Abstract:
An instrument for use in resecting a portion of a greater tubercle of a humerus in shoulder arthroplasty is provided. The instrument includes a guide support that has a first end coupled to a long bone. The guide support extends laterally and over the greater tubercle. The instrument also includes a cutting guide movably coupled to the guide support. The cutting guide including curved frame for abutting the humerus.

Description:
TECHNICAL FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to the field of orthopaedics, and more particularly, to an implant for use in arthroplasty. 
       BACKGROUND OF THE INVENTION 
       [0002]    Patients who suffer from the pain and immobility caused by osteoarthritis and rheumatoid arthritis have an option of joint replacement surgery. Joint replacement surgery is quite common and enables many individuals to function properly when it would not be otherwise possible to do so. Artificial joints are usually comprised of metal, ceramic and/or plastic components that are fixed to existing bone. 
         [0003]    Such joint replacement surgery is otherwise known as joint arthroplasty. Joint arthroplasty is a well-known surgical procedure by which a diseased and/or damaged joint is replaced with a prosthetic joint. In a typical total joint arthroplasty, the ends or distal portions of the bones adjacent to the joint are resected or a portion of the distal part of the bone is removed and the artificial joint is secured thereto. 
         [0004]    One type of joint replacement surgery is shoulder arthroplasty. During shoulder arthroplasty, the humeral head must be resected to allow for the insertion of a humeral stem into the intramedullary canal of the humerus. The proximal end of the humerus includes the humeral head, which articulates with the glenoid of the shoulder in a ball and socket fashion. The humeral head is nearly hemispherical in form. 
         [0005]    The prostheses typically used for shoulder arthroplasty include a stem portion designed to extend into the intramedullary canal of the humerus and a head portion designed to replace the humeral head. The head portion of the prosthesis extends angularly from the stem portion. The resection of the natural humeral head must be made so that the angle of the cut corresponds to the angle between the stem and head portions of the prosthesis. In addition, the rotation of the cut varies to adjust to bone wear or capsular looseness. 
         [0006]    Patients who have massive rotator cuff tears experience proximal migration of the humerus. When this occurs, part of the humeral head will contact the acromion, which can cause pain and loss of shoulder function. By providing a humeral head with an extended articulating surface, a metal surface with a low coefficient of friction will contact the acromion and reduce pain. The extended articulating surface also increases the surface of articulation in the artificial shoulder joint in abduction and external rotation. 
         [0007]    When implanting a proximal humeral resurfacing implant with an extended articulation surface, removal of part or all of the humeral greater tubercle is needed. After the initial humeral head resection is made, a portion of the greater tubercle must also be removed. The cut that achieves this is perpendicular to the longitudinal axis of the humerus and allows for the backside of the extended articulation surface to sit on the most superior portion of the humerus. 
         [0008]    One surgical technique used in shoulder arthroplasty is called the deltopectoral approach. This approach requires detachment of the anterior portion of the rotator cuff from the humerus in order to gain adequate exposure to the joint. This is not ideal for the patient because the disturbance of the anterior cuff can compromise the function of the shoulder. 
         [0009]    A second technique used in shoulder arthroplasty is the anterosuperior approach. Unlike the deltopectoral approach, the anterosuperior approach spares the anterior portion of the rotator cuff. However, it requires disturbance of other soft tissue structures, namely the origin of the anterior deltoid and the acromial insertion of the coracoacromial ligament, which can also compromise shoulder function. 
         [0010]    Clearly, neither of these approaches is ideal for the patient. What would be ideal is a third technique that spares the anterior rotator cuff, the origin of the anterior deltoid, and the insertion of the coracoacromial ligament. A soft tissue approach of this type has been identified, but there is not adequate instrumentation to guide the resection of the greater tubercle of the humerus from this approach. The soft tissue approach provides exposure to the humerus from the lateral side. Therefore, an instrument that aids the resection of the greater tubercle of the humerus from the lateral direction is needed. 
       SUMMARY OF THE INVENTION 
       [0011]    According to one embodiment of the present invention, an instrument for use in resecting a portion of a greater tubercle of a humerus in shoulder arthroplasty is provided. The instrument includes a guide support having a first end coupled to the humerus. The guide support extends laterally and over the greater tubercle. The instrument also includes a cutting guide that is movably coupled to the guide support. A curved frame is included in the cutting guide and is for abutting the humerus. 
         [0012]    According to another embodiment of the present invention, a method for resecting a greater tubercle in a humerus is provided. The method includes providing a guide support and a cutting guide. The cutting guide is moveable relative to the guide support and has a curved frame. The guide support is coupled to an instrument inserted into the humerus, such that the guide support extends laterally and over the greater tubercle. The cutting guide is coupled to the guide support and the cutting guide is adjusted so that the curved frame abuts a portion of the humerus. The cutting guide is secured in a position relative to the guide support and the greater tubercle is resected. 
         [0013]    According to yet another embodiment of the present invention, an instrument for guiding the resection of a greater tubercle of a humerus is provided. The humerus has a longitudinal axis. The instrument includes a guide support in a fixed position relative to the humerus. The guide support extends laterally and over the greater tubercle. A cutting guide is moveably coupled to the guide support. The cutting guide is adapted to guide the resection of the greater tubercle at an angle perpendicular to the longitudinal axis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    For a more complete understanding of the present invention and the advantages thereof, reference is now made to the following description taken in connection with the accompanying drawings, in which: 
           [0015]      FIG. 1A  is a perspective view of a humerus; 
           [0016]      FIG. 1B  is a perspective view of an instrument according to one embodiment of the present invention on a humerus, with the humeral head resected; 
           [0017]      FIG. 1C  is a perspective view of the instrument of  FIG. 1B  on the humerus with also the greater tubercle resected. 
           [0018]      FIG. 2  is a sectional side view of a guide support of the instrument of  FIG. 1 ; 
           [0019]      FIG. 3  is a top view of a cutting guide of the instrument of  FIG. 1 ; 
           [0020]      FIG. 4  is a front view of the cutting guide of  FIG. 3 ; 
           [0021]      FIG. 5  is an isometric view of the cutting guide of  FIG. 3 ; and 
           [0022]      FIG. 6  is a flow chart describing a method of using an instrument according to one embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0023]    Embodiments of the present invention and the advantages thereof are best understood by referring to the following descriptions and drawings, wherein like numerals are used for like and corresponding parts of the drawings. 
         [0024]      FIGS. 1A-1C  illustrate a shoulder arthroplasty and an instrument  10  according to one embodiment of the present invention. Turning first to  FIG. 1A , a humerus  12  is shown. The humerus  12  includes a humeral head  14  and a greater tubercle  16 . During shoulder arthroplasty, the humeral head  14  is resected, resulting in a planar surface  18 , as shown in  FIG. 1B . After the humeral head  14  is resected, a broach  20  is inserted into the humerus  12 . As shown, the planar surface  18  is at an angle to both a longitudinal axis  22  and a medial-lateral axis  24 . During the shoulder arthroplasty, the humeral head  14  would be resected and a cavity will be prepared in the humerus  12  to receive a stem of an implant. 
         [0025]    As shown in  FIG. 1B , the instrument  10  includes a guide support  26  and a cutting guide  28 . The guide support  26  is at an angle that is parallel to the surface of the broach  20 . Preferably, the guide support  26  is also parallel to the planar surface  18  of the resected humeral head  14 . In some embodiments, the angle between the guide support  26  and the longitudinal axis  22  is between about 30 degrees and about 60 degrees. In some embodiments, the angle is between about 40 degrees and about 50 degrees. The guide support  26  couples to a cutting guide arm  30  of the cutting guide  28 . The cutting guide  28  includes a cutting surface that abuts the lateral edge of a greater tubercle  16 . The cutting guide  28 , as will be described later, is used to resect the greater tubercle  16  to create a flat planar surface  32  ( FIG. 1C ) that is parallel to the medial-lateral axis  24  and perpendicular to the longitudinal axis  22 . 
         [0026]    Turning now to  FIG. 2 , a sectional side view of the guide support  26  will be described. One end of the guide support  26  includes a stud  33  for placement in the broach  20 . In the illustrated embodiment, the stud  33  includes threads  34  for engaging a captured screw  35 . The captured screw  35  includes threads  36  for engaging the broach  20  ( FIG. 1 ) placed in the cavity of the humerus  12 . It should also be understood that other locking mechanisms such as taper locks, locking tabs, bolts, quick connects, ball plungers, etc. . . . may be used. The stud  33  is used to lock the guide support  26  in position relative to the broach  20 . It is important to note that the guide support  26  extends off of the broach  20  and out of the shoulder joint in the lateral direction, which allows for a lateral approach for resection of the greater tubercle  16 . An anti-rotation flange  37  is included that mates with the broach  20  to prevent the guide support  26  from rotating relative to the broach  20 . 
         [0027]    At the other end of the guide support  26  is a guide support slot  38  for receiving the cutting guide  28  as will be described below. Above the slot  38  is a boss  39 . The boss  39  includes a locking member  40 , in the illustrated embodiment, threads, for engaging a knob  42  ( FIG. 1 ) that will secure the guide support  26  to the cutting guide  28 . Although threads  40  and the knob  42  are shown, other known locking mechanisms, such as taper locks, locking tabs, bolts, quick connects, ball plungers, ratchets, teeth, etc. . . . may be used. 
         [0028]    Turning now to  FIG. 3 , the cutting guide  28  according to one embodiment of the present invention will be described. As shown in  FIG. 3 , the cutting guide  28  includes the cutting guide arm  30  that couples to the guide support  26  by sliding into the cutting guide slot  38  and locking the arm  30  into position via the boss  39 . Because the cutting guide slot  38  has a width that is larger than the width of the cutting guide arm  30 , the cutting guide arm  30  can be adjusted slightly about the longitudinal axis  22 . The cutting guide arm  30  can also be easily slid through the cutting guide slot  38  prior to tightening the knob  42  to obtain the optimal location for the cutting guide  28  relative to the humerus  12 . 
         [0029]    The cutting guide  28  also includes a curved frame  46 . The curved frame  46  includes a cutting surface  48  that is curved so as to nest against the outer portion of the humerus  12 . The curve of the cutting surface  48  is designed to closely resemble the radius of curvature of the humerus  12 . In some embodiments, the curve of the cutting surface  48  has a radius of between about 20 cm and 30 cm. In some embodiments, the curve of the cutting surface  48  has a radius of between about 22 cm and 26 cm. 
         [0030]    As shown in  FIG. 1B , the cutting guide arm  30  is slidably engagable with the guide support  26 . The knob  42  is turned to lock the cutting guide arm  30  in the desired position relative to the humerus  12 . During use, the surgeon would slide the cutting saw along the top part of the cutting surface  48  to resect the greater tubercle  16 , leaving the planar surface  32  as shown in  FIG. 1C . Although the illustrated embodiment shows a smooth arm, the cutting guide arm  30  could include teeth. In such an embodiment, the knob  42  would be a push-button that includes a ratchet or gear for engaging the teeth. When pressed, the push button would release the teeth. 
         [0031]    Turning now to  FIG. 4 , a front view of the cutting guide  28  is shown. As shown, the curved frame  46  creates a viewing area  50 . The viewing area  50  allows the surgeon to view the cutting area during the surgery. As shown in  FIGS. 3 and 5 , the viewing area  50  is curved, creating a large open area for the surgeon to view the cutting area. As discussed above, when the surgeon is inserting the cutting guide arm  30  into the guide support slot  38 , the surgeon can toggle the cutting guide arm  30  relative to the guide support  26 , which moves the frame  46 . By being able to move the frame  46 , the surgeon can adjust the viewing area  50  to best view the surgical area. 
         [0032]    Turning now to  FIG. 6 , a flow chart of the use of an instrument according to one embodiment will be described. First, at step s 60 , the humeral head  14  is resected and the broach  20  is inserted at step s 62 . At step s 64 , the broach  20  is mated with the stud  33  to affix the guide support  26  to the humerus  12 . The cutting guide arm  30  is then placed in the guide support slot  38  and translated until the curved cutting surface  48  of the cutting guide  28  contacts the humerus  12 . If desired, the surgeon at step s 66  can adjust the cutting guide  28  to obtain the optimal line of sight and placement of the cutting tool. Then, at step s 68 , the knob  42  is used to secure the cutting guide  28  in place. The cutting tool (not shown) is then placed on top of the cutting surface  48  and used to resect the greater tubercle  16  at step s 70 . After the resection is complete, the stud  33  is loosened and the entire instrument  10  can be removed from the broach  20  (step s 72 ). Trialing and implantation can follow as known in the art. In some embodiments, the instrument  10  is made of stainless steel. The stainless steel may also be coated, so as to protect against wear. In other embodiments, other medical grade metals or materials may be used. 
         [0033]    Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions, and alterations can be made therein without departing from the spirit and scope of the present invention as defined by the appended claims.