Abstract:
A fastener, driving device, and method are provided for repairing a tear in soft tissue of a patient, such as a meniscal tear in a knee. The fastener has a distal section having a narrowing cross section toward the distal end and a helical protrusion along a central section between the proximal end and the distal end. Along a distal section extending from the distal end, the helical pitch is substantially constant; along a central section between the distal section and the proximal end, the helical pitch decreases from the distal end to the proximal end. The substantially constant pitch along the distal section assists in preventing a stripping of the helical section. At the proximal end is a head having a diameter greater than a major root diameter of the central section. The head is for improving the tissue retention characteristics of the fastener.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS  
       [0001]    This application is a continuation-in-part of and incorporates by reference co-pending application Ser. No. 09/542,100, filed Apr. 4, 2000, commonly owned with the present application. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to surgical devices and methods for repairing tissue tears and, more particularly, to a device and method for repairing a soft-tissue tear in a knee.  
           [0004]    2. Description of Related Art  
           [0005]    The repair of soft tissue tears represents a persistent problem in orthopedic practice. It is known to apply sutures and various types of fixation devices to such tears.  
           [0006]    Among the soft tissue sites that require fixation are the menisci of the knee. The material of the menisci is collagenous, and the fibers are oriented generally circumferentially. Posterior peripheral tears of the menisci may be treated by an open technique, wherein sutures are placed along the tear. An arthroscopic technique may also comprise placing sutures along the tear, but in this method through a cannula.  
           [0007]    There are a number of fastener-type devices that are known in the art: Screiber (U.S. Pat. No. 4,873,976); Bays et al. (U.S. Pat. Nos. 4,884,572 and 4,895,148); Winters (U.S. Pat. No. 5,059,206); and Justin and Winters (U.S. Pat. Nos. 5,503,634 and 5,730,744). Bone screws are disclosed by Huebner et al. (U.S. Pat. Nos. 5,562,672 and 5,871,486).  
         SUMMARY OF THE INVENTION  
         [0008]    It is an object of the present invention to provide a fastener, delivery device, and method for repairing a tear in soft tissue.  
           [0009]    It is a further object to provide such a fastener that is made from a nontoxic, biocompatible, bioabsorbable plastic specially designed to maintain its structural integrity during the healing of the tear and to prevent tissue abrasion.  
           [0010]    It is an additional object to provide such a fastener having a shape designed to compress the tear.  
           [0011]    It is another object to provide such a fastener shaped to resist forces tending to pull apart the meniscal tear during healing.  
           [0012]    It is also an object to provide such a fastener that resists stripping and has superior tissue retention characteristics.  
           [0013]    These and other objects are attained with the fastener and delivery device system and method of the present invention, a fastener designed for repairing a tear in soft tissue of a patient, a particular exemplary embodiment comprising a meniscal tear in a knee, although this is not intended as a limitation. The fastener has a proximal end, a distal end, and a distal section having a narrowing cross section toward the distal end. In use an insertion of the fastener into soft tissue is facilitated by this narrowed distal end, which takes the form in a preferred embodiment of a generally conical-shaped distal tip.  
           [0014]    The fastener further has a helical protrusion along a central section between the proximal end and the distal end. Along a distal section extending from the distal end, the helical pitch is substantially constant; along a central section between the distal section and the proximal end, the helical pitch decreases from the distal end to the proximal end. In use the decrease in the helical pitch along the central section can serve to bring two sides of the tear into apposition as the fastener is advanced across the two sides of the tear in a screwing motion. The substantially constant pitch along the distal section assists in preventing a stripping of the helical section.  
           [0015]    At the proximal end is a head having a diameter greater than a major root diameter of the central section. The head is for improving the tissue retention characteristics of the fastener.  
           [0016]    In an alternate embodiment of the fastener, the variable-pitch helical protrusion has means for resisting an axial force from pulling the fastener out of the tear and from pulling the two sides of the tear apart. Specifically, the resisting means comprises the helical protrusion having a buttress form.  
           [0017]    In a preferred embodiment, the fastener material comprises a biodegradable plastic biocompatible with the soft tissue of the patient. The material is specifically designed to be biodegradable within a first time span greater than or equal to a second time span over which the sides of the tear can knit together. This feature permits the fastener to remain in place for as long as required for the tear to heal, but ultimately to biodegrade and be dissipated harmlessly into the patient&#39;s system.  
           [0018]    The material is further designed to have elastomeric properties compliant with those of the meniscus in order to confer biofunctionality.  
           [0019]    A further feature of the present invention comprises a delivery device for introducing the above-described fastener into the area of the patient&#39;s soft tissue to be repaired. A feature of the fastener permitting a mating with a delivery device comprises the fastener&#39;s having an axial bore extending along the helical axis proceeding from the proximal end. The bore preferably has a noncircular cross-sectional shape so that an elongated driving device having a noncircular cross-sectional shape and dimensioned to pass into the bore can enter the bore and turn the screw. The fastener can then be advanced into the soft tissue by being rotated by the driving device in a direction having a handedness commensurate with the helically shaped protrusion. Simply put, the fastener appears as a variable-pitch screw that is internally drivable by rotation of an elongated member inserted into its bore.  
           [0020]    The elongated driving device of the present invention for driving the fastener as described above has a distal end having means for mating with the fastener proximal end, and a proximal end having means for being rotationally driven. In use the fastener is mated with the driving device distal end, the fastener and distal end of the driving device are positioned adjacent the tear, and the means for being driven is rotated in a direction having a handedness commensurate with the helically shaped protrusion, thereby advancing the fastener across the tear.  
           [0021]    In a specific embodiment of the system, the driving device further has a noncircular cross-sectional shape along a distal section adjacent the distal end. The fastener bore as described above has a noncircular cross-sectional shape dimensioned to permit the distal section of the driving device to pass into the bore and to permit relative axial sliding and rotational coupling movement therebetween. The axial slidability permits the driving device to be mated by sliding the driving device distal section into the fastener bore and to be removed once the tear has been breached by sliding the driving device out of the bore.  
           [0022]    The method of the present invention is for repairing a tear in soft tissue of a patient. The method comprises the steps of providing a fastener having the features as described above. The fastener is then inserted into an area of soft tissue adjacent the tear. The distal end of the fastener is manipulated to a position generally normal to a long axis of the tear, and the fastener is driven across the tear in a screwing motion. The decrease in the helical pitch serves to bring two sides of the tear into apposition as the fastener is advanced.  
           [0023]    The features that characterize the invention, both as to organization and method of operation, together with further objects and advantages thereof, will be better understood from the following description used in conjunction with the accompanying drawing. It is to be expressly understood that the drawing is for the purpose of illustration and description and is not intended as a definition of the limits of the invention. These and other objects attained, and advantages offered, by the present invention will become more fully apparent as the description that now follows is read in conjunction with the accompanying drawing. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0024]    [0024]FIG. 1 is a side perspective view of the fastener of the present invention.  
         [0025]    [0025]FIG. 2 shows the fastener in cross section.  
         [0026]    FIGS.  3 A- 3 D illustrates the method for repairing a knee meniscal tear.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0027]    A description of the preferred embodiments of the present invention will now be presented with reference to FIGS.  1 - 3 D.  
         [0028]    The preferred exemplary embodiment of the present invention comprises a fastener, driving device, and method for repairing a soft-tissue tear in a patient. The system  10  of the present invention comprises a fastener  20  and an elongated driving device  60 .  
         [0029]    In a preferred embodiment shown in FIGS. 1 and 2, the fastener  20  has a root portion  21  that has a proximal end  22 , a distal end  23 , and a length  24 . The root portion  21  further has a distal section  25  tapering toward the distal end  23 , in this specific embodiment the distal section  25  generally forming a cone. Alternatively, a self-tapping distal section could be implemented. In use an insertion of fastener  20  into soft tissue is facilitated by the conical-shaped distal section  25 . The proximal section  30  of the root portion  21  has a substantially constant radius.  
         [0030]    Atop the root portion  21  a helical protrusion (i.e., a thread)  26  proceeds along a central section  27  between the proximal end  22  and the distal end  23 . A short section adjacent the distal end  23  is substantially smooth and does not have a helical protrusion thereon. The protrusion  26  has a helical pitch along the central section  27 , with a substantially constant value  28  along the distal section  25  proximal of the distal end  23 . Extending proximal of the distal section  25 , along a proximal section  30 , the helical protrusion  26  has a variable value  31 , decreasing in a proximal direction to the proximal end  22 . In use the decrease in helical pitch along the proximal section  30  serves to bring two sides S 1 ,S 2  of a tear T into apposition as the fastener  20  is advanced across the two sides S 1 ,S 2  of the tear T in a screwing motion.  
         [0031]    Preferably the helical protrusion  26  has a buttress form for resisting an axial force from pulling the fastener out of the tear and from pulling the two sides of the tear apart. The “buttress form,” is a term known in the art of tool making, and is known to have advantages in applications involving high stresses along the longitudinal (helical) axis in one direction. The “pressure flank,” the face of the protrusion taking the thrust, is generally desired to be nearly perpendicular to the helical axis so that the radial component of the thrust is reduced to a minimum.  
         [0032]    In fastener  20  the helical protrusion  26  further has a leading face  32  facing the distal end  23 . The leading face  32  makes a first angle  33  with a helical axis vector  34  having a directionality pointing from the proximal  22  to the distal end  23 . The leading face  32  adjacent the proximal end  22  serves to resist an axial force in the direction of the helical axis vector  34 .  
         [0033]    In fastener  20  the helical protrusion  26  further has a trailing face  36  facing the proximal end  22 . The trailing face  36  makes a second angle  37  with the helical axis vector  34 . The trailing face  36  adjacent the distal end  23  serves to resist an axial force in a direction opposite the direction of the helical axis vector  34 .  
         [0034]    The helical protrusion  26  also has a radial depth measured from the surface of the root portion  21  to the crest of the helical protrusion  26 . The thread depth  40  along the proximal section  30  has a substantially constant value. The thread depth  42  along the distal section  29  decreases from the value  40  along the proximal section  30  to a minimum value at the distal end  43  of the helical protrusion  26 .  
         [0035]    The fastener material in the preferred embodiment comprises a biodegradable plastic biocompatible with the soft tissue of the patient. Exemplary materials include a nontoxic blend of polycaprolactone and polyglycolide, a blend of polylactide and polyglycolide, pure polydioxanone, poly(ethylene oxide):poly(butylene terephthalate), polyorthoester, polyhydroxybutyrate, or cross-linked collagen. The material is designed to be sufficiently flexible and strong to withstand natural knee movement during healing. The material is also designed to be biodegradable within a first time span greater than or equal to a second time span over which the sides S 1 ,S 2  of the tear T can knit together. In other words, the material is resorbed over a time span commensurate with the healing process, so that, once the tear T is healed, the fastener  20  can gradually degrade, leaving a healed meniscus with no foreign material embedded therein.  
         [0036]    In the preferred embodiment, fastener  20  further has an axial bore  44  therethrough generally along the helical axis  34 . In an alternate embodiment, the bore  44  may not extend completely through to the distal end  23 . In the embodiment illustrated herein, bore  44  proceeds from proximal end  22  to distal end  23 , and has a noncircular cross-sectional shape to permit an elongated driving device having a noncircular cross-sectional shape to pass into bore  44  and to advance fastener  20  into the meniscus M by being rotated in a direction having a handedness commensurate with the helically shaped protrusion  26  (see FIG. 3C). The cross-sectional shape  45  of the bore, as shown in FIG. 2, is triangular, although this is not intended as a limitation, as other noncircular bores may be contemplated by one of skill in the art.  
         [0037]    The fastener  20  further has a head  46  affixed the root&#39;s proximal end  22 , the bore  44  extending therethrough as well. The head  46  has a diameter  47  at least as great as a maximum diameter  48  of the helical protrusion  26  and a substantially smooth periphery  49 .  
         [0038]    The driving device of a preferred embodiment comprises an elongated driving device  60  comprising a needle  50  inserted through an elongated tubular member  70 .  
         [0039]    The needle  50  has a length  51 , a proximal end  52 , and a pointed distal tip  53  (see FIG. 3B). Needle  50  further has a cross-sectional triangular shape along at least a distal section dimensioned axially to be slidable through the bore  44  of the fastener  20  and rotationally to drive the fastener  20  (FIG. 3C).  
         [0040]    In use needle  50  is axially movable distalward to a first position wherein the needle tip  53  protrudes from distal end  23  of fastener  20  (FIG. 3A). In this position, needle tip  53  can pierce the tissue to be repaired (FIG. 3B), aiding in advancing fastener  20 , preparatory to rotating needle  50  and to, hence fastener  20 , which are rotationally coupled.  
         [0041]    A further component of system  10  comprises a cannula member  70  for protecting fastener  20  during insertion into the soft tissue area adjacent the tear T (see FIGS.  3 A- 3 D). Cannula member  70  has a proximal end  71  and a distal end  72 . In addition, cannula member  70  has an axial bore  73  therethrough from distal end  72  to proximal end  71 . Bore  73  is dimensioned to permit the fastener  20  and the needle  50  to fit therein and to permit sliding and rotational movement therebetween.  
         [0042]    Cannula member  70  has a length  74  shorter than needle length  51  permitting distal tip  53  and proximal end  52  of needle  50  to protrude from distal end  72  and proximal end  71 , respectively, of the cannula member  70 .  
         [0043]    In the embodiment contemplated for repairing a knee meniscus, the needle, the tubular member, and the cannula member all similarly have a curve therein for enabling an operator to manipulate the system into a position to approach a soft tissue tear around a curved radius. In the preferred embodiment, this curve comprises a 10-30 degree generally upward bend.  
         [0044]    The method of the present invention for repairing a tear T in soft tissue of a patient, shown in FIGS.  3 A- 3 D for repairing a meniscal tear, comprises the steps of moving the needle  42  axially through the bore  44  of the fastener  20 , the distal tip  53  of the needle  50  emerging from the distal end  23  of the fastener  20  (FIG. 3A). The needle tip  53  then pierces the tear T, and the needle  50  is advanced across both sides S 1 ,S 2  (FIG. 3B).  
         [0045]    The fastener  20  is inserted over the needle  50  into an area of soft tissue adjacent the tear T. The operator then manipulates the distal end  23  of the fastener  20  to a position generally normal to the long axis of the tear T (FIG. 3C).  
         [0046]    The next step comprises driving the fastener  20  across the tear T in a screwing motion (FIG. 3C), the decrease in the helical pitch  31  serving to bring two sides of the tear S 1 ,S 2  into apposition as the fastener  20  is advanced (FIG. 3D). Given the rotationally coupled needle  50  and fastener  20 , the driving step comprises rotating the needle  50  and hence the fastener  20 . Since the needle  50  and fastener  20  are axially slidable relative to each other, the needle  50  can then be removed from the fastener  20  and all instruments removed from the surgical site once the sides of the tear have been drawn together (FIG. 3D).  
         [0047]    It may be appreciated by one skilled in the art that additional embodiments may be contemplated, including fasteners, systems, and methods for repairing other soft tissue tears, such as in the shoulder.  
         [0048]    In the foregoing description, certain terms have been used for brevity, clarity, and understanding, but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such words are used for description purposes herein and are intended to be broadly construed. Moreover, the embodiments of the apparatus and method illustrated and described herein are by way of example, and the scope of the invention is not limited to the exact details of construction.  
         [0049]    Having now described the invention, the construction, the operation and use of preferred embodiment thereof, and the advantageous new and useful results obtained thereby, the new and useful constructions, and reasonable mechanical equivalents thereof obvious to those skilled in the art, are set forth in the appended claims.