Every year, 25,000 people in the United States have entire arm amputations and 61,000 people have partial hand amputations (Kulley 2003). These unfortunate victims must approach all daily activities differently for the rest of their lives. What can we do to help them? Metal prosthetics were used during the Renaissance Period and the rubber hand was invented in response to Civil War victims (Kulley 2003). Over time, these inventions have evolved into amazing tools for victims all around the world. There are many ways for patients to control their upper extremity prostheses available on the market, as well as experiments being tested off the market. In which of these experiments does the future of control for upper extremity prostheses lie?

Current Techniques for Controlling Upper Extremity Prostheses

There are several different types of upper extremity prosthetics from the Boston Arm to the Utah Arm to arms made of memory alloy to plastic arms. Many are available on the market and proven effective as prosthetic devices. However, what are the patient’s options for controlling their new limbs?

Myoelectric signal processing is currently the most widely-used mode of control for prosthetics. Myoelectric prosthetic devices take the muscles’ electrical signals and apply them to multifunctional prosthetics to provide patient control. The myoelectric method has been proven to be quite reliable in multiple cases and is often considered the best form of prosthetic control. However, this mode of control is often preferred by below elbow amputees only because myoelectric processing is limited to controlling only one joint at a time, thus having limited degrees of freedom (Parker 2006).

Neuroelectric signal processing is another mode of control that overcomes the myoelectric method’s shortcomings. Neuroelectric prosthetic devices take nerve-signal patterns and match them with motions commonly performed by the limb, the prosthetic is then programmed to generate a desired response. The neuroelectric method has the advantage of controlling multiple degrees of freedom, however it is more expensive than myoelectric signal processing (Sorensen 2005).

Targeted Reinnervation

Targeted reinnervation is a largely improved version of myoelectric control that produces more signals to control the prosthetic. It involves the invasive denervation of the amputated muscle and the anastomosis of those peripheral nerve endings to parts of muscles that are functionless in the body. This is an incredibly constructive procedure that employs functionless muscle areas to amplify nerve signals so that the patient can control their external prosthesis (Kuiken 2006).

This procedure, unlike myoelectric control, allows the patient to have multiple degrees of freedom. Targeted reinnervation doesn’t harm other muscles in the body and no function is lost because it only involves non-functional muscles. The biggest advantage of targeted reinnervation is that it may give real sensory feedback to the patient. A prosthetic arm that uses targeted reinnervation is already on the market and provides users with 20 degrees of freedom, it’s light and compact, and contains shape memory alloy (Kulley 2003).

Although targeted reinnervation has many positive aspects, it carries some disadvantages as well. It is an invasive procedure that involves a long, detailed surgical procedure. All the nerves must be consistently reinnervated over each surface area of the muscle because too little nerves per unit area of the muscle will not cause sufficient stimulation. It is also difficult to get separate signals from each muscle area, therefore the signals are hard to interpret and there is too much noise for the prosthetic to interpret the signal (Kuiken 2006).

Brain-Computer Interfaces

Brain-computer interfaces (BCIs) are a largely improved type of neuroelectric control and are a way for the brain to communicate directly with computers. BCIs use electrodes (sensors) to detect and analyze neural signals from the brain and convert them into electronic impulses that computers can understand (Cichocki 2003). There are three main types of BCIs that all have the same function and use the same basic methods.

Invasive BCIs have an electrode that’s smaller than a contact lens implanted directly on the brain’s grey matter, usually on the primary motor cortex. The electrode picks up extremely clear signals since it reads neuron firing directly from the brain. This can be disadvantageous as well because increasing amounts of scar tissue develop on the surface of the brain and the signal that the BCI receives gets weaker over time (Reinberg 2006). Additionally, this electrode must be surgically implanted into the patient’s head, which brings about all the complications of brain surgery such as hemorrhaging, weakness, brain damage, infection, and in rare cases even death (Medline Plus 2005).

Partially invasive BCIs use the same electrode as invasive BCIs, but it is not implanted directly on the brain even though it lies inside the skull. The electrode picks up neural firing from the surface of the brain (Fitzpatrick 2006). Partially invasive BCIs also have the problem of scar tissue build-up, but less builds up since the electrode is not in direct contact with the brain (Tresco 2006). They also have all the same complications of brain surgery as invasive BCIs do.

Non-invasive BCIs have electrodes carefully placed on a cap that the patient wears on their head. The electrodes pick up sensorimotor rhythms recorded from the scalp (McFarland 2004). This method has no complications of brain surgery and does not involve any direct contact with the brain, just the scalp. Because these BCIs are not picking up neuron firing directly from the brain, they often don’t pick up clear signals. Since there are always multiple neurons firing simultaneously in the brain, the signals that non-invasive BCIs pick up from the scalp are very noisy and are often misunderstood or not understood at all by the computer. Additionally, the cap cannot be worn for long periods of time due to electrode and skin problems with long recording times and the fact that when the patient gets sweaty, signals cannot be properly attained by the cap (Birbaumer 2006).

Limb Regeneration

Limb regeneration is the restoration of a lost or damaged limb via tissue repair. Many lower species have the ability to regenerate their limbs and these species have been studied in great depth to figure out why humans don’t have the same ability. Humans have the ability to regenerate epithelial tissue, but only in single cell layers like mucosa and epidermis. An exception to this is the phenomenon of children being able to regenerate their distal fingertips with no medical intervention (Gurtner 2006).

This is possible because the body reactivates developmental pathways by which the original tissue was created. The original tissue gets recreated by stem cells that have the potency to differentiate into various tissues in our bodies. Embryonic stem cells have the most potential because they have not fully differentiated, therefore researchers can manipulate them to develop into whatever tissue desired. This theory has been proven in vitro with embryonic stem cells, however the role of stem cells in the adult body is still ambiguous. It has been proposed that one somatic cell has enough genetic information to create an entire organism all on its own; hence reprogramming this somatic cell to differentiate into a desired product is possible. The idea of using retroviruses through gene therapy has been introduced to reprogram the DNA of a somatic cell, unfortunately this is a very controversial issue that the body’s immune system may even reject (Gurtner 2006).

Another possibility of limb regeneration lies in tissue engineering, which is the biological development of replacements and restorations for damaged tissues (Gurtner 2006). Tissue engineering of artificial skin has already been proven successful for thousands of burn victims across the country (MacFarlane 1997). Any artificial tissue or organ can be manufactured through tissue engineering, the trick is to make it compatible with the adult human body.

When scientists combine these two amazing discoveries of stem cells and tissue engineering, regenerative limbs may be created. A bioengineered scaffold can be created via tissue engineering to stick to and blend in with the area of the body in which the limb will be regenerated onto. This scaffold will be made of nature and artificial substances as well as growth factors that stimulate the proliferation of cells. If stem cells are incorporated into this scaffold, they will be able to proliferate and blend in to the wound as the scaffold degrades. With the aid of the proper growth factors and constant regulation, the stem cells can then potentially grow an entire limb! Disadvantages to this theory include, but are not limited to immune rejection of the limb, a vascular system going through the limb, regeneration in response to wounds, and the limb’s response to the environment (Gurtner 2006).

Business Analysis of this Technology

From a business perspective, this is an undying field. In the United States, about 10,000 upper limb prosthetics are sold per year, doctors and patients alike will always be looking for a better way to control their new prosthetic body parts (Kulley 2003). An entire prosthetic arm costs the patient $10,000-$15,000 on average, but can potentially cost up to $35,000. The average insurance company covers up to $1,500 a year for prosthetics and the patient pays for the remainder. It will only cost approximately $1000 to manufacture a prosthetic limb (Freeman 1998). Targeted reinnervation surgery costs over $2000 per patient (Kuiken 2006a) and a noninvasive BCI currently costs patients about $5000 per unit (Anon 2006).

Recommendation About Which Path to Follow for New Products

I believe that this company should invest their time and money into BCIs rather than targeted muscle reinnervation. The strategy of myoelectric control has been underway for many years and now it’s time for neuroelectric control to take over this industry. Neuroelectric control is in fact the more advanced way of monitoring impulses between the motor system and the brain and can ensure multiple degree of freedom movement (Kulley 2003). If we support this technique, it will open up many doors for our company to make new prosthetic devices that will collaborate with it. Think of the possibilities of a person that can’t even use the restroom on their own being able to work online independently. This is a revolutionary possibility that will change the lives of thousands of people and our company should definitely be a part of it.

-Amy Shah

This entry was posted on Friday, November 3rd, 2006 at 10:23 pm and is filed under General. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.