Abstract:
A device is provided to lock the residual limb of an amputee into a prosthesis. The device is comprised of rolling elements within a tapered housing which accepts a smooth plunger, such as a wire, cable, or rod connected to a suspension sleeve, with minimal resistance while opposing removal of the plunger from the locking device until the rolling elements have been retracted with a release mechanism. The nature of this device allows it to compensate for irregularities or wear in the plunger while continuing to securely lock the prosthesis to the sleeve. This locking device will function properly with a certain amount of misalignment between the lock and the plunger.

Description:
RELATED APPLICATIONS 
   The present application is a continuation of U.S. Ser. No. 10/121,196 filed Apr. 12, 2002 which is being allowed to become abandoned. 

   FIELD OF THE INVENTION 
   The present invention is an improved locking device for attaching a prosthesis to a suspension sleeve on a residual limb. 
   BACKGROUND OF THE INVENTION 
   Various methods of attaching a prosthesis to an amputee&#39;s residual limb have been utilized over the years. Despite advances in materials and design many of the older methods are still being used. The earliest methods were strap and belt type suspension systems. In this design, the amputee inserted the residual limb into the prosthesis and tightened a belt, typically made from leather, to hold the prosthesis to the limb. This design was fraught with practical difficulties, but for many years was the only design available. A second-generation design improvement uses flexible inner integral suction suspension sockets. These designs are especially useful for above-knee prostheses. The amputee simply pulls the prosthesis over the residual limb, while the flexible interior of the socket adheres to the limb creating a vacuum that suctions the prosthetic in place. A valve is installed within the socket to break the suction. 
   More recent designs have employed mechanical connectors, combined with a removable roll-on suction suspension sleeve. These mechanical connectors consist of: 1) lanyard systems utilizing a braided or twisted polymeric cord attached to the end of the suction suspension sleeve which passes through the socket where it can be secured external to the prosthesis; 2) shuttle lock systems, having a ring attached to the suspension sleeve to receive a pin inserted through the socket; 3) a ratchet type shuttle lock system, using a barbed plunger extending from the end of the suction suspension sleeve and engaging a ratchet mechanism on the prosthesis; and 4) gear driven clutch lock systems using a plunger with teeth to engage a gear mounted to a shaft turning on a one-way bearing where the plunger once engaged with the gear is restricted from upward vertical movement. 
   Most recently, smooth pin lock systems have been devised in an attempt to overcome the drawbacks of the earlier mechanical lock systems such as Gramnas U.S. Pat. No. 5,298,290 (&#39;290). Gramnas uses a washer to lock the plunger. The washer is housed such that when the plunger pierces the interior of the washer the washer becomes biased against the plunger by springs, which flank the washer. The springs are actuated by a single bearing. The bearing serves to compress one spring while leaving the other to bias the washer against the interior of the housing. Thus the washer becomes angled and the plunger is prevented from exiting the lock. Because the Gramnas design does not rely on gears or ratchets to secure the sleeve to the socket less play is introduced into the lock. Despite the improvements that the smooth pin lock system offers, it has not been a complete solution and has introduced its own disadvantages. 
   All of the automatic locking mechanical connectors (ratcheting shuttle, gear driven clutch, and smooth pin) have the drawback of requiring the plunger and the lock to be aligned on the same axis. The nature of the design of the ratcheting shuttle and gear driven clutch type locks permits a certain amount of play or backlash that allows the residual limb to piston within the socket. The lanyard and shuttle lock systems do not automatically lock and cannot accommodate volume changes in the residual limb without manual adjustments. Volume changes occur as the amputee bears weight on the residual limb causing swelling or shrinkage in the fleshy portion of the residual limb. Limb shrinkage loosens the fit in the socket and causes the residual limb to slip deeper into the prosthesis. The practical result is that additional play is introduced requiring the amputee to make frequent adjustments to maintain a snug fitting. The ratcheting shuttle lock also suffers from this drawback because the discrete locking steps are spaced too widely to make fine adjustments. 
   Smooth pin systems must conform to tight tolerances in order to work properly. As components wear, the retention of the prosthesis becomes less secure. This is particularly true in smooth pin systems such as the Gramnas invention, where the smooth pin is restricted from moving out of the lock by a washer that contacts the plunger with a narrow and limited surface area. Over time, the limited surface area of the washer becomes worn, introducing unwanted play or backlash into the locking mechanism. An additional drawback to the washer design is that it is incapable of accepting flexible plungers because the angle generated by the washer is insufficient to prevent a flexible plunger from snaking out of the lock housing. The design therefore requires the plunger and the lock to be aligned on the same axis. When the lock is manufactured with less than perfect alignment in the socket the washer is subject to extraordinary wear causing the locking mechanism to fail prematurely. 
   A further drawback common to all the mechanical connectors is that they are necessarily manufactured with materials that can withstand the rigors of the locking mechanism. Commonly, the moving and contacting parts are fabricated from high carbon bearing grade steel and hardening the various parts, such as by heat treatment. Such steel bearing grade parts, however, are highly subject to corrosion, particularly when the prosthesis is used in environments offering exposure to liquids or other contaminants. Internal corrosion of the locking device can lead to seizure and failure of the moveable components. 
   Efforts to overcome the corrosion problem by forming the moving components of a corrosion resistant metal alloy, such as austenitic stainless steel (type 300 series) typically are not practical since such corrosion resistant steel cannot be hardened to the extent necessary for satisfactory life of the moving components. Alternately, forming the moving components of martensitic stainless steels, such as 440C, may provide a bearing grade steel which is hardenable. However, the corrosion resistance is less than that of the 300 series stainless steels. The result is that neither grade of stainless is suitable for the current lock designs. Therefore, amputees that live active lifestyles, who are prone to get their prosthesis wet are forced to live with locking mechanisms that corrode or fail to operate with peak efficiency. 
   The present invention addresses these potentially troublesome issues while combining the ease of use of an automatic lock with the stepless adjustability of the clutch and smooth pin lock. 
   BRIEF SUMMARY OF THE INVENTION 
   This invention is designed to securely lock a sleeve fitted to the amputee&#39;s residual limb to a corresponding prosthesis without discrete steps and with little to no backlash during engagement. The invention utilizes a plunger on the sleeve, which is engaged in the prosthesis then detaches when a release mechanism is operated. Rolling elements in the prosthesis portion lock onto the plunger without the need to hold it in perfect alignment, allowing a certain amount of angular misalignment when mounting the lock in the prosthesis. Because the lock is permanently molded or laminated into the socket of the prosthesis during fabrication, a design that can function with imperfect alignment offers advantages to the manufacturer or technician by reducing the likelihood that the prosthesis would need to be re-fabricated. Such a design, also offers advantages to the amputee by reducing the difficulty of adapting to a poorly aligned socket. 
   This device is also designed to compensate for dimensional variances in the plunger that may occur between plungers of different construction, for example, solid wire or flexible stranded cable, as well as variances that may occur throughout the life of the plunger due to wear. 
   Another significant advantage of the invention, not addressed by the prior art, is that the moving components, which include the plunger and rolling elements, can be made of softer materials, which are more resistant to oxidation in wet or humid environments. Examples of suitable materials include but are not limited to austenitic stainless steel, titanium, and brass. This feature will allow the amputee to use the locking device in aquatic sports with less concern of the lock rusting or corroding. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a partial sectional view of a prosthetic socket containing a prosthetic lock according to the invention. 
       FIG. 2   a  is a cross-sectional front plan view of a prosthetic lock according to the invention with a plunger in an unlocked position just before making initial contact with a rolling element. 
       FIG. 2   b  is a complementary side plan view of the locking device as illustrated in  FIG. 2   a  showing the cam follower at the top of the cam track. 
       FIG. 3   a  is a cross-sectional front plan view of a prosthetic lock according to the invention with a plunger contacting a rolling element with sufficient force to compress the lock spring. 
       FIG. 3   b  is a complementary side plan view of the locking device as illustrated in  FIG. 3   a  showing the cam followers descending the cam track in response to the initial compression of the lock spring. 
       FIG. 4   a  is a cross-sectional front plan view of a prosthetic lock according to the invention with the plunger in a locked position. 
       FIG. 4   b  is a complementary side plan view of the locking device as illustrated in  FIG. 4   a  showing the cam follower descending the cam track in response to the plunger compressing the lock spring to a locking depth. 
       FIG. 5   a  is a cross-sectional front plan view of the prosthetic lock according to the invention with the plunger released from the locked position by the release mechanism. 
       FIG. 5   b  is a complementary side plan view of the locking device as illustrated in  FIG. 5   a  showing the cam follower fully descended along the cam track to an unlocking position. 
       FIG. 6  is a partial section front plan view of a prosthetic lock according to the invention with a flexible plunger with an off-axis translation 
       FIG. 7  is a partial section view of a prosthetic release mechanism according to the invention. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring now to the drawings and in particular to  FIG. 1 , a cross-sectional view of a prosthetic socket  15  with a smooth plunger  30  engaged in a locking device  10  is shown. The plunger  30  is attached to the distal end of a sleeve  6  adapted to fit over the residual limb of an amputee. Typical sleeve materials are urethanes, thermoplastic elastomers, or silicone based polymers. The socket  15  and locking device  10  are secured to the proximal end of a prosthesis, typically a prosthetic limb. The plunger  30  is shown fully engaged within the locking device  10 . The distal end  31  of the plunger has passed through the locking device  10  and occupies the prosthetic socket plunger cavity  16 . The plunger  30  may be tubular or rigid as depicted in  FIG. 2   a , or flexible such as the braided or twisted cable depicted in  FIG. 6 . 
   In a preferred embodiment the plunger  30  should be substantially smooth along its length, however, as in the case of braided cable, ridges in and around the circumference of the plunger  30  are not objectionable. In addition, the plunger  30  should not be limited to a cylindrical form and may also be a multifaceted prismatic member (triangular, rectangular, hexagonal, etc.). Typically, the locking device  10  contains a release mechanism  19  that detaches the plunger  30  by depressing a release button  22 , shown in  FIG. 1 . Also shown is button shield  23  to prevent accidental release of the locking device  10 . The release mechanism  19  is not essential to the success of the invention and may be any one of a variety of means to disengage the plunger  30  from the locking device  10 . For instance, cam mechanisms that are linearly or radially actuated, a pin hinged linkage, or gear-to-gear or gear-to-rack mechanisms that may be actuated by a pushing member or a drawing member may be used. An exemplerary release mechanism is disclosed in more detail in  FIG. 7 . 
     FIGS. 2   a - b ,  3   a - b ,  4   a - b , and  5   a - b  depict the plunger  30 , at various stages of engagement with the locking device  10 . For convenience of illustration plunger  30  is shown in isolation from sleeve  6  (shown in  FIG. 1 ) in which it is secured during use. 
     FIG. 2   a  shows the locking device  10  in an unlocked position with no plunger  30  engaged in the lock. The plunger  30  is shown entering the proximal end of the lock housing  20  just before making initial contact with rolling elements  35 . Once separated by the plunger  30 , the rolling elements  35  remain in contact with the tapered interior  32  of the clutch lock body  29  due to force applied by a lift such as, lock spring  37 , which biases the rolling element retainer  36  to the top most portion  33  of the tapered interior  32 . The shape of the rolling elements  35  may be cylindrical, spherical, elliptical or any other shape that allows rolling elements  35  to contact the tapered lock-housing interior  32  when force is applied by the plunger  30 . The number of rolling elements  35  may also be variable. The embodiment shown in  FIG. 2   a  has three rolling elements  35  within the rolling element retainer  36 , but it is possible to have a larger plurality or only one rolling element  35  in a properly configured retainer  36 . For instance, single rolling element  35  requires that at least one interior surface not be tapered. With a single cylindrical rolling element  35 , only one wall of the retainer  36  would need to be tapered. 
   As illustrated in  FIG. 2   a  the rolling elements  35  have not yet begun to be forced outward. Before the plunger comes into contact with the rolling elements  35  the lock spring  37  has not yet been compressed. Cam followers  27  are shown attached by the cam spacers  28  to the rolling element retainer  36 . The cam follower  27  are shown between upper cam track wall  34   a  and lower cam track wall  34   b.    
     FIG. 2   b  shows the exterior of the locking device  10  and the position of cam follower  27  when plunger  30  is in the uncompressed position depicted in  FIG. 2   a . The cam follower  27  is at the top of radial cam track  18 . 
     FIG. 3   a  shows the plunger  30  beginning to penetrate the interior of the clutch lock body  29 . The downward force placed on the rolling elements  35  begins to compress the lock spring  37 . The rolling elements  35  begin to spin or roll along the walls of tapered interior  32  as the plunger  30  is inserted deeper into the clutch lock body  29 . The rolling element retainer  36  and rolling elements  35  descend within the tapered interior  32  of the clutch lock body  29 . As illustrated, a small clearance space has developed between the retainer  36  and the top most portion  33  of the tapered interior  32 . 
     FIG. 3   b  shows the exterior of the locking device  10  and the position of cam follower  27  when the plunger  30  is in the position depicted in  FIG. 3   a . The cam follower  27  has descended down the cam track  18  a distance, which corresponds to the partial compression of the lock spring  37 . 
     FIG. 4   a  shows the plunger  30  after fully penetrating the clutch lock body  29 . In addition the plunger distal end  31  has passed through the lock spring  37  and out of the locking device  10 . Once the distal end  31  has passed the rolling elements  35 , and the full diameter of plunger  30  is disposed between those elements  35 , the plunger  30  resists removal. Notably, in this locked position the plunger  30  may still pass freely downward through the rolling elements  35  of the locking device  10  until the plunger face  17  strikes the plunger guide  21 . 
   In the locked position shown in  FIG. 4   a  the plunger  30  has moved the rolling elements  35  down the tapered interior  32  to a position where the width of the interior  32  is just adequate to accommodate the plunger  30  and the rolling elements  35 . This position generally results after the full diameter of plunger  30  has passed the equator of the rolling elements  35 . At this point the plunger  30  cannot be retrieved from the locking device  10  without activating the release mechanism. 
   After the plunger  30  has passed the equator of the rolling elements  35  it cannot be removed from the locking device  10  because the rolling elements  35  are biased upwards by lock spring  37  and inwards against plunger  30  by the tapered interior  32 . Pulling the plunger  30  upward in the direction that would remove it from the lock  10  causes the plunger  30  to frictionally interface with rolling elements  35 , which are thereby encouraged to roll up the tapered interior  32  of the clutch lock body  29 . This action causes the rolling elements  35  to be even more tightly compressed against the plunger  30 . Because rolling elements  35 , plunger  30  and the tapered interior  32  are not made of compressible material, the plunger  30  and rolling elements  35  in rolling element retainer  36  effectively form a wedge, which cannot be moved upwards within the lock  10 . While the rolling elements  35 , plunger  30  and tapered interior  32  are not made of compressible material, they are preferably made of softer more corrosion resistant materials than prior art prosthetic locking devices. Examples include corrosion resistant grades of stainless steel, titanium, and other corrosion resistant alloys. This is possible because the invention, unlike prior locks, displaces wear over a larger surface area and requires less force to initially secure and hold the prosthesis in place. Because the rolling elements  35  roll and spin during the locking process no single portion of the rolling elements  35  consistently contacts the plunger  30 . The plunger  30  also being cylindrical offers more surface area to contact the rolling elements. The use of a plurality of spherical rolling elements acts to both distribute the contacting portions of rolling elements  35  over the entire surface of those elements, and to maximize the number of contacts between plunger  30  and rolling elements  35 . 
     FIG. 4   b  shows the exterior of the locking device  10  and the position of cam follower  27  when plunger  30  and retainer  36  are positioned as depicted in  FIG. 4   a . The cam follower  27  has descended down the cam track  18  a distance, which corresponds to the partial compression of the lock spring  37 . The lock spring  37  does not need to compress further to accommodate any length of plunger  30 , because the width of the tapered interior  32  is adequate at this point to accommodate the plunger  30  and the rolling elements  35 . Thus even as the plunger  30  is inserted further until the plunger face  17  interfaces with guide  21 , there is no additional downward pressure to further compress the lock spring  37 . 
     FIG. 5   a  shows the plunger  30  in an unlocked position as the release mechanism has compressed the lock spring  37  to the extent that the rolling elements  35  are no longer in intimate contact with both the plunger  30  and the tapered interior  32 . So long as the release mechanism holds the lock spring  37  in this compressed position the plunger  30  can be pulled back through the top  11  of the locking device  10 , because the rolling elements  35  will not simultaneously engage both plunger  30  and tapered interior  32  and roll upward as the plunger  30  is removed. 
     FIG. 5   b  shows the exterior of the locking device  10  and the position of cam follower  27  when the retainer  36  is in the position depicted in  FIG. 5   a . The cam follower  27  has descended to the bottom of the cam track  18 , a distance, which corresponds to the nearly total compression of the lock spring  37 . The cam follower  27  is typically placed in this position by a radially actuated release mechanism. A linearly actuated release mechanism is disclosed in greater detail below in connection with  FIG. 7 . 
     FIG. 6  illustrates a unique feature of the present invention, which allows flexible plungers  30  to enter the locking device  10  at irregular angles while maintaining reliable locking function. This is particularly beneficial when the locking mechanism has been cast into the prosthetic socket or limb at an imperfect angle. As shown in  FIG. 6  the plunger  30  has entered the locking device  10  at a slight angle from the right side of the plunger guide  21 . The rolling elements  35  accommodate the angled entry directing the plunger  30  through the rolling element retainer  36  and the locking device  10  while establishing a reliable lock. As previously described once the full diameter of plunger  30  has passed the equator of the rolling elements  35  it cannot be removed through the locking device top  11 . Other locking devices that allow angular plunger  30  entry usually impart some amount of play in the locking hold. The present invention provides a consistent lock while minimizing any play or looseness due to an angled entry. Furthermore, it should be noted that both the shank portion  30   a  that is gripped by the lock and the stem portion  30   b  that leads the plunger  30  into the locking device are flexible. 
     FIG. 7  illustrates one embodiment of the release mechanism  19  that can be used with the invention. The plunger  30  is shown fully engaged within the locking device  10 . The plunger  30  is released by pressing the release button  22  that communicates via release pin  25  to release cam  26 . The release cam  26  has a downwardly slanted face  26   a , which pushes the cam follower  27  downward in the linear cam track  18  in the clutch lock body  29 . Cam follower  27  is connected to the rolling element retainer  36 . As the downward slanted face  26   a  passes over cam followers  27 , both cam followers  27  and attached rolling element  36  move downward compressing the lock spring  37  to the extent shown in  FIG. 5 . The rolling element retainer  36  also moves the rolling elements  35  downward within the tapered interior  32  to a wider portion. The width of the tapered interior  32  at this point is such that rolling elements  35  do not simultaneously contact both the plunger  30  and the tapered interior  32  of the clutch lock body  29 , thereby effecting the release of the plunger  30  from the locking device  10 . Release button  22  is normally held in the locked position by the release spring  24  and may be protected from accidental actuation by a button shield  23  as shown in  FIG. 1 . 
   While a preferred embodiment has been shown and described, it will be understood that it is not intended to limit the disclosure, but rather it is intended to cover all modifications and alternate methods falling within the spirit and the scope of the invention as defined in the appended claims.