Abstract:
A torque limiting mechanism used for securing fasteners is described. The torque limiting mechanism consists of a shaft, a torque gear having a plurality of ball bearings, a threshold bearing and a variable force applying subassembly. The torque limiting mechanism further consisting of a lock bushing and retaining ring placed circumferentially around the proximal end of the shaft. The lock bushing and retaining ring reduce structural misalignments and increase the accuracy of the device.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. provisional application Ser. No. 61/379,938, filed on Sep. 3, 2010. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates to surgical tools for aiding in installing orthopedic prostheses, and more specifically, to an improved torque limiter device for installing orthopedic implants. 
       BACKGROUND OF THE INVENTION 
       [0003]    Torque limiting devices have been utilized in various medical applications. For example, torque limiter devices have been used to fasten nuts and bolts that are utilized to secure surgical implements such as orthopedic implants. As such, it is important that these devices enable the user to apply a consistent and exacting amount of torque. The delivery of an exact amount of torque is critical in securing an implant or other surgical implement in the correct position without causing damage to the implant and the patient. 
         [0004]    Prior art torque limiting devices are typically constructed with torque gear teeth that tend to bind against the shaft within the torque limiter device. These prior art devices are typically designed such that as the torque gear is rotated within the device, the gear tends to rotate at a slight angle, away from its horizontal position relative to the longitudinal shaft. This misalignment of the torque gear with respect to the longitudinal shaft within these prior torque limiters creates a frictional interference within the device. Such misalignments results in inaccurate torque outputs as well as increased mechanical wear of the device. 
         [0005]    In addition, these prior art torque limiter devices are typically constructed with a plurality of intricate and complex components that are intended to fit and work precisely together. However, the complexity and increased number of components generally result in tolerance stack up and other structural misalignments. The cumulative effects of these misalignments further contribute to the inaccuracy of the device as well as to the increased mechanical wear of the device. These inaccuracies are particularly prevalent at low torque ranges, especially when applying a torque at less than 20 inch-lbs. Moreover, it has been known that the act of pushing down on the handle of these prior art devices during their normal standard use could result in the application of an additional 0.5 to 2 inch-lbs. of torque, particularly at these low torque ranges. Since it is critical that the precise amount of torque be applied during surgical procedures, over torqueing a fastener could damage the surgical implant and may result in undesirable patient outcomes. 
         [0006]    The torque limiter device of the present invention addresses these shortcomings of the prior art. The present invention provides a more accurate device that is designed with a less complicated torque limiting mechanism. The torque limiting mechanism of the present invention minimizes these structural misalignments with the incorporation of a lock bushing and retaining ring within the device. The lock bushing and retaining ring ensure that the shaft of the mechanism rotates true and unobstructed. The simplified novel design further corrects the misalignment issues of the prior art and thus improves the accuracy with which torque is applied. Therefore, the features and structural design of the torque limiting device of the present invention ensure that the proper amount of torque is delivered while securing an implant fastener, thus minimizing possible structural damage to the implant and ensuring patient safety. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention provides a torque limiter device that is designed to secure a threaded fastener such as a bolt, screw or nut to a specified torque value. Fasteners are often used in surgical applications such as to secure an orthopedic implant or other device within the body. The present invention can be used as a hand held instrument or may be utilized as a power driven device. The torque limiting mechanism of the present invention primarily comprises a housing, an elongated body with a plurality of springs or washers, a threshold bearing, a torque gear, and a series of ball bearings. These components are arranged circumferentially about the elongated body or shaft such that the washers or springs compress the threshold bearing against the torque gear. The torque gear, which is connected to the elongated body or shaft, compresses against the ball bearings, which in turn compress against an internal surface of the housing. The mechanism further comprises a lock bushing and retaining ring that reside at the proximal end of the elongated body. The lock bushing and retaining ring ensure proper alignment and minimize lateral movement of the components within the device, particularly the elongated shaft with respect to the series of ball bearings and the torque gear. Such improvements in alignment of the elongated shaft with respect to the torque gear afforded by the lock bushing and retaining ring contribute to the increased accuracy of the present invention. 
         [0008]    Furthermore, the structural design of the torque limiter device of the present invention comprises fewer components than those of typical prior art devices. As previously mentioned, the torque gear of the present invention lacks the gear teeth, which tend to bind against the shaft of the device. Therefore, elimination of these gear teeth reduces this binding problem. Furthermore, the overall reduction in the number of components reduces the complexity of the instrument and minimizes stack up and alignment, issues that plague previous devices. 
         [0009]    The housing of the device is also designed with a series of cavities that are dimensioned such that the components of the device seat properly therewithin. Specifically, this feature of the present invention contributes to the proper alignment of the components within the device, particularly that of the elongated body and ball bearings as they rotate in applying torque. 
         [0010]    The improved structural alignments afforded by the features of the present invention directly translate into increased accuracy and precision of the instrument. Specifically, the design features of the present invention reduce the tendency of the elongated shaft to bind with the torque gear. In addition, the features of the present invention reduce tolerance and component stack up issues therewithin. The features of the device of the present invention, therefore, provide a torque limiter device with improved accuracy and performance as compared to prior torque limiting devices. Such improvements in accuracy of the instrument minimize the possibility of implant damage and resulting patient harm. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
         [0011]      FIG. 1  illustrates a side view of the torque limiter device of the present invention. 
           [0012]      FIG. 2  shows an end view of the present torque limiter device. 
           [0013]      FIG. 3  illustrates a cross-sectional view of the torque limiter device. 
           [0014]      FIG. 4  shows an exploded view of the components comprising the torque limiter device of the present invention. 
           [0015]      FIG. 5  illustrates a perspective view of an embodiment of the lock bushing. 
           [0016]      FIG. 5A  illustrates a cross-sectional view of the lock bushing. 
           [0017]      FIG. 6  shows a side view of an embodiment of the retaining ring. 
           [0018]      FIG. 7  shows a perspective view of an embodiment of the torque gear. 
           [0019]      FIG. 8  illustrates a perspective view of an embodiment of the thrust bearing. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0020]    Referring now to the figures,  FIGS. 1-5 ,  5 A and  6 - 8  illustrate embodiments of a torque limiter device assembly  10  of the present invention and associated components. The device assembly  10  comprises a torque limiter device  12  and an adapter  14  connected therebetween. The torque limiter device  12 , having a distal end portion spaced apart from a proximal end portion, further comprises a torque limiting mechanism  16  therewithin. The torque limiting mechanism  16  resides within a housing  18  of the device  12 . A handle portion  20  is fluidly connected to the proximal end of the housing  18  of the device  12 . 
         [0021]    As shown in  FIG. 3 , the housing portion  18  has a first cavity  22  with a first cavity opening  24  that extends from the distal end of the housing  18 . The first cavity  22  transitions into a second cavity  26 , and the second cavity  26  further transitions into a third cavity  28 . The second cavity  26  is proximal of the first cavity  22  and the third cavity  28  is proximal of the second cavity  26 . In a preferred embodiment, the opening  24  of the first cavity  22  has a curved cross-section. More preferably, the opening  24  of the first cavity  22  has a round cross-section. However, it is contemplated that the opening  24  of the first cavity  22  as well as the openings of the other cavities within the housing  18  may be of a number of cross-sectional shapes not limited to circular, rectangular, triangle, hexagonal and the like. These cavities  22 ,  26 ,  28  of the housing  18  are dimensioned such that the components of the torque limiting mechanism  16  reside therewithin. It is preferred that the first cavity  22  is dimensioned such that its diameter is greater than the diameter of the second cavity  26  and the second cavity  26  is dimensioned such that its diameter is greater than the third cavity  28 . In a preferred embodiment, the first cavity  22  has a diameter ranging from about 1.0 cm to about 5.0 cm. The first cavity  22  further having a first cavity depth  30  ranging from about 1 cm to about 5 cm. 
         [0022]    The second cavity  26  transitions proximally from the first cavity  22  in a stepwise manner. The second cavity  26  has a second cavity opening  32  that extends from the proximal end of the first cavity  22 . In a preferred embodiment, the second cavity  26  has a diameter from about 1 cm to about 4 cm and a second cavity depth that ranges from about 1 cm to about 5 cm. The third cavity  28  transitions proximally from the second cavity  26  in a stepwise manner. The third cavity  28  preferably has a diameter from about 1 cm to about 3 cm and a third cavity depth that ranges from about 1 cm to about 5 cm. A housing throughbore  34  extends from the proximal end of the third cavity  28  through the proximal end of the housing  18 . It is preferred that the housing throughbore  34  has a diameter that is less than the diameter of the third cavity  26 . 
         [0023]    An elongated body or shaft  36 , having a proximal end portion  38  spaced apart from a distal end portion  40 , is positioned within the housing  18  of the device  12 . The shaft  36  further has an elongated throughbore  42  extending therethrough. In a preferred embodiment, the shaft  36  is centered in the housing  18  such that the shaft  36  is parallel to a longitudinal axis A-A extending from the proximal end of the device  12  to the distal end thereof. 
         [0024]    The proximal end portion  38  of the shaft  36  resides within the housing  18 , specifically within the opening of the third cavity  28  within the housing  18 . A bearing  44  having a bearing throughbore  46  is preferably positioned proximal of the shaft  36 . The bearing throughbore  46  and shaft throughbore  42  are positioned such that they are co-axial with the housing throughbore  34 . 
         [0025]    Furthermore, the bearing throughbore  46  is positioned co-axial to a cannulation  48  which extends through the handle portion  20 . The cannulation  48  preferably extends from the proximal end of the housing throughbore  34  to the proximal end of the handle  20 . The cannulation  48  is designed to allow for a thorough cleaning within the device  12 . In a preferred embodiment, the cannulation  48  provides an opening for the introduction and subsequent draining of cleaning solutions therewithin. Furthermore, the cannulation  48  allows for the insertion of a catheter, a needle, a sheath, or the like within the device  12 , if so desired. In a preferred embodiment, the cannulation  48  has a diameter ranging from about 0.5 cm to about 5 cm. 
         [0026]    The distal end portion  40  of the shaft  36  may comprise a socket opening  50 . The socket opening  50  provides an opening that is designed to mate with a nut, bolt, screw or another shaft. In a preferred embodiment, the socket opening  50  may have a cross-sectional shape comprising a rectangle, a square, a triangle, an oval, a hexagonal or the like. 
         [0027]    In a preferred embodiment, a lock bushing  52  is positioned circumferentially around the outer diameter of the proximal end portion  38  of the shaft  36 , as illustrated in  FIG. 3 . The lock bushing  52 , as shown in  FIGS. 4 ,  5  and  5 A, has a distal surface  54  that is spaced apart from a proximal surface  56 . The distal surface  54  is further designed such that it is angled with respect to longitudinal axis A-A. In a preferred embodiment, the distal surface  54  of the lock bushing  52  slopes downwardly at a lock bearing angle  58  ranging from about 35° to about 50° with respect to longitudinal axis A-A. The lock bearing angle  58  is herein defined as the angle between tangent line B-B and longitudinal axis A-A. 
         [0028]    The proximal surface  56  of the lock bushing  52  preferably is about perpendicular with respect to longitudinal axis A-A. In a preferred embodiment, the lock bushing is positioned within the second cavity  26  such that its outer diameter approximates the diameter of the second cavity  26 . Furthermore, the lock bushing  52  is positioned such that its proximal surface  56  contacts a first retaining ring  60  and its distal surface  54  faces toward the distal end of the device  12 . 
         [0029]    The first retaining ring  60  ( FIG. 6 ) is positioned circumferentially around the proximal end portion  38  of the shaft  36  proximal of the lock bushing  52 . The retaining ring  60  is preferably positioned such that it abuts a proximal wall surface  62  of the second cavity  26 . Furthermore, the first retaining ring  60  has an outer diameter that approximates the inner diameter of the second cavity  26 . The first retaining ring  60  in concert with the lock bushing  52  provides structural stability and improved alignment of the elongated body  36 . The first retaining ring  60  and lock bushing  52  allow for the shaft  36  to freely rotate within the second cavity  26 . At the same time, they prevent lateral movement of the shaft  36  such that the shaft  36  does not become skewed or cocked from the central longitudinal axis A-A. In addition, the first retaining ring  60  serves as a “back stop” to prevent the lock bushing  52  from travelling proximally down the shaft  36 . 
         [0030]    A plurality of ball bearings  64  are positioned circumferentially around the shaft  36 . In a preferred embodiment, eight ball bearings  64  are positioned about the shaft  36 . However, it is contemplated that more or less than eight ball bearings  64  may be used. As shown in  FIG. 3 , each of the ball bearings  64  resides between a torque gear  66 , positioned distal of the ball bearings  64 , and a proximal wall surface  68  of the first cavity  22  and the distal surface  54  of the lock bushing  52 . These three points of contact position each of the series of balls  64  such that migration and lateral movement of the ball bearings  64  is minimized. 
         [0031]    Furthermore, each of the ball bearings  64  is nested in a recess  70  provided in the proximal surface  68  of the first cavity  22  of the housing  18 . The recess  70  provides a seat within which the ball bearing  64  rotates. In addition, the recess  70  prevents migration and lateral movement of the ball bearing  64 . In a preferred embodiment, each recess  70  is dimensioned such that a portion of the diameter of the ball bearing  64  resides therewithin. The recess  70  also provides a frictional connection between the housing  18  and the handle  20  of the device  12  to the torque gear  66  and elongated body or shaft  36 . It is at this point where the proximal surface  68  of first cavity  22  of the housing  18  meets the ball bearings  64 . 
         [0032]    In a preferred embodiment, a proximal surface  72  of the torque gear  66  comprises a series of discrete individual divots  74  ( FIG. 7 ) that are positioned radially around a throughbore  76  of the torque gear  66 . In a further embodiment, the torque gear  66  comprises an equal number of divots  74  as there are ball bearings  64 . It is further preferred that these divots  74  are positioned equidistant from longitudinal axis A-A within the proximal surface  72  of the gear  66 . 
         [0033]    In addition, each divot  74  is dimensioned such that when the ball bearing  64  is positioned therewithin, the equator of the ball bearing  64  is above the proximal surface  72  of the torque gear  66 . In a preferred embodiment, the divot  74  penetrates from about 0.25 cm to about 1.0 cm within the proximal surface  72  of the torque gear  66 . Therefore, each of the ball bearings  64  is sandwiched between the divot  74  of the proximal surface  72  of the torque gear  66  and the proximal surface  68  of the first cavity  22  of the housing  18 . 
         [0034]    In a preferred embodiment, the throughbore  76  of the torque gear  66  comprises a cross-sectional shape that is hexagonal. This preferred hexagonal shape, provides a plurality of contact surfaces where the gear  66  and the outer surface  78  of the shaft  36  meet. However, it is contemplated that other non-limiting cross sectional shapes could also be used such that a frictional fit between the shaft  36  and the torque gear  66  is established. As the torque gear  66  is rotated, the inner surface contact surfaces create a frictional interference with the outer surface of the shaft  36  which, in turn, causes the shaft  36  to rotate with the gear  66 . The torque gear  66  preferably comprises a distal surface  80  that is planar and is substantially perpendicular with respect to longitudinal axis A-A. 
         [0035]    A thrust bearing  82  is positioned distal of the torque gear  66  ( FIG. 8 ). The thrust bearing  82  comprises a disc  84  with a cylindrical outer diameter. A plurality of balls  86  reside within the thickness of the bearing  82 . In a preferred embodiment, the balls  86  are positioned with their equator aligned with the center of the thickness of the disc  84  such that a portion of each of the balls  86  extends past a proximal and distal surface  88 ,  90  of the thrust bearing  82 . Furthermore, it is preferred that a series of eight balls  86  are positioned around the thrust bearing  82 . However, the bearing  82  can be designed with more or less number of balls  86 . The thrust bearing  82  preferably comprises an outer diameter ranging from about 1 cm to about 5 cm with an inner diameter ranging from about 1 cm to about 4 cm. It is preferred that a throughbore  92  of the thrust bearing  82  has a cross-sectional shape that is curved and more preferably circular. The thrust bearing  82  resides between a flat washer  94  positioned distal of the bearing  82  and the torque gear  66 . Specifically, the balls  86  of the thrust bearing  82  contact the distal surface  80  of the torque gear  66 . 
         [0036]    A variable force applying subassembly  96  resides distal of the washer  94 . The variable force applying subassembly  96  is designed to generate a compressive force that is biased in a proximal direction through the device  12 . In a preferred embodiment, the variable force applying subassembly  96  may comprise an adjustment nut  98  and a plurality of Belleville washers  100  arranged front to back in a single stack or multiple stack formation. Alternatively, a spring (not shown) or plurality of springs (not shown) or in combination with the plurality of Belleville washers  100  may also comprise the subassembly  96 . The washers  100  and/or springs are further positioned between the flat washer  94  and the adjustment nut  98 . Therefore, the plurality of Belleville washers  100  or spring (not shown) provides a compressive force that is transferred through the components of the limiter device  12 . In a preferred embodiment, the biasing force generated through compression of the washers  100  and or springs of the variable force applying subassembly  96  compresses the components in a proximal direction against the inner proximal surface  68  of the first cavity  22  within the housing  18 . It is this compressive force, generated by the subassembly  96  that correlates to the torque limit of the device  12 . 
         [0037]    The number and type of Belleville washers  100  and/or springs that comprise the subassembly  96  determine the amount of biasing or compressive force and thus the torque limit of the device  12 . Increasing the number of Belleville washers  100  within the subassembly  96  generally increases the amount of the compressive force provided by the subassembly  96 . In turn, this increases the amount of torque that is delivered by the device  12 . Alternatively, providing a spring (not shown) with an increased torsion moment can also increase the compressive force and the torque amount. Furthermore, multiple stacks of washers  100  can also be provided in combination with the series of Belleville washers  100  and the spring or springs (not shown). The adjustment nut  98 , positioned distal of the Belleville washers  100 , provides a means by which the washers  100  and/or springs are compressed, thus resulting in the force that is applied by the variable force applying subassembly  96 . For example, a torque range from about 5 inch-lbs to about 15 in-lbs can be generated through the use of a series of springs, whereas a torque range from about 25 in-lbs to about 50 in-lbs can be generated through multiple stacking of a plurality of Belleville washers  100 . 
         [0038]    In a preferred embodiment, the compressive force provided by the variable force applying subassembly  96  compresses against the flat washer  94  which, in turn, compresses against the thrust bearing  82 . The thrust bearing  82  thus biases against the plurality of the ball bearings  64  which, in turn, bias against the proximal surface  68  of the first cavity  22 . The ball bearings  64  are thus in a biased frictional contact relationship with the housing  18  and the torque gear  66  and shaft  36 . 
         [0039]    An enclosure  51  may be positioned over the housing  18  within which, comprises the components of the torque limiting mechanism  16 . In a preferred embodiment, the enclosure  51  may be in a threaded relationship with the housing  18 . Alternatively, the enclosure  51  may be welded or adhered to the housing  18 . An enclosure opening  53  is provided at the distal end of the enclosure  51 . The opening  53  allows for the passage of the of the shaft  36  therethrough. As shown in  FIG. 3 , a second retaining ring  55  may be positioned circumferentially around the shaft  36  within the enclosure opening  53 . The second retaining ring  55  helps minimize lateral movement of the distal end  40  of the shaft  36  as well as ensure that the shaft  36  remains in a parallel orientation with longitudinal axis A-A. 
         [0040]    In operation, torque is applied to the device  12  through rotation of the handle  20 , either through manual rotation by the user or through rotation of a connected motor (not shown). Initially, as torque is applied, rotation of the handle  20  rotates the connected housing  18 . Rotational movement of the housing  18 , in turn, rotates the torque gear  66 , which is connected to the housing  18  through the frictional interference contact relationship of the ball bearings  64  and the inner surface of the housing, provided by the variable force applying subassembly  96 . 
         [0041]    Once the torque is applied to the handle  20  through its rotation by an operator exceeds the compressive force applied by the variable force applying subassembly  96 , the frictional interference contact between the ball bearings  64  and the housing  18  is overcome. Then the handle  20  and connected housing  18  begin to rotate freely without engaging the torque gear  66  and shaft  36 . Therefore, at this point rotation of the handle  20  no longer drives rotation of the elongated body or shaft  36 . The applied torque being delivered to the fastener or shaft has therefore been limited. 
         [0042]    In addition to the torque limiter device  12 , an adapter  14  may be provided with the device assembly  10 . The adapter  14 , having an adapter distal end portion spaced from an adapter proximal end portion, comprises an adapter elongated body  102 , an adapter collar  104 , an adapter spring  106 , and a series of o-rings  110  and retaining rings  112 . 
         [0043]    As previously mentioned, the adapter is designed to connect to the distal end portion  40  of the shaft  36  of the torque limiter device  12 . In a preferred embodiment, a proximal end portion  114  of the adapter elongated body  102  is connected with the distal end portion  40  of the shaft  36  of the torque limiter device  12 . The adapter  14  may be connected to the limiter device  12  through a number of non-limiting means including, welding, soldering, a pin and groove connection or a snap fit mechanism. 
         [0044]    The adapter  14  is the conduit between the torque limiter device  12  and a shaft  116  of a secondary device. A secondary device is herein defined as the object with which torque is to be applied. Non-limiting examples of secondary devices comprises a fastener, such as a bolt, screw, nut or a shaft of an auxiliary tool or the like. As such, the distal end of the adapter body  118  may be designed with a variety of cross-sectional shapes including, but not limited to, a rectangle, a square, an oval, a circle, a triangle, or a hexagonal. Furthermore, an adapter body distal end depth  120  may range from about 1 cm to about 10 cm depending on the shape and size of the fastener. 
         [0045]    The adapter  14  is primarily comprised of a spring  106  and ball mechanism. This ball and spring mechanism, illustrated in  FIGS. 3 and 4 , is designed to bias against the outside wall of the fastener thereby securing the fastener therewithin. As illustrated in.  FIGS. 3 and 4 , the adapter elongated body  102  extends parallel to longitudinal axis A-A with an adapter throughbore  125  extending therethrough. 
         [0046]    In a preferred embodiment, two opposing balls  122  are positioned about midway between the distal and proximal portions  118 ,  114  of the adapter elongated body  102 . These balls  122  reside within a ball opening  124  that is formed within an adapter body sidewall  126 . The ball opening  124  is constructed such that a portion of the ball  122  may extend past the adapter sidewall inner surface  126 . In a preferred embodiment, from about 5 percent to about 15 percent of the diameter of the ball  122  extends beyond the adapter body sidewall inner surface  126 . It is this portion of the ball  122  that contacts the outer surface of a fastener that has been inserted into the adapter socket  119 . 
         [0047]    The adapter spring  106  is positioned distal of the balls  122 . The spring  106  is further positioned circumferentially around the adapter throughbore  125 . In addition, the adapter o-ring  110  is positioned circumferentially around the adapter throughbore  125  and proximal of the spring. This o-ring  110 , which is preferably positioned between the adapter spring  106  and a raised outer wall of the adapter throughbore  125 , acts as “back stop” for the spring  106 . Residing proximal of the ball  122  is a first adapter retaining ring  112 A and a second adapter retaining ring  112 B. 
         [0048]    The collar  104 , having a distal opening spaced apart from a proximal opening, is positioned over these components and serves as an adapter  14  housing. The collar  104  is in a slidable relationship with the throughbore  125 . As illustrated in  FIGS. 3 and 4 , the collar  104  is constructed such that it slides proximally towards the handle  20 . 
         [0049]    In a preferred embodiment, the collar  104  is designed with a series of inner wall surfaces. A lip  128  resides at the distal end of the collar  104 . This lip  128  extends circumferentially around the adapter throughbore  125 . A lip end  130  contacts the outer surface of the adapter throughbore wall. Proximal of the lip  128  resides a first adapter inner wall surface  132  that extends circumferentially around the throughbore  125  and longitudinally from the lip end surface. The position of the first adapter inner wall surface  132  and the lip  128  provides a space within which the spring  106  moves. An adapter cavity  134  resides proximal of the first inner wall surface  132 . The cavity  134  is positioned circumferentially within the inner wall of the adapter collar  104 . The cavity  134  is further dimensioned such that the ball or balls  122  fit therewithin. As the collar  104  is moved in a proximal direction against the spring  106 , the cavity  134  is therefore positioned over the ball  122  or balls  122  within the adapter  14 . 
         [0050]    Positioning the cavity  134  over the balls  122  allows for the balls  122  to move upwardly into the cavity  134  when a fastener and the like is inserted therewithin. As shown in  FIGS. 3 and 4 , the collar  104  is moved in a proximal direction such that the cavity  134  is slid over the balls  122 . The shaft of a fastener or like secondary instrument is then positioned within the throughbore  125  of the adapter  14 . As the fastener is inserted therein, the balls  122  are forced to travel upwardly such that a portion of the diameter of the balls  122  extends past an outer surface of the adapter body  14  and into the cavity  134  above. Once the fastener is properly received in the adapter  14 , the collar  104  is allowed to move in a distal direction, back to its original starting position. The adapter spring  106  applies a force against the lip of the collar  104  which returns the collar  104  to its original distal position. A second adapter wall surface  136 , residing proximal of the cavity  134 , is slid over the opening  124  and the ball  122  therewithin. This second adapter wall surface  136  biases a portion of the ball  122  onto the outer surface of the inserted fastener, securing it therewithin. The first and second retaining rings  112 A,  112 B positioned proximal of the second adapter wall surface provide a means of securing the collar  104  to the adapter body  102 . 
         [0051]    Once the fastener or like secondary device is secured within the socket  119  of the adapter, the torque limiting device  12  of the present invention is ready for use. The operator may rotate the handle  20  in either a clockwise or counterclockwise direction. As the device  12  is rotated, the handle  20 , which is in frictional contact with the ball bearings, rotates the elongated body  36  of the device  12 . The elongated body  36  in turn, rotates the adapter  14  at its distal end which then rotates the fastener therewithin. 
         [0052]    The force applied by the compressed Belleville washers  100  or spring (not shown) within the housing  18  of the handle  20  of the device biases the ball bearings  64  within the thrust bearing  82 . These thrust bearing balls  86  in turn apply a biasing force against the distal surface of the torque gear  66  in a proximal direction. The biasing force is then transferred to the ball bearings  64  which, in turn, bias against the proximal surface of the first cavity wall  68  within the housing  18 . These series of biasing forces from the Belleville washer  100  at the distal end of the device  12  to the proximal wall surface  68  of the housing  18  provide a frictional interference connection between the torque gear  66  and the handle  20 . Once a specified torque value has been exceeded by rotation of the handle  20 , the force of the torque applied to the handle  20  exceeds the force applied by the Belleville washers  100 . At this point, the frictional connection between the ball bearings  64  and the handle  20  is overcome and the handle  20  begins to rotate about the longitudinal axis A-A without turning the torque gear  64 . The locking bushing  52  positioned proximally adjacent the ball bearings  64  applies a distal force counter to the proximal force applied by the Belleville washers  100 . This counter force provides additional alignment of the ball bearings  64  and ensures translational movement of the shaft  36  of the device  12  is minimized. Additionally, the locking bushing  52  ensures that the ball bearings  64  prevent side movement of the bearings  64 , thus ensuring correct alignment between the bearings  64  and the housing  18 . 
         [0053]    Furthermore, the retaining ring  60  positioned proximal of the locking bushing prevents translational movement of the elongated body  36  of the device  12 . Therefore, the retaining ring  60  ensures that the elongated body  36  within the device  12  remains parallel to the longitudinal A-A axis, thereby preventing the type of binding that is prone to the prior art devices. 
         [0054]    The attached drawings represent, by way of example, different embodiments of the subject of the invention. Multiple variations and modifications are possible in the embodiments the invention described here. Although certain illustrative embodiments of the invention have been shown and described here, a wide range of modifications, changes, and substitutions is contemplated in the foregoing disclosure. In some instances, some features of the present invention may be employed without a corresponding use of the other features. Accordingly, it is appropriate that the foregoing description be construed broadly and understood as being given by way of illustration and example only, the spirit and scope of the invention being limited only by the appended claims.