Patent Publication Number: US-2017360580-A1

Title: Prosthetic knee

Description:
TECHNICAL FIELD 
     The disclosure relates to a prosthetic knee for use with a prosthetic system. 
     BACKGROUND 
     Artificial limbs, including leg prostheses, employ a wide range of technologies to provide solutions suitable to many differing needs. For a trans-femoral amputee, basic needs in a leg prosthesis include stability, both while standing and during the stance phase of a walking gait, and mechanical compatibility with the walking (or running) gait, and some manner of knee flexion during stance and swing phases of a gait. Certain tradeoffs exist between security and stability and walking or running performance (dynamic behavior). 
     A simple, non-articulable leg prosthesis (having no movable knee) may provide maximum stability but does not provide for an ideal gait. Also, sitting may be awkward if a person cannot bend his knee. Available articulating prosthetic knees provide improved walking or running performance but are lacking in stability and control. They are also mechanically complex, expensive, or both. This can be especially problematic for low activity users, such as elderly or fresh amputees not yet very skilled in controlling the knee. 
     The amount of control or stability required can vary from user to user, while known prosthetic knees have no adjustability. 
     There is a need for a prosthetic knee that provides stability in stance and simulates more natural knee movement in swing. 
     SUMMARY 
     The disclosure describes various embodiments of a prosthetic knee providing a construction and design that facilitates stability in stance while also simulating more natural knee movement. The embodiments also can conveniently lock the knee in stance on demand. 
     The embodiments described can include a prosthetic knee that includes a housing, a chassis, and a brake member pivotally connected to the housing at a first location point and to the chassis at a second location point. The brake member prevents rotation of the housing relative to the chassis when the knee is loaded by a user instance, providing stability to the user. A knee shaft extends through the brake member and is secured within a cavity defined by the housing. 
     An extension assist system includes a biasing mechanism arranged to compress and push the knee back toward extension when the knee is in flexion, resulting in knee movement that is more natural and fluid. The biasing mechanism is located inside of the chassis and operatively connected to the knee shaft via an extension assist link. 
     The extension assist link includes a body portion operatively connected to the biasing mechanism and a pair of arm portions in at least one slot defined by the knee shaft. The arm portions are pivotally connected to the knee shaft at a third location point located a distance from the first location point. By connecting the arm portions to the knee shaft within the at least one slot, the extension assist link can advantageously distribute pressure and provide extra strength to the knee in supporting loads. The arm portions also provide additional support in the knee to resist bending moments. 
     According to a variation, the lower surface of the extension assist link defines a convex portion that is complementary shaped to a concave recess defined by the upper surface of a piston between the biasing mechanism and the extension assist link, providing consistent and smooth contact between the piston and the extension assist link. 
     According to a variation, a lock piece is pivotally connected to the housing and movable between a locked position in which the lock piece is engaged with a stop surface protruding from the brake member, and an unlocked position in which the lock piece is disengaged from the stop surface. In the locked position, the engagement between the lock piece and stop surface prevents rotation between the housing and the brake member substantially preventing flexion of the knee. The large contact surface area between the lock piece and stop surface reduces the lock piece inadvertently slipping off of the stop surface. This allows the knee to be safely and securely locked such as during training, rehabilitation, and or other particularly demanding situations. The lock piece can also be easily moved to the unlocked position, providing excellent control to the user. 
     According to a variation, a brake-play adjustment fastener is on the chassis that engages the brake member. Friction components of the knee may wear over time and develop brake play. If this occurs, the play at a contact point between the brake member and chassis should be adjusted. This can be adjusted using the brake-play adjustment fastener, which rotates the entire brake member around the first location point. 
     According to a variation, a brake sensitivity screw and biasing mechanism are within a screw hole formed in the brake member. The load required to activate the brake member can be advantageously regulated to the individual user&#39;s weight and preferences by changing the brake member preload using the brake sensitivity adjustment screw. 
     Additional features and advantages of embodiments of the present disclosure will be set forth in the description that follows, and in part will be obvious from the description, or may be learned by the practice of such exemplary embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features, aspects, and advantages of the present disclosure will become better understood regarding the following description, appended claims, and accompanying drawings. 
         FIG. 1  is schematic view showing a prosthetic system. 
         FIG. 2  is an isometric view of a prosthetic knee according to an embodiment. 
         FIG. 3  is an isometric view of the housing removed from the prosthetic knee of  FIG. 2  for ease of reference. 
         FIG. 4  is an isometric view of the shaft removed from the prosthetic knee of  FIG. 2  for ease of reference. 
         FIG. 5  is an isometric view of the brake clamp removed from the prosthetic knee of  FIG. 2  for ease of reference. 
         FIG. 6  is a front view of the brake clamp in  FIG. 5 . 
         FIG. 7  is a cross-sectional view of the prosthetic knee of  FIG. 2  in full extension according to an embodiment. 
         FIG. 8  is a cross-sectional view of the prosthetic knee of  FIG. 2  in flexion according to an embodiment. 
         FIG. 9  is an isometric view of the extension assist link removed from the prosthetic knee of  FIG. 2  for ease of reference. 
         FIG. 10  is a back view of the prosthetic knee of  FIG. 2 . 
         FIG. 11  is a detailed cross-sectional view of the prosthetic knee of  FIG. 2  showing the manual lock mechanism. 
         FIG. 12  is an isometric view of the manual lock mechanism removed from the prosthetic knee of  FIG. 2  for ease of reference. 
         FIG. 13  is a side view of the prosthetic knee of  FIG. 2 . 
     
    
    
     DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS 
     A better understanding of different embodiments of the invention may be had from the following description read with the accompanying drawings in which like reference characters refer to like elements. 
     While the disclosure is susceptible to various modifications and alternative constructions, certain illustrative embodiments are in the drawings and are described below. It should be understood, however, there is no intention to limit the disclosure to the embodiments disclosed, but on the contrary, the intention covers all modifications, alternative constructions, combinations, and equivalents falling within the spirit and scope of the disclosure. 
     For further ease of understanding the joint disclosed, a description of a few terms is necessary. The term “upper” has its ordinary meaning and refers to a location above, or higher than another location. Likewise, the term “lower” has its ordinary meaning and refers to a location below, or underneath another location. The term “posterior” also has its ordinary meaning and refers to a location behind or to the rear of another location. The term “anterior” has its ordinary meaning and refers to a location ahead or to the front of another location. Lastly, the terms “left” and right” have their ordinary meaning and as used refer to the left and right sides when viewing the prosthetic knee from the anterior side. 
       FIG. 1  schematically depicts a prosthetic system  1000  for a residual limb  1001 . The system  1000  includes a socket assembly  1003  that embraces a residual limb, a prosthetic knee  1007  connected to the socket assembly  1003  by an adaptor  1011 , a pylon  1013  connecting the knee  1007 , and a foot  1015  connecting to the pylon  1013 . The prosthetic knee  1007  can be any of the prosthetic knee disclosed embodiments. 
     In order to better understand the operation of the prosthetic knee described, a basic discussion of the gait cycle is provided. A gait cycle defines the movement of the leg between successive heel contacts of the same foot. The gait cycle has two phases: stance and swing. The stance phase has three time periods: heel-strike, mid-stance and toe-off. During mid-stance, the knee joint will be at full extension. An actual knee joint will have flexion between heel-strike and mid-stance and between mid-stance and toe-off. This is called “stance flexion.” Not all prosthetic joints provide for stance flexion, and for those that do, they are mechanically complex, expensive, or both. These prosthetic joints typically require frequent maintenance and replacement. The amount of stance flexion required can vary from user to user, while most prosthetic knees have no adjustability. 
     Maximum flexion of the knee joint, while walking, will occur at the end of the toe-off phase. Maximum flexion is typically determined in part by the speed at which a person is walking. The faster a person walks the greater maximum flexion, while the slower a person walks, the lesser maximum flexion. In a natural knee, maximum flexion can be controlled and limited via the musculature of the leg. In a prosthetic knee joint, some artificial means of controlling and limiting maximum flexion are typically provided. Immediately following the end of the toe-off phase begins the swing phase. 
     While the stance phase has three time periods, the swing phase has two time periods: acceleration and deceleration. The acceleration phase begins immediately following the maximum flexion during the toe-off phase. During the acceleration phase, the lower portion of the leg, comprising the shin and foot, swings back towards full extension. In a natural knee joint, a deceleration phase follows the acceleration phase, during which the lower portion of the leg continues to swing towards full extension. Some prosthetic joints do not provide for any deceleration during the swing phase. Other prosthetic joints provide deceleration by using costly and bulky hydraulic or pneumatic cylinders. The deceleration required can vary from user to user, while most prosthetic joints have no adjustability. 
       FIGS. 2-13  illustrate a first embodiment of a prosthetic knee  100  for a prosthetic system or assembly. The knee  100  includes a housing  102 , a chassis  104 , and a load-dependent brake system  101  connecting the housing  102  and the chassis  104 . As seen in  FIG. 2 , a pyramid adaptor  108  or a 4-prong adaptor can be positioned at a top of the housing  102  and a distal tube clamp attachment  110 , having a socket head cap screw  112 , for tightening can be positioned at the bottom of the chassis  104 . 
     The load-dependent brake system  101  is arranged to selectively prevent rotation of the housing  102  relative to the chassis  104  when the knee  100  is loaded by a user in stance. When the load on the knee  100  is released, the load-dependent brake system  101  can be released so the knee  100  can swing or the housing  102  can rotate relative to the chassis  104 . This advantageously provides more natural and controlled movement of the knee. The load-dependent brake system  101  can include a brake member  106 , a knee shaft  122 , and brake sleeve  160 . 
       FIG. 3  shows the housing  102  removed from the knee  100  for ease of reference. The housing  102  includes a main body  114  with first and second flanges  116 ,  118  that protrude from the main body  114  towards the posterior or back of the housing  102 . The housing  102  defines a cavity  103  in the bottom side thereof. The first flange  116  and the second flange  118  can be parallel to each other and can each include a fastener hole  120 . The inner surface of each of the first and second flanges  116 ,  118  can define a keyway  128 . The keyway  128  can be a generally rectangular slot or groove. The upper portion of the housing  102  defines a recess  211  and a pair of opposed retaining pin holes  125 . 
     Referring now to  FIG. 4 , the knee shaft  122  of the load-dependent brake system  101  is insertable within the cavity  103  of the housing  102  so the knee shaft  122  is located inside of the cavity  103 , extending between the first and second flanges  116 ,  118 . The knee shaft  122  is shown as a cylindrical body but can be any suitable shape. A fastener hole  124  can be defined in each end of the knee shaft  122 . 
     The knee shaft  122  can be non-rotatably attached to the housing  102 . For instance, the knee shaft  122  can be selectively retained within the cavity  103  of the housing  102  via at least one fastener  126  (shown in  FIG. 2 ) respectively positioned in at least one fastener hole  120  of the housing and at least one of the fastener holes  124  defined in the knee shaft  122 . A key  130  is defined on each end of the knee shaft  122 . 
     When the knee shaft  122  is inserted into the cavity  103 , the keys  130  slide into the keyway  128  defined by the housing. This prevents relative rotation between the knee shaft  122  and the housing  102 . It also provides a solid connection between the knee shaft  122  and the housing  102  by increasing the contact surface area between them. It further aligns the fastener holes  120  and the fastener hole  124 , facilitating assembly and/or disassembly of the knee  100 . 
     The knee shaft  122  can define a through hole or pin hole  196  extending between its opposing ends. The pin hole  196  can be generally parallel and eccentrically positioned relative to a first location point  150  or knee axis (shown in  FIG. 8 ) described below. A posterior surface of the knee shaft  122  can also define at least one slot  198  that intersects the pin hole  196  between the opposing ends of the knee shaft  122 . The posterior surface of the knee shaft  122  is defined as being generally opposed an anterior surface of the knee shaft  122  facing the second location point  148 . 
     As shown, the at least one slot can comprise a pair of slots  198 . In other embodiments, the at least one slot  198  can comprise a single slot sized and configured to receive arm portions of the extension assist link described below. The pin hole  196  and the slots  198  are discussed in more detail below. 
     Referring now to  FIGS. 5 and 6 , the brake member  106  can be a brake clamp movably connecting the housing  102  and the chassis  104  to one another. The brake clamp  106  can be pivotally connected to the housing  102  and pivotally connected to the chassis  104 , allowing the housing  102  and the chassis  104  to be movably connected together. 
     The brake clamp  106  defines a main body  135  having an upper part  105  and a lower part  107  attached to the upper part  105 . The upper part  105  can have a width that is greater than a width of the lower part  107 . The brake clamp  106  defines side portions  134 ,  136  protruding from the upper part  105  towards the anterior of the brake clamp  106 . 
     The side portions  134 ,  136  can be spaced apart and generally parallel to each other. A pivot pin hole  138  can be defined in each of the side portions  134 ,  136 . A posterior surface of the brake clamp  106  defines a pair of slots  201  that generally correspond to the slots  198  of the knee shaft  122  when the knee shaft  122  is positioned within the cavity  103  of the housing  102 . The posterior surface of the brake clamp  106  is defined as generally opposed an anterior surface of the brake clamp formed on the terminal ends of the side portions  134 ,  146   
     A protruding step  207  can be defined on the brake clamp  106 . The step  207  can be between the slots  201  defined in the brake clamp  106 . The step  207  can have any suitable configuration but is shown as a substantially ramp-like protrusion forming a stop surface  137  and an upper curved surface. The stop surface  137  extends generally perpendicular to the outer radial surface of the brake clamp  106 . This can create more normal contact between the step  207  and a lock piece described below, reducing the lock piece inadvertently sliding off the step  207 . The upper curved surface of the step  207  helps the lock piece to slide or move past the step  207  until the knee  100  reaches full extension. In other embodiments, the step  207  can be a generally rectangular member, a triangular member, or any other appropriate member. 
     The step  207  can be attached to the brake clamp  106  or integrally formed on the brake clamp  106 . The step  207  can have a width that is less than a width of the brake clamp  106 . The width of the step  207  can generally correspond to a width of the recess  211  in the housing  102 . 
     The brake clamp  106  also defines a shaft hole  132  extending therethrough. The shaft hole  132  can be generally parallel to the pivot pin holes  138 . At least a portion of the brake clamp  106  is positionable within the cavity  103  of the housing  102 , with the knee shaft  122  extending through the shaft hole  132 . The brake clamp  106  can also define a slot  152  between the upper part  105 , the lower part  107 , and a contact pad  154  attached to a bottom side of the lower part  107 . 
     The knee shaft  122  is rotatably received within the shaft hole  132  such that relative rotation between the housing  102  and the brake clamp  106  is possible. For instance, the housing  102  and the knee shaft  122  are rotatable about the first location point  150  extending through the knee shaft  122 . Optionally, washers and/or bushings can be provided on the knee shaft  122  between the components of the knee  100  to help properly align, space, and/or fasten the individual components of the knee  100 . 
     As seen in  FIGS. 7 and 8 , the chassis  104  defines a main body  156  and an upper portion  144  upwardly extending therefrom. The upper portion  144  defines a pivot pin hole  146  passing therethrough. A pivot pin  140  can be retained at each end by bearings  142  respectively positioned in the pivot pin holes  138  of the brake clamp  106 . The pivot pin  140  passes through the pivot pin holes  138  and the pivot pin hole  146 . The upper portion  144  of the chassis  104  is pivotally between the side portion  134  and the side portion  136  of the brake clamp  106 . The chassis  104  includes a contact pad  158  attached to an upper side of the main body  156 . 
     The basicbrake function of the load-dependent brake system  101  will now be explained. When the knee  100  is loaded (e.g., foot on the ground) as shown in  FIG. 7 , the load-dependent brake system  101  moves to a braked configuration or state in which a second location point  148  or actuation axis allows relative rotation between the brake clamp  106  and the chassis  104 , which loads a contact point between the contact pad  154  on the brake clamp  106  and the contact pad  158  on the chassis  104 . This causes compression of the slot  152  defined by the brake clamp  106 , which causes compression of the brake sleeve  160 , which is fixedly attached to the brake clamp  106 . 
     The brake sleeve  160  is disposed within the shaft hole  132  and between the brake clamp  106  and the knee shaft  122 . Compression of the brake sleeve  160  on the knee shaft  122  creates friction against the knee shaft  122 , preventing rotation of the knee  100  about the first location point  150 . More particularly, compression of the brake sleeve  160  creates friction that prevents rotation of the housing  102  about the first location point  150 . The brake sleeve  160  can be a C-shaped brake sleeve or any other appropriate brake sleeve. The brake sleeve  160  may be formed of metal such as copper, rubber, or any other material which would provide sufficient compression when the knee is loaded. 
     When the load is released from the knee  100 , the load-dependent brake system  101  can move to a released configuration or state, in which the slot  152  and the brake sleeve  160  decompress, allowing the knee  100  to swing around the first location point  150  to the flexion position in  FIG. 8 . 
     A brake sensitivity adjustment system  109  can adjust the load required to activate the load-dependent brake system  101 . The brake sensitivity adjustment system  109  includes a brake sensitivity adjustment screw  162  and a biasing mechanism  164 . The biasing mechanism  164  can be a spring or any other suitable resilient member. The brake sensitivity adjustment screw  162  and the biasing mechanism  164  can be arranged within an adjustment screw hole  166  ( FIG. 6 ) defined in the brake clamp  106 . The biasing mechanism  164  can be within the adjustment screw hole  166  between the lower part  107  and the brake sensitivity adjustment screw  162 . The biasing mechanism  164  engages the lower part  107  of the brake clamp  106  and extends across the slot  152  to where it engages the brake sensitivity adjustment screw. The biasing mechanism  164  adjusts the load required to compress the slot  152  when the brake sensitivity adjustment screw  162  is turned. 
     Turning the brake sensitivity adjustment screw  162  in a first direction (tightening), compresses the biasing mechanism  164 , increasing the compression preload of the brake clamp  106  or the force required to close the slot  152  of the brake clamp  106 . Turning the brake sensitivity adjustment screw  162  in a second direction (loosening), allows the biasing mechanism  164  to decompress, decreasing the compression preload of the brake clamp  106 . By adjusting the compression preload of the brake clamp  106 , the load required to activate the knee brake can be regulated to the individual user&#39;s weight and/or preferences, providing more natural and controlled movement of the knee  100 . 
     A brake-play adjustment system  113  can adjust play that may develop in the load-dependent brake system  101 . The brake-play adjustment system  113  can include a brake-play adjustment fastener or screw  168  and a contact pad  170 . The brake-play adjustment screw  168  extends into a hole  172  defined in the upper portion  144  of the chassis  104 . The contact pad  170  is secured within a recess defined on the anterior of the brake clamp  106 . The brake-play adjustment screw  168  is arranged to adjustably engage the contact pad  170  on the brake clamp  106 . 
     Different components of the load-dependent brake system  101  may wear over time and develop brake-play (e.g., an unwanted slight rotation in the braked state). If this occurs, the play can be adjusted by using the brake-play adjustment screw  168 . For instance, turning the brake-play adjustment screw  168  in a first direction (tightening) advances the brake-play adjustment screw  168  within the hole  172 , engaging the contact pad  170  on the brake clamp  106 . This engagement creates a moment around the second location point  148 , which rotates the brake clamp  106  relative to the chassis  104  about the second location point  148 . The position of the brake clamp  106  relative to the chassis  104  can be controlled and/or regulated, helping to maintain the contact point between the contact pad  154  on the brake clamp  106  and the contact pad  158  on the chassis  104 , which limits play in the load-dependent brake system  101 . 
     In swing phase, the knee  100  is returned to full extension via an extension assist system  115 . A central component of the extension assist system  115  is a biasing mechanism or extension assist spring  178  compressed when the knee  100  is flexed, and pushes the knee  100  back to extension. The extension assist spring  178  is located inside the chassis  104  and operatively connected to the knee shaft  122  via a piston  174  and an extension assist link  182 . 
     The piston  174  and extension assist spring  178  are retained within an extension assist housing including an inner housing  176  secured within a cavity  180  defined in the main body  156  of the chassis  104 . The extension assist housing can also include an external housing  184  provided coaxially with the inner housing  176  in the cavity  180 . The external housing  184  is arranged to receive the inner housing  176 , the piston  174 , and a spring guide  186  and the extension assist spring  178 . 
     In some embodiments, the external housing  184  can be adjustable. For instance, a clinician or user can rotate the external housing  184 , moving it in an axial direction (e.g., upwards or downwards) to alter the compression of the extension assist spring  178 . This can vary the biasing force applied to the piston  174  by the extension assist spring  178 , and the biasing force applied to an extension assist link  182  by the piston  174 . The level of biasing force generated by the extension assist system  115  on the knee  100  toward extension can be adjusted as desired or for example, to the user&#39;s walking speed. 
     Stored mechanical energy within the extension assist spring  178  when compressed can be adjusted by rotating the external housing  184  via an opening  127  defined in the posterior or rear of the chassis  104 . This advantageously allows the extension assist system  115  to be adjustable and/or accessible to the user or clinician without having to disassemble the knee  100 . For instance, a clinician can adjust the compression of the extension assist spring  178  without having to remove a pylon from the distal tube clamp attachment  110  of the chassis  104 . 
     The extension assist link  182  can exhibit any suitable configuration but is shown in  FIG. 9  having a body portion  188  and first and second arm portions  190 ,  192  protruding from the body portion  188 . The body portion  188  can connect the first and second arm portions  190 ,  192  to one another. The body portion  188  can include a cross member extending between the arm portions  190 ,  192  and a base extending generally downward from the cross member to a distal end or lower surface of the extension assist link  182 . 
     The first and second arm portions  190 ,  192  are shown generally parallel to each other, each defining a pin hole  194 . A lower surface of body  188  of the extension assist link  182  can define a convex portion that is complementary shaped to a concave recess defined by the upper surface of the piston  174 , providing consistent and smooth surface contact between the piston  174  and the extension assist link  182 . 
     As best seen in  FIG. 10 , the arm portions  190 ,  192  of the extension assist link  182  can be within the slots  198  defined in the knee shaft  122 . The slots  198  can advantageously accommodate movement of the arm portions  190 ,  192  relative the knee shaft  122  and help limit rotation of the knee shaft  122 . 
     The extension assist link  182  can be pivotally connected to the knee shaft  122  at a third location point  203  (best seen in  FIG. 8 ) within the slots  198 . The arm portions  190 ,  192  can be symmetric regarding the central plane of rotation. By connecting the arm portions  190 ,  192  to the knee shaft  122  with the slots  198 , the extension assist link  182  can advantageously distribute pressure and provide extra strength to the knee  100  in supporting loads. The extension assist link  182  is also advantageous since the arm portion  190  is connected to the arm portion  192  by the body portion  188 , providing additional support in the knee  100  to resist a bending moment. 
     The third location point  203  is located a distance from the first location point  150 , about which the knee shaft  122  and the housing  102  rotate. This creates an eccentric connection between the extension assist link  182  and the knee shaft  122 . Rotation of the knee shaft  122  moves the extension assist link  182  in an upward direction or a downward direction. The third location point  203  can comprise a connection pin extending through the pin holes  194  in the extension assist link  182  and the pin hole  196  in the knee shaft  122 . The slots  201  defined in the brake clamp  106  can accommodate movement of the arm portions  190 ,  192  relative to the brake clamp  106 . 
     In the swing phase or when the knee  100  is brought from the extension position (shown in  FIG. 7 ) to the flexion position (shown in  FIG. 8 ), the load-dependent brake system  101  is in the release state and the housing  102  and knee shaft  122  can rotate about the first location point  150 . Because the extension assist link  183  is eccentrically connected to the shaft, this rotation moves the extension assist link  183  and the piston  174  in a downward direction, compressing the extension assist spring  178  within the cavity  182 . 
     The stored mechanical energy in the extension assist spring  178  then moves the extension assist spring  178  back toward its equilibrium position, which pushes the piston  174  in an upward direction. This forces the extension assist link  182  away from the spring guide  186 , causing the knee shaft  122  and the housing  102  to rotate about the first location point  150 , which forces the knee  100  back toward the extension position. 
     Referring to  FIGS. 11 and 12 , the knee  100  can include a locking system  117  allowing the knee  100  to be completely locked in one or more different positions. The manual locking system  117  can include a lock piece  205  and the step  207  defined on the brake clamp  106 . 
     The lock piece  205  can have any shape but is shown having a generally wedge-like shape. The lock piece  205  has a body portion  119 , first and second side arm portions  121  extending from the body portion  119 , and a gap  123  defined between the side arm portions  121 . Each of the side arm portions  121  can define a pin hole  209  extending therethrough. 
     The lock piece  205  can be within the recess  211  ( FIG. 3 ) defined by the housing  102  and pivotally connected to the housing  102  via a retaining pin  213  extending through the pin holes  209 . Opposing ends of the retaining pin  213  can be within the retaining pin holes  125  in the housing  102 . The lock piece  205  can be fixedly attached to the retaining pin  213  so the lock piece  205  and the retaining pin  213  rotate together. Alternatively, the lock piece  205  can be rotatably attached to the retaining pin  213  so the lock piece  205  can rotate relative to the retaining pin  213 . The retaining pin  213  can be integral to the lock piece  205  or the retaining pin  213  can be separate from the lock piece  205 . 
     The lock piece  205  is rotatable between an unlocked position and a locked position. In the unlocked position, the lock piece  205  is rotated away from the brake clamp  106  so the lock piece  205  clears the step  207 , allowing flexion or movement of the knee  100 . 
     In the locked position, the lock piece  205  is rotated toward the brake clamp  106  and engages the stop surface  137  of the step  207 . This prevents flexion of the knee  100 , advantageously limiting movement of the knee  100  during training, rehabilitation, and/or other particularly demanding situations. 
     The posterior surface of the lock piece  205  may have a geometric shape which corresponds to the stop surface  137  defined by the step  207 . For instance, the posterior surface of the lock piece  205  and the stop surface  137  can both be planar or can form complementary angles. In other embodiments, the stop surface  137  can include a slot or groove configured to receive a key member defined on the lock piece  205 . In other embodiments, the stop surface  137  can include a concave portion corresponding to a convex portion of the posterior surface of the lock piece  205 . The posterior surface of the lock piece  205  can be defined as being generally opposed the portion of the lock piece carrying the retaining pin  213 . 
     The step  207  can be molded on the surface of the brake clamp  106 , which can have a solid construction protruding from a profile of the brake clamp  106  or the outer portion of the brake clamp  106  at the base of the step  207 . As seen, the lock piece  205  can also have a construction arranged to resist deformation or failure, helping to provide solid contact between the lock piece  205  and the stop surface  137 . The size of the stop surface  137  and/or step  207  extending above the profile of the brake clamp  106  also forms a larger contact surface area between the stop surface  137  and the lock piece  205 , reducing the lock piece  205  inadvertently slipping off of the step  207 . 
     At least one the lock piece  205  or the step  207  can have a wider or thicker configuration, providing a greater locking strength. The stop surface  137  and/or the lock piece  205  can be formed from metal, plastic, or another rigid material providing solid contact. 
     The lock piece  205  can be biased toward the locked position. For instance, a biasing mechanism or torsion spring  215  can be loaded on the retaining pin  213  and positioned between the side arm portions  121  of the lock piece  205 . The torsion spring  215  can include a first arm  131  insertable in a small hole formed in the brake clamp  106  and a second arm  133  arranged to engage the housing  102 . Stored mechanical energy in the torsion spring  215  biases the lock piece  205  toward the locked position. 
     A release system  139  can allow a user or clinician to manually move the locking system  117  to the unlocked position. For instance, when the lock piece  205  is in the locked position, and hence the knee  100  in a locked state, sitting down can be difficult. The release system  139  can allow a user to release the lock piece  205  from the locked position to the unlocked position. As seen in  FIG. 13 , the release system  139  can include a lanyard, tether, or cable  217  attached to the lock piece  205  that includes a handle portion. The cable can be threaded through the lock piece  205 . A user can thread a distal end of the cable  217  through a fastener  225  having a tubular configuration, through the lock piece  205 , and back through the fastener  225 . The user can then adjust the length of the cable  217  as desired. With the length of the cable  217  adjusted, the user then can secure (e.g., crimp) the fastener  225  on the cable  217 , securely attaching the cable to the lock piece  205 . 
     To manipulate the release system  139 , the user can pull on the cable handle to lift the lock piece  205  to the unlocked position. When the user releases the cable, the lock piece  205  can return to the locked position when the knee  100  reaches full extension, allowing the lock piece  205  to engage the stop surface  137  defined on the step  207 . Optionally, the retaining pin  213  includes a head portion defining a recess arranged to receive a tool. The tool can manually rotate the retaining pin  213  which if fixedly attached to the lock piece  205  will rotate the lock piece  205 . 
     The locking system  117  can include a locking feature arranged to selectively deactivate the lock piece  205 . As seen in  FIGS. 12 and 13 , a set screw  219  can be disposed within a hole  141  (best seen in  FIG. 3 ) defined in the housing  102 . The set screw  219  is arranged to selectively engage a recess  145  defined in the lock piece  205 . 
     To deactivate the locking function of the lock piece  205 , a user can pull on the cable  217  or lift the lock piece  205  while tightening the set screw  219  such that it engages the recess  145  on the lock piece  205 , preventing movement of the lock piece  205  into the locked position. 
     To activate the locking function of the lock piece  205 , the user can unscrew the set screw  219  until it disengages from the recess  145 . Optionally, the set screw  219  can be turned using a hex key  223  in  FIG. 14  or another appropriate type of tool. 
     Alternatively, the housing  102  can define a plurality of holes so rotation of the locking piece  205  can be locked in a number of different positions. 
     In other embodiments, the lock piece can have a generally triangular shape, a generally rectangular shape, or any other suitable shape. In other embodiments, the extension assist link can have any suitable configuration such as a bar, a rod, an H-like member, or any other appropriate linking structure. Further, while the extension assist mechanism is described including an extension assist spring, in other embodiments, the extension assist mechanism can include a resiliently compressible member/material, an elastic member, or any other appropriate member. In addition, while the load-dependent brake system is described including a brake clamp, in other embodiments, the brake clamp  106  can be omitted. The knee can load-dependent brake system comprising a load-dependent ratchet mechanism connecting the housing and the chassis, a friction based brake mechanism, a torsion spring type brake mechanism, a locking cam-type brake mechanism, combinations thereof, or any other suitable load-dependent brake system. The knee can include a single axis knee or the knee can include multiple knee axes. 
     While the load-dependent brake system is described including a brake clamp, other types of braking mechanisms are possible. For instance, the brake clamp can be omitted and the knee can include a load-dependent ratchet mechanism connecting the housing and the chassis. In other embodiments, the knee can include a friction based brake mechanism, a torsion spring type brake mechanism, combinations thereof, or other suitable type of load-dependent brake system. 
     Further, the brake sensitivity adjustment system is described comprising a brake adjustment screw and resilient member, however, it will be appreciated that other types of brake sensitivity adjustment systems are possible. For instance, the brake sensitivity adjustment system can include one or more interchangeable resilient members or springs disposed within the sensitivity adjustment screw hole between the lower part of the brake clamp and a plug member. The one or more springs can be selected based on one or more properties (e.g., stiffness) to achieve a desired compression preload of the brake clamp. While the brake-play adjustment system is described including a play adjustment screw and play adjustment contact pad, in other embodiments, the brake-play adjustment system can include any suitable play adjustment mechanism. 
     In other embodiments, the lock mechanism can be formed at different locations on the knee so the knee can be locked in positions other than full extension. In other embodiments, the lock mechanism can include a torsion bar or any other suitable resilient member to bias the lock piece. 
     While the foregoing embodiments have been described and shown, alternatives and modifications of these embodiments, such as those suggested by others may be made to fall within the scope of the invention. While the hinge has been described in combination with a knee brace, it will be understood that the principles described may be extended to other types of orthopedic and prosthetic devices.