Ball-and-Socket Limbs: Things of the Past?

We've posted about a lot of different types of budding prosthetic technology, but most of those solutions are still far in the future, and even then, their affordability and accessibility to the widespread public are issues. It may be some time before computerized exoskeletons and mind-reading electrode prosthetics become the norm.

Right now, ball-and-socket prosthetic limbs are the standard. These prosthetics technically do their job: replace an absent limb. However, the cups that cover what is called the 'residual limb' often cause uncomfortable chafing and alter the way a person walks, which can strain other parts of the body, like the back. The limbs themselves have evolved—they are lighter and easier to control—but the way they attach to the body has hardly changed.

Researchers at University College of London have developed an alternative way to attach prosthetic limbs to the body. The ITAP (Intraosseous Transcutaneous AmputationProsthesis) circumvents the need for a cup by attaching directly to the user's bone, which allows weight loads and impacts to be felt through the skeleton instead of through soft tissue.

"[M]y ability to know where [my foot] is improved dramatically because you can feel it through the bone,” trial participant Mike O’Leary told the Guardian. “A textured road crossing, I can feel that. You essentially had no sensation with a socket, and with ITAP you can feel everything."

What is neat is that, although there is direct attachment to the bone, prosthetics can still be easily and quickly removed with a safety device at the top of the prosthetic limb. It works similarly to a ski binding, so in the event of high stress on the prosthetic, like during a fall, the ITAP's safety device releases, preventing damage to the bone or implant.

But how do metal and flesh fuse together without infection? For their inspiration, the researchers turned to deer. Deer antlers are weight-bearing bones that extrude from the skin, which is just the sort of thing needed for a new prosthetic design. Research on the antlers showed that deer antler bone is actually porous under the skin, which allows soft tissues to grow into the pores and create more stable tissues around the antler. Outside the skin, the antlers are less porous in order to prevent buildup of bacteria, which means less chance for infection. The ITAP is designed in a similar way, using a porous surface beneath the skin so that soft tissues can infiltrate the metal.

As of now, the ITAP is only available for clinical investigation for those with above-the-knee amputations, but if data from the trials looks good, the ITAP limb could be seen soon in specialist clinics across the UK. The United States FDA is hesitant to jump on board with the prosthetic design as it does not allow direct skeletal attachment (DSA) procedures. However, if researchers can prove that their prosthetic attaches to the bone safely and does not cause infection, the FDA may approve the ITAP for commercial availability in the US.