Abstract:
A bone cutting assembly. The bone cutting assembly includes a guide pin having a distal tip that may be securely inserted into a bone to define a cutting axis and a housing having a cam surface and features which allow the housing to be temporarily secured to the bone. The bone cutting assembly further includes a burr mounting arm which can be fitted on to the guide pin so that it can swing around the cutting axis and also translate up and down the guide pin. The burr mounting arm is configured to act against the cam surface as it is swung around the guide pin, so that the arm is caused to move up or down relative to the guide pin by the action of the cam surface.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    This is a continuation application of U.S. patent application Ser. No. 13/348902 which was a divisional of U.S. patent application Ser. No. 12/062952, entitled “HUMERAL ROTATING BURR GUIDE”, each of which are incorporated herein by reference in their entireties. 
     
    
     TECHNICAL FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to the field of orthopaedics, and more particularly, to an instrument for use in arthroplasty. 
       BACKGROUND OF THE INVENTION 
       [0003]    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. 
         [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 cavity 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 capsulor looseness. 
         [0006]    There are eight essential variables relating to humeral arthroplasty. These include: the diameter of curvature of the prosthesis; the percentage of the sphere with this diameter that will be used as prosthetic articular surface; the superior/inferior position of the articular surface relative to the humerus; the anterior/posterior position of the articular surface relative to the humerus; the medial/lateral articular aspect of the articular surface with respect to the humerus; the anterior/posterior angulation (flexion/extension) of the articular surface relative to the prosthesis; the medial/lateral angulation (varus/valgus) of the prosthesis relative to the humerus; and, the rotational alignment of the prosthetic head with respect to the humeral axis. The goal of prosthetic arthroplasty is to duplicate the normal orientation of the humeral articular surface as well as its diameter of curvature and percentage of the sphere. 
         [0007]    Many orthopaedic companies currently provide anatomically variable prosthesis with stems that facilitate adjusting the prosthesis to more accurately reflect the anatomy of the individual. For anatomically variable prostheses, most surgical techniques call for a “freehand” cut of the humeral head. Others have rudimentary guides that facilitate a planar cut but only allow for anterior/posterior (version) or medial/lateral adjustment of the cutting plane. 
         [0008]    When the humeral head resection is made free hand, the elbow of the patient is flexed to 90° with the patient&#39;s forearm aimed at the midline of the operating surgeon&#39;s trunk. The humerus is externally rotated to provide the recommended degree of retrotorsion in relation to the axis of elbow motion. The resection is directed away from the surgeon, allowing the surgeon to reproduce the desired retrotorsion in the bone cut. A trial prosthesis may also be placed along the proximal humeral shaft as a guide for the proper inclination of the resection. The possibility for error exists with this free hand approach. Inaccurate resection can result in an ill-fitting prosthesis which may cause complications for the patient and may eventually require replacement of the prosthetic device. 
         [0009]    Also, when implanting a proximal humeral resurfacing implant with an extended articulation surface, removal of part or all of the humeral greater tubercle is needed. This removal should allow for proper fitting and fixation of the implant and the extended articulation surface to the resurfaced humeral head and requires cutting in two planes. However, current cutting guides only allow for the cutting of the humeral greater tubercle in one plane at a time. Therefore, the surgeon would need to perform at least two cutting steps (and possibly use two different tools) to properly prepare the humerus. There is a need for a cutting guide that allows for a surgeon to be able to properly remove the humeral greater tubercle in a single step. 
       SUMMARY OF THE INVENTION 
       [0010]    According to one embodiment of the present invention, a cutting guide for removal of bone during arthroplasty is provided. The cutting guide includes a housing having a three-dimensional guide path as well as an arm coupled to the housing. The arm extends through the guide path and includes a burr. As the arm is slid along the path, the burr simultaneously cuts in two planes. 
         [0011]    According to another embodiment of the present invention, a method for resecting a portion of a bone in arthroplasty is provided. The method includes providing a housing having a three-dimensional guide path. An arm is placed in the housing, such that the arm is movable along the three-dimensional guide path. The arm is coupled to the burr. The method also includes simultaneously resecting a portion of the bone in a plurality of planes with the burr. 
         [0012]    According to yet another embodiment of the present invention, a cutting guide for cutting a form of a head of a bone during arthroplasty is provided. The cutting guide includes a housing adapted to be placed on the head of the bone and an arm rotatably coupled to the housing. A burr is coupled to the arm such that the burr is adapted to cut the from of the bone as the arm rotates about the housing. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    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: 
           [0014]      FIG. 1  is a perspective view of a humeral cutting guide on a humerus; 
           [0015]      FIG. 2  is a perspective view of the humeral cutting guide of  FIG. 1 ; 
           [0016]      FIG. 3  is a perspective view of a portion of  FIG. 2 ; 
           [0017]      FIG. 3A  is a partially see-through view of a portion of the humeral cutting guide of  FIG. 1 ; 
           [0018]      FIG. 4A  is a medial-lateral view of a resurfaced humeral head; 
           [0019]      FIG. 4B  is a lateral-medial view of a resurfaced humeral head; 
           [0020]      FIG. 5  is a flow chart describing the operation of the humeral cutting guide; 
           [0021]      FIG. 6  is perspective view of an alternative embodiment of the present invention; and 
           [0022]      FIG. 7  is an exploded view of the embodiment shown in  FIG. 6 . 
       
    
    
     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]    For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings and described in the following written specification. It is understood that no limitation to the scope of the invention is thereby intended. It is further understood that the present invention includes any alterations and modifications to the illustrated embodiments and includes further applications of the principles of the invention as would normally occur to one skilled in the art to which this invention pertains. 
         [0025]    Referring now to  FIGS. 1 and 2 , a cutting guide  10  is provided that allows for the cutting of a humeral head  12 . The cutting guide  10  is used to remove a portion of the humeral head  12  to allow for the placement of an implant (not shown). The cutting guide  10  includes a housing  14 . The housing  14  includes a three-dimensional guide path, such as a slanted parabolic slot  16  for coupling to a burr  18 . The slot  16  extends longitudinally and laterally. The slot  16  defines the path that the burr  18  will cut. The multi-directional nature of the slot  16  enables the burr  18  to move both in the proximal/distal plane and also the medial/lateral plane—thereby allowing for a multiplanar cut. 
         [0026]    An arm  20  extends through the slot  16  and includes a burr-attachment end and a quick-connect end. The burr-attachment end is coupled to the burr  18 . The arm  20  is held in place in the slot  16  by an adjustable cylinder  22 . The arm  20  includes a burr restraint portion  24  that is used to hold the burr  18  on its path. The adjustable cylinder  22  allows the surgeon to adjust the distance between the burr  18  and the housing  14 , which will be described in more detail in reference to  FIG. 3  below. The quick-connect end  20   b  of the arm  20  allows the surgeon to hold the burr with one hand while holding a drill portion with the other hand. 
         [0027]    The adjustable cylinder  22  includes an opening  26  that extends longitudinally through the adjustable cylinder  22 . The opening  26  is adapted to receive a guide pin  28 . As shown in  FIG. 1 , the guide pin  28  extends through opening  26  and a post  29  of the housing  14  into a humerus  30  for holding the cutting guide  10  in place relative to the humeral head  12 . 
         [0028]    The housing  14  also includes a pair of pin holes  31   a,    31   b  on the sides to align the housing anteriorly and posteriorly on the humeral head  12 . Pins  32   a,    32   b  fit through the pin holes  31   a,    31   b  to further affix the housing  14  to the humeral head  12 . The pins  32   a,    32   b  prevent the cutting guide  10  from sliding around on the humeral head  12 . 
         [0029]    Turning now to  FIG. 3 , a perspective view of the arm  20  is shown. An elongated slot  33  extends through the arm  20 . The elongated slot  33  is dimensioned so as to receive the guide pin  28 . The arm  20  also includes a plurality of notches  34  that are adapted to correspond with an adjustable pin (not shown). In the embodiment shown in  FIG. 3A , the notches  34  extend around the arm  20  and engage a movable ridge  36  on the inside of the adjustable cylinder  22  ( FIG. 3A ). The ridge  36  couples with one of the notches  34 , locking the arm  20  in a particular location relative to the housing  14 . A button  38  is included on the top of the adjustable cylinder  22 . As best shown in  FIG. 3A , when the button  38  is pressed, the ridge  36  disengages the notch  34  so the user can slide the arm  20 . In some embodiments of the present invention, the arm  20  may include markings to aid the surgeon in measuring the distance between the cylinder  22  and the burr  18 , which will adjust the radius of the cut area. 
         [0030]    In an alternative embodiment, the cylinder  22  may include a notch and the arm  20  may include ridges. In other embodiments, other known releasable locking mechanisms may be used. 
         [0031]    Returning now to  FIG. 2 , the restraint portion  24  includes a positioning member  39 . The positioning member  39  allows the user to adjust the burr  18  up or down. By being able to adjust the vertical location of the burr  18 , the user can control the depth that the burr  18  will cut. The vertically adjustable piece  39  includes a screw  40  that can be adjusted to different heights, allowing the burr  18  to be adjusted. 
         [0032]    In another embodiment, the burr  18  may not be vertically adjustable. Instead, there may be provided a plurality of burrs that have different depths, which would allow for different heights to be cut. 
         [0033]      FIGS. 4A and 4B  show a top and a side view of the humerus  30 . As illustrated, the humerus  30  includes a greater humeral tubercle  44  (best seen in  FIG. 1 ) that needs to be either partially or wholly removed. The greater humeral tubercle  44  includes a radius R and a depth D. The cutting guide  10  of the present invention will be able to cut both the radius R and the depth D in a single step, as will be described below. 
         [0034]    Turning now to  FIG. 5 , a method for using the cutting guide  10  will be described. First, at step s 50 , a humeral head  12  is resurfaced using a spherical reamer over the guide pin  28 . The reamer allows for a flat surface to be created on the top of the humeral head  12 . At step s 52 , the length of the arm  20  is adjusted to the desired length. Next, at step s 54 , the cutting guide  10  is placed over the guide pin  28 . The housing  14  of the cutting guide  10  sits on the flat on the top of the humeral head  12 . The post  29  fits into the reamed hole. Next, at step s 56 , the cutting guide  10  is aligned using the pin holes  31   a,    31   b  on the housing  14 . Pins  32   a,    32   b  are placed in the pin holes  31   a,    31   b  at step s 56  to prevent rotation of the housing  14 . At step s 58 , the arm  20  and adjustable cylinder  22  are then placed over the guide pin  28  in the parabolic slot  16  of the housing  20 . The burr  18  is then placed into the restraint portion  24  of the arm  20  at step s 60 . At step s 62 , the depth of the burr  18  will be adjusted (if so desired). The arm  20  is then rotated and translated along the parabolic slot  16  to resect the radius R and depth D simultaneously on the humerus  30  at step s 64 . After the required part of the greater tubercle  42  is removed, the cutting guide  10  is then removed from the guide pin  28  and the trialing and implantation of the prosthesis can occur. 
         [0035]    In some embodiments, step s 52  may take place after the arm  20  is placed over the guide pin  28 . In some embodiments, step  62  may not be included. In those embodiments, multiple burrs of different sizes may be included and the surgeon selects one of the burrs depending on the depth the surgeon would like to cut. 
         [0036]    By placing the cutting guide  10  on the guide pin  28  that is used in other cutting procedures, reproducible and properly placed cuts can be more easily achieved. Also, because of the three-dimensional parabolic nature of the slot  16 , the radius and the depth can be cut simultaneously, allowing for resection in multiple planes. Also, in some embodiments both the arm  20  and the burr are adjustable relative to the housing  14 , both the radius and the depth to be cut can be adjusted depending upon the anatomy of the patient or the need of the surgeon. 
         [0037]    Turning now to  FIGS. 6 and 7 , another embodiment of the present invention will be described. A cutting guide  100  is provided that includes an arm  102  that couples to the burr  18 . The cutting guide  100  further includes a housing  104 . The housing  104  includes an opening  106  to enable the housing  104  to slide over the guide pin  28 . The cutting guide  100  also includes a stem hole stabilizer  108  that attaches to the housing  104  via a threaded portion  110  as shown in  FIG. 6 . The threaded portion  110  engages a threaded opening  112  in the housing  104 . The housing  104  and stem hole stabilizer  108  can be adjusted vertically relative to the guide pin  28  via a screw  114  that locks the housing in position on the guide pin  28 . 
         [0038]    In use, the arm  102  swings along a curved path on the humeral head  12 , guiding the burr  18 . The swinging of the arm  102  causes the burr  18  to cut off a radius of the greater tubercle. In other words, the burr  18  swings along an arcuate path on the greater tubercle. In this embodiment, another cutting guide would need to be used to cut the appropriate depth. 
         [0039]    In one embodiment, the burr  18  is made of a stainless steel having a hardness between about  40  and  55  on the Rockwell scale. In embodiments where the burr  18  is only intended to be used once, the burr may be made of a softer metal. In other embodiments, the burr  18  may be made of a softer metal, but may be coated with stainless steel having the hardness described above. The arm  20  may be made of stainless steel or other sterilizable metals. The arm  20  itself may also be a one-time instrument made of a polymer material. The housing  14  may also be made of stainless steel or other sterilizable metal. In other embodiments, the housing may also be made of a polymer material. In the above-described invention, the path cut was an arcuate path that included both a radius and a depth. In other embodiments, the multi-dimensional guide path could be designed so as to cut other dimensions that result in two planes being simultaneously cut. For example, in some embodiments, the path may be a parabolic slot that cuts both a radius and a width. In other embodiments, the path may be of a different shape that cuts an oval or a rectangle while simultaneously cutting another dimension. 
         [0040]    Although the above-embodiments have been described being used with a humeral head, it should be understood that the cutting guide of the present invention may be used to cut other bones in preparation of arthroplasty. 
         [0041]    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.