Abstract:
A modular humeral head resurfacing implant including a head, an anchoring stem, and a modular extended articulation flange. The head includes an exterior hemispherical articulating surface defining a terminating rim, an interior concave surface opposite to the exterior articulating surface, and a first coupling mechanism proximate to the terminating rim. The anchoring stem is coupled to the interior concave surface and extends along a stem axis that extends through an axial center of the head. The articulation flange includes a second coupling mechanism configured to cooperate with the first coupling mechanism to fasten the articulation flange to the head and an outer articulating surface that is curved along substantially its entire length and is substantially flush with the exterior hemispherical articulating surface when the articulation flange is fastened to the head.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 14/538,876, filed Nov. 12, 2014, which application is a divisional application of U.S. patent application Ser. No. 12/696,516 filed on Jan. 29, 2012, which is a continuation application of U.S. patent application Ser. No. 11/258,341 filed on Oct. 25, 2005, which is a continuation-in-part application of U.S. patent application Ser. No. 10/669,971 filed on Sep. 24, 2003. The disclosures of the above applications are incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to prosthetic implants. In particular, the present invention relates to a humeral resurfacing implant. 
     BACKGROUND OF THE INVENTION 
     The humerus is the longest and largest bone of the human upper extremity. It is divisible into a body and two extremities. The upper extremity comprises a head that is joined to the body by a constricted portion generally called the neck. The head is nearly hemispherical in form and articulates with the glenoid cavity of the scapula or shoulder blade. The humerus is secured to the scapula by the rotator cuff muscles and tendons. 
     It is not uncommon for the exterior surface of the humeral head to be damaged or defective. Conventionally, a variety of humeral head resurfacing implants exist for repairing humeral head surfaces. While conventional humeral head resurfacing implants are suitable for their intended uses, such implants are subject to improvement. 
     Conventional humeral head resurfacing implants fail to accommodate patients having inadequate rotator cuff muscles. Specifically, conventional implants do not permit articulation between the implant and the concave undersurface of the coracoacromial arch of the scapula, the coracoacromial arch being a structural component of the shoulder comprising the coracoacromial ligament, coracoid process, and acromion. Thus, there is a need for a humeral head resurfacing implant that permits articulation with the coracoacromial arch in patients having inadequate rotator cuff muscles. 
     SUMMARY OF THE INVENTION 
     The present teachings provide for a modular humeral head resurfacing implant including a head, an anchoring stem, and a modular extended articulation flange. The head includes an exterior hemispherical articulating surface defining a terminating rim, an interior concave surface opposite to the exterior articulating surface, and a first coupling mechanism proximate to the terminating rim. The anchoring stem is coupled to the interior concave surface and extends along a stem axis that extends through an axial center of the head. The modular extended articulation flange protrudes from only a portion of the head when fastened thereto and is operable to articulate with at least one of a bone and a ligament. The articulation flange includes a second coupling mechanism configured to cooperate with the first coupling mechanism to fasten the articulation flange to the head and an outer articulating surface that is curved along substantially its entire length and is substantially flush with the exterior hemispherical articulating surface when the articulation flange is fastened to the head. 
     The present teachings also provide for a humeral head resurfacing implant including a head, an anchoring stem, and a modular extended articulating flange. The head includes an exterior hemispherical articulating surface defining a terminating rim. The terminating rim defines a rim plane extending from a first side of the terminating rim to a second side of the terminating rim. The head also includes an interior concave surface opposite to the exterior articulating surface and a first coupling mechanism proximate to the terminating rim. The anchoring stem is coupled to the interior concave surface and extends along a stem axis that extends through an axial center of the head and through the rim plane, the stem axis is perpendicular to the rim plane. The modular extended articulating flange protrudes from only a portion of the head and extends across the rim plane when fastened to the head. The articulating flange includes a second coupling mechanism that is coupled to the first coupling mechanism to fasten the articulating flange to the head. 
     The present teachings also provide for a method of resurfacing a humeral head of an implant site. The method includes the following: resurfacing the humeral head so as to form a generally spherical surface; selecting a modular extended articulation flange having a first coupling mechanism from a plurality of modular extended articulation flanges of different sizes; attaching the first coupling mechanism of the modular extended articulation flange to a second coupling mechanism proximate to a terminating rim of a resurfacing humeral head implant including an exterior hemispherical articulating surface defining the terminating rim and an interior concave surface opposite to the exterior articulating surface; and positioning the resurfacing humeral head implant on the resurfaced surface of the humeral head. 
     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 the preferred embodiment 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 present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a perspective view of an implant according to the present invention; 
         FIG. 2  is bottom view of the implant of  FIG. 1 ; 
         FIG. 3A  is a cross-sectional view taken along line  3 - 3  of  FIG. 2 ; 
         FIG. 3B  is a cross-sectional side view of the implant of the present invention according to an additional embodiment; 
         FIG. 4  is a perspective view of a typical implantation site prepared to receive the implant of  FIG. 1 ; 
         FIG. 5  is a perspective view of the implant of  FIG. 1  implanted at the implantation site of  FIG. 4 ; 
         FIG. 6  represents a monolithic implant according to an embodiment of the invention; 
         FIGS. 7A-7D  represent a modular prosthetic head; 
         FIGS. 8A-8D  represent an alternate modular prosthetic; 
         FIGS. 9 and 10  represent an alternate modular prosthetic utilizing a snap-ring fixation mechanism; 
         FIG. 11  represents a tool for use to implant the prosthesis shown in  FIGS. 7A-10 ; and 
         FIGS. 12-22  represent the preparation of a humerus to accept the implant shown in  FIGS. 7A-10 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiments is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. 
     With initial reference to  FIGS. 1 through 3 , a resurfacing implant according to the present invention is illustrated and identified at reference numeral  10 . The implant  10  is typically divided into, as illustrated in  FIG. 3 , a lateral region A and a medial region B, which is in relation to the implant position in the patient. The implant  10  generally includes a resurfacing head  12 , an anchoring device or stem  14 , and an extended surface  16 . The extended surface  16  may be located in the lateral region A, as illustrated, or at any other position about a periphery of the head  12 . The head  12  includes an exterior surface  18  and an interior surface  20  opposite the exterior surface  18 . The exterior surface  18  is generally convex, or dome-shaped, and smooth. The interior surface  20  is generally concave. 
     The interior surface  20  is also generally dome-shaped and substantially mirrors the exterior surface  18 . The interior surface  20  is generally concave. The interior surface  20  may be smooth or may include features, such as pores or coatings that facilitate bonding of the interior surface  20  to a resurfaced implant site. The interior surface  20  may be bonded to the implant site with or without bone cement. The interior surface  20  optionally terminates at an annular rim  24 . 
     The stem  14  extends from the interior surface  20 . The stem  14  may optionally be tapered such that the diameter of the stem  14  is at its greatest at the interior surface  20 . To facilitate cooperation between the stem  14  and the implant site, the stem  14  may optionally include one or more details, such as flutes  26 . In addition to or in place of flutes  26 , the stem  14  may include surface features, such as pores or coatings, to enhance the creation of a bond between the stem  14  and the implant site. 
     In some applications, the extended surface  16  is located in the lateral region A to engage a surface or bone, such as at least one portion of the coracoacromial arch. However, the extended surface  16  may be located at any other position about the rim  24  to engage a variety of different bones and/or ligaments. The extended surface  16  is generally comprised of an outer surface  28 , a base surface  30 , and an inner surface  32 . The outer surface  28  is typically a continuation of the exterior surface  18 . The outer surface  28  may be of any suitable shape or configuration, however, in many instances, the outer surface  28  is curved or rounded to follow the general shape of the exterior surface  18 . The outer surface  28  extends about a portion, but less than an entirety of the annular rim  24 . The extended surface  16  generally extends beyond an equator of the hemispherical head  12 , which is generally defined by the rim  24 . As seen in  FIG. 3A , the extended surface  16  extends from the head  12  in a planar and/or cylindrical manner. 
     The base surface  30  generally extends from the outer surface  28  toward the stem  14  at approximately a right angle to the outer surface  28 . The base surface  30  may be generally planar or may include various surface features to enhance interaction between the base surface  30  and the implantation site. The base surface  30  is typically shaped to accommodate the curvature of the annular rim  24 . The length of the base surface  30  determines, in part, the width of the extended surface  16 . 
     The inner surface  32  extends from the base surface  30  toward the interior surface  20 . The inner surface  32  extends from the base surface  30  at an approximate right angle to the base surface  30 . The inner surface  32  may be of any suitable shape but is typically shaped to generally accommodate the curvature of the annular rim  24 . In some applications, the inner surface  32  may be wedged shaped, typically in the shape of a “V”, to generally facilitate interaction between the implant  10  and the implantation site by providing a surface that matches the shape of a prepared bone that is to receive the implant  10 . The shape of the inner surface  32 , such as the wedge shape, may be used to act as a further aide to maintain the implant  10  in its desired position and prevent rotation of the implant  10  at the implantation site. 
     If the extended surface  16  is of a relatively small width, the inner surface  32  may be an extension of the interior surface  20  ( FIG. 3A ). As illustrated in  FIG. 3B , if the extended surface  16  is of a relatively large width, the inner surface  32  is not a continuation of the interior surface  20 , but is connected to the interior surface  20  by an upper surface  34 . The upper surface  34  runs generally parallel to the base surface  30  and may be, for example, planar or curved. The upper surface  34  forms a step on the extended surface  16 . 
     The implant  10  may be made of any suitable biocompatible material, but is typically made from a metal such as cobalt chrome or titanium. The interior surface  20  may be coated with a suitable material, such as titanium plasma spray or hydroxyapatite, to enhance the adhesion of the interior surface  20  to the implantation site or to enhance the effectiveness of any material, such as bone cement, that may be used to affix the interior surface  20  to the implantation site. The stem  14  may optionally be provided with a blasted finish, with or without hydroxyapatite, or a micro-bond finish, with or without hydroxyapatite. As a further option, bone cement may be used as an aide to retain the implant  10  in position. 
     The implant  10  may be of various different sizes and dimensions depending on the sizes and dimensions of the implant site. For example, to accommodate patients having large humeral heads, the implant  10  may be of a greater overall size than that required to accommodate patients having smaller humeral heads. Further, the shape of the exterior surface  18  may be customized to insure proper articulation at the implant site. Implants  10  of various different shapes and sizes may be packaged together and sold in a single kit. 
     With reference to  FIGS. 4 and 5 , the implantation and operation of the implant  10  will be described in detail. While the implant  10  is generally described as a humeral head resurfacing implant, it must be noted that the implant  10  may be used in a variety of different applications. The implantation site generally includes a humerus  36  and a shoulder blade or scapula  38 . The humerus  36  is generally comprised of a head  40 , a neck  42 , and a stem  44 . The scapula  38  is generally comprised of a glenoid cavity  46  that receives the head  40 , a coracoacromial arch  48 , and a coracoid process  50 . 
     To receive the implant  10 , a portion of the exterior surface of the humeral head  40  is resurfaced and/or removed to accommodate the resurfacing head  12  of the implant  10  such that, when implanted, the implant head  12  does not generally increase the overall dimensions of the humeral head  40 . The head  12  is further resected at  52  to accommodate the extended surface  16 . This resection at  52  may be performed with or without the use of a resection jig. To minimize bone loss, the resection at  52  often takes the shape of a “V”, however, the resection  52  may be of various other shapes or configurations. The “V” shape may also prevent rotation of the head  12 , even though the interaction between the stem  14  and the implant site is more than adequate to secure the head  12  into position. 
     To receive the stem  14 , which is generally referred to as a short stem  14 , a peg hole  54  is formed within the head  40  using conventional instruments and techniques. The hole  54  is formed with dimensions substantially similar to the dimensions of the stem  14  and is positioned such that when the stem  14  is seated within the hole  54 , the exterior surface  18  closely approximates the outer surface of the humeral head  40 . The hole  54  extends generally only through a portion of the humeral head  40  and does not necessarily extend to the stem  44  or within the intramedullary canal of the humerus. To ensure proper placement of the implant  10 , a trial implant (not shown) may be positioned at the implantation site before the implant  10  is implanted. 
     The trial implant is substantially similar to the implant  10 . A stem of the trial implant is placed within the hole  54  and the shoulder joint is reduced. If necessary, the head  40  is reamed to better approximate the size and shape of the interior surface  20 . After the proper position of the trial implant is noted, the trial is removed and the stem  14  of the implant  10  is seated within the hole  54 . The implant  10  is then positioned such that it is in substantially the same position as the trial implant. The particular size of the implant  10  is chosen according to the size and dimensions of the patient&#39;s humeral head  40  and scapula  38 . It must be noted that typically the stem  14  only extends through a portion of the head  40  and does not enter, or replace, the natural stem  44  of the humerus  36 . 
     As illustrated in  FIG. 5 , the implant  10  is orientated at the humeral head  40  such that the extended surface  16  is positioned at or near the coracoacromial arch  48 . The extended surface  16  may either abut, or closely abut, the coracoacromial arch  48 . When the patient&#39;s rotator cuff muscles are inadequate, the extended surface  16  typically contacts the coracoacromial arch to provide metal on bone articulation with the coracoacromial arch  48 . However, the extended surface  16  may be rotated to any other position to engage other bones, ligaments, or surfaces other than, or in addition to, the coracoacromial arch  48 . 
     While interaction between the stem  14  and the hole  54  is typically suitable to secure the implant  10  within the hole  54 , the stem  14  may optionally be secured within the hole  54  using a suitable adhesive, such as bone cement  56 . The optional bone cement  56  may be inserted within the hole  54 , typically before the implant  10  is placed within the hole  54 . The flutes  26  of the stem  14  assist in forming a cement mantle between the stem  14  and the hole  54  to receive the bone cement  56 . The optional tapered configuration and blasted finish of stem  14  further enhances the bond between the implant  10  and the head  40  by providing a mechanical interface. To still further secure the implant  10  to the head  40 , a suitable adhesive, such as bone cement, may be placed between the interior surface  20  and the head  40  and various coatings may be applied to the interior surface  20 , such as titanium plasma, to create a bond between the interior surface  20  and the head  40 . 
     With the implant  10  in place upon the humeral head  40 , patients with inadequate rotator cuff muscles are provided with a device that permits articulation between the humerus  36  and the coracoacromial arch  48 . This articulation between the humerus  36  and the coracoacromial arch  48  enhances range of motion in the patient&#39;s shoulder and reduces patient discomfort. 
       FIG. 6  represents a monolithic resurfacing implant according to the teachings of an alternate embodiment. The implant  60  includes a resurfacing head  62 , an anchoring device or stem  64  and an extended bearing member  66 . The head  62  has a generally spherical articulating bearing surface  68  and an interior coupling surface  70 . 
     The stem  64  is coupled to the interior surface  70  and can have various surface features  72  to facilitate the coupling of the implant to a resected humerus. Disposed between the articulating surface  68  and the internal surface  70  of the implant  60  is a base surface  71 . The base surface  71  is congruent with the base surface  73  of the bearing member  66 . The internal surface  70  defines a generally spherical surface  74 , which seats against a resected spherical bearing surface  76  of the humerus. Additionally, the interior surface  70  defines three flat intersecting surfaces  78 A-C. Optionally, the surfaces  78 A and B intersect with surface  780  at obtuse angles. The surfaces  78 A-C are supported by the corresponding resected surfaces in the humeral head. 
     As shown in  FIGS. 6, 7A-7D and 8A-8D , the extended surface can vary in radial width W and length L. As shown in  FIG. 7A-8D , the extended surface can be an additional modular component  80 , which can be coupled to the head using varying fixation mechanisms  81 . In this regard, the fixation mechanism can take the form of a pair of interference fit members including a male member  82  extending from the modular component  80  and a female member  83  recessed within the head  12  to provide, for example, a Morse taper lock there between. Additionally, as shown in  FIGS. 8B-8D , the fixation member can be a fastener such as a screw. 
     As shown in  FIGS. 7A-7D , the modular component  80  has an exterior articulating surface  84  which can have varying radii of curvature which are congruent with the articulating surface  68 . The modular component  80  can also include the male member  82  and the female member  83  to provide a Morse taper connection between the modular component  80  and the head  12 . Additionally shown is an anti-rotation member  86  in the form of a pin. As shown in  FIGS. 8A-8D , the additional modular components  80  can include a flange  85  having a through hole  91 . The modular components  80  can be coupled to the implant  60  by inserting the fastening mechanism  81  through the hole  91  of the flange  85  and into cooperation with the threaded bore  89 . The threaded bore  89  can optionally be parallel or perpendicular to the fixation stem  64 . 
       FIGS. 9 and 10  represent cross-sectional and exploded views of an alternative prosthetic. The additional modular component  80 ′ is coupled to the interior coupling surface  70  via a ring lock  87 . The ring  87  is configured to couple the annular modular component  80 ′ using the groove  88  defined on the bearing surface  68 , and a groove  90  defined on an interior surface  92  of the modular component  80 ′. 
       FIG. 11  represents a cutting guide  98  which allows for the preparation of the humerus. In this regard, the cutting guide  98  allows for the removal of tuberosities to make room for an extended implant. The cutting guide  98  has a main body  100  and a cannulated handle  102 . The underside  104  of the main body has a spherical concave surface  108  that relates to the spherical radius of a spherical cutter  109  used to prepare the humerus. The guide  98  is configured to be fully seated on the resurfaced humeral head  76 . A plurality of slots  106  are formed within the main body  100  for viewing the resurfaced head to determine if the guide is well seated. Additional holes  107  are formed in the guide main body  100 , which accept a plurality of guide pins  110 . These pins  110  prevent the rotation of the cutting guide  100  during the resection of the humerus. 
     Further defined in the cutting guide main body  100  are a plurality of angled cutting slots  112 , which are configured to match the flats  78 A- 78 C created on the inner surface on the resurfacing implant. In this regard, the angled slots  112  can form compound angles with respect to each other. Additional groups can be formed on an exterior peripheral surface of the main body to facilitate the removal of material. To insure the cutting guide is properly oriented, markings  114  can be formed on the outside surface of the cutting guide. These markings are intended to allow the relative rotation and placement of the cutting guide with respect to predetermined or known anatomical locations, such as the bicipital groove. 
     The handle  102  defines a through passage  116  or aperture, which is configured to slidably accept a Steinmann pin  118 . It is envisioned that the handle can be removable from the body portion to facilitate the resection through the number of slots in the main body. 
       FIGS. 12-22  represent the preparation of the humerus to accept any of the aforementioned prosthetics.  FIG. 12  represents the first step in inserting the extended articulating surface humeral resurfacing head. First, a drill guide  120  is used to locate the center of the humeral head. The drill guide  120  has a generally spherical concave inner surface  122 , which is configured to conform to the generally spherical surface of the humeral head. The drilling guide has a cannulated handle  124 , which is used to direct the placement of the Steinmann pin  118 . 
     As shown in  FIG. 12 , the Steinmann pin  118  is disposed through the guide to mark the location of the center of the head. As also shown in  FIG. 13 , a spherical surface cutter  126  is placed over the Steinmann pin and used to ream the surface of the head to remove a predetermined amount of biological tissue (see  FIG. 14 ). Optionally, the reaming continues until bone is shown coming through a plurality of holes  128  within the cutter. 
     The cutting guide  100 , as shown in  FIG. 16 , is placed over the Steinmann pin  118 . The cutting guide  100  is rotated so that the marking  114  on the exterior surface of the cutting guide is lined up with the bicipital groove. The additional guide pins  110  are then placed through the guide holes  107  in the guide to prevent relative rotation of the cutting guide  100  with respect to the humerus during the resection of the humeral head. 
     At this point, a rotational or reciprocal cutting tool  130  is placed within the cutting grooves  112  formed in the cutting guide  100 . This tool is used to form a plurality of flat surfaces  132  on the humerus. At this point, the anti-rotation pins and cutting guide are removed from the resected humerus. A spade bit  134  is placed over the Steinmann pin  118  and rotated until a stop ledge  136  touches the humeral head. Both the spade bit  134  and Steinmann pin  118  are removed from the humerus. A trial head (see  FIG. 19 ) is then placed onto the resurfacing bone and used to check the full range of motion and correct soft tissue tensioning. Lastly, the final prosthetic is placed onto the bone and impacted into place. 
       FIGS. 20-22  represent the placement of the prosthetic  60  onto the prepared humerus. As can be seen, the exterior portion  66  is positioned to allow proper articulation of the repaired joint. A trialing head  60 ′ is positioned to the prepared humerus. The head  60  is then coupled to the resected humerus as previously described. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.