This document helps amputees monitor all current and future surgical techniques that may improve the use of bionic limbs and/or reduce pain.
Agonist-antagonist Myoneural Interface (AMI)
AMI surgically recreates muscle pairs that would otherwise be severed during amputation. This re-establishes the brain’s ability to track a phantom limb’s position based on the position of the related muscle pair. Correlate this to the movement of a bionic limb and, voila, the brain can then effectively track the position of that device.
Because this procedure restores part of the natural connection between the brain and a missing limb, it can also help reduce phantom pain.
Osseointegration for limbs involves inserting a metal rod into an arm or leg bone. The bone then fuses with the rod in a manner similar to fracture healing. More recent innovations include the addition of fully integrated myoelectric sensors implanted in adjacent muscles for improved user control of bionic devices, and a fully integrated neural interface for sensory feedback.
There are some significant health risks with this procedure, but it also appears to be a valuable option for bionic limb solutions going forward.
Targeted Muscle Reinnervation (TMR)
TMR is the surgical reassignment of nerves to alternative muscles. Because the nerves can grow into this new, healthy muscle tissue, this can prevent the formation of neuromas and decrease phantom pain. This relocation of nerves can also provide new muscle sites for myoelectric control, which may be necessary depending on the location of the amputation.
Interestingly, new variations of this surgery are evolving including combining it with RPNI (see below).
Regenerative Peripheral Nerve Interface (RPNI)
RPNI is is sometimes referred to as a “mini-TMR”. It leaves the nerve in the same physical space but wraps it in a small muscle graft, often taken from the patient’s thigh muscle. The nerve can then grow into this grafted muscle tissue, innervating it. This can not only prevent the formation of neuromas and decrease phantom pain — it can also amplify muscle signals for improved myoelectric control.
As with TMR, new variations of RPNI are still evolving.
Targeted Sensory Reinnervation (TSR)
Targeted sensory reinnervation is a method where the skin over a target muscle is denervated, then reinnervated with nerve fibers from an amputated limb. When this piece of skin is touched, it provides the amputee with the sensation that the missing limb is being touched.
This technique may be a valuable option between surgically implanted electrodes (i.e. a neural interface) and Transcutaneous Electrical Nerve Stimulation (TENS).
Implantable Myoelectric Sensors
Implantable myoelectric sensors attempt to solve the problems with skin-surface sensors by interfacing directly with target muscles. Additionally, their ability to read deeper muscle movements lays the groundwork for more sophisticated user control systems that can read, identify, and act upon multiple arm/hand movements simultaneously.
Two big questions remain: Are these benefits worth invasive surgery? And will this technology last or will it eventually be replaced by much-improved skin-surface sensors?
Neural Interface Surgery
Implanted neural interfaces are currently the leading option to provide true sensory feedback from bionic limbs. Certainly, they have demonstrated the most capability in this regard. But they also have significant drawbacks including cost, the risk of scarring, and a nagging problem with precision.
We have little doubt that scientists will eventually perfect this technology. The question is whether it will be superseded by less invasive solutions.
More to Come…
We still have one more surgical to cover, though it is just being explored at this point: a new outpatient procedure involving spinal cord stimulators that may restore sensory feedback without the need for a neural interface.
Why These Surgical Techniques Are Important
This website is primarily about bionic devices and their underlying technologies.
However, bionic technologies are not going to restore near-natural capabilities on their own. To do this, they need to integrate with natural systems. That requires surgery.
Some of the techniques in this article will eventually be absorbed into standard amputation procedures, though they will likely remain as separate procedures for existing amputees for many decades. Others may be replaced by non-surgical procedures, such as injectable sensors.
It is impossible to plot this future out with any certainty. That’s why we’ve written this article and all its supporting articles. We want to help people stay informed of their surgical options as technology progresses. Because we continuously update all our articles, you can do that simply by bookmarking this page and periodically checking it.
For a comprehensive description of all current upper-limb technologies, devices, and research, see our Complete Guide to Bionic Arms & Hands.
For a comprehensive description of all current upper-limb technologies, devices, and research, see our Complete Guide to Bionic Legs & Feet.