Abstract:
A bone clamp having a ratchet mechanism including ratchet teeth having rounded peaks with curved valleys therebetween and a curved pawl having a curvature similar to the valleys spanning the peaks of the ratchet teeth. The ratchet mechanism of the current invention distributes the interaction forces between the ratchet teeth and the pawl and therefore is resistive to shear stresses which could otherwise compromise the structural integrity of the ratchet mechanism.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to bone clamps, and, more particularly, to a bone clamp having an improved rachet mechanism. 
     2. Description of the Related Art 
     Bone clamps are well known in the medical profession and can be used, e.g., to engage broken bones for movement thereof. Bone clamps are reusable devices and therefore longevity is a desirable characteristic. Generally, bone clamps are utilized to move broken bones into aligned position or hold bone fragments together while surgical procedures (e.g., installation of a screw, plate, pin, or wire) are performed. When performing surgery to repair a broken bone, it is important to clamp the bone fragments together while a mending device (e.g., a screw, plate, pin, or wire) is being installed so that the bone fragments can be maintained in alignment with substantially no gaps therebetween. For example, bone clamps may be utilized to hold bone plates in position across a bone fracture and/or to align the fractured bones while the bone plate(s) are affixed thereto. 
     Typically, bone clamps utilize a rachet mechanism to control movement of the bone clamp and to maintain the bone clamp in locked position once it is operatively positioned. Ratchets utilized with prior art bone clamps are generally of two types: (1) a unidirectional rachet, e.g., of the type utilized with standard forceps, and (2) a bidirectional ratchet having a selectively actuatable lock mechanism to retain the pawl in locked position between two consecutive rachet teeth. 
     Ratchets of the second type (i.e., bidirectional ratchets) utilize rachet teeth formed by opposing ramp surfaces  90 ,  92  as illustrated in FIG.  10 . Similarly, pawl  94  is formed by opposing ramp surfaces  96 ,  98 . Opposing ramp surfaces  90 ,  92  and  96 ,  98  are substantially linear and culminate in a point. As pawl  94  is moved relative to the ratchet teeth, the peak of the pawl contacts the peaks of successive ratchet teeth and the interaction forces between the ratchet and the pawl will be concentrated at the peak of the pawl and the peaks of the ratchet teeth. The concentration of force causes a substantial shear stress at the peaks which will lead to fractures and rounding of the peaks (both of the pawl and of the ratchet teeth) as the bone clamp is repeatedly used. Such rounding of the peaks impairs the utility of the rachet since the pawl will be easily moveable relative to the rachet teeth and there will exist less contact surface area between the pawl and subsequent rachet teeth when the pawl is locked in position therebetween. 
     Ratchets of the first type (i.e., unidirectional ratchets) are less desirable than bidirectional ratchets since they assist in controlling movement of the clamp actuating members in one direction only. Furthermore, unidirectional ratchets utilize pawls and ratchet teeth having substantially linear ramp surfaces culminating in a point and therefore suffer from the same drawbacks as described above with respect to bidirectional ratchets. 
     What is needed in the art is a bone clamp having a bidirectional rachet for controlling the movement of the clamp actuating members which does not suffer from the disadvantages described above. 
     SUMMARY OF THE INVENTION 
     The present invention comprises a bone clamp having a bidirectional rachet mechanism which does not utilize substantially linear opposing ramp surfaces culminating in a point to form the pawl and the ratchet teeth. The rachet mechanism of the current invention comprises a plurality of rachet teeth formed from a plurality of rounded peaks having a plurality of curved valleys therebetween, and a curved pawl having substantially the same curvature as the valleys of the rachet teeth. The rounded structure of the rachet and pawl of the present invention eliminates the interaction of a pair of sharp peaks as in the prior art. The interaction forces between the rachet and the pawl of the current invention are more evenly distributed than in the ratchet mechanisms of the prior art due to the rounded surfaces of the ratchet teeth and the pawl of the present invention. Therefore, the present invention lessens the detrimental effect of the interaction forces between the ratchet and the pawl. 
     The invention, in one form thereof, comprises a bone clamp including a first clamp member and a second clamp member as well as a ratchet mechanism, which is resistive to shear stress, for controlling actuation of the first clamp member. Actuation of first clamp member relative to the second clamp member places the bone clamp in either a clamped or an unclamped position. 
     The invention, in another form thereof, comprises a bone clamp including a first clamp member and a second clamp member as well as a ratchet mechanism for controlling actuation of the first clamp member relative to the second clamp member. The ratchet mechanism of this form of the current invention includes a plurality of ratchet teeth comprising a plurality of curved peaks with a plurality of valleys therebetween, and a pawl which selectively contacts each of the plurality of ratchet teeth. 
     The invention, in yet another form thereof, comprises a bone clamp including a first clamp member and a second clamp member as well as a ratchet mechanism for controlling actuation of the first clamp member relative to the second clamp member. The ratchet mechanism of this form of the current invention includes a plurality of ratchet teeth comprising a plurality of peaks with a plurality of valleys therebetween and a curved pawl selectively contacting each of the plurality of ratchet teeth. 
     The invention, in another form thereof, comprises a bone clamp including a first clamp member and a second clamp member as well as a rachet mechanism for controlling actuation of the first clamp member relative to the second clamp member. Actuation of the first clamp member relative to the second clamp member places the bone clamp in either a clamped or an unclamped position. The rachet mechanism of this form of the current invention includes a plurality of rachet teeth comprising a plurality of peaks with a plurality of curved valleys therebetween, and a pawl which selectively contacts each of the plurality of rachet teeth. 
     An advantage of the present invention is the ability to provide a bidirectional rachet in which interaction forces between the pawl and rachet teeth are more evenly distributed than in the bidirectional ratchets of the prior art. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The above-mentioned and other features and advantages of this invention, and the manner of obtaining them, will become more apparent and the invention itself will be better understood by reference to the following description of embodiments of the invention taken in conjunction with the accompanying drawings, wherein: 
     FIG. 1 is a perspective view of a bone clamp in accordance with the present invention; 
     FIG. 2 is a side elevational view thereof; 
     FIG. 3 is a fragmentary, exploded, perspective view of a rachet in accordance with the present invention; 
     FIGS. 4A and 4B are fragmentary side elevational views illustrating the operation of a rachet in accordance with the present invention; 
     FIG. 5 is a fragmentary side elevational view illustrating the rachet of the present invention in locked position; 
     FIG. 6 is a bottom elevational view of a pawl in accordance with the present invention; 
     FIG. 7 is a front elevational view thereof; 
     FIG. 8 is an axial elevational view of a lock nut in accordance with the present invention; 
     FIG. 9 is a sectional view thereof; and 
     FIG. 10 is a fragmentary side elevational view of a rachet and pawl of the prior art. 
     Corresponding reference characters indicate corresponding parts throughout the several views. The exemplification set out herein illustrates a preferred embodiment of the invention and such exemplification is not to be construed as limiting the scope of the invention in any manner. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings, and particularly to FIG. 1, one exemplary embodiment of bone clamp  10  in accordance with the present invention is illustrated. Generally, bone clamp  10  is formed from first clamp member  34 , second clamp member  36 , ratchet member  46 , and clamp plunger  18 . 
     First clamp member  34  is pivotally connected to second clamp member  36  via pivot screw  40 . Second clamp member  36  comprises stationary handle  16  and guide member  26 . Clamp plunger  18  is operably positioned through guide channel  20  in guide member  26  for axial displacement relative thereto. Guide member  26  further includes support arm  22  holding gripping point  12 . Clamp plunger  18  includes gripping point  12  on the distal end thereof. As illustrated in FIG. 2, supplemental grip end  88  can be affixed to clamp plunger  18  to extend the axial length thereof. 
     First clamp member  34  is formed from moveable handle  14  and actuation member  24  separated by pivot point  42 . Actuation member  24  includes Y-shaped end  38  having a slot  32  sized to accommodate clamp plunger  18 . Clamp plunger  18  includes first and second flanges  28 ,  30  (FIG. 2) which are positioned on either side of Y-shaped end  38 . Actuation of actuation member  24  causes Y-shaped end  38  to contact either first flange  28 , or second flange  30  and thereby actuate clamp plunger  18 . 
     Movement of moveable handle  14  causes actuation of actuation member  24  and consequently clamp plunger  18 , thus moving the clamp into operable clamped position. Movement of moveable handle  14  is controlled via rachet member  46 . Rachet member  46  comprises two rows of rachet teeth  56 ,  58  and pawl  44 . Rows of ratchet teeth  56 ,  58  are separated by gap  60  and are affixed to, or are integral with stationary handle  16 . Pawl  44  is operably connected to moveable handle  14  via pawl connecting screw  62 . 
     As illustrated in FIG. 3, moveable handle  14  is positioned above rows of ratchet teeth  56 ,  58  (moveable handle  14  may or may not contact the portion of ratchet member  46  opposite to rows of ratchet teeth  56 ,  58 ). Moveable handle  14  includes elongate aperture  78  (FIG. 4A) through which pawl connecting screw  62  may pass. As illustrated in FIG. 3, pawl connected screw  62  traverses threaded lock nut aperture  68  in lock nut  48 , spring  54 , pawl aperture  66  in pawl  44 , and finally elongate aperture  78  in movable handle  14 . Retaining pin  70  is positioned through retaining pin aperture  72  and creates an interference fit with pawl connecting screw  62  to resist axial displacement thereof. 
     FIGS. 4A and 4B illustrate the ratchet of the current invention in assembled form. Lock nut  48  is positioned as illustrated in FIGS. 4A and 4B to allow movement of pawl  44  relative to pawl connecting screw  62  and ratchet teeth  58 . Ratchet teeth  58  include peaks  82  with curved valleys  84  therebetween. The curvature of pawl  44  matches the curvatures of valleys  84  as illustrated in FIG.  4 A. FIG. 4B illustrates movement of pawl  44  along ratchet teeth  58 . As illustrated, pawl  44  moves longitudinally along pawl connecting screw  62  as pawl  44  moves between successive ratchet teeth. 
     Spring  54  biases pawl  44  toward rows of ratchet teeth  56 ,  58  and encourages contact of pawl  44  with valleys  84 . Pawl  44  includes spring contact surface  76  against which an end of spring  54  rests. As illustrated in FIGS. 6 and 7, pawl  44  includes spring retaining surfaces  80  to assist in positioning spring  54  (FIG. 4A) against spring contact surface  76 . The opposing end of spring  54  rests against spring recess  64  of lock nut  48 . Lock nut  48  further includes screw head recess  74  (FIGS. 8 and 9) which, in one embodiment, will receive the head of pawl connecting screw  62  when lock nut  48  is in unlocked position. As illustrated in FIG. 3, pawl  44  includes first and second pawl guides  50 ,  52  which, as illustrated in FIG. 1, are positioned on opposing sides of rows of ratchet teeth  56 ,  58  respectively. First and second pawl guides  50 ,  52  function to guide pawl  44  as it travels along rows of ratchet teeth  56 ,  58 . 
     Once the bone clamp is operatively positioned and placed in clamped position, lock nut  48  may be rotated so that threaded lock nut aperture  68  (FIG. 3) interacts with threads  86  of pawl connecting screw  62  to axially displace lock nut  48  and lock pawl  44  in position as illustrated in FIG.  5 . 
     While this invention has been described as having an exemplary design, the present invention can be further modified within the spirit and scope of this disclosure. This application is therefore intended to cover any variations, uses, or adaptations of the invention using its general principals. Further, this application is intended to cover such departures from the present disclosure as come within known or customary practice in the art to which this invention pertains and which fall within the limits of the appended claims.