canal is progressively reamed using the proximal cone reamers until the desired proximal fit is achieved. 
         [0043]    Following the proximal sleeve preparation, re-trialing may be performed using the proximal trial spacer, trial neck body, trial neck, and trial head component over the distal reamer. If re-trialing is not performed following the proximal sleeve preparation, then the distal reamer component may be removed. 
         [0044]    With respect to  FIG. 8 ,  FIG. 8  is a cutaway view of the femur  100  with portions of a hip implant and implant instrumentation. The stem  14  and sleeve  26  are prepared for implant. The sleeve  26  is slid over the distal end of the stem  14  and seated on the stem  14 . A stem insertion instrument  126  attaches to the proximal end of the stem  14  generally along the long axis of the stem. The stem/sleeve assembly is impacted into the femur using a mallet against the driving platform. The stem inserter should not impinge on the trochanter. This may cause inadequate stem seating, trochanteric fracture or varus positioning. The surgeon may assess height and neck pocket orientation as the stem advances into the desired position. If a cautery pin mark was made during the trialing step, it can be used as a reference. The stem inserter instrument  126  is then disengaged when the stem is properly seated in the canal. 
         [0045]    Turning now to  FIGS. 9 through 11 ,  FIGS. 9 through 11  are cutaway views of the femur  100  with portions of a hip implant  14 ,  26  and  34  and hip instrumentation  132  according to an aspect of the invention. Once the stem  14  is seated, it is recommended that re-trialing be performed using the trial neck and head components. Fine-tuning of offset, leg length, and version can be made with the modular neck options. Once proper neck orientation is determined, the modular neck trial is replaced with the modular neck implant  34  prior to impaction. All taper surfaces should be protected, clean and dry prior to assembly to ensure a good taper lock. Once the neck  34  is verified in the desired orientation prior to final impaction, the surgeon impacts the final neck  34  and head implant component  130  simultaneously with the head/neck impaction tool  132 . Correct selection of the neck length and cup, and stem positioning are important. Muscle looseness and/or malpositioning of components may result in loosening, subluxation, dislocation, and/or fracture of the component and/or bone. A final ROM check may ensure desired implant outcome prior to closing with the implants implanted. 
         [0046]    In view of the foregoing, it will be seen that the several advantages of the invention are achieved and attained. 
         [0047]    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. 
         [0048]    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.