The effects of graded motor imagery and its components on phantom limb pain and disability in upper and lower limb amputees: a systematic review protocol

Amputation is the removal of a body extremity which is generally caused by severe trauma, circulatory disorders, neoplasm, deformities and infection of the limb. In case of gangrene, infection or neoplasm, amputation is carried out as a control strategy for pre-operative pain or a disease process in the affected limb; in some cases, however, amputation surgery is performed as a preventative procedure for the abovementioned complications [31]. Despite this attempt to alleviate patients’ pain and disability, up to 80 % of amputees report phantom limb pain (PLP) post-amputation surgery [8]. PLP is defined as persistent painful sensations perceived in the missing portion of the amputated limb [7]. Previous research associates PLP with peripheral changes such as increased nociceptive input from the residual limb [39] and reduced near-surface blood-flow [34]. However, recent evidence suggests that PLP is a sensory output primarily driven by cortical changes in the brain [10]. Neuroimaging studies of patients with PLP revealed neuroplastic alterations of the somatotopic organization of the cortical and sub-cortical areas of the brain [9, 13]. These changes are characterized by the anatomical shifting of neighbouring somatosensory [18] and motor [4] areas into a deafferented cortical area of the brain contralateral to the amputated limb. Furthermore, these neuroplastic changes are positively correlated to the severity of PLP [15, 17]. These neuroplastic alterations can be reverted, with a correlation between the reversal of neuroplastic changes and pain relief in amputees with PLP [1, 11, 20].

Graded motor imagery (GMI) is a treatment strategy which has been shown to mitigate the severity of PLP and disability using a sequence of strategies including laterality recognition, explicit motor imagery and mirror visual feedback [22].

Laterality recognition, the ability to distinguish left from right, is dependent on the intact body schema in the brain and is important in the planning of movement [32]. This left/right judgement is inaccurate and delayed in amputees with PLP [25]. In this first phase of GMI, images representing the amputated limb are presented randomly on a computer screen. The patient is then instructed to match the side of the presented limbs by pressing either the left or right key. During this task, emphasis is put on accuracy and speed.

Laterality recognition is alternately known as implicit motor imagery, primarily because the patient is unconscious of mental movement processes involved to match the limb presented on the computer screen [5].

During the explicit motor imagery phase of GMI, the patient mentally moves the amputated limb to adopt a desirable posture presented on the computer screen [14].

The last strategy of GMI is mirror visual feedback, during which the amputated limb is concealed behind a mirror with the intact limb positioned comfortably in front of the mirror. This superimposes the ocular image of the intact limb on the phantom limb [28]. The patient is shown a picture of the unaffected limb in an easy to attain position. The patient then simultaneously moves the intact limb and the phantom limb (through imagination) to the presented position while observing the reflection of the intact limb in the mirror. This phase can commence with gross movements, progress to fine motor tasks and ultimately functional tasks.

GMI is consistent with sequential activation of cortical premotor and motor networks [23]. The GMI intervention is founded on the principle of graded increase in activity, similar to that implemented in physiotherapy treatment modalities [2]. This graded exposure to activity aims to promote cortical re-organization without triggering the protective pain response.

Laterality recognition/implicit motor imagery tasks activate premotor and supplementary motor areas, with an exception of the primary motor (M1) cortex [24]. Laterality recognition is therefore fundamental in preparation for subsequent phases of the GMI programme.

Explicit motor imagery activates the somatosensory (S1), premotor and M1 cortices contralateral to the phantom limb [17]. Activation of these areas is proposed to alleviate the perception of pain associated with imagination and observation of movement. This phase builds upon laterality recognition and serves as a foundation for the successive GMI phase.

Mirror visual feedback addresses changes in the S1 and M1 cortices [26]. In addition, it provides visual input to the brain, that movement is executed normally without inhibition [21]. The therapeutic effect associated with mirror visual feedback may be due to activation of mirror neurons in the brain hemisphere contralateral to the amputated limb [3]. These mirror neurons have been shown to fire during observation and execution of movement [16, 30].

Several studies [3, 19, 20, 22, 36, 38], investigating the effectiveness of GMI and its different components on PLP, have drawn contrasting conclusions regarding the efficacy and applicability of GMI in clinical practice.

This systematic review will therefore gather and critically appraise all relevant data, to generate a substantial conclusion and recommendations for clinical practice and research on this subject.

It is important to note that Plumbe and associates have published a protocol with a similar topic. Despite this similarity, there is a significant distinction between the two protocols. In their review, Plumbe et al. [27] indicate that they will investigate the efficacy of GMI on chronic pain. However, this review will explore the effects of GMI and its components, specifically on PLP and disability. Bowering et al. [2] conducted a systematic review on a topic of interest. However, there is a need to update their review as there have been new studies since their publication.