We're working on a prosthetic arm prototype that challenges the status quo in a couple of ways. First, the socket consists of multiple hard "counters" that transmit arm motion to the terminal device. In contrast to standard hard sockets that sometimes cross the elbow (or any more proximal joint), the counters are secured to the arm by a soft fabric matrix that allows the full motion of the joint. In this way, no compromises need be made when creating a secure connection with the bones of the arm, at the same time as their full motion is allowed.
Second, the counters are held together by a loop of lacing that also doubles as the flexible hinges of the arm. This prototype uses boa lacing, and the flexible hinges cross the forearm in front of the cubital fold and encircle the residual limb with a figure 8, as shown below. The lacing and boa reel can also be seen in the cover photo of an early prototype.
The counters and lacing system allow the arm to breathe through the soft mesh socket material, in contrast to traditional hard composite and unbreathable silicone liners or inner proflex sockets. It is, in essence, more like an athletic shoe than a dutch wooden shoe--something I've been saying that we needed for years.
We'll have more to share soon.