Abstract:
Distensible ligaments and distensible ligament systems are provided, including apparatuses, systems, devices, hardware, methods, and combinations for distensible systems.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to devices and methods for use in spinal repair, and more particularly, to devices, systems and methods for stabilizing the spine. 
       BACKGROUND 
       [0002]    Corrective and other surgeries of the human body often require the implantation of ligaments, for example, to replace or augment existing ligaments or effect changes in position or alignment between bone structures, e.g., intervertebral spinal ligaments. Current implants have a limited elasticity/elongation, which may not be optimal. Accordingly, there is a need for improved ligament systems. 
       SUMMARY 
       [0003]    One embodiment of the present invention includes a unique distensible ligament system. Another embodiment of the present invention is a unique distensible ligament. Other embodiments include apparatuses, systems, devices, hardware, methods, and combinations for distensible ligament systems. Further embodiments, forms, features, aspects, benefits, and advantages shall become apparent from the description and figures provided herewith. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0004]    The description herein makes reference to the accompanying drawings wherein like reference numerals refer to like parts throughout the several views, and wherein: 
           [0005]      FIG. 1  schematically illustrates a system for controlling tension in a ligament, in particular, in a distensible ligament system, in accordance with an embodiment of the present invention. 
           [0006]      FIG. 2  graphically illustrates a distensible ligament system in accordance with an embodiment of the present invention. 
           [0007]      FIGS. 3A-3C  depict a gate of a variable receiver of an embodiment of the present invention in three different positions. 
           [0008]      FIG. 4  illustrates a ligament and variable receiver in accordance with an embodiment of the present invention. 
           [0009]      FIGS. 5A and 5B  depict a cross sectional view of a distensible ligament in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    For purposes of promoting an understanding of the principles of the invention, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It will nonetheless be understood that no limitation of the scope of the invention is intended by the illustration and description of certain embodiments of the invention. In addition, any alterations and/or modifications of the illustrated and/or described embodiment(s) are contemplated as being within the scope of the present invention. Further, any other applications of the principles of the invention, as illustrated and/or described herein, as would normally occur to one skilled in the art to which the invention pertains, are contemplated as being within the scope of the present invention. 
         [0011]    Referring now to the drawings, and in particular,  FIG. 1 , a system  10  for controlling tension in a ligament is schematically depicted. System  10  includes a distensible ligament system  12 , a sensor  14 , a drive unit  16  with a power supply  18 , and a controller  20 . Controller  20  is communicatively coupled to sensor  14  via a communications link  22 . Controller  20  is communicatively coupled to drive unit  18  via a communications link  24 . 
         [0012]    Distensible ligament system  12  is implanted into a living patient, e.g., a human patient, and includes a ligament  26 , an anchor  28  having a receiver  30 , and an anchor  32  having a variable receiver  34 . Ligament  26  is defined by a major axis  36  extending along the length of ligament  26 . Ligament  26  may be symmetric about major axis  36 . Ligament  26  includes a first lengthwise extent, e.g., a span  38 , and a second lengthwise extent, e.g., a span  40 . As described herein, span  40  may have different physical characteristics than span  38 . 
         [0013]    It is contemplated that ligament  26  may be flexible, tear resistant, and/or suturable. Ligament  26  may be fabricated from synthetic flexible materials in the form of fabrics, non-woven structures, two or three dimensional woven structures, braided structures, and chained structures. Ligament  26  may also be fabricated from natural/biological materials, such as autograft or allograft, taken from patellar bone-tendon-bone, hamstring tendons, quadriceps tendons, or Achilles tendons, for example. Growth factors or cells can be incorporated into ligament  26  for bone ingrowth and bony attachment or for soft tissue ingrowth. Possible growth factors that can be incorporated include transforming growth factor β1, insulin-like growth factor 1, platelet-derived growth factor, fibroblast growth factor, bone morphogenetic protein, LIM mineralization protein (LMP), and combinations thereof. 
         [0014]    Possible ligament  26  materials include synthetic resorbable materials such as polylactide, polyglycolide, tyrosine-derived polycarbonate, polyanhydride, polyorthoester, polyphosphazene, calcium phosphate, hydroxyapatite, bioactive glass and combinations thereof. Possible ligament  26  materials also include natural resorbable materials such as autograft, allograft, xenograft, soft tissues, connective tissues, demineralized bone matrix, and combinations thereof. Possible ligament  26  materials further include nonresorbable materials such as polyethylene, polyester, polyvinyl alcohol, polyacrylonitrile, polyamide, polytetrafluorethylene, poly-paraphenylene terephthalamide, cellulose, shape-memory alloys, titanium, titanium alloys, stainless steel, and combinations thereof. 
         [0015]    Anchor  28  is structured for anchoring into a bone tissue location  42 , e.g., a pedicle of a spinal vertebra. Receiver  30  is structured to secure span  38  of ligament  26  to anchor  28 . Anchor  32  is structured for anchoring into a bone tissue location  44 , e.g., a pedicle of a spinal vertebra. Variable receiver  34  is structured to secure span  40  to anchor  32 . It should be understand that systems are contemplated that include more than two anchors, and anchors engaged to more than two vertebrae or other bone structures, such as the pelvis. 
         [0016]    In addition, variable receiver  34  is structured to perform an in vivo release of at least a portion of span  40  of ligament  26 , thus extending the length of ligament  26  as between anchors  28  and  32 . That is, variable receiver  34  is structured to release at least a portion of span  40  to relieve tension in ligament  26  subsequent to implantation into the patient, e.g., after completion the implantation surgery and closure of the surgical site. This may allow, for example, implantation of ligament  26  during a surgical procedure, after the completion of which the patient may be free to go home; distension of ligament  26  may then be performed without a further surgical procedure. 
         [0017]    It is contemplated that anchors  28  and  32  may be, for example, interference screws or anchors, gull anchors, suture anchors, pin fasteners, bone screws with spiked washers, staples, and buttons. In addition, it is contemplated that the anchors may be made from resorbable materials, nonresorbable materials, and combinations thereof. Possible synthetic resorbable materials include polylactide, polyglycolide, tyrosine-derived polycarbonate, polyanhydride, polyorthoester, polyphosphazene, calcium phosphate, hydroxyapatite, bioactive glass, and combinations thereof. Possible natural resorbable materials include cortical bone, autograft, allograft, and xenograft. Possible nonresorbable materials include carbon-reinforced polymer composites, shape-memory alloys, titanium, titanium alloys, cobalt chrome alloys, stainless steel, and combinations thereof. 
         [0018]    Sensor  14  is coupled to ligament  26 , and is structured to provide a tension signal indicative of the tension in ligament  26 . Sensor  14  may include, for example, a strain gage. In the present embodiment, sensor  14  is positioned inside ligament  26 . In other embodiments, it is alternatively contemplated that sensor  14  may be located external to ligament  26 , e.g., mounted on an external surface of ligament  26 , or mounted on anchor  28 , receiver  30 , anchor  32  or receiver  34 , in which case, for example, the tension in ligament  26  may be sensed indirectly. 
         [0019]    Drive unit  16  is coupled to variable receiver  34 . Drive unit  16  is structured to receive a control signal, and in response thereto, to drive variable receiver  34  from a one position to another position, e.g., as described herein, to perform the in vivo release of ligament  26 . Drive unit  16  may be, for example, a geared motor, a linear actuator, or any electromechanical drive capable of providing motive force to drive variable receiver  34  into the desired position. 
         [0020]    Power supply  18  is a battery. It is alternatively contemplated that in other embodiments, other types of power sources may be employed, such as a subdermally implanted induction coil. 
         [0021]    Controller  20  is configured to execute program instructions to generate a control signal in response to a tension signal from sensor  14  that is indicative of tension in ligament  26 , and to provide the control signal to drive unit  16 . Controller  20  may be, for example, similar to the controller of a pacemaker, an implantable pump, or an external pump. 
         [0022]    In the present embodiment, controller  20  is microprocessor based, and the program instructions are in the form of software stored in a memory (not shown). However, it is alternatively contemplated that the controller and program instructions may be in the form of any combination of software, firmware and hardware, including state machines, and may reflect the output of discreet devices and/or integrated circuits, which may be co-located at a particular location or distributed across more than one location, including any digital and/or analog devices configured to achieve the same or similar results as a processor-based controller executing software or firmware based instructions. 
         [0023]    Communications link  22  may be a digital and/or analog communications link, and may be a wired communication link, a wireless connection, an optical cable link or any system capable of transmitting a signal from sensor  14  to controller  20 . Similarly, communications link  24  may be a digital and/or analog communications link, and may be a wired communication link, a wireless connection, an optical cable link or any system capable of transmitting a signal from controller  20  to drive unit  18 . In addition, communications link  24  may be a unidirectional communications link, or may be a bidirectional communications link capable of transmitting information from drive unit  18  to controller  20 , e.g., feedback information indicative of the position of variable receiver  34 . 
         [0024]    Referring now to  FIG. 2 , aspects of distensible ligament system  12 , in particular, variable receiver  34 , are further described. Receiver  34  is a variable latch that is structured to move between a plurality of positions, e.g., to move between one position and another position to perform the in vivo release of ligament  26 . The plurality of positions may be a continuum, e.g., extending continuously between two extreme positions. In the present embodiment, receiver  34  in the form of a gate  46  having an eccentric  48  and variable opening  50 . Variable opening  50  extends in a direction transverse to the major dimension of ligament  26 , i.e., transverse to major axis  36 . Gate  46  is structured to increase the size of variable opening  50  in the transverse direction. It will be understood that other mechanisms that provide a variable opening may be used in other embodiments of the present invention. 
         [0025]    Eccentric  48  includes a drive shaft  52  that is turned by drive unit  16  in order to rotate eccentric  48  about an axis of rotation  54 . In one form, axis of rotation  54  is substantially perpendicular to an axis through the major dimension of ligament  26 , i.e., major axis  36 , although other embodiments may employ different orientations of axis of rotation  54 . The rotation of eccentric  48  about axis of rotation  54  increases or decreases the size of variable opening  50 , depending upon the direction of rotation. 
         [0026]    For example, referring now to  FIGS. 3A-3C , receiver  34  is illustrated with eccentric  48  in three different positions.  FIGS. 3A-3C  are cross sectional views of the depiction of  FIG. 2 . It will be understood that eccentric  48  is rotatable into other positions not illustrated herein.  FIG. 3A  illustrates gate  46  with eccentric  48  in a first position having a size  56  of variable opening  50  transverse to major axis  36 . A rotation of eccentric  48 , e.g., in direction  58 , results in a larger size  60  of variable opening  50 , e.g., as illustrated in  FIG. 3B . A further rotation of eccentric  48  results in a still larger size  62  of variable opening  50 , e.g., as depicted in  FIG. 3C . 
         [0027]    Referring now to  FIG. 4 , aspects of distensible ligament system  12  are yet further described.  FIG. 4  is a cross sectional plan view of the depiction of  FIG. 2 , and illustrates one embodiment of ligament  26  and variable receiver  34 . 
         [0028]    In the embodiment of  FIG. 4 , span  40  of ligament  26  increases in ligament transverse dimension, e.g., direction  64  that is transverse to major axis  36  of ligament  26 . As depicted in the present Figures, span  40  of ligament  26  has a generally circular cross section. However, it will be understood that other cross sections may be employed, such as a relatively flat cross section that has a major dimension in transverse direction  64 . Span  40  increases in transverse dimension with increasing distance from span  38 , i.e., in the direction extending from receiver  30  to variable receiver  34 . In the present embodiment, span  40  includes a plurality of nodes  66  and a corresponding plurality of segments  68 . In the depicted embodiment, three (3) nodes  66  are depicted—nodes  66 A,  66 B and  66 C. 
         [0029]    Segments  68  may increase in transverse dimension with increasing distance from span  38 . For example, transverse dimension  70  of ligament  26  is greater than transverse dimension  72 , which is greater than transverse dimension  74 . Similarly, nodes  66  may successively increase in transverse dimension with increasing distance from span  38 . For example, transverse dimension  76  is greater than transverse dimension  78 , which is greater than transverse dimension  80 . 
         [0030]    By increasing in transverse dimension with increasing distance from span  38 , a ramped wedge-like structure is obtained. Although nodes  66  with segments  68  are employed in the present embodiment to yield a wedge structure, it will be understood that other geometries may be employed in other embodiments of the present invention. For example, in one elemental form, span  40  may be a single segment that increases in transverse dimension, e.g., linearly nor nonlinearly, with increasing distance from span  38  in the direction of major axis  36 . 
         [0031]    In any event, one skilled in the art will readily appreciate that the wedge structure described herein allows tension in ligament  26  to be reduced by opening variable receiver  34  to permit distension of additional portions of span  40  into the tensile zone of ligament  26  located between receiver  30  and variable receiver  34 . 
         [0032]    In one form, the operation of system  10  for controlling tension in ligament  26  may be described as follows. During a surgical procedure, distensible ligament system  12 , sensor  14  and drive system  16  with power supply  18  are implanted into the patient, and the surgical wounds are sutured or otherwise closed. Controller  20  may also be implanted during the same or a different surgical procedure, unless an external controller  20  is employed. Prior to or subsequent to the surgical procedure, controller  20  may be activated, e.g., turned on and booted. 
         [0033]    During the surgical procedure, distensible ligament system may be initially set to have a variable opening  50  corresponding roughly to transverse dimension  74  of ligament  26 . Transverse dimension  80  of node  66 A is greater than transverse dimension  74 , and hence, the length of ligament  26  as between receiver  30  and receiver  34  will not increase beyond the set point. 
         [0034]    If subsequent movement of the patient or other conditions result in the tension in ligament  26  exceeding a predetermined limit, controller  20  directs the operations of drive unit  16  to reduce the tension. For example, sensor  14  transmits a signal to controller  20  indicative of tension in ligament  26 . Controller  20  executes program instructions to compare tension with a first predetermined threshold. Upon the occurrence of the tension reaching or exceeding the first predetermined threshold, controller  20  generates a control signal to instruct drive unit  16  to open gate  46  a predetermined amount. The predetermined amount may be based on the degree to which the tension in ligament  26  exceeds the threshold. 
         [0035]    In the present embodiment, the control signal is operative to direct drive unit  16  to rotate eccentric  48  by a predetermined amount from one position to another position, e.g., in rotational direction  58 , which increases the size of opening  50 , e.g., to a size corresponding roughly to transverse dimension  72  of ligament  26 . Tension is released as a portion of span  40  is released into the now larger variable opening  50  until being stopped by the larger transverse dimension  78  of node  66 B. An in vivo release of tension in ligament  26  is thus performed. 
         [0036]    If subsequent movement of the patient or other conditions result in the tension in ligament  26  again exceeding a predetermined limit, controller  20  directs the operations of drive unit  16  to reduce the tension again. Sensor  14  transmits a signal to controller  20  indicative of tension in ligament  26 . Controller  20  executes program instructions to compare tension with a second predetermined threshold. The second predetermined threshold may be the same as, greater than, or less than the first predetermined threshold. Upon the occurrence of the tension reaching or exceeding the second predetermined threshold, controller  20  generates another control signal to instruct drive unit  16  to open gate  46  another predetermined amount, which may be the same or different than the first predetermined amount. The predetermined amount may be based on the degree to which the tension in ligament  26  exceeds the threshold. 
         [0037]    The control signal is operative to direct drive unit  16  to rotate eccentric  48  by a predetermined amount from one position to another position, e.g., in rotational direction  58 , which increases the size of opening  50 , e.g., to a size corresponding roughly to transverse dimension  70  of ligament  26 . Tension is released as a second portion of span  40  is released into the even larger variable opening  50  until being stopped by the larger transverse dimension  76  of node  66 C. A second in vivo release of tension in ligament  26  is thus performed. 
         [0038]    Referring now to  FIGS. 5A and 5B , another embodiment of a distensible ligament is illustrated. The embodiment of  FIGS. 5A and 5B  is a ligament  82  having a plurality of nodes  84 , illustrated as nodes  84 A,  84 B and  84 C. Extending from either side of nodes  84  are lineal extents  86 , illustrated as lineal extents  86 A,  86 B and  86 C and  86 D. In the present embodiment, nodes  84  and lineal extents  86  may be constructed of the same material and fabricated similar to that described above with respect to ligament  26 . They may also be the product of an assembly of elements which can occur during manufacture of each component, or thereafter. The material of nodes  84  and lineal extents  86  has a given elasticity/elongation and compressibility, which is known in the art, e.g., determined by the weave pattern, or structure, and/or the mechanical properties of the material used to make nodes  84  and lineal extents  86 . Each node  84  includes an opening  88 , illustrated as openings  88 A,  88 B and  88 C. Openings  88  extend in a direction transverse to the length of ligament  82 . Disposed within openings  88  are cushions  90 , illustrated as cushions  90 A,  9 B and  90 C. Nodes  84  with openings  88  and cushions  90  may have a different tensile elasticity than lineal extents  86 . In embodiments of the present invention, the compressibility of nodes  84  may be different than the compressibility of lineal extents  86 . In addition, openings  88  may be in the form of cavities and/or tunnels in ligament  82 , which may be filled with cushion  90  material. 
         [0039]    Cushions  90  may be made from a polymeric material, a hydrophilic material or a gel, and may have a different elasticity and/or compressibility than the material of nodes  84  and segments  86 . Cushions  90  may be absorbable, and may be made from any compressible/deformable material suitable for implantation into a living being, such a human being. 
         [0040]    Cushions  90  are transverse springs internal to ligament  82 , and are used to control the overall distension of ligament  82  under tension. Other embodiments may employ other types of transverse spring elements that also provide a spring force to nodes  84  in a direction transverse or obliquely to the major axis of ligament  82 , that is, transverse or in an oblique orientation to the axis extending along the length of ligament  82 . 
         [0041]    Ligament  82  may be coupled to bone tissue by anchors  92 , e.g., having integral receivers, illustrated as anchors  92 A and  92 B. Anchors  92  with integral receivers may be similar to anchor  28  and receiver  30  of the previous embodiment. Anchor  92 A may be secured to a first spinal vertebra or pelvic bone, and anchor  92 B may be secured to a second spinal vertebra or pelvic bone, e.g., adjacent to the first spinal vertebra or pelvic structure. 
         [0042]    Although the material of nodes  84  have the same elasticity as that of lineal segments  86 , the inclusion of openings  88  in nodes  84  results in a geometry that lends additional elasticity/elongation to ligament  82 , e.g., beyond that permitted by weave pattern and material properties. Thus, under tension, the nodes may collapse and flatten, and hence be elongated, resulting in a distension of ligament  82  greater than that which would be obtained in a ligament of the same material as nodes  84  and lineal extents  86 , and the same length as ligament  82 , but not having nodes  84  with openings  88  and cushions  90 . The size and shape of openings  88  and the material of cushions  90  may be selected to yield a desirable elongation characteristic of ligament  82 . 
         [0043]    Embodiments of the present invention include a distensible ligament system which may include a ligament having a first span and a second span extending from the first span. The distensible ligament system may also include a first anchor including a first receiver. The first anchor may be structured for anchoring into a first bone tissue location. The first receiver may be structured to secure the first span to the first anchor. The distensible ligament system may also include a second anchor having a second receiver. The second anchor may be structured for anchoring into a second bone tissue location. The second receiver may be structured to secure the second span to the second anchor. The second receiver may be structured to perform an in vivo release of at least a portion of the second span. 
         [0044]    In one refinement of the embodiment the second receiver includes a variable latch having a first position and a second position, and may include a drive unit structured to drive the variable latch from the first position to the second position to perform the in vivo release. 
         [0045]    In another refinement of the embodiment the second receiver includes a gate having a variable opening. The gate may be structured to increase a size of the opening. 
         [0046]    In another refinement of the embodiment the gate may include an eccentric having an axis of rotation. The rotation of the eccentric about the axis of rotation increases the size of the opening. 
         [0047]    In another refinement of the embodiment the axis of rotation is substantially perpendicular to an axis through the major dimension of the ligament. 
         [0048]    In another refinement of the embodiment the second span may include a segment having a ligament transverse dimension that increases with increasing distance from the first span. 
         [0049]    In another refinement of the embodiment the second span may include a plurality of nodes of successively increasing ligament transverse dimension. 
         [0050]    Another embodiment of the present invention is a system for controlling tension in a ligament which may include a sensor structured to provide a tension signal indicative of tension in the ligament. The system for controlling tension in a ligament may also include a variable receiver structured to perform an in vivo release of at least a portion of the ligament. The system for controlling tension in a ligament may also include a drive unit coupled to the variable receiver. The drive unit may be structured to receive a control signal, and in response thereto, to drive the variable receiver from a first position to a second position to perform the in vivo release. The system for controlling tension in a ligament may also include a controller communicatively coupled to the sensor and to the drive unit. The controller may be configured to execute program instructions to generate the control signal in response to the tension signal from the sensor. 
         [0051]    In one refinement of the embodiment the sensor may be coupled to the ligament. 
         [0052]    In another refinement of the embodiment the sensor may be positioned in the ligament. 
         [0053]    In another refinement of the embodiment the controller may be communicatively coupled to the sensor via a wireless connection. 
         [0054]    In another refinement of the embodiment the controller may be communicatively coupled to the drive unit via a wireless connection 
         [0055]    In another refinement of the embodiment the controller may be configured to execute program instructions to compare the tension with a first threshold, and transmit the control signal to the drive unit upon the occurrence of the tension reaching or exceeding the first threshold. The control signal may be operative to direct the drive unit to drive the variable receiver into the second position to perform the in vivo release, wherein the in vivo release releases a first portion of the ligament. 
         [0056]    In another refinement of the embodiment the drive unit may also be structured to drive the variable receiver into a third position different from the second position based on the control signal. The controller may be configured to execute program instructions to compare the tension with a second threshold greater than the first threshold, and transmit the control signal to the drive unit upon the occurrence of the tension reaching or exceeding the second threshold. The control signal may be operative to direct the drive unit to drive the variable receiver into the third position to perform the in vivo release, and the in vivo release releases a second portion of the ligament. 
         [0057]    Another embodiment of the present invention is a distensible ligament system which may include a ligament having a first span and a second span extending from the first span. The distensible ligament system may also include a means for anchoring the first span to a first bone tissue location, a means for anchoring the second span to a second bone tissue location, and a means for performing an in vivo release of at least a portion of the second span from the means for anchoring the second span. 
         [0058]    One refinement of the embodiment may include a means for driving the means for performing the in vivo release. 
         [0059]    Another refinement of the embodiment may include a means for determining tension in the ligament, and a means for controlling the means for performing based on an output of the means for determining. 
         [0060]    Another embodiment of the present invention is a distensible ligament which may include a first extent having a first elasticity. The first extent may be structured for anchoring at a first bone tissue location. The distensible ligament may also include a node extending from the first extent. The node may have a second elasticity different from the first elasticity. The distensible ligament may also include a second extent extending from the node. The second extent may have the first elasticity, and the second extent may be structured for anchoring at a second bone tissue location. 
         [0061]    In one refinement of the embodiment the node may include a transverse opening in the ligament. 
         [0062]    Another refinement of the embodiment may include a transverse spring disposed in the transverse opening. The transverse spring may have a spring rate that determines the second elasticity. 
         [0063]    In yet another refinement, the node has a different compressibility than the compressibility of the first extent. 
         [0064]    In still another refinement, the node varies in width from the first extent. 
         [0065]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment(s), but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims, which scope is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures as permitted under the law. Furthermore it should be understood that while the use of the word preferable, preferably, or preferred in the description above indicates that feature so described may be more desirable, it nonetheless may not be necessary and any embodiment lacking the same may be contemplated as within the scope of the invention, that scope being defined by the claims that follow. In reading the claims it is intended that when words such as “a,” “an,” “at least one” and “at least a portion” are used, there is no intention to limit the claim to only one item unless specifically stated to the contrary in the claim. Further, when the language “at least a portion” and/or “a portion” is used the item may include a portion and/or the entire item unless specifically stated to the contrary.