Abstract:
A fossa-eminence prosthesis having a nonanatomic surface that is relatively flatter than the native fossa. The articular eminence of the patient can be surgically reduced before implanting the prosthesis.

Description:
FIELD OF THE INVENTION 
       [0001]    The invention is a fossa-eminence prosthesis for a temporomandibular joint. 
       BACKGROUND OF THE INVENTION 
       [0002]    Metal fossa-eminence prostheses (hemijoint replacements) are generally known and commercially available. These devices are materials that are rigidly fixed to the articular fossa and/or materials that resurface the articular fossa to reverse bone-on-bone contact in patients with osteoarthritis or fibrous/osseous ankylosis. There remains a continuing need to improve fossa-eminence type prostheses. Prostheses that enhance joint motion are desirable. Improved instruments for use with eminence fossa implant surgical procedures involving fossa-eminence prostheses would also be desirable. 
       SUMMARY OF THE INVENTION 
       [0003]    An improved fossa-eminence prosthesis in accordance with one embodiment of the invention has a nonanatomic surface that is relatively flatter than the native (healthy or diseased) articular fossa. In another embodiment of the invention the mid-part of the prosthesis is thicker than other parts to provide the relatively flatter surface. The articular eminence of the patient can be reduced before implanting the prosthesis. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]      FIG. 1  is a right side view of a portion of a human skull illustrating an articular normal non-pathologic temporomandibular joint including a healthy articular disc between the mandible fossa of the temporal bone and the condylar process of the mandible. 
           [0005]      FIG. 2  is a right side view of a portion of a human skull, without the mandible, having a prosthesis in accordance with one embodiment of the present invention. 
           [0006]      FIG. 3  is a right side view of the skull and prosthesis shown in  FIG. 2 , with the mandible and its condyle engaged with the fossa of the prosthesis. 
           [0007]      FIG. 4  is a view of the skull and prosthesis shown in  FIG. 2 , showing the fossa of the prosthesis from below the skull. 
           [0008]      FIG. 5  is a back view of the prosthesis shown in  FIG. 2 . 
           [0009]      FIG. 6  is a bottom view of the prosthesis shown in  FIG. 2 . 
           [0010]      FIG. 7  is a front view of the prosthesis shown in  FIG. 2 . 
           [0011]      FIG. 8  is an interior view of the prosthesis shown in  FIG. 2 . 
           [0012]      FIG. 9  is a side view of the prosthesis shown in  FIG. 2 . 
           [0013]      FIG. 10  is a top view of the prosthesis shown in  FIG. 2 . 
           [0014]      FIG. 11  is a sagittal view of a portion of a temporomandibular joint having a prosthesis  10  in accordance with another embodiment of the present invention. Prosthesis  10  has an overall relatively flat contour design to ease the movement of the mandibular condyle  12  and reduce the obstructive effect of articular eminence  14 . The eminence was reduced during the surgical procedure. The mandibular condyle  12  can be smoothed during the surgical procedure. The mid region of the prosthesis  10  over the glenoid (articular) fossa  20  is thicker in other surrounding regions to provide the relatively flat surface of the design. 
           [0015]      FIG. 12  is a coronal view of a portion of a temporomandibular joint and prosthesis  10  shown in  FIG. 11 . The mid region  22  of the prosthesis  10  is thicker than the other regions to provide the relatively flat contoured shape. The region  24  of the prosthesis  10  over the medial part of the glenoid fossa  20  has a slight curvature. 
           [0016]      FIG. 13  is a view of a portion of a human skull showing the anatomy of the natural temporal (articular) fossa (i.e., before surgery in accordance with one embodiment of the invention. 
           [0017]      FIG. 14  is a view of the portion of the skull shown in  FIG. 13  following surgical reduction of the articular eminence and recontouring of the glenoid fossa. 
           [0018]      FIG. 15  is a view of the portion of the skull shown in  FIG. 14  with an implanted prosthesis in accordance with the present invention. 
           [0019]      FIGS. 16A and 16B  are isometric and side views, respectively, of a first retractor in accordance with one embodiment of the invention that can be used to surgically implant the prosthesis shown in  FIG. 2 . 
           [0020]      FIGS. 17A-17D  are views of a second retractor in accordance with another embodiment of the invention that can be used to surgically implant the prosthesis shown in  FIG. 2 . 
           [0021]      FIGS. 18A and 18B  are isometric and side views, respectively, of a third retractor in accordance with another embodiment of the invention that can be used to surgically implant the prosthesis shown in  FIG. 2 . 
           [0022]      FIGS. 19A and 19B  are plan and side views, respectively, of a scraper in accordance with another embodiment of the invention that can be used to surgically implant the prosthesis shown in  FIG. 2 . 
           [0023]      FIGS. 20A and 20B  are detailed plan and side views, respectively, of the working end of the scraper shown in  FIGS. 19A and 19B . 
           [0024]      FIG. 21  is a side view of a first burr in accordance with one embodiment of the invention that can be used to surgically implant the prosthesis shown in  FIG. 2 . 
           [0025]      FIG. 22  is a detailed side view of the working end of the burr shown in  FIG. 21 . 
           [0026]      FIG. 23  is a side view of a second burr in accordance with another embodiment of the invention that can be used to surgically implant the prosthesis shown in  FIG. 2 . 
           [0027]      FIG. 24  is a detailed side view of the tooling end of the burr shown in  FIG. 23 . 
           [0028]      FIGS. 25A-25D  are illustrations of a left side prosthesis in accordance with another embodiment of the invention that does not have a posterior projection.  FIG. 25A  is a side view from the anterior side (looking anterior to posterior);  FIG. 25B  is a plan view of the surface engaged by the mandibular condyle (i.e., in a direction from the bottom of the skull);  FIG. 25C  is an end view from the lateral side (looking lateral to medial); and  FIG. 25D  is an isometric view showing the surface engaged by the mandibular condyle. Locations for four screw holes on the lateral side are shown by dots. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0029]    The present invention is an implant surgically placed in the temporomandibular joint fossa/eminence (temporal bone) anatomy. The implant has a relatively flat nonanatomic surface that is surgically fit following osseous recontouring of TMJ fossa-eminence anatomy. It can be stabilized by endosseous screws. 
         [0030]      FIGS. 2-15  and  25 A- 25 D illustrate several embodiments of metal fossa-eminence prostheses (hemijoints) in accordance with the present invention. The prostheses differs from the duplication of healthy human fossa-eminence anatomy (e.g., that shown in  FIG. 1 ) in that they are generally flatter and have broader temporal surface coverage. These characteristics of the device are achieved at least in part by reducing portions of the articular eminence prior to implantation, and making the mid-part of the device thicker than other parts. The base of the valley in the mid-part is therefore higher than in an anatomical duplicate. The illustrated fixation endosseous screws are also improved to be more effective and user friendly. The flat design reduces the obstructing anatomy of the articular eminence to provide enhanced condyle motion. Use of the prosthesis in connection with eminoplasty and condyloplasty allow for favorable joint healing and biomechanics. 
         [0031]    The retractor shown in  FIGS. 16A and 16B  can be used for tissue retraction. The retractor has an approximately 180° circular loop or hook on one and an approximately 135° circular loop or hook on the other end. This retractor can be used to retract the tissue after preauricular flap development. Different ends can be alternated to fit the thickness and depth of tissue to be retracted. 
         [0032]    The retractor shown in  FIGS. 17A-17D  can be used for protecting and retracting the condyle away from the fossa during fossa-eminence debridement and recontouring. One end is wider than the other end. The wide end fits on the deep medial part of the fossa and keeps the convex surface of the condyle inferiorly depressed from the fossa and eminence. This gives surgical access for osteoplasty of the fossa/eminence. The condyle and associated tissue can also be protected from rotary instruments. The retractor is flexible and can be bent to an L shape as shown in  FIGS. 17C and 17D . 
         [0033]    The retractor shown in  FIGS. 18A and 18B  is a modified channel retractor that can be used for isolating the condyle. The working end is scoop shaped with rounded square angles. The working edge engages the condylar neck inferiorly and isolates the condyle medial pole superiorly. This rotates the mandible laterally allowing access to the medial portion of the mandibular condyle for reshaping. 
         [0034]      FIGS. 19A and 19B  and  20 A and  20 B are illustrations of a scraper that can be used for clearing osseous debris present on the fossa and condyle. It is a modified molt curette, and has a concave oblong round scoop working end. The working edges are thin, slightly curved, and sharp. The scraper can also be used for elevating the periosteum at all depths of bone exposure. 
         [0035]    The burr shown in  FIGS. 21 and 22  can be used for emino-fossa plasty. The burr is generally pear shaped and configured for cutting both on the end and the side. The cutting edge and angle make it self-cleaning as it reshapes (osteoplasty) the articular eminence and all dimensions of the articular fossa. The burr can also be used to reshape the condyle. 
         [0036]    The burr shown in  FIGS. 23 and 24  can be used for removing osteophytes and reshaping all dimension of the condyle. It is a self-cleaning side cutting burr. 
         [0037]    The embodiments of the prostheses shown in  FIGS. 25A-25D  are marked to illustrate some example of the dimensions of the devices. Other embodiments of the invention can have other dimensions. Dimension A, the overall height (i.e., in the superior-inferior direction), can, for example, be about 2-10 mm. This is the overall height the prostheses cover in this direction, and is different than the thickness of the prostheses themselves. The thicknesses of the prostheses are not uniform in these embodiments, and can, for example, range from about 1-6 mm. The middle region is typically relatively thicker. Dimension B, the overall width (i.e., in the medial-lateral direction) can, for example, be about 17-33 mm. Dimension C, the overall length (i.e., in the posterior-anterior direction) can, for example, be about 14-30 mm. Dimension D, the angle of the screw holes, can be about 10-30°. Stock prostheses in accordance with the present invention can be distributed in a range of sizes (e.g., with a range of temporal surface areas and a range of thicknesses) suitable for patients having different jaw sizes. 
         [0038]    Although the invention has been described with reference to preferred embodiments, those skilled in the art will recognize that changes can be made in form and detail without departing from the spirit and scope of the invention.