The majority of patients who lose a major limb, whether that’s an arm or a leg, will have to resort to reconstruction using a prosthetic device – an artificial leg, an artificial arm, or something of that kind. And that's been the case for literally thousands of years, as there are historical precedents of patients having artificial limbs as far back as Ancient Egypt.
However, trying to fix an artificial limb to an amputation stump is really difficult, because the body was never designed for it. Although we try really hard to create a comfortable, form-fitting, prosthetic socket, it often ends up causing problems that can be painful. It hurts because the fit has to be tight in order for the artificial limb not to move around in a way that is then functionally useless. Pain can also be caused because nerve stumps in the residual limb are often sensitive and are now being squashed inside the socket of the prosthetic limb. Friction between the skin and the socket of the prosthesis can also cause infections due to skin ulceration or inflammation of irritated hair follicles.
In the case of a lower-limb amputee, walking can be very restricted, sometimes to just a few hundred metres, or the patients may only be able to wear the device for half the day. Likewise, with the upper limb, as well as the problems of attaching the prosthesis, the majority of the prostheses we have at present are very poor in terms of their function. With current technology, it's impossible to have an artificial limb that reproduces exactly the movements and abilities of a missing hand.
At the Royal Free, we've taken advantage of revolutionary developments in both surgical and prosthetic technology, which have come about over the past decade. One of these is osseointegration, in which a piece of metal is placed into the residual bone in an amputation stump. The bone then accepts the metal as if it was part of itself. Such technology has been around for 50 years, but mainly in the context of artificial teeth.
We don't really understand why this process occurs, but it's something that we can exploit and reproduce time and time again, to the extent that it is now so widespread in dental treatment that there are probably upwards of 75,000 dental implants inserted every year in the UK.
We are now able to use the same technology to put an implant into the bone within the amputation stump. A small part of the implant protrudes through the skin to provide a secure point of attachment for the prosthetic limb that does not rely on the use of a socket, straps or anything of that nature. All the patient has to do is attach or detach the prosthesis from the bone anchor, using a simple click-off/click-on or screw mechanism.
As the forces that are applied to that limb are now traveling through the bony skeleton, rather than through soft skin and muscle, it is biomechanically easier for the patient to use their prosthesis in a way that approaches normal.
For example, in the upper limb, because it is so much more secure, you can do things like lifting the prosthesis above your head – if you try to do something like that with a conventional socket-fitted prosthesis attached over the shoulder, the prosthesis falls off because it's just not designed to cope with that.
The other big revolutionary step occurred back in 2004, with the introduction of a surgical technique called targeted muscle reinnervation, which is a completely radical departure from anything that has been done before. Amputees experience two major problems as far as the nerves are concerned.
The first is called phantom limb pain. It is a symptom that can be quite hard to describe. Nearly all amputees experience some sensation of the limb being present, although obviously it has been amputated. In some patients this sensation develops into pain, typically a crushing, cramping, or burning sensation, and the perceived position of the missing part can be very abnormal.
Every second of every day, we all receive feedback that tells our brains what our limbs are doing and where they are in space, but when you amputate a limb, that feedback disappears. The brain then starts to scrabble around looking for feedback from the missing limb. Instead, what happens over time is that the perception becomes distorted and changed because the feedback is no longer there.
Targeted muscle reinnervation (TMR) is a procedure to reconnect the nerve stumps in the amputated part to muscles within the amputation stump, which are currently redundant. We can use those muscles to provide a target for those nerve endings which then provides feedback to the central nervous system, tricking the brain into thinking that the limb is present.
When the nerves grow through and that feedback starts to kick in, the phantom limb pain either diminishes or disappears altogether. This is the first time that there's been a reliable surgical technique for addressing phantom limb pain.
The second issue that the TMR procedure deals with is neuroma pain. After amputation, nerves try to grow, but can't make contact with the amputated part because it isn’t there. Instead, they can form a ball of scarred nerves that are very sensitive, so that when patients have their amputation stump touched it is often so uncomfortable that they can't wear a socket-fitted prosthesis. Targeted muscle reinnervation helps to instruct the nerves not to grow this ball of scar tissue, taking away this element of the pain.
A third benefit of the surgery is that, by repurposing those muscles in the amputation stump, we can provide the patient with the means to control a prosthetic limb much more easily. Currently, this is mainly applicable in the context of upper-limb amputees, but it may be extended to lower limbs in the future.
We have a regular monthly clinic where we, the physiotherapists, the prosthetists, psychologists, and anaesthetist ascertain whether somebody would be a good candidate for these kinds of treatments. For someone who is visiting from abroad for treatment, that kind of clinic would be very suitable as it also enables the patient to have carry out all of their scans and tests during a single visit. We would have an answer on whether or not the patient is suitable for surgery – if so, they could go ahead with surgery in a relatively short period of time. Patients receiving surgery should expect to be in hospital for three to five days, followed by a period of residential rehabilitation. The duration of rehab depends on whether the surgery is for an upper or lower limb problem, the patient’s bone density and the complexity of the procedure, but this would range from a few weeks up to one-year after surgery.
