Phantom limb pain (PLP) affects a significant number of patients (50 – 85%) following amputation. A degree of non-painful residual tingling or squeezing is described as a phantom sensation, in contrast to phantom limb pain when the missing part becomes painful, cramping or being altered in size or shape.
PLP may often be exacerbated by physical factors such as changes in weather or temperature, or emotional factors such as increased stress. There can be localised nociceptive pain and sensitivity over the stump following amputation; the intensity of stump pain can be positively correlated to the feeling of PLP. Despite this being a commonly recognised problem following amputation, the causes of phantom pain remain poorly understood. With recent developments in the understanding of pain and an awareness of the adaptations that can occur both in the dorsal horn, spinal cord, cingulate and somatosensory cortex, managing phantom limb pain becomes increasingly complex. In the upper limb, the majority of amputations we see are traumatic, and usually involve the finger or fingertip, in the literature many of the subjects have experienced mid radial amputation of the hand. In these cases patients should be screened for post traumatic stress disorder, as often there are significant psychosocial implications in addition to the adjustment to the new hand aesthetics.
Mirror therapy was first described by Ramachandran in the mid 1990s, claiming that phantom limb pain could be abolished when amputees observed reflected images of the remaining limb, the ‘phantom’ being placed out of sight behind a mirror. Since then mirror therapy has been adopted as a treatment approach both for phantom pain and Complex Regional Pain Syndrome. However, there is still a lack of convincing evidence supporting this approach in the literature (Moseley 2008, Barbin 2016) This may be in part due to the multifactorial nature of pain; mirror therapy in isolation would not normally be the sole treatment – nor should it be. Mirror therapy relies on purely visual feedback.
Prosthetic fingers are becoming increasingly realistic as silicone prostheses become available. These devices help overcome the stigma and psychological impact of these disfiguring injuries. In addition they may help maintain the ‘map’ on the sensorimotor cortex. It has been reported that being able to massage and manipulate prosthetic gloves or digits helps reduce phantom limb pain.
Virtual reality as part of rehabilitation has been receiving increasing amounts of publicity (North and South ‘Pain – surprising new treatments that work’ Nov 2017) A number of studies have examined the usefulness of virtual reality in reducing PLP (Mercier et al 2009, Ortiz-Catalan 2014). In contrast to the visual feedback used in mirror therapy, attempting to move the phantom limb requires the motor cortex to become involved. It has been proposed that being able to ‘move’ the phantom limb out of awkward or uncomfortable positions is related to significant reductions in PLP. Studies have measured electrical activity in the amputated stump whilst patients attempt to move the limbs of an avatar created in a virtual reality (Oritz-Catalan et al 2016) Involving more of the motor cortex responsible for the missing limb has shown to give promising results in the management of PLP, especially where sensations of altered or telescoping sensations of the limb are present. The advantages of virtual reality over the repetitive and somewhat uninteresting exercises during mirror therapy make augmented reality an engaging tool that can be incorporated with gaming, increasing social interaction and a feeling of achievement.
Gaming and Neuroplasticity
Constraint- induced therapy has been proposed as an effective way of modifiying neuroplastic changes following stroke. By immobilising the unaffected limb intense focus is placed on the neural networks controlling movement and sensation of the affected limb. Including an element of competition makes the activities more interesting and challenging. I was lucky enough to observe this in action on a recent visit to the Royal Melbourne Hospital’s Handhub. Whilst catering for patients with neurological problems such as CVA, the patients attended for intense periods of exercises on a number of hand controlled games, including Able-X. Feedback from patients I saw was that the games were challenging and interesting, and had resulted in increased hand functionality – an area that can often be neglected following stroke and brain injury.
This intense focus on a specific activity during a gaming activity is in common with some of the interventions used following peripheral nerve injury rehabilitation and also with the electrode placement on motor control experiments using virtual reality for amputees.