Abstract:
Instruments for applying tension to a securing device, such as a cable or wire, for securing bones in place and fastening implants, such as plates, to bones. In some forms, the tensioning instrument is configured with minimal parts for ease of manufacturing and allowing single use applications. The instrument may include a pretensioning mechanism for applying desired preload before connecting a cable to be tensioned to the instrument. The instrument may be sized and configured to remain attached to a tensioned cable while other cables are connected to a bone. In another form, the instrument may be expandable to remove any slack from the securing device and apply tension thereto.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
       [0001]    The application claims the benefit of U.S. Patent Application No. 62/004,022 filed May 28, 2014, which is hereby incorporated by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to apparatuses for tensioning securing devices and, more specifically, to apparatuses for tensioning securing devices in a variety of medical procedures 
       BACKGROUND 
       [0003]    Securing devices, such as cables or wires, are often used in orthopedic surgery for securing bones in place and for fastening implants, such as plates, to the bones. In one type of procedure, a cable having a pair of opposite ends is positioned around one or more bones. The cable has a connector at one end, and the other end is inserted into the connector to form a loop of the cable around the bone or bones. As used herein, the term bone may refer to a bone, a bone fragment, or a portion of a bone. The term cable may refer to metal and non-metal cables, wires, or other elongate securing devices that are configured to be tensioned by a tensioning instrument. 
         [0004]    A tensioning instrument may be used to apply tension to the cable and constrict the loop of cable about the bone or bones and an implant, such as a bone plate. Tensioning instruments may be very complex and include, for example, a cable locking mechanism, a cable tensioning mechanism, a detachable re-tension mechanism, and a tension scale. Some prior tensioning instruments use different mechanisms to provide each of these features, which increases the cost and size of the tensioning instrument. 
         [0005]    Some surgeries require multiple cables to be implanted that each require tensioning. One prior tensioning instrument that may be used in such a surgery is a pistol-type tensioner having a detachable tip for holding tension in each surgical cable. During surgery, the tensioning instrument is used to apply a desired amount of tension to a first cable, the tip is engaged to the cable to hold tension in the cable construct, the tip is detached, a new tip is connected to the tensioning instrument, and the tensioning instrument is moved to the next cable. This procedure is repeated until all of the cables have been tensioned. Connectors on the cables are then crimped to secure the cables on the bones. One problem with this approach is that once a cable has been tensioned and the tensioning instrument detached from the tip, the tension in the cable may change, for example, due to tensioning of another cable around nearby bones. In that case, re-tensioning of the cable would be necessary. However, the operator would not be aware of the change in tension unless the tensioning instrument is re-connected to the first tip and used to gauge the tension in the first surgical cable. 
         [0006]    Some known tensioning instruments have numerous components, are relatively large, and are quite complex. These instruments are designed to be reused, due to their relatively high cost and complexity. However, complex instruments are often difficult to clean properly after use, often requiring a skilled technician to disassemble the instrument and clean individual parts before reassembling. Accordingly, complex tensioning instruments are relatively expensive and are associated with ongoing cleaning expenses with each use. 
       SUMMARY 
       [0007]    In accordance with one aspect of the present invention, a tensioning instrument is provided that enables a user to quickly and easily apply a desired amount of tension to a securing device such as a surgical cable. In numerous forms, the tensioning instrument is configured with a minimal number of parts for ease of manufacture and use, and also for reducing costs to permit single use applications, eliminating the need for cleaning of the instrument for reuse. In some forms, the tensioning instrument is configured to maintain the selected amount of tension while other cables are tensioned, eliminating the need for retensioning the cable that has already been tensioned. 
         [0008]    In one form, a cable-tensioning instrument includes a distal shaft member defining a first cable passageway portion that extends through the distal shaft member about a longitudinal axis for receiving a cable. A proximal locking member defines a second cable passageway portion that extends therethrough aligned with the longitudinal axis and terminates at a proximal end of the proximal locking member. The proximal locking member includes a cable anchoring portion for fixing the cable thereto. A rotatable actuator is disposed about the distal shaft member for shifting the distal shaft member with respect to the proximal locking member along the longitudinal axis to tension a cable that extends through the first and second cable passageway portions and is fixed to the cable anchoring portion. In one form, the cable anchoring portion includes a cleat portion spaced from the proximal end of the proximal locking member for receiving a portion of the cable thereabout for fixing the cable to the proximal locking member. The cable anchoring portion may include a groove at the proximal end of the proximal locking member that is oriented transversely with respect to the longitudinal axis and that is in communication with the second cable passageway for receiving a cable extending from the second cable passageway for guiding the cable at least partially toward the cleat portion, such that the cable may be wrapped at least partially around the cable anchoring portion to secure the cable to the proximal locking member. The cleat portion and the transversely oriented groove may each have a v-shaped terminal portion for capturing the cable therein via an interference fit to encourage secure fixation of the cable to the proximal locking member. The cleat portion in one form opens distally to allow the cable extending from the second passageway at the proximal end of the proximal locking member to be wrapped around the proximal locking portion between the groove at the proximal end and the cleat portion. 
         [0009]    The distal shaft member may include a threaded portion for engaging with a mating threaded portion of the rotatable actuator such that rotation of the rotatable actuator shifts the proximal locking member linearly along the longitudinal axis. The distal shaft member may also include an indexing portion for inhibiting rotation of the distal shaft member with respect to the proximal locking member when the rotatable actuator is rotated with respect to the distal shaft member. For example, the proximal locking member includes an interior cavity having a non-cylindrical configuration, such as a generally rectangular shape, and the indexing portion has a corresponding non-cylindrical configuration for engaging with the interior cavity to inhibit rotation of the distal shaft member with respect to the proximal locking member. In some forms, the proximal locking member includes a cylindrical surface portion about which the rotatable actuator is rotatably mounted. 
         [0010]    In another form, a cable-tensioning instrument includes a body including a distal tip defining an opening for receiving a cable. A passageway extends along a longitudinal axis from the distal tip opening to a proximal end opening for receiving a cable to be tensioned therethrough. A rotatable drive shaft is disposed within the instrument body and an actuator is connected to the drive shaft for rotating the drive shaft. A traveler member disposed about the drive shaft and configured to shift therealong when the drive shaft is rotated by the actuator. A locking mechanism is configured to fix a cable thereto and is operably engaged with the traveler member to be shifted along the longitudinal axis by the traveler member. In particular, the traveler member biases the locking mechanism away from the distal tip of the instrument body to tension the cable fixed to the locking mechanism when the actuator is actuated by a user. Advantageously, the instrument may be sized and configured to fit within a palm of a user&#39;s hand, which allows the instrument to be left temporarily in place after tensioning a cable while other cables are tensioned using additional instruments. This way, the tension applied to the cable may remain constant, or if needed to be adjusted, may be done quickly and easily by actuating the actuator. 
         [0011]    In one form, a biasing member is operably engaged with the traveler member and the locking mechanism for providing a biasing force operable to urge the locking mechanism proximally away from the distal tip for applying tension to the cable. Optionally, a tension indicator is connected to the traveler member for indicating the amount of tension applied to the cable. The locking mechanism may be provided with a lever with an opening disposed therein for receiving at least a portion of the tension indicator. 
         [0012]    The drive shaft may include a threaded portion and the traveler member may have a mating threaded portion for engaging with the threaded portion of the drive shaft to shift the traveler member therealong when the drive shaft is rotated by the actuator. The drive shaft includes a longitudinally-oriented passage that extends through the shaft and forms at least part of the tool passageway for receiving the cable therein. 
         [0013]    The instrument body may include a distal member including the distal tip and a proximal portion having a longitudinally oriented slot. The traveler member may include an index portion which engages with the longitudinally oriented slot to inhibit rotation of the traveler member when the drive shaft is rotated so that the traveler member translates along a length of the drive shaft when the drive shaft is rotated. Further, the instrument body may also have a proximal member which includes the locking mechanism, and the proximal portion of the distal member can include a smooth outer surface for being received in and slidingly engaged with a corresponding interior portion of the proximal member such that the proximal and distal members are configured to shift with respect to one another along the longitudinal axis to apply tension to the cable. 
         [0014]    The actuator may take the form of a rotary member having a drive head for engaging with a mating tool for rotating the rotary member. The rotary member is operably connected to the distal member and the drive shaft for rotating the drive shaft via a corresponding rotation of the rotary member. In one form, a drive gear connected to the rotary member and a mating driven gear connected to the drive shaft are in operable engagement such that rotation of the rotary member causes a corresponding rotation of the gears and the drive shaft. 
         [0015]    In some forms, the tensioning instrument has a pretensioning mechanism that allows a predetermined preload tension to be applied to the cable. The pretensioning mechanism is adjusted to set a desired preload before the tensioning instrument is connected to the surgical cable. Once the pretensioning mechanism is set at the desired preload, the cable is attached to the instrument and the operator simply actuates a release to apply the preload of the pretensioning mechanism to the cable. In some forms a coil spring may be used to pretension the tensioning mechanism, and in other forms, the instrument itself is effectively a resilient biasing mechanism that relies on its resiliency to tension the cable. As discussed in greater detail below, this functionality allows a user to configure a plurality of tensioning instruments to provide a common amount of tension to a plurality of surgical cables and allows for quick and simple operation. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0016]      FIG. 1  is a perspective view of a tensioning instrument in accordance with the present invention; 
           [0017]      FIG. 2  is an exploded perspective view of the tensioning instrument of  FIG. 1 ; 
           [0018]      FIG. 3  is a perspective view of the tensioning instrument of  FIG. 1 ; 
           [0019]      FIG. 4  is a perspective view of the tensioning instrument of  FIG. 1 ; 
           [0020]      FIG. 5  is a proximal end view of the tensioning instrument of  FIG. 1 ; 
           [0021]      FIG. 6A  is perspective view of components of the tensioning mechanism of the tensioning instrument of  FIG. 1 ; 
           [0022]      FIG. 6B  is a cross-sectional view of the tensioning instrument of  FIG. 1  with the tensioning mechanism in the locked configuration; 
           [0023]      FIG. 6C  is a cross-sectional view of the tensioning instrument of  FIG. 1  with the tensioning mechanism in the released configuration; 
           [0024]      FIG. 7  is a perspective view of an alternate tensioning instrument in accordance with the present invention; 
           [0025]      FIG. 8  is an exploded perspective view of the tensioning instrument of  FIG. 7 ; 
           [0026]      FIG. 9  is a perspective view of the tensioning instrument of  FIG. 7 ; 
           [0027]      FIG. 10  is a side cross-sectional view of the tensioning instrument of  FIG. 7  taken along the superior-inferior plane along the longitudinal instrument axis; 
           [0028]      FIG. 11  is an exploded perspective view of the instrument of  FIG. 7 ; 
           [0029]      FIG. 12A  is a perspective view of an alternate tensioning instrument in the locked orientation in accordance with the present invention; 
           [0030]      FIG. 12B  is a perspective view of the instrument of  FIG. 12A  in the load or release configuration; 
           [0031]      FIG. 13  is an exploded perspective view of the tensioning instrument of  FIG. 12A ; 
           [0032]      FIG. 14  is a proximal perspective view of the tensioning instrument of  FIG. 12A ; 
           [0033]      FIG. 15  is side view of the tensioning instrument of  FIG. 12A ; 
           [0034]      FIG. 16  is a side cross-sectional view of the tensioning instrument of  FIG. 12B  taken along the superior-inferior plane along the longitudinal instrument axis; 
           [0035]      FIG. 17  is a top cross-sectional view of the tensioning instrument of  FIG. 12B  taken along the transverse plane along the longitudinal instrument axis; 
           [0036]      FIG. 18  is a perspective view of an alternate tensioning instrument in accordance with the present invention; 
           [0037]      FIG. 19A  is a perspective view of the tensioning instrument of  FIG. 18  in the unlocked or release configuration and the unloaded configuration; 
           [0038]      FIG. 19B  is a perspective view of the tensioning instrument of  FIG. 18  in the locked and preloaded configurations; 
           [0039]      FIG. 20  is an exploded perspective view of the tensioning instrument of  FIG. 18 ; 
           [0040]      FIG. 21  is an exploded perspective view of components of the locking mechanism of the tensioning instrument of  FIG. 18 ; 
           [0041]      FIG. 22A  is a side cross-sectional view of the tensioning instrument of  FIG. 18  in the unlocked or release configuration and the unloaded configuration taken along the superior-inferior plane along the longitudinal instrument axis; 
           [0042]      FIG. 22B  is a side cross-sectional view of the tensioning instrument of  FIG. 18  in the locked and preloaded configurations taken along the superior-inferior plane along the longitudinal instrument axis; 
           [0043]      FIG. 23  is a perspective view of an alternate tensioning instrument demonstrating a compressed and an expanded configuration in accordance with the present invention; 
           [0044]      FIG. 24  is a perspective view of the tensioning instrument of  FIG. 23  in the expanded configuration; 
           [0045]      FIG. 25  is a perspective view of the tensioning instrument of  FIG. 23  in the compressed configuration; and 
           [0046]      FIG. 26  is a side cross-sectional view of the tensioning instrument of  FIG. 23  taken along the superior-inferior plane through the centerline of the instrument. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    With reference to  FIGS. 1 and 2 , a tensioning instrument  10  is provided for tensioning a securing device, such as a cerclage cable about a bone. The cerclage cable construct may include a cable and a cerclage connector disposed at one end of the cable for locking the cerclage cable about the bone. The instrument  10  includes a body with a shaft portion  12  which defines a longitudinal passageway  14  that extends into the head portion  16  of the body. A tensioning mechanism  18  is connected to the head portion  16  and includes an actuator, such as a knob  20 , which is rotated to turn a pair of geared wheels  22 ,  24  between which the cable is threaded. As shown in  FIG. 5 , the wheels  22 ,  24  are configured with toothed perimeter portions  22   a ,  24   a  which mesh with each other to transmit torque from the knob  20  from drive wheel  22  to driven wheel  24 . Between the toothed perimeter portions  22   a ,  24   a  is a central recessed cable gripping portion  22   b ,  24   b , which is configured with a plurality of ridges or teeth for gripping a cable located between the gripping portions  22   b ,  24   b  of each wheel  22 ,  24 . Drive wheel  22  is mounted on a shaft portion  21  which is connected to knob  20  and is driven thereby. The tensioning mechanism also includes a spring member  38  which acts as a pawl or ratchet and engages with the drive wheel  22  to keep the wheels  22 ,  24  from derotating, i.e., turning in a direction (counterclockwise and clockwise, respectively) that would allow the cable to unwind and lose tension or be released from between the wheels  22 ,  24 . 
         [0048]    The instrument  10  includes a release mechanism in the form of a release lever  26 , which is operably connected to driven wheel  24  via movable pin  28 . The movable pin  28  is located within an elongate groove  30  in the head portion  16 , which allows the pin  28  and driven wheel  24  to translate away from the wheel  22  to allow the cable to be released from between the two wheels. The release lever  26  is pivotally connected to the head portion  16  via a pin  32  which extends through a pair of openings  33  in the proximal end portion  34  of the lever. A pair of arcuate grooves  36  are located in the proximal end portion  34  of the release lever  26  in which the pin  28  is movably captured. The grooves  36  are configured to move the pin  28  and driven wheel  24  away from the drive wheel  22 . In particular, the grooves  36  have a radius that changes slightly such that as the release lever  26  is pivoted away from the shaft portion  12 , the groove urges the pin  28  toward the pin  32 . Because pin  28  is captured in elongate groove  30 , the pin is permitted to shift.  FIGS. 6B and 6C  show the release lever  26  in the closed and released positions, respectively. The movement of the driven wheel  24  is shown in  FIG. 6C , which corresponds to the release configuration of the tensioning mechanism. 
         [0049]    In operation, the release lever  26  is opened to move the driven wheel  24  away from the drive wheel  22  to allow a cable to be threaded through the passageway  14  and between the wheels. With the distal end of the shaft portion  12  abutted with the cable connector, the release lever  26  is then closed to lock the cable between the wheels  22 ,  24  in the gripping portions  22   b ,  24   b  thereof. The knob  20  is then rotated in a clockwise direction by the user to tension the cable. Once the desired tension is reached, the user will crimp or lock the cable connector and can then remove the instrument by once more opening the release lever  26 . The loose cable end can then be removed from the instrument  10 . 
         [0050]    Although this embodiment and some of the following embodiments are shown without a scale for displaying tension, one could be added as would be apparent to one of skill in the art. The body of the instrument  10  may be preferably made of a plastic, and in view of the few number of parts and use of affordable materials, may lend itself to be a single-use device, eliminating the need for cleaning after use. 
         [0051]    Another tensioning instrument in accordance with the present invention is disclosed in  FIGS. 7-11 . As shown in  FIGS. 8 and 11 , the instrument  100  includes a distal shaft member  110 , an actuator in the form of a rotatable barrel  112 , and a proximal locking member  114 . The distal shaft member  110  includes a distal end for engaging with a cable connector, a first passageway portion  116  that extends through the distal shaft member along the longitudinal axis of the shaft, and a proximal threaded portion  118 . At the proximal end of the distal shaft member  110  is an indexing feature having a non-cylindrical configuration, i.e., in the form of a square-like protrusion  120  which includes rollers  122  for engaging with a complimentary shaped interior cavity  124  of the proximal locking member  114 , which prevents the distal shaft member  110  from rotating with respect to the proximal locking member  114 , but allows the proximal locking member  114  to translate with respect to the distal shaft member  110 , i.e., longitudinally along the tool axis. 
         [0052]    The proximal locking member  114  includes a distal end portion  126  for engaging with the barrel actuator  112 , a grip portion  128 , a second passageway portion  135  that extends through the proximal locking member aligned with the longitudinal tool axis, and a proximal cable anchoring portion  130 . The cable anchoring portion  130  is advantageously configured to securely fix poly cable. For example, the cable anchoring portion  130  includes a pair of opposed recesses or cleat portions  132 ,  134  which together function as a cleat for wrapping the cable thereabout and have terminal portions having a v-configuration for capturing the cable therein via a friction or interference fit. The cleat portion  134  is spaced from the proximal end of the cable anchoring portion  130 , and the v-shaped portion of the cleat portion opens distally for securely fixing the cable therein. As shown in  FIG. 8 , the proximal end of the proximal locking member  114  includes an opening  136  disposed in the transversely oriented groove or recess  132  so that the cable may pass through the proximal locking member and then be wrapped about the proximal cable anchoring portion  130  between the groove  132  and cleat portion  134  to lock the cable in place. 
         [0053]    As shown in  FIG. 11 , the rotatable barrel actuator  112  has a generally cylindrical configuration with a throughopening including a distal threaded portion  138  for engaging with the proximal threaded portion  118  of distal shaft member  110 , and a proximal smooth cylindrical surface portion  140  for being rotatably mounted on the distal end portion  126  of the proximal locking member  114 . 
         [0054]    In operation, the cable is threaded through the first passageway portion  116  at the distal end of the distal shaft member  110 , and the second passageway portion  135 , exiting at the proximal opening  136 . The free end of the cable is then wound tightly about the proximal cable anchoring portion  130  including the cleat portions  132 ,  134  to lock the cable in place. Then the barrel actuator  112  is rotated clockwise to advance both the actuator  112  and the proximal locking member  114  proximally with respect to the distal shaft member, which effectively increases the length of the instrument and pulls the cable proximally, thereby tensioning the cable. Once the cable reaches the desired tension, the cable may be clamped and then removed from the instrument by unwrapping the cable from the cable anchoring portion  130 . 
         [0055]    The body of the instrument  100  may be preferably made of a plastic, and in view of the few number of parts and use of affordable materials, may lend itself to be a single-use device, eliminating the need for cleaning after use. 
         [0056]    Another tensioning instrument in accordance with the present invention is disclosed in  FIGS. 12A-17 . As shown in  FIGS. 12A and 13 , the instrument  200  includes a tensioning mechanism including a tensioning screw  210  attached to a drive bevel gear  212  and a driven bevel gear  214  mounted on a drive shaft  216 . The tensioning screw  210  and bevel gears  212 ,  214  are at least partially disposed in a distal housing portion  218 , which includes a distal tip  220  and a proximal cylindrical portion  222  which includes indexing slot  224 , which extends longitudinally along a superior portion of the proximal cylindrical portion  222 . 
         [0057]    The drive shaft  216  has a passageway  217  extending therethrough and includes a distal portion  226  and a threaded proximal portion  228 , which has a larger diameter than the distal portion  226 . A traveler member in the form of annular ring member  230  is threadedly mounted on the threaded proximal portion  228  and includes a keyed portion  232 , which is located within indexing slot  224  to keep the annular ring member  230  from rotating when the shaft  216  is rotated by the tensioning screw  210 . When the shaft  216  is rotated, the annular ring member  230  is driven proximally on the threaded proximal portion  228  of the shaft, thereby compressing tensioning spring  236  against an interior wall of the proximal housing member  238 . The annular ring member  230  also includes a recess  234  for mounting with an indicator  237 , which indicates the amount of tension applied to the cable. 
         [0058]    The proximal housing member  238  is movably mounted on the proximal cylindrical portion  222  of the distal housing portion  218 , such that when the tensioning screw  210  is rotated, the proximal housing member  238  is urged proximally. However, because a cable extends through the body of the instrument  200  and is locked to the locking mechanism  240  at the proximal end of the proximal housing member  218 , the cable prevents substantial movement of the proximal housing member  218  once any slack is removed from the cable, and further compression of the spring  236  increases tension on the cable. 
         [0059]    The locking mechanism  240  is of similar construction to that disclosed in U.S. patent application Ser. No. 13/730,597, filed Dec. 28, 2012, which is incorporated by reference herein in its entirety. In particular, the locking mechanism includes a lever  242 , which is mounted on an inner cylindrical member  244  for rotating the inner cylindrical member. An outer annular member  246  is partially rotatably mounted on the inner cylindrical member  244  with a limited amount of play to assist with locking the cable which extends through openings  248 ,  250  in both the inner cylindrical member  244  and the outer annular member  246 , which are aligned when the locking mechanism is in the unlocked or release configuration, as shown in  FIG. 16 . When the lever  242  is rotated distally, the openings  248 ,  250  will become slightly misaligned, thereby crimping the cable between the openings as described in U.S. patent application Ser. No. 13/730,597. The locking mechanism  240  includes a release mechanism  252  including spring loaded buttons  254 ,  256  which engage with movable shafts  257  which lock the lever  242  in the closed, locked position until the buttons are depressed to release the locking lever  242   
         [0060]    In operation, the cable is inserted through the distal tip  220  and strung through the body of the instrument and through the openings  248 ,  250  of the locking mechanism  240 . The lever is the rotated from the load or release configuration shown in  FIG. 12B  to the locked configuration shown in  FIG. 12A , thereby locking the cable in place. The tensioning screw  210  is then rotated by a driver, either manually or with a power tool. Advantageously, the tensioning screw may be provided with a head that is identical to the bone screws used in attaching a bone plate to the bone, such that the same driver may be used. As the tensioning screw is rotated, the annular ring member  230  is driven proximally on the threaded proximal portion  228  of the shaft, thereby compressing tensioning spring  236  and applying tension to the cable. Once the desired tension is achieved as indicated by the indicator  237  on the scale  258  disposed on the lever  242 , the instrument  200  may be left in place as other cables are being tensioned. Thus, if the tension in one cable changes as other cables are tensioned, the user may simply apply the driver once more and adjust the tension as needed. Once all of the cables are appropriately tensioned and locked or crimped, the instrument may be removed by depressing the buttons  254  of the release mechanism  252  to release the cable and simply pull the instrument  200  away from the cable. Advantageously, the instrument  200  is configured to be relatively small, i.e. can fit in the palm of the user&#39;s hand, or is less than 4 inches long from the distal tip  220  to the proximal end. In one form, the instrument is approximately 3¼ inches long with the lever  242  in the closed position. Moreover, because it may be left in place while other cables are tensioned, no retensioner is needed. 
         [0061]    Another tensioning instrument in accordance with the present invention is disclosed in  FIGS. 18-22B . As shown in  FIGS. 18 and 20 , the instrument  300  includes distal housing member  302  with a hollow cylindrical portion  306  and a distal end portion  304 . The outer surface of the hollow cylindrical portion  306  includes distal and proximal annular grooves  308 ,  310  for engaging with mating balls  313 ,  315  ( FIGS. 22A ,  22 B) of the actuator mechanism, which includes sleeve  312 , which is operably connected to the proximal housing member  314  and is spring biased in the distal direction by spring  316  against retaining ring  318 . A narrower bore shaft member  311  is operably connected to the interior of the distal housing member  302  for protecting the cable from the spring  320 . 
         [0062]    The proximal housing member  314  has a generally cylindrical configuration with a hollow interior for housing tensioning spring  320  therein. A locking mechanism  322  is located at a proximal end of the housing member  314  having a similar configuration to the locking mechanism  240  shown in  FIGS. 12A-17 , except the release mechanism takes a different configuration. Accordingly, description of the lever  324 , inner cylindrical member  326 , and outer annular member  328  and other related components is omitted for sake of brevity. The release mechanism takes the form of a slide lock member  330  mounted to the proximal housing member  314 , which slides over a mating portion  332  of the lever  324  to lock the lever in place once the lever is rotated into the locked configuration (See  FIGS. 19B ,  22 B). The lever  324  is released by sliding the slide lock member  330  distally. 
         [0063]    With reference to  FIGS. 22A and 22B , the tensioning instrument  300  is initially in an unloaded configuration as shown in  FIG. 22A , wherein the spring  220  is uncompressed. The instrument is then preloaded with the predetermined amount of tension, which is determined by factors including the spring used and distance between the annular grooves  308 ,  310 , i.e., the amount of compression of the spring. To preload the instrument  300 , the sleeve  312  is shifted proximally to allow the balls captured in the annular groove  310  to be displaced outwardly, thereby allowing the distal housing member  302  and the proximal housing member  314  to move relative to one another. The housing members  302 ,  314  may then be urged together against the resistance of the spring  320  until the balls of the release mechanism become captured in the distal annular groove  308 , thereby locking the housing members  302 ,  314  with respect to one another with the spring  320  in a compressed configuration. The cable may then be inserted through the passageway in the instrument  300  through the distal tip  304  and through the locking mechanism  322 . The locking mechanism is then moved from the loading or release configuration into the locked configuration by rotating the lever  332  to be flush against the proximal housing member  314  and sliding the slide lock member  330  over the mating portion of the lever  324  to lock the lever in place. With the cable now locked, the user may then release the actuator sleeve  312  by pulling it proximally, thereby applying the biasing force of the spring  320  to the cable, such that now the cable prevents expansion of the housing members  302 ,  314  apart from one another, which tensions the cable. Thus, provided there is little or no slack in the cable, the instrument  300  will not expand significantly and will not return to the initial unloaded configuration until the cable is released from the locking mechanism  322 . Further, given the relatively long length of the spring  320 , small variations in the displacement of the spring, e.g., due to slack in the cable prior to tensioning, will have minimal effect on the amount of tension applied to the cable. Accordingly, the instrument will consistently apply the desired amount of tension. 
         [0064]    Accordingly, the instrument  300  applies a predetermined amount of tension to the cable without need for a retensioner or any adjustment once the instrument is attached to the cable and tension has been applied. Further, the instrument may be preloaded by a surgical technician, reducing the amount of time needed to tension the cables. Provided that the instrument is left in place while other cables are tensioned, the spring will compensate for any changes in tension in the cable automatically and thereby eliminate the need for a retensioner. 
         [0065]    Another tensioning instrument in accordance with the present invention is disclosed in  FIGS. 23-26 . The instrument  400  is preferably of unitary construction and formed from a resilient material, and preferably a superelastic material such as nitinol. The instrument has first and second leg portions  402 ,  404 , which are connected via a hinge portion  406 , which has a generally arcuate configuration. In the expanded configuration of the instrument, the leg portions  402 ,  404  are preferably splayed apart by approximately 90 degrees, although other configurations are possible. The legs  402 ,  404  may be compressed together by a tool to put the instrument in the compressed configuration. 
         [0066]    The first leg portion  402  includes a single aperture  408  through which the cable  422  is initially fed. The cable  422  is then thread through a pair or apertures  410 ,  412  in the second leg portion  404 . The longitudinal axes of the apertures  410 ,  412  in the second leg portion  404  are preferably oriented to be transverse to one another such that the cable  422  is cinched and held in place when the cable passes therethrough. In particular, the opening of the first aperture  410  on the inner facing surface  414  of the second leg portion  404  is located further from the hinge  406  than the opening of the first aperture  410  in the outer facing surface  416  of the second leg portion  404 . Similarly, the opening of the second aperture  412  on the inner facing surface  414  of the second leg portion  404  is located closer to the hinge  406  than the opening of the second aperture  412  in the outer facing surface  416  of the second leg portion  404 . In other words, the apertures  410 ,  412  diverge from one another as they extend through the thickness of the second leg portion  410  from the inner facing surface  414  to the outer facing surface  416 . Given that the cable is sufficiently thick relative to the apertures&#39; size, the circuitous or divergent path provided by the apertures  410 ,  412  will capture the cable when tension is applied by the user or by expansion of the leg portions  402 ,  404  apart from one another. This way no further locking mechanism is needed, thereby simplifying manufacture and use of the instrument  400 . 
         [0067]    In operation, as shown in  FIG. 23 , the instrument  400  is first compressed by an inserter instrument and then the cable  422  is fed through the aperture  408  in the first leg portion. The cable  422  is then fed through the second aperture  412  and then back through the first aperture  410  and returning back through the aperture  408  in the first leg portion  402 . The outer surface  418  of the first leg portion  402  is abutted against the bone plate  420  and the cable is pulled taught manually. Next, the instrument releases the second leg portion  404  while the first leg portion  402  is abutted against the bone plate  420 . Due to the resilience of the material, the second leg portion  404  will be urged away from the first leg portion  402  thereby pulling on and tensioning the cable  422  with a predetermined amount of force determined by the resiliency of the material. The instrument  400  may be left in place while other instruments  400  are used to tension other cables, and no retensioning will be necessary, as the resiliency of the material will automatically compensate for changes in tension when other cables are applied to the bone or bone plate. Due to the simplicity of the instrument  400 , the instrument may be easily cleaned and reused if desired. 
         [0068]    Those skilled in the art would recognize that a wide variety of modifications, alterations, and combinations can be made with respect to the above described embodiments without departure from the spirit and scope of the invention, in that such modifications, alterations, and combinations, are to be viewed as being within the scope of the invention.