Abstract:
Bicentric hinges for use in braces and methods for operating knee braces and other types of braces are disclosed herein. In one embodiment, a hinge includes a plate and first and second members rotatably coupled to the plate. The first member is rotatable about a first axis of rotation between a first position and a second position. The second member is rotatable about a second axis of rotation between a third position and a fourth position independent of the rotation of the first member about the first axis of rotation. The second axis of rotation is spaced apart from the first axis of rotation. The first and second members are configured to be attachable to a frame. In another embodiment of the invention, a method of operating a knee brace hinge includes pivoting a first member about a first axis of rotation from a first position to a second position, and rotating a second member about a second axis of rotation from a third position to a fourth position after the first member has substantially reached the second position. The second axis of rotation is spaced away from the first axis of rotation. The method further includes returning the first member to the first position and the second member to the third position.

Description:
TECHNICAL FIELD  
         [0001]    The present invention relates to bicentric hinges for use in braces.  
         BACKGROUND  
         [0002]    Knee braces are widely used to stabilize and protect the knee joint. For example, knee braces are often used to prevent damage to the anterior cruciate ligament, posterior cruciate ligament, medial collateral ligament, lateral collateral ligament and/or miniscus in a knee joint. Knee braces are particularly useful to protect the knee joint during vigorous athletic activities such as running, basketball, football and skiing, and they are also used to stabilize the knee joint during recovery or rehabilitation from surgery or an injury.  
           [0003]    A knee brace typically includes an upper frame, a lower frame, and a hinge connecting the upper frame to the lower frame. The upper frame often has straps that wrap around the quadriceps or hamstring, and the lower frame often has straps that wrap around the calf. Each portion of the frame is configured to fit the shape of the corresponding portion of the leg. The hinge allows the lower frame to pivot relative to the upper frame as the knee bends. Many braces have a hinge on each side of the knee joint to give the brace additional strength.  
           [0004]    Conventional hinges for knee braces include a single axis pivot, two gears and a four-bar linkage. The conventional geared hinge mechanisms typically have two rotating gears with interlocking teeth. The single axis pivot and geared hinge mechanisms have several disadvantages. First, the single axis pivot and geared hinge mechanisms limit the range of flexion of the leg. Second, the single axis pivot and geared hinges do not simulate the natural movement of the knee joint when the leg bends or extends. The motion of the human knee joint is quite complex and does not rotate uniformly from extension to flexion. Because the single axis pivot and geared hinge mechanisms cannot simulate the natural movement of the knee joint, the knee brace may force the knee into an unnatural position at extension or flexion if the straps on the knee brace are tight. This coupled with forces induced during activity may injure the knee joint. Moreover, a user may loosen the straps to avoid the discomfort resulting from the unnatural movement of the knee joint. If the straps on the knee brace are loose, however, the knee brace will slide down the leg during an activity. Such movement of the knee brace during an activity is uncomfortable and annoying. Additionally, as the knee brace slides down the leg, the straps might not be tight enough to provide the necessary support to the knee.  
           [0005]    A four-bar linkage hinge mechanism better simulates the motion of the knee during flexion and extension than geared hinges. Four-bar linkage hinges, however, have several disadvantages. First, the motion of a four-bar linkage hinge is complex, making it difficult to set and adjust stops that limit the range of motion of the knee brace. As a result, patients may not accurately limit the range of motion with four-bar linkage hinge mechanisms. Second, four-bar linkage hinges are bigger than many other types of hinges. A big knee brace hinge can make it more difficult to pull clothes over the brace, and large hinges may interfere with the other knee joint during activities. Therefore, four-bar linkage hinges are not widely used in knee braces.  
         SUMMARY  
         [0006]    The present invention is directed toward a bicentric hinge for use in a brace and a method for operating such bicentric hinges. In one embodiment of the invention, a hinge includes a plate, a first member rotatably coupled to one section of the plate, and a second member rotatably coupled to another section of the plate. The first member is rotatable about a first axis of rotation between a first position and a second position. The second member is rotatable about a second axis of rotation between a third position and a fourth position. The first and second members can rotate independently of each other. The first and second members, for example, do not have teeth directly engaged with each other. The second axis of rotation is spaced apart from the first axis of rotation. The first and second members can be configured to be attachable to a frame, or they can be integral portions of the frame.  
           [0007]    An embodiment of operating a knee brace hinge includes pivoting the first member about the first axis of rotation from the first position to the second position, and then rotating the second member about the second axis of rotation from the third position to the fourth position. The second member begins pivoting after the first member has substantially reached the second position in one particular embodiment. The method further includes returning the first member to the first position and the second member to the third position. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0008]    [0008]FIG. 1 is an isometric view of a knee brace with a hinge in accordance with one embodiment of the invention.  
         [0009]    [0009]FIG. 2 is an exploded view of a plate, a first hinge member, and a second hinge member of the hinge of FIG. 1.  
         [0010]    [0010]FIG. 3A is a top plan view of an assembly including a resilient member with the plate, the first hinge member, and the second hinge member of FIG. 2.  
         [0011]    [0011]FIG. 3B is a top plan view of an assembly including a first torsion spring attached to a first hinge member and a second torsion spring attached to a second hinge member in accordance with another embodiment of the invention.  
         [0012]    [0012]FIG. 4 is a top plan view of first and second adjustable range restrictors.  
         [0013]    [0013]FIG. 5A is a top plan view of an adjustable range restrictor system in accordance with one embodiment of the invention.  
         [0014]    [0014]FIG. 5B is an isometric view of the adjustable range restrictor system of FIG. 5A with the first and second adjustable range restrictors removed from a cover plate.  
         [0015]    [0015]FIG. 6 is an isometric exploded view of a hinge and range restrictor in accordance with an embodiment of the invention.  
         [0016]    FIGS.  7 A- 7 C are top plan views illustrating a hinge with a rocker in accordance with another embodiment of the invention. 
     
    
     DETAILED DESCRIPTION  
       [0017]    The following disclosure describes several embodiments of bicentric hinges and methods for operating anatomical braces with such hinges. Many specific details of certain embodiments of the invention are set forth in the following description and in FIGS.  1 - 7  to provide a thorough understanding of such embodiments. One skilled in the art, however, will understand that the invention may have additional embodiments or that the invention may be practiced without several of the details described in the following description. For example, even though many embodiments of the bicentric hinge are described with reference to a knee brace, they can also be used in elbow braces or other braces.  
         [0018]    [0018]FIG. 1 is an isometric view of a knee brace  60  including an upper frame  30 , a lower frame  32 , and hinges  10  connecting the upper frame  30  to the lower frame  32 . The upper frame  30  can include at least one strap  20  to wrap around the quadriceps or hamstring, and the lower frame  32  can also include one or more straps. In other embodiments, the upper and lower frames  30  and  32  can have different configurations and include different configurations of straps. For example, the knee brace  60  can also include a flexible, elastic sleeve  62  coupled either directly or indirectly to the upper and lower frames  30  and  32 .  
         [0019]    [0019]FIG. 2 is an exploded view and FIG. 3A is a top plan view of one embodiment of the hinge  10 . In this embodiment, the hinge  10  includes a back plate  200 , a first hinge member  260 , and a second hinge member  261 . The first hinge member  260  rotatably mounts to the back plate  200  and is configured to attach to the upper frame  30  (FIG. 1) to permit the upper frame  30  to pivot about the back plate  200 . The second hinge member  261  also rotatably mounts to the back plate  200  and is configured to attach to the lower frame  32  (FIG. 1) to permit the lower frame  32  to pivot about the back plate  200  independently of the upper frame  30 . Accordingly, the upper and lower frames  30  and  32  pivot independently about two different axes of rotation.  
         [0020]    Referring to FIG. 2, the first hinge member  260  is a generally flat plate with a front surface  266  and a back surface (not shown) opposite the front surface  266 . Between the front surface  266  and the back surface are a top edge  276 , a bottom edge  274  and a side edge  272  configured for attachment to a portion of the upper frame  30 . For example, the first hinge member  260  can include two apertures  262  and  264  proximate the side edge  272  for receiving fasteners (not shown) to connect the upper frame  30  to the first hinge member  260 . The second hinge member  261 , similarly, has a front surface  267  and a back surface (not shown) opposite the front surface  267 . Between the front surface  267  and the back surface are a top edge  277 , a bottom edge  275  and a side edge  273  configured for attachment to a portion of the lower frame  32 . The second hinge member  261  can also include two apertures  263  and  265  proximate the side edge  273  for receiving fasteners (not shown) to connect the lower frame  32  to the second hinge member  261 . In additional embodiments, the first hinge member  260  can be an integral portion of the upper frame  30  and the second hinge member  261  can be an integral portion of the lower frame  32 . The first and second hinge members  260  and  261  can have different configurations in other embodiments.  
         [0021]    Referring to FIGS. 2 and 3 together, the first hinge member  260  is pivotally connected to the back plate  200  by a fastener  320 . The first hinge member  260  rotates relative to the back plate  200  about a first axis of rotation A 1  (FIG. 3A). The first hinge member  260  has a pin  252  that projects from the front surface  266  and the back surface. In additional embodiments, the pin  252  can have a different configuration or shape. For example, the pin  252  can extend or project from either the front surface  266  or the back surface. The portion of the pin  252  projecting from the back surface is received within an annular slot  220  in the back plate  200 . The annular slot  220  is accordingly centered about the first axis of rotation A 1  with a centerline at a radius R 1  corresponding to the distance from the first axis of rotation A 1  to the pin  252 . Accordingly, as the first hinge member  260  rotates relative to the back plate  200  about the first axis of rotation A 1 , the pin  252  slides in the annular slot  220 . A first endpoint  224  and a second endpoint  226  of the slot  220  define the maximum range of motion for the first hinge member  260 . Accordingly, the length of the slot  220  determines the pivoting range of the first hinge member  260  relative to the back plate  200 . In additional embodiments, the slot  220  can have different lengths to change the pivoting range of the first hinge member  260 . In other embodiments, the position of the slot  220  and the pin  252  can be different, such as the slot  220  can be in the first hinge member  260  and the pin  252  can be attached to the back plate  200 .  
         [0022]    The second hinge member  261  is pivotally connected to the back plate  200  by a fastener  322 . The second hinge member  261  rotates relative to the back plate  200  about a second axis of rotation A 2  (FIG. 3A). The second hinge member  261  has a pin  253  that projects from the front surface  267  and the back surface. In additional embodiments, the pin  253  can have a different configuration or shape. For example, the pin  253  can extend or project from either the front surface  267  or the back surface, or there can be two separate pins extending from each surface. The portion of the pin  253  projecting from the back surface is received within an annular slot  222  in the back plate  200 . The annular slot  222  is accordingly centered about the second axis of rotation A 2  with a centerline at a radius R 2  corresponding to the distance from the second axis of rotation A 2  to the pin  253 . As the second hinge member  261  rotates relative to the back plate  200  about the second axis of rotation A 2 , the pin  253  slides in the annular slot  222 . A first endpoint  225  and a second endpoint  227  of the slot  222  define the maximum range of motion for the second hinge member  261 . The length of the slot  222  determines the pivoting range of the second hinge member  261  relative to the back plate  200 . In additional embodiments, the slot  222  can have a different length to change the pivoting range of the second hinge member  261 . In other embodiments, the position of the slot  222  and the pin  253  can be different, such as the slot  222  can be in the second hinge member  261  and the pin  253  can be attached to the back plate  200 .  
         [0023]    Referring to FIG. 3A, the curved edge  270  on the first hinge member  260  is spaced away from the curved edge  271  on the second hinge member by a gap G. Accordingly, the first hinge member  260  and the second hinge member  261  pivot independently about the two different axes of rotation A 1  and A 2 . Because the hinge has two different and independent axes of rotation, it better simulates the natural motion of the knee joint. This is expected to mitigate the sliding of the knee brace down the leg and reduce exerting unnatural forces against the knee joint.  
         [0024]    In the illustrated embodiment, the back plate  200  has a cutout portion  250 . The cutout portion  250  allows the first and second hinge members  260  and  261  to rotate through the full pivoting range without the upper and lower frames  30  and  32  (FIG. 1) striking the back plate  200 .  
         [0025]    In the illustrated embodiment, the first hinge member  260  and the second hinge member  261  are operatively coupled by a resilient member  300 . The resilient member  300  has a first end  302  attached to the first hinge member  260  and a second end  304  attached to the second hinge member  261 . The first end  302  is received within an aperture  282  in the first hinge member  260 . A channel  284  connects the aperture  282  to an edge  268  and is sized to receive a portion of the resilient member  300 . Similarly, the second end  304  of the resilient member is received within an aperture  283  of the second hinge member  261 . A channel  285  connects the aperture  283  to the edge  277  and is sized to receive a portion of the resilient member  300 . The first end  302  and the second end  304  of the resilient member  300  are enlarged so that they are not pulled through the smaller channels  284  and  285 . In one embodiment, the first end  302  and the second end  304  of the resilient member  300  have a donut shape with a pin in the center. In other embodiments, the first end  302  and second end  304  of the resilient member  300  can be clamped or bonded.  
         [0026]    The resilient member  300  is elastic and provides resistance to the hinge members  260  and  261  during flexion. In one embodiment, urethane can be used; in other embodiments other materials may be used. The resilient member  300  stretches as the first hinge member  260  rotates in a direction D 1  and/or the second hinge member  261  rotates in a direction D 2 . The resilient member  300  urges the first hinge member  260  to rotate in a direction D 3  and the second hinge member  261  to rotate in a direction D 4 . Accordingly, when no external force is placed on the first and second hinge members  260  and  261 , the pins  252  and  253  are drawn toward the first endpoints  224  and  225  of the slots  220  and  222 . When an external force is applied to the first hinge member  260  causing rotation in the direction D 1 , the resilient member  300  stretches elastically and rides along a curved edge  270  of the first hinge member  260 . In the illustrated embodiment, the curved edge  270  has a radius R 3 . In one embodiment, the curved edge  270  may not have a constant radius. Similarly, when an external force is applied to the second hinge member  261  causing rotation in the direction D 2 , the resilient member  300  stretches elastically and rides along a curved edge  271  of the second hinge member  261 . In the illustrated embodiment, the curved edge  270  has a radius R 4  that is greater than the radius R 3 . In additional embodiments, the radius R 3  can be equal to or greater than the radius R 4 .  
         [0027]    The resilient member  300  and the radii of the hinge members  260  and  261  operate together to control the rotation of the hinge members  260  and  261 . For example, when R 3  is less than R 4 , the first hinge member  260  rotates in direction D 1  for an arc length before the second hinge member  261  rotates for an arc length in direction D 2 . This is because greater external force must be applied to rotate a member with a greater radius in light of the counter force applied by the resilient member  300 . Accordingly, in the illustrated embodiment, when an external force is applied to the hinge  310 , the first hinge member  260  rotates first because its radius R 3  is less than the radius R 4  of the second hinge member  261 . The second hinge member  261  will begin to rotate after the pin  252  of the first hinge member  260  has rotated through at least a portion of its range of motion. The rotation of one hinge member before the rotation of the other hinge member simulates the natural anatomical motion of the knee joint during extension and flexion. A better simulation of the natural motion of the knee joint reduces the movement of the brace down the leg of the user and the tendency of the knee brace to force the knee into unnatural positions.  
         [0028]    [0028]FIG. 3B is a top plan view of an assembly including a first torsion spring  398  attached to a first hinge member  360  and a second torsion spring  399  attached to a second hinge member  361  in accordance with another embodiment of the invention. Each torsion spring  398  and  399  is also attached to the back plate  200 . The first torsion spring  398  urges the first hinge member  360  to rotate in the direction D 3  and the second torsion spring  399  urges the second hinge member to rotate in the direction D 4 . Accordingly, when no external force is placed on the first and second hinge members  360  and  361 , the pins  252  and  253  are drawn toward the first endpoints  224  and  225  of the slots  220  and  222 . In one embodiment, the torsion springs can have different spring coefficients causing one hinge member to rotate before the other.  
         [0029]    [0029]FIG. 4 is a top plan view of the hinge  310  of FIG. 3A with first and second adjustable range restrictors  402  and  404 . FIG. 5A is a top plan view of an adjustable range restrictor system  406  in accordance with one embodiment of the invention. FIG. 5B is an isometric view of the adjustable range restrictor system  406  of FIG. 5A with the first and second adjustable range restrictors  402  and  404  removed from a housing  540 . As explained in more detail below, the adjustable range restrictor system  406  allows a user to adjust the pivoting range of the first hinge member  260  and/or the second hinge member  261 .  
         [0030]    Referring to the illustrated embodiment in FIG. 4, the fastener  320  is received in an aperture  432  of the first adjustable range restrictor  402  so that the first adjustable range restrictor  402  is positionable about the first axis of rotation A 1 . The first adjustable range restrictor  402  has an annular slot  422  extending about the first axis of rotation A 1  with a centerline at the radius R 1 . The slot  422  is positioned and sized to receive the pin  252  of the first hinge member  260 . Accordingly, when the first hinge member  260  pivots, the pin  252  moves within the slot  422 . Similarly, the fastener  322  is received in an aperture  430  of the second adjustable range restrictor  404  so that the second adjustable range restrictor  404  is positionable about the second axis of rotation A 2 . The second adjustable range restrictor  404  has an annular slot  420  extending about the second axis of rotation A 2  with a centerline at the radius R 2 . The slot  420  is positioned and sized to receive the pin  253  of the second hinge member  261 . Accordingly, when the second hinge member  261  pivots, the pin  253  can move within the slot  420 . In the illustrated embodiment, the length of the slot  420  is approximately equal to the length of the slot  222 , and the length of the slot  422  is approximately equal to the length of the slot  220 . In other embodiments, the slots  420  and  422  can have different lengths.  
         [0031]    The first and second adjustable range restrictors  402  and  404  can be rotated so that their slots  422  and  420  limit the rotation of the first and second hinge members  260  and  261 . For example, referring to the embodiment in FIG. 4, the first adjustable range restrictor  402  is positioned so that the slot  422  is offset from the slot  220  of the first hinge member  260 . Consequently, a first endpoint  424  of the slot  422  and the second endpoint  226  of the slot  220  define stops for the pin  252  to limit the rotation of the first hinge member  260  about the first axis of rotation A 1 . The first adjustable range restrictor  402  can be rotated further in the direction D 1  to further limit the rotation of the first hinge member  260 . Conversely, the first adjustable range restrictor  402  can be rotated in the direction D 3  to increase the range of rotation. The second adjustable range restrictor  404  can similarly be positioned about the second axis of rotation A 2  so that the slot  420  is offset from the slot  222  of the second hinge member  261  to define stops for the pin  253  that limit the rotation of the second hinge member  261  about the second axis of rotation A 2 .  
         [0032]    The adjustable range restrictors  402  and  404  are held in place by the housing  540 . Referring to FIGS. 5A and 5B, at least a portion of the outer edge  442  of the first adjustable range restrictor  402  has teeth  412 , and the outer edge  440  of the second adjustable range restrictor  404  also has teeth  414 . The housing  540  has a recess  570  with teeth  550  that engage the teeth  412  and  414  of the first and second adjustable range restrictors  402  and  404 . When the housing  540  is attached to a front plate  400  (FIG. 4), the teeth  550  preclude the first and second adjustable range restrictors  402  and  404  from rotating about the first and second axes of rotation A 1  and A 2 . The housing  540 , for example, can have a lip  560  that snap-fits onto the front plate  400  to lock the first and second range restrictors  402  and  404  in desired positions for limiting the range of motion. The first and second adjustable range restrictors  402  and  404  are rotatably adjusted by removing the housing  540 , rotating the first and second adjustable range restrictors  402  and  404 , and replacing the housing  540 . The configuration of the teeth  412 ,  414  and  550  in the illustrated embodiment permits the first and second adjustable range restrictors  402  and  404  to be adjusted in 10-degree increments. In additional embodiments, the teeth  412 ,  414  and  550  can be sized and spaced differently.  
         [0033]    One advantage of the embodiment of the range restrictor system  406  shown in FIGS.  4 - 5 B is the ease with which a user can adjust the pivoting range of the first and second hinge members  260  and  261 . It will be appreciated that the range restrictor system  406  can have other configurations. For example, in additional embodiments, other types of devices can be used to restrict the first and second adjustable range restrictors  402  and  404  from rotating about the first and second axes of rotation A 1  and A 2 . For example, the front plate  400  could have a projection with teeth that engage the teeth of one or both of the adjustable range restrictors  402  and  404 , thus eliminating the need for the housing  540 . In the illustrated embodiment, the front plate  400  is similar to the back plate  200 , but is positioned on the other side of the hinge member  260  and  261 . In still other embodiments, the front plate  400  can have a different configuration, or the hinge may not have the front plate  400 . In further embodiments, the first and second adjustable range restrictors  402  and  404  can be placed proximate to the first and second hinge members  260  and  261 , or the adjustable range restrictor system  406  can be placed adjacent to the back surface of the back plate  200 . In additional embodiments, the hinge may not have the adjustable range restrictor system  406 .  
         [0034]    [0034]FIG. 6 is an exploded view of the hinge  10  of FIG. 1. In the illustrated embodiment, the first and second hinge members  260  and  261  are held between the back plate  200  and the front plate  400  by the fasteners  320  and  322 . The hinge  10  may have spacers  600 ,  620 ,  630  and  632  to assist the first and second hinge members  260  and  261  to rotate more easily between the plates  400  and  200 . The spacers  600  and  630  each have an aperture  604  through which the fastener  320  is placed, and an aperture  602  through which the first pin  252  is placed. Similarly, the spacers  620  and  632  each have an aperture  624  through which the fastener  322  is placed, and an aperture  622  through which the second pin  253  is placed. In additional embodiments, the spacers  600 ,  620 ,  630  and  632  can have different configurations, or the hinge  10  may not have one or more of the spacers  600 ,  620 ,  630  and  632 . The range restrictor system  406  attaches to the front plate  400  as explained above.  
         [0035]    [0035]FIG. 6 also illustrates the compactness of the hinge  10  and the range restrictor system  406 . The hinge  10  and the range restrictor system  406  together can have a thickness of between 0.125 inch and 1 inch. In one embodiment, the hinge  10  and the range restrictor system  406  together have a thickness of approximately 0.31 inch. The compact size of the hinge  10  and the range restrictor system  406  makes it easier to wear clothes over the knee brace and reduces the potential of having the hinge interfere with the other knee joint during activities.  
         [0036]    FIGS.  7 A- 7 C are top plan views illustrating a hinge  710  in accordance with another embodiment of the invention. The hinge  710  is similar to the hinge  10  described above, and like reference numbers refer to like components in FIGS.  1 - 7 C. In the illustrated embodiment, the hinge  710  includes a first hinge member  660  with a first recess  662  and a second hinge member  661  with a second recess  663 . The first and second hinge members  660  and  661  are pivotally coupled to the back plate  200 . Referring to FIG. 7A, the pin  252  of the first hinge member  660  is positioned at the first endpoint  224  of the slot  220  in the back plate  200 , and the pin  253  of the second hinge member  661  is positioned at the first endpoint  225  of the slot  222  in the back plate  200 . The hinge  710  also includes a rocker  650  attached to the back plate  200 . The rocker  650  has a flexible arm  698  and a head  697  positioned between the first hinge member  660  and the second hinge member  661 .  
         [0037]    When the hinge  710  is in the full-extension position shown in FIG. 7A, the head  697  is proximate a curved edge  670  of the first hinge member  660  and at least partially within the second recess  663  of the second hinge member  661 . Because the head  697  of the rocker  650  is at least partially within the second recess  663  of the second hinge member  661 , the second hinge member  661  is effectively jammed and restricted from movement. Accordingly, a force applied to either hinge member  660  or  661  will cause the first hinge member  660  to pivot in a direction S 1  about the first axis of rotation A 1 .  
         [0038]    Referring to FIG. 7B, the first hinge member  660  has pivoted about the first axis of rotation A 1  to a position where the pin  252  is at the second endpoint  226  of the slot  220  in the back plate  200 . The first hinge member  660  accordingly cannot pivot further about the first axis of rotation A 1  in the direction S 1 . In this position, the head  697  of the rocker  650  is received at least partially within the first recess  662  of the first hinge member  660 , releasing the bending force on the arm  698 . In this position the head  697  is free to move between the two recesses  662  and  663 . As the second hinge member  261  begins to rotate about the second axis of rotation A 2 , the cam shape of the surface  671  forces the head  697  of the rocker  650  into the recess  662  of the first hinge member  660 , effectively jamming and precluding rotation of the first hinge member  660  about the first axis of rotation A 1 .  
         [0039]    Referring to FIG. 7C, the second hinge member  661  has pivoted about the second axis of rotation A 2  to a position where the pin  253  is at the second endpoint  227  of the slot  222  in the back plate  200 . The second hinge member  661  accordingly cannot pivot further about the second axis of rotation A 2  in the direction S 2 . Throughout the rotation of the second hinge member  661  from the position in FIG. 7B to the position in FIG. 7C, the head  697  of the rocker  650  remains in the first recess  662  of the first hinge member  660  precluding the first hinge member  660  from pivoting about the first axis of rotation A 1 . Because the head  697  of the rocker  650  is at least partially within the first recess  662  of the first hinge member  660 , the first hinge member  660  requires a greater force to rotate in a direction S 3  than the force required for the second hinge member  661  to rotate in a direction S 4 . Accordingly, the rocker  650  encourages the second hinge member  661  to pivot in the direction S 4  about the second axis of rotation A 2  before the first hinge member  660  pivots in the direction S 3  about the first axis of rotation A 1 . In additional embodiments, the hinge  710  can have a rocker with a different configuration, or the hinge may not have a rocker. Furthermore, FIGS.  7 A- 7 C illustrate the full range of extension (FIGS.  7 A-B) and flexion (FIGS.  7 B-C) of the illustrated embodiment. Other embodiments can also have this range of extension and flexion without the rocker  650  or other components.  
         [0040]    From the foregoing, it will be appreciated that specific embodiments of the invention have been described herein for purposes of illustration, but that various modifications may be made without deviating from the spirit and scope of the invention. Accordingly, the invention is not limited except as by the appended claims.