The present invention relates to prosthetic devices, and in particular to a prosthetic device that may sense points of high pressure contact with a patient's residual limb and locally reduce those pressures on a dynamic basis.
Lower limb amputees may be fitted with a prosthetic leg that attaches to their residual limb by means of a socket surrounding the residual limb. In such cases, it is important that the socket fit closely to the residual limb so that the amputee has a sense that the prosthetic limb is secure and stable and the forces of walking are distributed evenly over the entire residual limb. It is also important that the fit not be so tight as to restrict blood flow or to be uncomfortable.
Unfortunately the volume of the residual limb changes significantly over time and even within the course of a day making a good fit between the residual limb and socket difficult to maintain. This change in the volume of the residual limb can be managed to some extent by the use of one or more socks which may be placed over the residual limb or removed from the residual limb at different times to adjust the fit of the socket.
Volume changes in the residual limb may also be accommodated by means of a socket incorporating one or more bladders that may be inflated manually by the patient, or automatically, to provide a desired pressure between the socket and the residual limb. For example, U.S. Pat. No. 6,585,774 describes a socket in a “pumping bladder” between the socket and the residual limb that makes use of forces developed during walking to pump additional fluids into other bladders within the socket to maintain a desired predetermined pressure between the socket and the residual limb. In this way, a good fit between the socket and the residual limb may be obtained despite variations in the volume of the residual limb.
A difficult problem for patients, even with padded sockets that properly conform to the surface of the residual limb, is the persistence of localized points of high pressure in the contact between the residual limb. Such persistent high pressure points can result from difficult to correct socket interface pressure that occurs during human activities such as running, jumping, leaning and lifting which cause large variations in the loading on the residual limb, and the need to maintain a relatively stiff interface between the residual limb and the socket to prevent undue “bouncing” movement of the prosthetic leg during use. Such persistent high pressure points may cause discomfort to the patient which can deter the use of the prosthetic leg and, in extreme cases, can cause tissue damage.