Abstract:
A screw, driving device, and method are provided for repairing a tissue injury of a patient, such as a meniscal tear in a knee or osteochondritis dissecans. The screw has a root, a distal section having a narrowing cross section toward the distal end, and a thread along at least a portion of the root between the proximal end and the distal end. Along a leading section extending from the distal end, the helical pitch is substantially constant; along a trailing section between the leading section and the root&#39;s proximal end, the helical pitch decreases. The substantially constant pitch along the leading 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 screw.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of and incorporates by reference application Ser. No. 09/542,100, filed Apr. 4, 2000, now issued U.S. Pat. No. 6,468,277, which is commonly owned with the present invention and which is incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to surgical devices and methods for repairing orthopedic injuries, and, more particularly, to devices and methods for repairing soft-tissue tears and for affixing soft tissue to bone. 
   2. Description of Related Art 
   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. The fixation of soft tissue to a bone, and that of bone pieces to each other, is an additional frequently encountered problem. A related condition, osteochondritis dissecans (OCD), results in the splitting of pieces of cartilage into a joint, such as a knee joint or shoulder joint. 
   Sutures, barbs, and various types of screws are known to be used to bring two sides of a tear into apposition; screws are also known for use in fixing two sections of bone together and for fixing a piece of soft tissue to bone. A number of fastener-type devices 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, 5,871,486, and 5,964,768). 
   SUMMARY OF THE INVENTION 
   It is an object of the present invention to provide a screw, delivery device, and method for repairing an orthopedic injury. 
   It is a further object to provide such a screw 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. 
   It is an additional object to provide such a screw having a shape designed to compress a tear and to pull soft tissue onto a bone. 
   It is another object to provide such a screw shaped to resist forces tending to pull apart a tear during healing or to pull soft tissue away from a bone. 
   It is also an object to provide such a screw that resists stripping and has superior tissue retention characteristics. 
   These and other objects are attained with the screw and delivery device system and method of the present invention, an orthopedic screw for repairing a tear in soft tissue of a patient, for affixing soft tissue to a bone, and for affixing a condyle to a bone surface. The fastener has a head at a proximal end and a root extending between the head and a distal end. A distal section of the root has 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 as a lead-in geometry of the root. 
   The fastener further has a helical thread, a protrusion that extends along at least a portion of the root. A leading end of the thread begins at a location in spaced relation from the distal end, and a trailing end of the thread meets the head at the root&#39;s proximal end. Along a leading section the thread extends from the leading end and has a substantially constant helical pitch; along a trailing section between the distal section and the trailing end, the thread has a helical pitch that decreases in a proximal direction, so that the pitch adjacent the head is smaller than that along the distal section. In use the decrease in the helical pitch along the trailing section serves to bring two pieces of tissue into apposition as the screw is advanced across the two pieces of tissue in a screwing motion. The substantially constant pitch along the leading section assists in preventing a stripping of the thread, which is more likely to occur with a screw having a variable pitch along a leading section. 
   At the proximal end the head has a diameter greater than a major root diameter of the proximal section. The head is for improving the tissue retention characteristics of the screw. 
   In an alternate embodiment, the thread also has means for resisting an axial force from pulling the screw out of the tissue and from pulling the two pieces of tissue apart. Specifically, the resisting means comprises the thread having a buttress form. 
   In a preferred embodiment, the screw 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 two pieces of tissue can knit together. This feature permits the fastener to remain in place for as long as required for the tissue to heal, but ultimately to biodegrade and be dissipated harmlessly into the patient&#39;s system. Alternatively, the material in some procedures may be desired to be nonbiodegradable and remain in place permanently or until surgical removal. 
   The material is further preferably designed to have elastomeric properties compliant with those of the tissue to be repaired in order to confer biofunctionality. 
   A further feature of the present invention comprises a delivery device for introducing the above-described screw into the area of the patient&#39;s tissue to be repaired. A feature of the screw permitting a mating with a delivery device comprises the screw&#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 screw can then be advanced into the target tissue by being rotated by the driving device in a direction having a handedness commensurate with the thread. Simply put, the screw is internally drivable by rotation of an elongated member inserted into its bore, which then also supports the screw by imparting additional rigidity during the driving procedure. This is a desired feature if the screw material is flexible. 
   The elongated driving device of the present invention for driving the screw as described above has a distal end having means for mating with the screw&#39;s proximal end, and a proximal end having means for being rotationally driven. In use the screw is mated with the driving device&#39;s distal end, the screw and distal end of the driving device are positioned adjacent the first piece of tissue, and the means for being driven is rotated in a direction having a handedness commensurate with the thread, thereby advancing the screw into the tissue pieces until the separation therebetween is breached. 
   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 screw&#39;s 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 tissue pieces have been joined together by sliding the driving device out of the bore. 
   The method of the present invention is for repairing an orthopedic tissue injury in a patient. The method comprises the steps of providing a screw having the features as described above. The screw is then inserted into an area adjacent the first piece of tissue. The distal end of the screw is manipulated to a desired position. In the case of a tear, the desired position is generally normal to a long axis of the tear, and the screw 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 screw is advanced. In the case of attaching and/or drawing two pieces of tissue together, the desired position is through one piece of tissue and adjacent the second piece. The screw is driven through the first piece of tissue and into the second, with the decrease in helical pitch bringing the two pieces of tissue together. 
   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 
       FIG. 1  is a side perspective view of the orthopedic screw of the present invention. 
       FIG. 2  shows the screw in cross section. 
       FIGS. 3A-3D  illustrate a method for repairing a knee meniscal tear. 
       FIGS. 4A-4C  illustrate a method for repairing osteochondritis dissecans. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   A description of the preferred embodiments of the present invention will now be presented with reference to  FIGS. 1-4C . 
   The preferred exemplary embodiment of the present invention comprises a system  10  comprising a screw  20  and an elongated driving device  60 , and a method for repairing a soft-tissue tear in a patient. 
   In a preferred embodiment shown in  FIGS. 1 and 2 , the screw  20  has a root  21  that has a proximal end  22 , a distal end  23 , and a length  24 . The root  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 as a lead-in geometry. Alternatively, a self-tapping distal section could be implemented. In use an insertion of screw  20  into the target tissue is facilitated by the conical-shaped distal section  25 . The proximal section  30  of the root  21  has a substantially constant radius. 
   A helical protrusion (i.e., a thread)  26  proceeds atop the root  21  between the proximal end  22  and the distal end  23 . A short section adjacent the distal end  23  is substantially smooth and is not threaded. The thread  26  has a helical pitch that has a substantially constant value  28  along a leading section  27  extending proximal of the distal end  23 . Extending proximal of the leading section  27 , along a trailing section  30 , the thread  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 trailing section  30  serves to bring two pieces S 1 ,S 2  of a tissue T into apposition as the screw  20  is advanced thereacross in a screwing motion. 
   Preferably the thread  26  has a buttress form for resisting an axial force from pulling the screw out of the tissue and from pulling the two pieces of tissue 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. 
   In screw  20  the thread  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 first angle  33  decreases from a first oblique angle  33 ″ adjacent the distal end  23  to a second oblique angle  33 ′ adjacent the proximal end  22 . The second oblique angle  33 ′ is therefore smaller than the first oblique angle  33 ″. The leading face  32  adjacent the proximal end  22  serves to resist an axial force in the direction of the helical axis vector  34 . 
   In screw  20  the thread  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 second angle  37  decreases from a first acute angle  37 ′ adjacent the distal end  23  to a second acute angle  37  adjacent the proximal end  22 . The second acute angle  37  is therefore smaller than the first acute angle  37 ′. 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 . 
   The thread  26  also has a radial depth measured from the surface of the root  21  to the crest of the thread  26 . The thread depth  40  along the trailing section  30  has a substantially constant value. The thread depth  42  along the leading section  29  decreases from the value  40  along the trailing section  30  to a minimum value at the distal end  43  of the thread  26 . 
   The screw material in the preferred embodiment comprises a biodegradable plastic biocompatible with the 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 pieces S 1 ,S 2  of the tissue T can knit together. In other words, the material is resorbed over a time span commensurate with the healing process, so that, once the tissue T is healed, the screw  20  can gradually degrade, leaving healed tissue with no foreign material embedded therein. 
   In the preferred embodiment, screw  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 screw  20  into the tissue, here shown as a meniscus M, by being rotated in a direction having a handedness commensurate with the thread  26  (see FIG.  3 C). The cross-sectional shape  45  of the bore, as shown in  FIG. 2 , is square, although this is not intended as a limitation, as other noncircular bores may be contemplated by one of skill in the art. 
   The screw  20  further has a head  46  extending from 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 thread  26  and a substantially smooth periphery  49 . 
   The driving device of a preferred embodiment comprises an elongated driver  60  comprising a needle  50  inserted through an elongated tubular member  70 . 
   The needle  50  has a length  51 , a proximal end  52 , and a pointed distal tip  53  (see FIG.  3 B). Needle  50  further has a square cross-sectional shape along at least a distal section dimensioned axially to be slidable through the bore  44  of the screw  20  and rotationally to drive the screw  20  (FIG.  3 C). 
   In use needle  50  is axially movable distalward to a first position wherein the needle tip  53  protrudes from distal end  23  of screw  20  (FIG.  3 A). In this position, needle tip  53  can pierce the tissue to be repaired (FIG.  3 B), aiding in advancing the screw  20 , preparatory to rotating the needle  50  and hence the screw  20 , which are rotationally coupled. 
   A further component of system  10  comprises a cannula member  70  for protecting the screw  20  during insertion into the 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 screw  20  and the needle  50  to fit therein and to permit sliding and rotational movement therebetween. 
   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 . 
   In an embodiment for repairing osteochondritis dissecans, the method comprises the steps of moving the needle  50  axially into the screw&#39;s bore  44 . Next the screw&#39;s distal end  23  is manipulated to a position adjacent a face F 1  of a piece of cartilage C that has separated from an adjacent piece of bone B. The cartilage C is pierced with the needle tip  53 , and the screw  20  is driven through the cartilage C and into the bone B in a screwing motion as above. The proximal decrease in the helical pitch serves to bring the cartilage C and the bone B into apposition as the screw  20  is advanced, until the screw head  46  is positioned atop the cartilage C, holding it in place. 
   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. 
   The method of the present invention for repairing a tear T in soft tissue of a patient, shown in  FIGS. 3A-3D  for repairing a meniscal tear, comprises the steps of moving the needle  42  axially through the bore  44  of the screw  20 , the distal tip  53  of the needle  50  emerging from the distal end  23  of the screw  20  (FIG.  3 A). The needle tip  53  then pierces the tear T, and the needle  50  is advanced across both sides S 1 ,S 2  (FIG.  3 B). 
   The screw  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 screw  20  to a position generally normal to the long axis of the tear T (FIG.  3 C). 
   The next step comprises driving the screw  20  across the tear T in a screwing motion (FIG.  3 C), the decrease in the helical pitch  31  serving to bring two sides of the tear S 1 ,S 2  into apposition as the screw  20  is advanced (FIG.  3 D). Given the rotationally coupled needle  50  and screw  20 , the driving step comprises rotating the needle  50  and hence the screw  20 . Since the needle  50  and screw  20  are axially slidable relative to each other, the needle  50  can then be removed from the screw  20  and all instruments removed from the surgical site once the sides of the tear have been drawn together (FIG.  3 D). 
   Another embodiment of the present invention comprises a method for repairing osteochondritis dissecans (OCD). In this method, illustrated in  FIGS. 4A-4C , a needle  50  is moved axially into the screw bore, as above. The screw&#39;s distal end  23  is manipulated to a position adjacent a top face F 1  of a piece of cartilage C that has separated from an adjacent piece of bone B (FIG.  4 A). 
   The cartilage C is pierced with the needle tip  53 , and the screw  20  is driven through the cartilage C and into the bone B in a screwing motion by rotating the needle  50  and hence the screw  20  (FIG.  4 B). The proximal decrease in the helical pitch serves to bring the cartilage C and the bone B into apposition as the screw  20  is advanced, until the screw head  46  is positioned against the top face F 1  the cartilage C (FIG.  4 C). 
   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. 
   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. 
   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.