Patent Publication Number: US-11648134-B2

Title: Prosthetic attachment system

Description:
TECHNICAL FIELD 
     The disclosure relates to attachment systems for a prosthetic socket. 
     BACKGROUND 
     A typical prosthetic leg and foot includes a socket, pylon, and foot. A socket is commonly referred to as the portion of a prosthesis that fits around and envelops a residual limb or stump, and to which prosthetic components, such as a foot, are attached. The socket must fit closely to the residual limb to provide a firm connection and support, but must also be sufficiently loose to allow for circulation. In combination with proper fitting, the socket must transfer loads from the residual limb to the ground in a comfortable manner. 
     To increase comfort, it may be provided that a prosthetic liner is arranged between the socket and the residual limb. In general, the prosthetic liner includes an elastomeric body having a closed distal end and an open proximal end that is pulled over the residual limb in the manner of a sock. The prosthetic liner adheres to the residual limb surface and generates the connection between the residual limb and the socket. 
     For attaching the prosthetic liner to the socket, locking pins may be provided at the distal end of the prosthetic liner and a corresponding attachment lock may be provided at the distal end of the socket, which locks the prosthetic liner to the socket after insertion into the socket. The attachment of the prosthetic liner to the socket can be released via an unlocking mechanism. 
     A further possibility for attaching a socket to a residual limb resides in what is known as vacuum suspension, in which the socket seals airtight against the prosthetic liner and air present in the space between the prosthetic liner and the socket is pulled or forced out. This creates a suction tending to retain the prosthetic liner within the socket. 
     These socket attachment systems have their drawbacks. For instance, vacuum suspension systems can only be used with sockets that are airtight. In addition, the strength and reliability of the connection between the prosthetic liner and the socket can be compromised and/or broken due to irregular loading of the socket by the user, excessive relative movement between the prosthetic liner and the socket, perspiration, and/or other factors. 
     Locking pin-type systems also tend to incorrectly lock if a user does not fully insert the locking pin into the lock. This can result in failure of the lock and/or significant injury to the user. In addition, too much free play between the locking pin and the lock can result in a slack connection, such that the residual limb undesirably moves up and down within the socket when the user is walking (known as pistoning). This can also create noise, which can be of great annoyance and embarrassment to the user. The free play may also lead to premature wear of the pin and lock components which can ultimately result in failure of the lock. Locking pin-type systems are also known to make optimum orientation of the residual limb/liner in the socket difficult. Further, the attachment lock is formed into the socket during manufacture. The orientation must therefore be selected before fitting is performed and thus is not tailored towards a specific patient. 
     There is thus a need for a prosthetic attachment system that provides a more reliable and secure connection between a residual limb and a prosthetic socket. There is also a need for a prosthetic attachment system that makes donning and doffing a prosthetic socket easier and more intuitive, and which minimizes pistoning and incorrect locking of the system. 
     SUMMARY 
     The disclosure describes various embodiments of a prosthetic attachment system providing a construction and design that facilitates a more reliable and secure connection between a residual limb and a prosthetic socket. 
     According to a variation, a prosthetic attachment system includes an insert arranged for connection to a distal end of a prosthetic liner and an attachment unit arranged for connection to a base distal end of a socket. The insert includes an outer radial surface defining a circumferential locking groove. The attachment unit comprises a body carrying a plurality of locking elements and defining a central opening for selectively receiving the insert. 
     The locking elements are distributed circumferentially about an axis of the body and are radially repositionable relative to the axis. A release mechanism is slidably positioned on an outer surface of the body. The release mechanism is repositionable on the body to move the prosthetic attachment system between a locked configuration in which the locking elements move radially inward relative to the axis of the body to lock the insert in the body and an unlocked configuration in which the locking elements move radially outward relative to the axis to release the insert from the body. 
     In the locked configuration, the locking elements engage the circumferential locking groove on the insert in a close-fitting manner and at multiple points distributed circumferentially about the axis of the body, enhancing a strength and/or a stiffness of the attachment between the insert and the attachment unit. As such, axial movement and tilting between the insert and attachment unit are prevented or substantially limited. This advantageously helps reduce the likelihood of undesirable free play and/or slack commonly found in locking pin-type systems which can result in user discomfort and/or failure of the prosthetic socket system. According to a variation, the attachment between the insert and the attachment unit is arranged to provide a selected amount of free play between the insert and the attachment unit. For instance, the attachment between the insert and the attachment unit can be arranged to prevent or substantially prevent relative axial movement but allow an amount of rotation or tilting between the insert and the attachment unit. 
     The secure attachment between the insert and the attachment unit also reduces noise generated at the attachment between the prosthetic liner and the socket during gait, which can be of great annoyance and embarrassment to the user. Moreover, the attachment between the residual limb and the socket can be automatically effectuated when the insert is inserted into the body, reducing the likelihood of user error and significant injury to the user. 
     According to a variation, when the user wishes to release the insert from the attachment unit, the user can push or pull the release mechanism downward along the outer surface of the body. This generally aligns an inclined surface on the release mechanism with the locking elements, providing a clearance or space for the locking elements to move radially outward. Simultaneously or nearly simultaneously, stored energy in the attachment unit can force a stop member below the body upwardly, driving the locking elements radially outward into engagement with the inclined surface of the release mechanism. The engagement between the inclined surface of the release mechanism and the locking elements may maintain the prosthetic attachment system in the locked position. 
     According to a variation, the attachment unit includes one or more alignment features for guiding the insert into the attachment unit, advantageously making donning of a socket easier by helping to properly align the insert with the attachment unit. Moreover, the insert and central opening can be relatively large compared to a conventional locking pin and corresponding pin hole, which facilitates alignment of the prosthetic liner within the socket. This is particularly advantageous for elderly users having limited dexterity. 
     The prosthetic attachment system of the present disclosure thus beneficially facilitates donning and doffing of a prosthetic socket as good hand dexterity and/or strength are not required to operate the attachment system. Rather, a prosthetic liner can be automatically locked in the socket and easily released from the socket with a simple manipulation of the release mechanism. In addition, the prosthetic attachment system can assist a user with placement of the prosthetic liner in the socket. Moreover, the prosthetic attachment system can be used with both conventional airtight sockets and adjustable sockets that are not airtight, increasing its versatility. 
    
    
     
       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 a side view of a prosthetic socket system according to an embodiment. 
         FIG.  2    is a top view of the prosthetic socket system of  FIG.  1   . 
         FIG.  3    is a side view of a prosthetic liner and a prosthetic attachment system according to an embodiment. 
         FIG.  4    is a cross section of the attachment system of  FIG.  3    in an unlocked configuration. 
         FIG.  5    is a cross section of the attachment system of  FIG.  3    in a locked configuration. 
         FIG.  6    is a side perspective view of a prosthetic socket system according to another embodiment. 
         FIG.  7    is a perspective view of the attachment unit of  FIG.  6   . 
         FIG.  8    is a partial cross section of the prosthetic socket system of  FIG.  6   . 
         FIG.  9   a    is a side perspective view of a prosthetic socket system including a prosthetic attachment system in a locked configuration according to another embodiment. 
         FIG.  9   b    is a side perspective view of the prosthetic socket system of  FIG.  9   a    showing the attachment system in an unlocked configuration. 
         FIG.  10    is a cross section of the attachment system of  FIG.  9     a.    
         FIG.  11   a    is a side view of the attachment system of  FIG.  9   a    in a locked configuration. 
         FIG.  11   b    is a side view of the attachment system of  FIG.  9   a    in an unlocked configuration. 
         FIG.  12   a    is a side perspective view of a prosthetic socket system according to another embodiment. 
         FIG.  12   b    is a partial cross section of the attachment system in  FIG.  12     a.    
         FIG.  13   a    is a bottom perspective view of a prosthetic socket system according to another embodiment. 
         FIG.  13   b    is a top perspective view of the lock body of  FIG.  13     a.    
         FIG.  14    is a side perspective view of a lock body according to another embodiment. 
         FIG.  15    is a cross section of a prosthetic socket system according to another embodiment. 
         FIG.  16    is a bottom perspective view of an attachment system according to another embodiment. 
         FIG.  17    is a cross section of the insert of  FIG.  16   . 
         FIG.  18    is a top perspective view of an attachment system according to another embodiment. 
         FIG.  19    is a bottom perspective view of the insert of  FIG.  18   . 
         FIG.  20    is a cross section of the insert of  FIG.  18   . 
         FIG.  21    is a side exploded view of an attachment system according to another embodiment. 
         FIG.  22    is a bottom perspective view of the insert of  FIG.  21   . 
         FIG.  23    is a side perspective view of a prosthetic socket system according to another embodiment. 
         FIG.  24    is a partial exploded view of the attachment system of  FIG.  23   . 
         FIG.  25    is another partial exploded view of the attachment system of  FIG.  23   . 
     
    
    
     DETAILED DESCRIPTION OF VARIOUS EMBODIMENTS 
     A better understanding of different embodiments of the disclosure 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 specific 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. 
     It will be understood that unless a term is expressly defined in this application to possess a described meaning, there is no intent to limit the meaning of such term, either expressly or indirectly, beyond its plain or ordinary meaning. Any element in a claim that does not explicitly state “means for” performing a specified function, or “step for” performing a specific function is not to be interpreted as a “means” or “step” clause as specified in 35 U.S.C. § 112(f). 
       FIGS.  1  and  2    illustrate a prosthetic socket system  10  according an embodiment including a socket  12 , a prosthetic liner, and a prosthetic attachment system  16  arranged to quickly and securely suspend the socket  12  on a residual limb donning the prosthetic liner. The attachment system  16  can include an insert arranged for connection to a distal end of the prosthetic liner and an attachment unit arranged for connection to a base or distal end of the socket  12 . The insert can include an outer radial surface defining a circumferential locking groove and the attachment unit can include a body carrying a plurality of locking elements and defining a central opening for selectively receiving the insert. 
     The locking elements of the body of the attachment unit are distributed circumferentially about a longitudinal axis  22  of the prosthetic socket system  10  and are radially repositionable relative to the longitudinal axis  22 . In an embodiment, the longitudinal axis  22  generally corresponds to an axis of the body. A release mechanism is slidably positioned on an outer surface of the body. The release mechanism is repositionable on the body to move the attachment system  16  between a locked configuration in which the locking elements move or shift radially inward relative to the longitudinal axis  22 , locking the insert in the body and an unlocked configuration in which the locking elements move or shift radially outward relative to the longitudinal axis  22 , releasing the insert from the body. 
     In the locked configuration, the locking elements of the body of the attachment unit selectively engage the locking groove on the insert in a close-fitting manner and at multiple points circumferentially distributed about the longitudinal axis  22 , enhancing a strength and/or a stiffness of the attachment between the insert and the attachment unit. As such, axial movement and tilting between the insert and body is substantially limited. This advantageously helps reduce the likelihood of undesirable free play and/or slack in the attachment system  16  which can result in user discomfort and/or failure of the prosthetic socket system  10 . According to a variation, the attachment between the insert and the attachment unit is arranged to provide a selected amount of free play between the insert and the attachment unit. For instance, the attachment between the insert and the attachment unit can be arranged to prevent or substantially prevent relative axial movement but allow an amount of rotation or tilting between the insert and the attachment unit. 
     It also reduces noise generated by the attachment system  16 , which can be of great annoyance and embarrassment to the user. Moreover, the attachment system  16  can automatically lock the insert in the body when it is received therein, reducing the likelihood of user error and significant injury to the user. 
     When a user wants to release the insert from the attachment unit, the user can push or pull the release mechanism downward along the outer surface of the body of the attachment unit. This generally aligns an inclined surface on the release mechanism with the locking elements, providing a clearance or space for the locking elements to move radially outward. Simultaneously or nearly simultaneously, stored energy in the attachment unit can drive the locking elements radially inward into engagement with the inclined surface of the release mechanism. The engagement between the inclined surface of the release mechanism and the locking elements may maintain the attachment system in the locked position. 
     It will be appreciated that the attachment unit can include one or more alignment features for guiding the insert into the attachment unit, advantageously making donning of the socket  12  easier by helping to properly align the insert and prosthetic liner with the attachment unit. It also helps to forgive poor alignment of the prosthetic liner within the socket  12 . Moreover, the insert and central opening can be relatively large compared to a conventional locking pin and corresponding pin hole, which facilitates alignment of the prosthetic liner  14  within the socket  12 . This is particularly advantageous for elderly users having limited dexterity. 
     Referring now the prosthetic socket system  10  generally, the socket  12  can be any suitable type of socket. For instance, the socket  12  can comprise a conventional socket that is rigid and has a general uniform shape which receives a portion of a residual limb. In the illustrated embodiment, the socket  12  comprises an adjustable socket including a base  18 , a plurality of longitudinal supports  20  connected to the base  18  and distributed about the longitudinal axis  22 , and a plurality of shell components  24  connected to the longitudinal supports  20 . The shell components  24  collectively form a socket wall defining a receiving volume  26  adapted to receive a residual limb. The base  18  is arranged to provide support for a distal end of the residual limb and can include at least a portion of the attachment system  16  for fixing or securing the residual limb or a liner to the base  18 . The longitudinal supports  20  are shown comprising medial and lateral supports but can be in any suitable configuration. 
     The socket  12  is radially adjustable between an open configuration and a closed configuration. In the open configuration, at least some of the longitudinal supports  20  and/or shell components  24  are free to move or are forced radially outward relative to the longitudinal axis  22  of the prosthetic socket system  10 , increasing the receiving volume  26  or increasing a circumference of the socket  12 . This effectively loosens the fit of the prosthetic socket  12  on a residual limb inserted in the receiving volume  26 , or decreases the loading on the residual limb from the socket wall. 
     In the closed configuration, at least some of the longitudinal supports  20  and/or the shell components  24  are moved or forced radially inward relative to the open configuration, decreasing the receiving volume  26  or decreasing the circumference of the socket  12 . It will be appreciated that movement of any portion of a longitudinal support  20  or a shell component  24  can move the socket  12  between the expanded and closed configurations. 
     A tensioning system  14  is arranged to selectively secure a residual limb within the receiving volume  26  by moving the socket  12  between the open/expanded and closed configurations. Other examples and additional details of suitable prosthetic sockets are included in U.S. Pat. Nos. 8,795,385, 9,248,033, 9,050,202, and U.S. patent application Ser. Nos. 14/704,572, 15/151,204, 15/888,403, and 15/888,288, each of which is incorporated by reference in its entirety. 
     With reference to  FIGS.  3 - 20   , various embodiments of the attachment system  16  are illustrated. For instance,  FIGS.  3 - 5    illustrate a prosthetic attachment system  100  according to an embodiment including an insert  102  and an attachment unit  112 . As shown in  FIG.  3   , the insert  102  is arranged to be connected to a prosthetic liner  104 . The prosthetic liner  104  can include a flexible and elongate liner body  106  formed from an elastomeric material. The liner body  106  defines an inner surface and an outer surface forming a liner profile between a closed distal end  108  and an open proximal end. It will be appreciated that the prosthetic liner  104  can be any suitable type of prosthetic liner. 
     The insert  102  can be connected to the closed distal end  108  in any suitable manner. For instance, the insert  102  can be threadedly attached to the closed distal end  108  of the prosthetic liner  104 . In other embodiments, the insert  102  can be integral to the prosthetic liner  104  or attached to the closed distal end  108  of the prosthetic liner  104  via at least one fastener. 
     The insert  102  includes an outer radial surface defining a locking groove  110  extending circumferentially about the insert  102  and an upper surface arranged for connection to the closed distal end  108  of the prosthetic liner  104 . The locking groove  110  can have any suitable cross-sectional shape but is shown having a concave cross-section. The insert  102  can be made of any suitable material. The material selection can depend on desired function. The insert  102  may include a stiff elastomeric material such as a stiff silicone, enhancing the durability and/or stability of the insert  102 . The insert  102  can include a stiff plastic material, a metal material, or any other suitable material. 
     The attachment unit  112  can be integral to a base or distal end of a socket or attached to the base or distal end of the socket. For instance, the attachment unit  112  can be connected to the base via at least one fastener. This can allow for existing sockets to be easily retrofitted with the attachment unit  112 . 
     The insert  102  can be automatically secured in or against the attachment unit  112  when the prosthetic liner  104  is positioned in the socket. For instance, the attachment unit  112  can be spring loaded to automatically lock the prosthetic liner  104  and the base of the socket together when the insert  102  is inserted in the attachment unit  112 , achieving prosthetic suspension. As described above, the attachment system  100  advantageously facilitates donning and doffing of the socket, and creates a secure attachment between the prosthetic liner  104  and a socket. The attachment unit  112  includes a body  114  and a release mechanism  116  comprising a collar movable positioned on the body  114 . The body  114  can include a support body  118 , a lock body  120 , and a stop member  122 . The body  114  can include a stiff plastic material, a metal material, or any other suitable material. 
     As best seen in  FIGS.  4  and  5   , the support body  118  includes an upper surface that can be in contact with and is arranged to cooperate with a bottom surface of the lock body  120  and an outer peripheral surface that can be in contact with and is arranged to cooperate with an inner surface  138  of the release mechanism  116 . The support body  118  defines an opening  124  having a generally closed bottom arranged for selectively receiving the stop member  122 . It will be appreciated that in other embodiments the support body  118  can be integrated with a base of a socket. 
     At least one resilient member  126  is disposed between the support body  118  and the stop member  122 . The at least one resilient member  126  can comprise a plurality of spring members  128  circumferentially distributed about the axis  25 . The spring members  128  collectively bias the stop member  122  away from the bottom of the support body  118 . The support body  118  can define a lower radial flange  130  extending under the release mechanism  116 . 
     The lock body  120  is supported on and/or connected to the support body  118 . The lock body  120  may be connected to the support body  118  in any suitable manner such as via one or more fasteners. While the lock body  120  is shown separate from the support body  118 , in other embodiments, the support body  118  and the lock body  120  may comprise a single body or member. 
     A central opening  130  is defined in the body  114  that is sized and configured to receive the insert  102 . For instance, the lock body  120  can define the central opening  130  and include an annular flange  132  surrounding the central opening  130  and extending axially upward and radially away from a top of the central opening  130  as shown in  FIG.  4   . The annular flange  132  can funnel or guide the insert  102  into the central opening  130 . This advantageously makes donning of the socket easier by helping to align the insert  102  with the attachment unit  112 . This also helps forgive poor alignment of the prosthetic liner  104  within the socket. Moreover, the insert  102  and central opening  130  can be relatively large compared to a conventional locking pin and corresponding pin hole, which facilitates alignment of the prosthetic liner  104  within a socket. This is particularly advantageous for elderly users having limited dexterity, as the user does not have to “thread the needle,” so to speak, increasing risk of incorrect attachment and injury, but rather the user is provided with an intuitive and forgiving attachment procedure. 
     A plurality of locking elements  134  are carried by the lock body  120 . The locking elements  134  can be mounted or otherwise attached to the lock body  120  in any suitable manner. For instance, the locking elements  134  can be mounted within holes  136  formed in the lock body  120  arranged for receiving the locking elements  134 . The holes  136  can be sized and shaped to generally correspond to the locking elements  134 . 
     The locking elements  134  are radially repositionable relative to an axis  25  of the body  114  such that the locking elements  134  can at least in part move into and out of the central opening  130  of the body  114 . The locking elements  134  can be made of any suitable rigid material. For instance, the locking elements  134  may be formed of steel. In other embodiments, the locking elements  134  may be formed of ceramic material or plastic material, reducing the overall weight and cost of the attachment unit  112 . The locking elements  134  are shown comprising ball bearing elements but can be any suitable locking elements such as, for example, ring segments or block elements. 
     The release mechanism  116  is slidably positioned on the body  114  such that the release mechanism  116  is axially repositionable along an outer surface of the body  114 . The release mechanism  116  includes an inner surface  138  defining a lower interior wall  140  generally corresponding to outer surfaces of the support body  118  and/or the lock body  120 , and an inclined surface  142  extending from the lower interior wall  140 . The inclined surface  142  extends upward and radially outward from the lower interior wall  140 . The inclined surface  142  can be an angled and/or conical surface extending around the central opening  130  of the lock body  120 . 
     The lower interior wall  140  can generally correspond to an outer periphery of the support body  118  comprising a pair of parallel sides connected by a pair of convex or semi-circular sides at opposite ends. This arrangement beneficially helps prevent relative rotation between the release mechanism  116  and at least the support body  118 . The lower interior wall  140  of the release mechanism  116  can comprise a generally upright surface. According to a variation, a top surface of the release mechanism  116  can define a shoulder  144  generally corresponding to the bottom of the annular flange  132  on the lock body  120 . Relative axial movement between the release mechanism  116  and the lock body  120  can be limited by engagement of the shoulder  144  with the bottom of the annular flange  132 . 
     Axial movement of the release mechanism  116  on the body  114  moves the attachment system  100  between an unlocked configuration (shown in  FIG.  4   ) and a locked configuration (shown in  FIG.  5   ) in which the locking elements  134  lock the insert  102  in the attachment unit  112 . 
     In the unlocked position, the at least one resilient member  126  bias the stop member  122  upwardly away from the support body  118  and into the central opening  130  of the lock body  120  such that an outer surface  146  of the stop member  122  contacts and drives the locking elements  134  radially outward, which, in turn, engage the inclined surface  142  on the release mechanism  116 . This engagement between the locking elements  134  and the inclined surface  142  holds or maintains the release mechanism  116  in a first or down position and the attachment system  100  in the unlocked configuration. 
     Optionally, the release mechanism  116  can compress one or more secondary spring members  148  (shown in  FIG.  3   ) disposed between the release mechanism  116  and the support body  118  when the release mechanism  116  is in the down position. For instance, the one or more secondary spring members  148  can be positioned between a lower radial flange  150  (shown in  FIG.  3   ) of the support body  118  and a lower surface of the release mechanism  116 . The one or more secondary spring members  148  can comprise a plurality of secondary spring members or a single secondary spring member surrounding the support body  118 . 
     When a user positions the prosthetic liner  104  into the socket, the insert  102  can be guided into the central opening  130  of the lock body  120  by the annular flange  132 , reducing the likelihood of incorrect liner alignment and improving ease of use. Moreover, the insert  102  and the central opening  130  are relatively large compared to a conventional locking pin and corresponding pin hole, which, in turn, facilitates simpler and easier alignment of the prosthetic liner  104  and donning of the socket. As the insert  102  moves through the central opening  130  of the lock body  120 , the bottom surface of the insert  102  engages and pushes down on the stop member  122  against the force of the at least one resilient member  126 , which, in turn, permits the locking elements  134  to move radially inward and the secondary spring members  148  to force the release mechanism  116  upward along the outer surface of the body  114  toward a second or up position. 
     As the release mechanism  116  moves upwardly along the outer surface of the body  114 , the lower interior wall  140  on the release mechanism  116  contacts and drives the locking elements  134  radially inward and into the locking groove  110  of the insert  102 . This moves the attachment system  100  into the locked configuration, securely locking the insert  102  in the attachment unit  112  and the prosthetic liner  104  in the socket. The attachment system  100  thus automatically attaches the prosthetic liner  104  to the socket when the insert  102  is inserted into the body  114 , reducing the likelihood of user error and significant injury to the user. This is advantageous because conventional locking pin-type systems tend to incorrectly lock if a user does not fully insert the locking pin into the lock, leading to potential damage or injury if the socket and liner detach during use. 
     In the locked configuration, the locking elements  134  engage the locking groove  110  in a close-fitting manner and at multiple points distributed circumferentially about the axis  25  of the body  114 , enhancing a strength and/or a stiffness of the attachment between the insert  102  and the attachment unit  112 . For instance, the locking elements  134  can create between about 2 and about 6 (e.g., about 4) physical connections between the body  114  and the insert  102  about the circumference of the insert  102 . As such, axial movement and/or tilting between the insert  102  and the attachment unit  112  are substantially limited. This advantageously helps reduce the likelihood of undesirable free play and/or slack commonly found in locking pin-type systems which can result in user discomfort and/or failure of the prosthetic socket system. It also makes the prosthetic suspension of a socket on a residual limb more reliable and less prone to failure due to movement, loading, and perspiration when compared to conventional vacuum suspension systems. Further, the attachment system  100  can be safely and conveniently used with a socket that is not airtight. 
     The stability of the attachment between the insert  102  and the attachment unit  112  also reduces noise generated at the attachment between the prosthetic liner and the socket during gait, which can be of great annoyance and embarrassment to the user. According to a variation, the attachment between the insert  102  and the attachment unit  112  is arranged to provide a selected amount of free play between the insert  102  and the attachment unit  112 . For instance, the attachment between the insert  102  and the attachment unit  112  can be arranged to prevent or substantially prevent relative axial movement but allow an amount of rotation or tilting between the insert  102  and the attachment unit  112 . 
     When the user wants to release the insert  102  and/or the prosthetic liner  104  from the attachment unit  112 , the user can move the release mechanism  116  downward on the body  114  against the force of the secondary spring members  148 . In an embodiment, the user can push or pull the release mechanism  116  downward along the outer surface of the body  114 . This generally aligns the inclined surface  142  of the inner surface  138  of the release mechanism  116  with the locking elements  134 , providing a clearance or space for the locking elements  134  to move radially outward. 
     Simultaneously or nearly simultaneously, stored energy in the at least one resilient member  126  forces the stop member  122  upwardly, driving the locking elements  134  radially outward into engagement with the inclined surface  142  of the release mechanism  116  and out of engagement with the locking groove  110 . These biased engagements prevent the release mechanism  116  from undesirably moving back toward the up position. The at least one resilient member  126  also allows a user to move the attachment system  100  toward the unlocked configuration with less strength and/or dexterity because the stored energy in the at least one resilient member  126  assists the user in moving the release mechanism  116  toward the down position, improving ease of use. 
     According to a variation, the attachment unit  112  and/or insert  102  can be arranged to provide an indicator (e.g., a click or vibration) when the attachment system  100  has moved to the locked configuration, helping a user determine when a socket is safely suspended on the residual limb. This advantageously improves ease of use and helps reduce the likelihood of injury to a user. 
     The attachment unit  112  and/or insert  102  may also be arranged to provide a unique indicator (e.g., a double click) when the attachment system  100  has moved to the unlocked configuration, signaling to a user that the socket is ready to be doffed. This advantageously improves ease of use and helps reduce the likelihood of over-exertion by the user. 
     The attachment system  100  can include at least one manipulation feature  152  arranged to help a user move the attachment system  100  between the locked configuration and the unlocked configuration. For instance, the at least one manipulation feature  152  can comprise a circumferential protruding part or ridge  154  on the release mechanism  116 . The ridge  154  is sized to assist the user in moving the attachment system  100  toward the unlocked configuration. 
     The attachment system  100  thus beneficially facilitates donning and doffing of a prosthetic socket as good hand dexterity and muscular strength are not required to operate the attachment system  100 . Rather, the prosthetic liner  104  can be automatically locked in the socket and easily released from the prosthetic liner  104  with a simple manipulation of the release mechanism  116 . In addition, the attachment system  100  can assist a user with placement of the prosthetic liner  104  in the socket, improving ease of use. Moreover, the attachment system  100  can be used with both conventional airtight sockets and adjustable sockets that are not airtight, increasing its versatility. 
     It will be appreciated that while the release mechanism  116  is shown as a collar, in other embodiments, it can comprise any suitable type of release mechanism. For instance, the release mechanism  116  can comprise one or more buttons, levers, cam mechanisms, handles, ramp members, combinations thereof, or any other suitable release mechanism. 
       FIGS.  6 - 8    illustrate a prosthetic socket system  30  according to another embodiment. It will be appreciated that the prosthetic socket system  30  may be similar in many respects to the prosthetic socket system  10  and may incorporate any feature described herein. 
     The prosthetic socket system  30  includes a socket  32 , a prosthetic liner  204 , and a prosthetic attachment system  200  arranged to quickly and securely suspend the socket  32  on a residual limb donning the prosthetic liner  204 . The socket  32  comprises an adjustable socket including a base  38 , and a plurality of longitudinal supports  40  connected to the base  38 . The longitudinal supports  40  are distributed about a longitudinal axis  42  of the prosthetic socket system  30 . For ease of reference, the socket  32  is shown without shell components attachable to the longitudinal supports  40 . 
     The attachment system  200  includes an insert  202  arranged for connection to the prosthetic liner  204  and an attachment unit  212  arranged for connection to the base  38  of the socket  30 . The attachment unit  212  includes a release mechanism  216  arranged to help move the attachment system  200  between a locked configuration in which the insert  202  is locked in the attachment unit  212 , and an unlocked configuration in which the insert  202  is released from the attachment unit  212 . Similar to the attachment system  100 , the attachment system  200  is arranged to automatically move to the locked configuration when the insert  202  is inserted in the attachment unit  212 . 
     The attachment unit  212  includes a body  214  having a support body  218 , a lock body  220 , and a stop member  222 . The release mechanism  216  comprises a collar movably positioned on the body  214 . The support body  218  includes a central portion  256  defining an opening  224  having a generally closed bottom arranged for selectively receiving the stop member  222 , a base section  258  below the central portion  256 , and a plurality of wall sections  260  extending upwardly from the base section  258 . 
     A radial space or gap  262  is formed between the central portion  256  and the wall sections  260  to accommodate axial movement of the release mechanism  216  on the body  214  between the wall sections  260  and the central portion  256 . This advantageously helps reduce the overall size and profile of the attachment system  200  because the main outer diameter of the release mechanism  216  is generally smaller than the outer diameter of the support body  218 . One or more circumferential gaps are formed between adjacent ones of the wall sections  260  to accommodate a manipulation feature of the release mechanism  216  described below when the attachment system  200  is in an unlocked configuration. 
     Referring to  FIG.  8   , at least one resilient member  226  is disposed between the support body  218  and the stop member  222 . The at least one resilient member  226  comprises a single central spring member  228  positioned within the opening  224  of the support body  218 . The central spring member  228  is arranged to bias the stop member  222  away from the bottom of the support body  218  or away from the base  38 . The lock body  220  carries a plurality of locking elements  234  and is supported by and/or attached to the support body  218 . The locking elements  234  are radially repositionable relative to the longitudinal axis  42 . In an embodiment, the longitudinal axis  42  generally corresponds to an axis of the body  214 . 
     The release mechanism  216  is slidably positioned on an outer surface of the body  214  such that the release mechanism  216  can be axially or vertically repositioned on the body  214  to radially reposition the locking elements  234  relative to the longitudinal axis  42 , which, in turn, moves the attachment system  200  between the locked configuration and the unlocked configuration. 
     The release mechanism  216  defines an inner surface  238  having a lower interior wall  240  and an inclined surface  242  extending upwardly and radially outwardly from the lower interior wall  240 . The lower interior wall  240  can generally correspond to the outer surface of the lock body  220  and the outer surface of the central portion  256 . For instance, the lower interior wall  240  can form a periphery having a pair of parallel sides connected by a pair of convex or semicircular sides at opposite ends. This arrangement beneficially helps prevent relative rotation between the release mechanism  216  and the body  214 . 
     The attachment system  200  can include at least one manipulation feature  252  (shown in  FIGS.  6  and  7   ) arranged to help a user move the attachment system  200  between the locked configuration and the unlocked configuration. The at least one manipulation feature  252  can comprise a button part  254  (shown in  FIGS.  6  and  7   ) on the release mechanism  216  sized and configured to assist a user in moving the attachment system  200  toward the unlocked configuration. 
     In the unlocked configuration, the central spring member  228  biases the stop member  222  upwardly within a central opening  230  of the lock body  220  such that an outer surface of the stop member  222  contacts and drives the locking elements  234  radially outward relative to the longitudinal axis  42 , which, in turn, engage the inclined surface  242  of the release mechanism  216 . 
     This engagement between the locking elements  234  and the inclined surface  242  of the release mechanism  216  holds or maintains the release mechanism  216  in a first or down position on the body  214 . According to a variation, one or more secondary spring members  248  are positioned between the base section  258  of the support body  218  and the release mechanism  216 . The one or more secondary spring members  248  can be compressed when the attachment system  200  is in the unlocked position and can comprise a plurality of secondary spring members or a single secondary spring member surrounding the support body  218 . 
     When the insert  202  is inserted into the central opening  230  of the lock body  220 , the insert  202  exerts a downward force on the stop member  222  against the force of the central spring member  228 , which, in turn, permits the locking elements  234  to move radially inward and the one or more secondary spring members  248  to force or drive the release mechanism  216  upward along the outer surface of the body  214  from a first position toward a second or up position. 
     As the release mechanism  216  moves upwardly, the lower interior wall  240  of the release mechanism  216  contacts and drives the locking elements  234  radially inward and into the locking groove  210  of the insert  202 . This moves the attachment system  200  to the locked configuration, locking or securing the insert  202  in the attachment unit  212 . In the locked configuration, the locking elements  234  engage the locking groove  210  in a close-fitting manner and at multiple points about the body  214 , enhancing a strength and/or a stiffness of the attachment between the insert  202  and the attachment unit  212 . As such, axial movement and/or tilting movement between the insert  202  and the attachment unit  212  are prevented or substantially limited. This advantageously helps reduce the likelihood of undesirable free play and/or slack commonly found in locking pin-type systems which can result in user discomfort and/or failure of the prosthetic socket system. It also makes the prosthetic suspension of a socket on a residual limb more reliable and less prone to failure due to movement, loading, and perspiration when compared to conventional vacuum suspension systems. Moreover, the insert  202  automatically locks in the attachment unit  212  when the insert  202  is received in the central opening  230 , reducing the likelihood of user error. 
     According to a variation, the attachment between the insert  202  and the attachment unit  212  is arranged to provide a selected amount of free play between the insert  202  and the attachment unit  212 . For instance, the attachment between the insert  202  and the attachment unit  212  can be arranged to prevent or substantially prevent relative axial movement but allow an amount of rotation or tilting between the insert  202  and the attachment unit. 
     When the user wants to release the insert  202  and the liner  204  from the attachment unit  212 , the user can move the release mechanism  216  downward on the body  214  against the force of the one or more secondary spring members  248 . If desired, the user can use the at least one button part  254  to move the release mechanism  216  downward on the body  214 . This generally aligns the inclined surface  242  of the release mechanism  216  with the locking elements  234  carried by the lock body  220 , providing a space or clearance for the locking elements  234  to move radially outward relative to the longitudinal axis  42 . Simultaneously or nearly simultaneously, stored energy in the central spring member  228  forces the stop member  222  upwardly within the body  214 , driving the locking elements  234  radially outward into engagement with the inclined surface  242  of the release mechanism  216 . This advantageously helps prevent the release mechanism  216  from inadvertently moving back toward the locked position. 
     The prosthetic liner  204  can thus be automatically locked in the socket  32  and easily released from the socket  32  with a simple, easy, and intuitive manipulation of the release mechanism  216  on the body  214 . 
       FIGS.  9 - 11    illustrate yet another embodiment of a prosthetic socket system  50 . It will be appreciated that the prosthetic socket system  50  may be similar in many respects to the prosthetic socket systems  10  and  30  and may incorporate any feature described herein. The prosthetic socket system  50  can include a socket  52  having a base  58 , a prosthetic liner  304 , and a prosthetic attachment system  300  arranged to quickly and securely suspend the socket  52  on a residual limb donning the prosthetic liner  304 . For ease of reference, the socket  52  is shown without longitudinal supports connectable to the base  58  or shell components connectable to longitudinal supports. 
     The attachment system  300  includes an insert  302  arranged for connection to the prosthetic liner  304 , and an attachment unit  312  arranged for connection to a base  58  of the socket  52 . The attachment unit  312  can be attached to the base  58  via a single fastener  313  (shown in  FIG.  10   ). 
     Like in other embodiments, the attachment unit  312  includes a release mechanism  316  arranged to help move the attachment system  300  between a locked configuration in which the insert  302  is locked in the attachment unit  312  (shown in  FIG.  9 A ) and an unlocked configuration in which the insert  302  is released from the attachment unit  312  (shown in  FIG.  9 B ). The attachment system  300  is arranged to automatically move to the locked configuration when the insert  302  is inserted in the attachment unit  312 . 
     Referring to  FIG.  10   , the attachment unit  312  includes a body  314  having a support body  318 , a lock body  320  carrying a plurality of locking elements  334  that are radially repositionable relative to an axis  62  of the body  314 , and a stop member  322 . The support body  318  defines an opening  324  arranged for selectively receiving the stop member  322 . The release mechanism  316  comprises a collar movably positioned on the body  314 . 
     In the unlocked position, a central spring member  328  biases the stop member  322  upwardly within a central opening  330  of the body  314  such that an outer surface of the stop member  322  contacts and drives the locking elements  334  radially outward, which, in turn, engage an inclined surface  342  on the release mechanism  316 . This engagement holds or maintains the release mechanism  316  in a first or down position on the body  314 . One or more secondary spring members  348  are positioned between the release mechanism  316  and the support body  318 . In the illustrated embodiment, the one or more secondary spring members  348  comprises a single spring member  362  with a central portion  356  of the support body  318  extending through a center of the spring member  362 . The single spring member  362  helps reduce the overall size of the attachment unit  312  by at least in part accommodating the support body  318 . 
     When the insert  302  is inserted into the central opening  330  of the lock body  320 , the insert  302  exerts a downward force on the stop member  322  against the force of the central spring member  328 . This permits the locking elements  334  to move radially inward and the spring member  362  to force or drive the release mechanism  316  upward along the outer surface of the body  314  toward a second or up position on the body  314 . As the release mechanism  316  moves upwardly, a lower interior wall  340  of the release mechanism  316  contacts and drives the locking elements  334  radially inward relative to the axis  62  of the body  314  and into a locking groove  310  of the insert  302 . This moves the attachment system  300  to the locked configuration, locking or securing the insert  302  in the attachment unit  312 . As discussed above, the locking elements  334  selectively engage a locking groove  310  of the insert  302  in a close-fitting manner and at multiple points about the axis  62  of the body  314 , enhancing a strength and/or a stiffness of the attachment between the insert  302  and the attachment unit  312 . 
     According to a variation, one or more channels  380  are formed in the support body  318  that traverse the opening  324 . The one or more channels  380  can have any suitable configuration but are shown comprising a single channel extending generally perpendicular to the axis of the body  314 . The one or more channels  380  are arranged such that when the attachment system  300  moves toward the locked configuration or the stop member  322  moves toward the bottom of the opening  324  air is permitted to vent from the opening  324  via the one or more channels  380 . This advantageously helps increase operational speed of the attachment system  300  by reducing the likelihood of an air cushion or pressure increase in the support body  318  that could slow down movement of the stop member  322  within the opening  324 . In other embodiments, the one or more channels can be formed in the lock body  320  such that the channels vent the central opening  330 . 
     When the user wishes to release the insert  302  and the liner  304  from the attachment unit  312 , the user can move the release mechanism  316  downward on the body  314 . This generally aligns the inclined surface  342  of the release mechanism  316  with the locking elements  334 , providing a space or clearance for the locking elements  334  to move radially outward and to disengage the locking groove  310 . Simultaneously or nearly simultaneously, stored energy in the central spring member  328  forces the stop member  322  upwardly along the outer surface of the body  314 , driving the locking elements  334  radially inward into engagement with the inclined surface  342  of the release mechanism  316 . 
     As shown in  FIGS.  10 ,  11     a  and  11   b , the attachment system  300  includes at least one manipulation feature  352  to help a user move the attachment system  300  between the locked configuration and the unlocked configuration. In the illustrated embodiment, the at least one manipulation feature  352  comprises a release handle  364  including a pair of arms  366  pivotally connected to the attachment unit  312  and a middle part  368  (shown in  FIGS.  9   a  and  9   b   ) extending between the arms  366 . It will be appreciated that the release handle  364  can have any suitable configuration. For instance, the release handle  364  may include a single arm attached to the body  314  that wraps in part around the body  314 . 
     The middle part  368  can be adapted to facilitate manipulation of the release handle  364 . For instance, the middle part  368  can have a size corresponding to one or two fingers of a user such that a user can use one or two fingers to comfortably push down on the release handle  364 , moving the attachment system  300  to the unlocked configuration. The middle part  368  can be flattened with a radial inner edge generally corresponding to the curvature of the body  314 , helping to reduce the overall size, profile, and weight of the attachment system  300 . 
     The arms  366  extend between the middle part  368  and the body  314  of the attachment unit  312 . The arms  366  can be attached to the body  314  via pivot connections  370  and to the release mechanism  316  via movable connection points  374 . 
     The pivot connections  370  can be defined by fasteners  372 . The movable connection points  374  can be defined by a key or pin  376  on each arm  366  arranged to interact with slots  378  defined by the release mechanism  316 . The slots  378  guide and carry the pins  376 . The slots  378  can be angled or inclined relative to horizontal. In other embodiments, the slots  378  can be curved. The pin  376  is spaced from the pivot connection  370  by a distance that can be controlled to adjust the axial displacement between the release mechanism  316  and the lock body  320  described below. 
     As seen, the arms  366  can have an increased width proximate the body  314 . For instance, each arm  366  can define an enlarged portion  381  including the pin  376  and at least part of the pivot connection  370 . This helps strengthen and facilitate the connection between the arms  366  and the body  314 . 
     When a user pushes down on the middle part  368 , the release handle  364  rotates about the pivot connections  370  in a first direction. This rotation moves the pins  376  along the slots  378 , which, in turn, pushes the release mechanism  316  toward the down position and the attachment system  300  toward the unlocked configuration. More particularly, sliding contact between the pins  376  and sliding contact areas  379  defined by the slots  378  pushes the release mechanism  316  downward on the body  314 . 
     It will also be appreciated that the length of the arms  366  between the middle part  368  and the pivot connections  370  can define a moment arm that provides a user a mechanical advantage, as the release handle  364  requires less user strength to move the attachment system  300  from the locked configuration to the unlocked configuration. This advantageously improves comfort and ease of use, especially for users with limited dexterity or cognition. 
     When the insert  302  is inserted into the central opening  330  of the lock body  320 , the spring member  362  forces or drives the release mechanism  316  upward along the outer surface of the body  314 . This axial movement of the release mechanism  316  on the body  314  generates sliding contact between the pins  376  and the slots  378 , which, in turn, rotates the release handle  364  about the pivot connections  370  in a second direction opposite the first direction, moving the release handle  364  back toward its original position as the attachment system  300  moves toward the locked configuration. 
     The release handle  364  thus provides a fast and intuitive mechanism to move the attachment system  300  from the locked configuration toward the unlocked configuration. Moreover, the release handle  364  can provide a visual indicator of the status of the attachment system  300 . For instance, if the release handle  364  is up, the user can easily surmise that the attachment system  300  is in the locked configuration, and if the release handle  364  is down, the user can likewise easily surmise that the attachment system  300  is in the unlocked configuration. 
     It will be appreciated that the attachment unit of the present disclosure can have any suitable configuration. For instance,  FIGS.  12   a  and  12   b    illustrate yet another embodiment of an attachment system  900  including a body without a distinct support body, helping to reduce the overall size and number of parts of the attachment unit. As shown, the attachment system  900  includes an insert  902  arranged for connection to a prosthetic liner and an attachment unit  912  arranged for connection to a base  98  of a socket  92 . 
     The attachment unit  912  includes a release mechanism  916  arranged to in part move the attachment system  900  between a locked configuration in which the insert  902  is locked in the attachment unit  912 , and an unlocked configuration in which the insert  902  is released from the attachment unit  912 . Similar to other embodiments, the attachment system  900  can be arranged to automatically move to the locked configuration when the insert  902  is inserted in the attachment unit  912 . At least one manipulation feature  952  comprising a release handle  964  is attached to the attachment unit  912  to help move the attachment system  900  between the locked and unlocked configurations. 
     The attachment unit  912  includes a body  914  comprising a lock body  920 , and a stop member  922 . The lock body  920  can be attachable to or integrated with the base  98  of the socket  92 . In other words, the body  914  does not include a separate support body. This can help reduce the overall size and number of parts of the attachment unit  912 , making installation and manufacturing of the attachment unit  912  simpler and easier. 
     At least one resilient member  926  comprising a single central spring member  928  is positioned between the stop member  922  and the base  98 . The central spring member  928  is arranged to bias the stop member  922  away from the base  98 . The lock body  920  carries a plurality of locking elements  934  and is supported by and/or attached to the base  98 . The locking elements  934  are radially repositionable relative to an axis  95  of the body  914 . The release mechanism  916  is slidably positioned on an outer surface of the body  914  such that the release mechanism  916  can be axially or vertically repositioned on the body  914  to radially reposition the locking elements  934  relative to the axis  95  of the body  914 , which, in turn, moves the attachment system  900  between the locked configuration and the unlocked configuration. 
     In the unlocked configuration, the central spring member  928  biases the stop member  922  upwardly within a central opening  930  of the lock body  920  such that an outer surface of the stop member  922  contacts and drives the locking elements  934  radially outward relative to the axis  95  of the body  914 , which, in turn, engages an inclined surface along the inner surface of the release mechanism  916 . 
     One or more secondary spring members  948  are positioned between the base  98  and the release mechanism  916 . The one or more secondary spring members  948  comprise a single secondary spring member  962  surrounding the lock body  920 . The single secondary spring member  962  can be a coil spring or any other suitable resilient member. As seen, at least a portion of the single secondary spring member  962  can be positioned within an annular recess  951  defined in a bottom surface of the release mechanism  916 , which, in turn, helps maintain the position of the single secondary spring member  962  within the attachment unit  912 . Optionally, an annular groove  953  can be defined in the upper surface of the base  98  to help maintain the position of the single secondary spring member  962 . 
     When the insert  902  is inserted into the central opening  930  of the lock body  920 , the insert  902  exerts a downward force on the stop member  922  against the force of the central spring member  928 , which, in turn, permits the locking elements  934  to move radially inward and the single secondary spring member  962  to force or drive the release mechanism  916  upward along the outer surface of the body  914  from a first position toward a second or up position. It will be appreciated that the central opening  930  of the lock body  920  is sized and configured to receive both the insert  902  and the stop member  922 . 
     As the release mechanism  916  moves upwardly, the inner surface of the release mechanism  916  contacts and drives the locking elements  934  radially inward into a locking groove  910  of the insert  902 . This moves the attachment system  900  to the locked configuration, locking or securing the insert  902  in the attachment unit  912 . This advantageously helps reduce the likelihood of undesirable free play and/or slack commonly found in locking pin-type systems which can result in user discomfort and/or failure of the prosthetic socket system. It also makes the prosthetic suspension of a socket on a residual limb more reliable and less prone to failure due to movement, loading, and perspiration when compared to conventional vacuum suspension systems. 
       FIGS.  13   a  and  13   b    illustrate yet another embodiment of a prosthetic socket system  70 . It will be appreciated that the prosthetic socket system  70  may be similar in many respects to the prosthetic socket systems  10 ,  30 , and  50  and may include any of the features described herein. The prosthetic socket system  70  can include a socket  72 , a prosthetic liner, and a prosthetic attachment system  400 . The socket  72  includes a base  78 , a plurality of longitudinal supports  80  connected to the base  78 , and a plurality of shell components  84  connected to the longitudinal supports  80 . 
     Similar to the other attachment systems, the attachment system  400  includes an attachment unit  412  having a body  414  comprising a support body  418  and a lock body  420 . The lock body  420  defines a central opening  430  and is arranged to carry a plurality of locking elements. 
     A plurality of petals or prongs  482  are distributed around the central opening  430  and extend upwardly and radially outwardly from an annular flange  432 . The prongs  482  can be spaced apart by spaces  484  and are sized and configured to help enhance capture of the distal end of a residual limb positioned in the socket  72 . The prongs  482  form an anatomically shaped receiving space on the lock body  420  adapted to receive the distal end of a residual limb. It will be appreciated that the prongs  482  can have any suitable configuration. For instance, the prongs  482  can be overmolded on the lock body  420 , integrally formed with the lock body  420 , or attached to the lock body  420 . The prongs  482  can be curved or rounded. The prongs  482  can have a generally triangular shape. The prongs  482  can have a generally rectangular shape or the prongs  482  can have any other suitable shape. 
     The prongs  482  help create a connection between the attachment unit  412  and a distal end of a prosthetic liner when the prosthetic liner is inserted in the socket  72 . Moreover, the prongs  482  both engage and align the distal end of the prosthetic liner within the socket  72 . The prongs  482  can thus control or help set the position of the prosthetic liner with respect to the attachment unit  412  when the liner is inserted in the socket  72 , facilitating proper positioning of the prosthetic liner with respect to the attachment unit  412 . This beneficially assists with donning the socket  72  for new or elderly users who may be unsure or unaware of how to properly don the socket  72 , making proper use of the prosthetic socket system  70  simpler and easier. 
     According to a variation, the prongs  482  can have a resilient, flexible, and/or semi rigid configuration that helps the lock body  420  enhance the connection between the liner and the attachment unit  412  as the socket  72  moves between open and closed configurations. For instance, as the socket  72  moves from the open configuration toward the closed configuration, at least some of the longitudinal supports  80  and/or shell components  84  are moved or forced radially inward relative to the open configuration, decreasing a receiving volume of the socket  72  or decreasing the circumference of the socket  72 . If a distal region of the shell components  84  engage with the prongs  482 , the shell components  84  can force the prongs  482  radially inward onto the distal end of the residual limb positioned on the attachment unit  412 , enhancing the connection between the prosthetic liner and the attachment unit  412 . This beneficially can help improve prosthetic suspension and ease of use. 
       FIG.  14    illustrates a body  514  of a prosthetic attachment system  500  according to yet another embodiment. The body  514  comprises a lock body  520  defining a central opening  530  for receiving an insert and is arranged to carry a plurality of locking elements  534 . The locking elements  534  are distributed circumferentially about an axis  501  of the body  514  and are radially repositionable relative to the axis  501 . The locking elements  534  are shown comprising discrete ring segments but may be any suitable locking elements. 
     Similar to other embodiments, a release mechanism can be slidably positioned on the lock body  520  to move the attachment system between a locked configuration in which the locking elements  534  shift radially inward relative to the axis  501  to lock the insert in the central opening  530  and an unlocked configuration in which the locking elements  534  shift radially outward relative to the axis  501 , which, in turn, releases the insert from the body  514 . 
     In the locked configuration, the locking elements  534  can extend along lengths of the locking groove of the insert. This increases the contact area between the locking elements  534  and the body  514 , which, in turn, strengthens the attachment between the insert and the body  514 . This advantageously makes the attachment of the socket to the residual limb more reliable and less prone to failure. 
       FIG.  15    shows a prosthetic attachment system  600  according to yet another embodiment. It will be appreciated that the attachment system  600  may be similar in many respects to the attachment systems  100 ,  200 ,  300 ,  400 , and  500 . The attachment system  600  includes an insert  602  arranged to be connected to a prosthetic liner and an attachment unit  612  comprising a distal portion of a socket  601 . The socket  601  can be a conventional socket that is rigid and has a general uniform shape. In other embodiments, the socket  601  can be an adjustable socket. 
     The insert  602  includes an outer radial surface defining a circumferential locking groove  610  and an upper surface arranged to engage a distal end of the liner. The insert  602  can be connected to the liner in any suitable manner. The attachment unit  612  comprises a body  614  defining a central opening  630  sized and configured to receive the insert  602 . The body  614  can exhibit any suitable shape and can be integral to the socket  601  or can be separate from and attached to the socket  601 . 
     A plurality of locking elements  634  are mounted or otherwise attached to the body  614  within at least one recess or groove  686  formed in a sidewall of the central opening  630 . The locking elements  634  can be any suitable locking elements but are shown as wheel members or ball bearings. The locking elements  634  can be made of any suitable material. 
     Similar to other embodiments, the attachment system  600  is movable between an unlocked configuration and a locked configuration (shown in  FIG.  15   ) in which the locking elements  634  are received in the locking groove  610 , locking the insert  602  in the body  614 . As shown, spring members  688  are located in the at least one recess  686  and bias the locking elements  634  radially inward and into the central opening  630 . As the insert  602  is inserted downward into the central opening  630 , the outer radial surface of the insert  602  engages and forces the locking elements  634  radially outward into the at least one recess  686 , which, in turn, compresses the spring members  688 . According to a variation, the outer radial surface of the insert  602  rotates the locking elements  634  as the insert  602  is moved downward through the central opening  630 , making insertion of the inert  602  in the central opening  630  easier. 
     When the locking groove  610  of the insert  602  is axially positioned in general alignment with the locking elements  634 , stored energy in the spring members  688  drives the locking elements  634  into the locking groove  610 , automatically and securely locking the insert  602  in the attachment unit  612 . Optionally, the insert  602  is sized and configured such that the locking elements  634  lock in the locking groove  610  when a bottom of the insert  602  is at or near a bottom of the central opening  630 . It will be appreciated that the attachment system  600  includes a release mechanism adapted to selectively release the locking elements  634  from the locking groove  610 . 
       FIGS.  16  and  17    illustrate an insert  702  for use in a prosthetic attachment system  700  according to another embodiment of the present disclosure. The insert  702  includes an outer radial surface defining a circumferential locking groove  710  and an upper surface arranged for connection to a distal end  703  of a prosthetic liner  704 . The upper surface of the insert  702  can have a concave shape or any other suitable shape. A bottom surface of the insert  702  defines an opening  790  arranged to receive a fastener  792  that threadedly attaches the insert  702  to the distal end  703  of the prosthetic liner  704 . The opening  790  can include a counter bore  794  for accommodating a head portion of the fastener  792 . 
     As shown, a spacer  796  is located between the insert  702  and the distal end  703  of the prosthetic liner  704 . A bottom surface of the spacer  796  defines an opening  798  for receiving the fastener  792  and/or a connecting portion  701  of the prosthetic liner  704 . 
     The insert  702  includes at least one positioning feature for generating an amount of play or movement in the attachment between the insert  702  and the prosthetic liner  704 . This selected amount of play or movement advantageously allows a user to more easily position the insert  702  in an attachment unit of the present disclosure and/or locate the attachment unit, facilitating donning of a prosthetic socket. In the illustrated embodiment, the at least one positioning feature comprises the opening  790  of the insert  702  being oversized relative to a shaft portion  705  of the fastener  792 . More particularly, a diameter of the opening  790  is greater than a diameter of the shaft portion  705 . The oversized opening  790  in combination with the concave shape of the upper surface of the insert  702  allows the insert  702  to float or move from side to side on the spacer  796 . The play or movement in the connection between the insert  702  and the prosthetic liner  704  beneficially allows at least some self-alignment or adjustment of the insert  702  while being inserted into an attachment unit, making donning of a prosthetic socket system easier. 
       FIGS.  18 - 20    illustrate an insert  1002  including at least one positioning feature according to another embodiment. The insert  1002  includes an outer radial surface defining a circumferential locking groove  1010  and an upper surface  1003  for connection to a distal end of a prosthetic liner. The upper surface  1003  can have a concave shape or any other suitable shape. An opening  1090  is defined in the insert  1002  for receiving a fastener  1092  arranged to attach the insert  1002  to the prosthetic liner. The opening  1090  can include a lower portion  1094  arranged to engage with a head portion  1098  of the fastener  1092 , and an upper portion  1096  arranged to receive a connecting portion of the prosthetic liner. 
     The insert  1002  includes at least one positioning feature for facilitating insertion of the insert  1002  in an attachment unit of the present disclosure. The at least one positioning feature comprises one or more deformable members arranged to provide an amount of play or self-adjustment in the connection between the insert  1002  and a prosthetic liner via deformation. The one or more deformable members can include a first deformable member  1005  located on the upper surface  1003  of the insert  1002 , and a second deformable member  1007  locating in the lower portion  1094  of the opening  1092 . 
     The first deformable member  1005  is arranged to engage with the distal end of the prosthetic liner and deform between the insert  1002  and the distal end of the prosthetic liner, which, in turn, allows for a small amount of movement or angular misalignment between the insert  1002  and the distal end of the prosthetic liner. The second deformable member  1007  is arranged to engage with the head portion  1098  of the fastener  1092  and deform between the insert  1002  and the fastener  1092 , which, in turn, allows for a small amount of movement or angular misalignment between the insert  1002  and the fastener  1092  and the distal end of the prosthetic liner. The play provided by the first and/or second deformable members  1005 ,  1007  in the connection between the insert  1002  and the prosthetic liner advantageously allows at least some self-alignment or adjustment of the insert  1002  while being inserted into the attachment unit, facilitating donning of a prosthetic socket system. 
     The deformable members  1005 ,  1007  can be separate from and attached to the insert  1002 . In other embodiments, the deformable members  1005 ,  1007  can be overmolded onto the insert  1002 . The deformable members  1005 ,  1007  can be made of elastomeric material, foam material, or any other suitable material. The deformable members  1005 ,  1007  can be resilient. The deformable members  1005 ,  1007  can comprise gaskets, rings, ring segments, bars, or any other suitable members. 
     According to a variation, the deformable members  1005 ,  1007  can be formed of one or more different materials selected to vary the amount of movement or play created between the insert  1002  and the prosthetic liner and/or fastener  1092 . For instance, the deformable members  1005 ,  1007  can be formed with materials having greater durometers to reduce the amount of deformation of the deformable members  1005 ,  1007 . The deformable members  1005 ,  1007  can be selected based on a size or dimension to vary the amount of movement or play created between the insert  1002  and the prosthetic liner and/or fastener  1092 . By way of example, a deformable member having a greater cross-sectional diameter may be selected to provide more movement or play than a different deformable member having a smaller cross-sectional diameter. 
       FIGS.  21  and  22    illustrate an insert  1102  including at least one positioning feature according to another embodiment. The insert  1102  includes an outer radial surface defining a circumferential locking groove  1110  and an upper surface arranged for connection to a distal end of a prosthetic liner. An opening  1190  is defined in the insert  1102  for receiving a fastener  1192  arranged to attach the insert  1102  to the prosthetic liner. 
     The insert  1102  includes at least one positioning feature for facilitating insertion of the insert  1102  in an attachment unit of the present disclosure. The at least one positioning feature comprises a rotating joint  1111  positionable in the opening  1190  of the insert  1102 . The rotating joint  1111  defines a through hole for receiving the fastener  1192  and interacts with the fastener  1192 . The rotating joint  1111  is arranged to allow a small or limited amount of rotation or play between the fastener  1192  and the insert  1102 , which, in turn, provides a small or limited amount of rotation or play between the prosthetic liner and the insert  1102 . The play provided by the rotating joint  1111  in the connection between the insert  1102  and the prosthetic liner advantageously allows at least some self-alignment or adjustment of the insert  1102  while being inserted into the attachment unit, facilitating donning of a prosthetic socket system. It will be appreciated that the rotating joint  1111  can comprise a swivel joint, a spherical bearing, or any other suitable rotating joint. The rotating joint  1111  may be formed of plastic material, metal, combinations thereof, or any other suitable material. 
       FIGS.  23 - 25    illustrate yet another embodiment of a prosthetic socket system  800 . It will be appreciated that the prosthetic socket system  800  may be similar in many respects to the prosthetic socket systems described above. The prosthetic socket system  800  can include socket  801 , a prosthetic liner  804 , and a prosthetic attachment system  805 . The socket  801  includes a base  807  and a plurality of longitudinal supports  809  connected to the base  807 . The attachment system  805  includes an insert  811  arranged for connection to the prosthetic liner  804  and an attachment unit  813  integrated with the base  807 . 
     The insert  811  can be made of any suitable material. The material selection can depend on desired function. The insert  811  can include an elastomeric polymer arranged to provide cushioning to a distal end of a residual limb. The insert  811  can include a plastic material having a stiff configuration, enhancing the durability of the insert  811 . 
     Referring to  FIG.  24   , the insert  811  can define a through-hole  815  for receiving and accommodating a fastener  817 . An upper surface of the insert  811  can define a concave surface arranged to engage or fit on the distal end of the prosthetic liner  804 . 
     The insert  811  includes one or more magnets  820  and/or ferromagnetic material. The magnets  820  can be disposed in one or more openings  819  formed in the upper surface of the insert  811 . This allows the magnets  820  to be concealed by the insert  811  when the insert  811  is attached to the prosthetic liner  804  (see  FIG.  18   ). In other embodiments, the magnets  820  can be attached to the outer surface of the insert  811  or incorporated into the material forming the insert  811 . 
     As seen in  FIG.  25   , the attachment unit  813  includes one or more magnets  822  and/or ferromagnetic material. The magnets  822  are arranged to create a magnetic connection between the prosthetic liner  804  (shown in  FIG.  18   ) and the socket  801  when the prosthetic liner  804  is inserted into the socket  801 . The attachment unit  813  defines a through opening  821  arranged to receive and accommodate a conventional locking pin. The attachment unit  813  includes a base part  823  and a removable part  825  attached to the base part  823 . The magnets  822  can include permanent magnets disposed in openings  827  defined in the removable part  825 . 
     When the prosthetic liner  804  is inserted into the socket  801 , the distal end of the prosthetic liner  804  is held against the attachment unit  813  by magnetic attraction between the insert  811  and the attachment unit  813 . This beneficially secures the prosthetic liner  804  to the socket  801 , improving suspension of the socket  801  on the residual limb. 
     The magnetic attraction between the insert  811  and the attachment unit  813  can also or alternatively help ensure a proper or correct positioning of the prosthetic liner  804  in the socket  801 . Proper positioning of the prosthetic liner  804  provides a good, comfortable fit and helps prevent or limit undesirable pistoning of the residual limb within the socket  801 . It can also help ensure that the length of the socket  801  is sized or adjusted to fit the residual limb. 
     According to a variation, the magnetic force or attraction between the insert  811  and the attachment unit  813  can be customized based on the individual needs of the user. For example, the magnetic strength of the magnets  820 ,  822  can be selected based on activity level. The level of magnetic force can be adjusted by varying the number of magnets and/or the strength of the magnets  820 . In other embodiments, the amount of magnetism can be varied by a clinician or user by adding more or less magnets or altering the position of the magnets  820 ,  822  such as in a modular fashion. 
     It will be appreciated that the magnetic attraction between the insert  811  and the attachment unit  813  can be adapted for pure suspension (similar to a locking pin or lanyard) or to maintain the distal end of the prosthetic liner  804  in a specific position relative to the base  807  of the socket  801 . The magnetic attraction between the insert  811  and the attachment unit  813  can also be an alternative to or used in combination with different attachment or tensioning systems. 
     Optionally, a hardness of the insert  811  can be selected to produce a click or knock when it contacts the attachment unit  813 , providing audible feedback to the user that the prosthetic liner  804  is correctly or properly positioned in the socket  801 . 
     While various aspects and embodiments have been disclosed herein, other aspects and embodiments are contemplated. For instance, in other embodiments, the insert can be attached to the socket and the attachment unit can be attached to the prosthetic liner. Moreover, the insert is shown as being attached to the distal end of the prosthetic liner but can be attached to any suitable portion of the liner. 
     In other embodiments, the attachment unit can be arranged such that movement of the release mechanism in an upward direction or away from the base part moves the attachment system toward the unlocked position, releasing the insert. Optionally, the attachment system may include a strap or tab attached to the release mechanism. The strap or tab can be made of fabric and arranged so that when a user pulls on the strap or tab, the attachment system moves toward the unlocked position. This beneficially requires less dexterity from the user. 
     In other embodiments, the attachment system of the present disclosure can be operatively connected to a tensioning system of the socket. This can allow for movement of the release mechanism toward the unlocked position to trigger a release of tension in the tensioning system, or movement of the release mechanism toward the locked position to trigger an increase in tension in the tensioning system. This can encourage a user to follow a sequence of steps when doffing or donning the socket, which can benefit users with poor cognition. For instance, this can encourage a user donning the socket to lock the insert into the attachment unit before tensioning the tensioning system. This arrangement can also decrease risk of injury to the user as the user cannot use the socket unless it is correctly or properly secured to the liner. 
     By providing a prosthetic attachment system as shown and described herein, the problems of existing attachment systems being difficult to operate, leading to incorrect usage, noise, and safety issues, is overcome by providing a more intuitive, forgiving, and simple connection between a prosthetic liner and the corresponding socket that facilitates accurate and secure attachment. 
     The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting. Additionally, the words “including,” “having,” and variants thereof (e.g., “includes” and “has”) as used herein, including the claims, shall be open ended and have the same meaning as the word “comprising” and variants thereof (e.g., “comprise” and “comprises”).