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VR Series #6 – Phantom Limb Pain [PLP]

11 May 2018
Ian Slater discusses how researchers use VR to create an experience of being present in a 3D environment where patients can move freely, grab things and interact with them.

Samsung are currently running a Do What You Can’t brand campaign to promote the Samsung Gear and its various uses: one of which is virtual reality… you know the one, inspiring sound track and an underlying message that doing the impossible is what Samsung do every day: can’t is only what you can’t do yet…

The Killers:All These Things That I Have Done

Where am I going with all this? Of relevance to us is the clip of the young prosthetic user who, after donning the VR gear, manages to walk between parallel bars as she sees two normal feet walking through the sand and gently lapping waves…

Accepting that the advert uses a degree of dramatic licence, before we look at the theory behind the use of VR for PLP it is helpful to consider the traditional method whereby a mirror box is used: the patient places the good limb onto one side of the mirror with the prosthetic limb on the other side. The patient then looks into the mirror on the side with the good limb and makes symmetrical movements with the prosthetic limb (by way of example imagine clapping hands). Because the patient is seeing the image of the good hand moving it appears that the phantom limb is also moving and (so the theory goes) the brain is tricked into thinking that the amputated limb is still present.

Now let’s look at VR.

In their study Restoring Movement Representation and Alleviating Phantom Limb Pain Through Short-Term Neurorehabilitation with a Virtual Reality System, Osumi et al enrolled 8 PLP patients who wore a head mounted display which showed a mirror-reversed computer image of an intact arm. By intending to move both arms simultaneously the patients perceived voluntary movement in their phantom limb. The study concluded that motivation was increased and that the use of a bimanual coordination task correlated with an alleviation of PLP.

A study from May 2017 conducted at Aalborg University in Denmark Virtual Reality Eases Phantom Limb Pain reported that 8 out of 10 amputees experience a feeling of discomfort in the limb that is no longer there.

Researchers used VR to create an experience of being present in a 3D environment where the patient could move freely, grab things and interact with them. Patients wore VR goggles and a glove. At the same time small electrodes were placed on the residual limb. The amputee then performed a number of tasks such as grabbing a pole that has to be twisted into different shapes or pushing different virtual buttons.

Clinical trials were undertaken on 3 patients at the China Rehabilitation Research facility in Beijing: two patients felt their PLP had eased whereas the third experienced a decrease in the frequency of attacks.

At the moment the system only works for upper body amputees although I understand that a version is currently being developed for lower limb amputees.

Encouraging signs but it remains very early days. There is still academic debate as to how exactly mirror therapy works and, whilst a recent study which undertook a literature review Virtual and Augmented Reality in the Treatment of Phantom Limb Pain by Dunn et al noted almost universal improvement, it was recorded that the studies were, in reality, all just case studies and / or case report series. No studies of ‘higher evidence’ (i.e. why it works) had been conducted thus limiting the strength of the findings.

As with so many things VR we are at the start of a journey where researchers and clinicians are attempting to use this technology to push the boundaries of treatment. One to watch but my feeling is that there is growing momentum which will lead to more and more research being published in the relatively near future.

Exciting times… maybe Samsung are right? Can’t is only what you can’t do yet !!

Further Reading