More general pondering on the pet project
I'm really intrigued by the whole design concept for the plug-in prosthesis. It's a possibility for arms and legs, but because we started with the leg, we'll continue along that thread. Let's assume here that we want the prosthesis to be easily removable; ideally, the user can take it off and stick it next to the door at bedtime, and just as easily reattach it in the morning. Convenience is key; this includes comfort, good mechanical performance (security, reliability, & durability), non-invasive & low-frequency maintenance, and power efficiency & self-sufficiency (just recharge the batteries overnight!).Now, the exact attachment point would depend largely on the location of the original amputation. Consider the issue, for example, of how many surviving muscles have retained functionality. We will consider the two general cases of amputation (1) below the knee and (2) above the knee.
Case 1: If the amputation was below the knee, let's assume that the muscles in the upper leg, which mobilize the knee joint, and their attachments to the lower leg are intact. In this case, the natural motion occurring throughout the knee joint is unimpaired; the prosthesis will only have to account for the structures & functions of the lower leg & foot. The prosthesis must also attach securely & comfortably to the termination of the limb. The implanted cybernetic interface (ICI, for simplicity's sake) could be anchored in the distal terminations of the tibia and fibula, assuming these bones are intact down to the point of amputation, with supporting structures placed radially outward through the tissue to support non-central, non-axial loading about the edges of the implant.
Case 2: If the amputation was above the knee, many of the surviving muscles in the upper leg have no purpose other than to serve as cosmetic padding to preserve the natural shape of the leg. The potentially useful muscles, namely those that move the upper leg relative to the torso, may or may not still serve this function; if the amputation was sufficiently high on the limb to disrupt the attachments of these muscles, further surgery should be performed to re-attach them higher up on the femur so as to restore functionality. The missing knee joint, its movement, and the previously discussed structures & functions of the lower leg must be replaced by the structures & functions of the prosthesis. The prosthesis must attach securely & comfortably to the termination of the upper leg, and also must move the entire lower leg independently of muscle action in the upper leg. The ICI would probably be anchored in the distal termination of the femur, with a supporting structure similar to that described above.
In either case, because we don't want miscellaneous protrusions on the limb surface of the ICI, the corresponding surface of the prosthetic will probably have the protruding/moving components of various mating/latching mechanisms to securely hold the prosthesis in place when it is attached. The distal terminations of the surviving nerve branches could be permanently wired via a highly-discriminatory electrode cuff, such as the FINE (discussed in an earlier post), to one or more "outlets" on the surface of the ICI, corresponding to electrical connectors on the attaching surface of the prosthesis.
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Labels: engineering, science
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