Efficacy and Mechanisms of Virtual Reality Treatment of Phantom Leg Pain

After amputation of an arm or leg, up to 90% of subjects experience a "phantom limb", a phenomenon characterized by persistent feelings of the missing limb. Many subjects with a phantom limb experience intense pain in the missing extremity that is often poorly responsive to medications or other interventions. The proposed work will contrast the efficacy of two virtual reality treatments for phantom limb pain: a 'Distractor' and an Active VR treatment. In the Distractor treatment, participants are engaged in a visually immersive virtual reality experience that does not require leg movements (REAL i-Series® immersive VR experience). In the Active VR treatment, subjects play a series of VR games using the virtual rendering of both legs.

Almost 2 million people in the US have had an amputation and up to 90% of people with limb amputation experience the persistent sensation of the missing extremity, a phenomenon known as a "phantom limb" (Weeks et al., 2010). Additionally, a significant proportion of individuals with a phantom limb - up to 85% in some studies - experience persistent and debilitating pain in the missing limb, a condition known as phantom limb pain (hereafter PLP). Although existing therapies provide pain relief in some cases, there is widespread agreement that current approaches fall short of bringing relief to most individuals with PLP (Weeks et al., 2010). The investigators recently completed a proof-of-concept study (Ambron et al., 2021) in which eight subjects with below knee amputations (BKA) underwent two virtual reality (VR) treatments for PLP. In an Active VR treatment, subjects played a variety of active games requiring leg movements while receiving high-quality visual feedback of the missing lower leg. Feedback about leg position was provided via an electromagnetic system using leg sensors (trackSTAR, Ascension Technologies Inc), and the program generated an image of the missing lower leg, visible as a first-person avatar. This treatment was contrasted with a "Distractor" treatment, in which participants were engaged in a visually immersive virtual reality experience that did not require leg movements (Cool!TM). Both treatments were associated with significant reductions in pain intensity, but the Active VR treatment was also associated with reductions in pain interference, depression, and anxiety. The specific aims of the current study are (i) to replicate our prior observations of efficacy of VR treatment in a larger sample of individuals with BKA; (ii) to test VR therapy in patients with above knee amputations; (iii) to compare the efficacy of Active VR treatment to Distractor VR treatment for PLP on measures of pain as well as psychological health and quality of life.

Forty individuals with above (AKA) or below (BKA) knee amputation suffering from chronic phantom limb pain (PLP) will be recruited and will be quasi-randomly assigned to Active VR versus Distractor VR treatments in 50:50 ratio.

Subjects assigned to the Active VR treatment will begin by selecting an avatar, with features such as gender and skin color that can be chosen according to preference. During treatment, they will participate in a variety of games and activities developed and used by our teams including Kick, Dog Food, Quest for Fire, Chess, Checkers, Sudoku, and surfing the internet. Subjects will have substantial flexibility to select games according to their interests but will be required to spend at least 30 minutes in each session in games that require forceful, large amplitude, movements of the amputated lower limb (e.g., Quest for Fire, Kick). Time spent and level of engagement as measured by movements of the avatar or, in the case of chess, checkers, solitaire, Sudoku, and internet surfing, the number of clicks produced with each leg will be recorded for each activity using custom software

Subjects assigned to the Distractor VR treatment will participate in REAL i-Series immersive VR experience (REAL system), which has been demonstrated to reduce pain in several studies but lacks the hypothesized "active ingredients" of our Active VR treatment (visual and auditory feedback of movement of an extrapolated amputated limb). Subjects will navigate through pleasant and relaxing VR environments; they will not see any rendering of their body and make no movements with their legs

8 twice-weekly interventions of 1 hour; baseline, pre-intervention; immediately after the end of the in intervention; 1 week after the end of the intervention; 8 weeks after the end of the intervention

Visual Analogue Scale of McGill Short Form Questionnaire (Melzack, 1987); 0 minimum score - 10 maximum score; higher scores indicate higher level of pain (worse outcome)

pre each intervention (8 sessions); immediately after each intervention (8 session); baseline, pre-intervention; immediately after the end of the intervention; 1 week after the end of the intervention; 8 weeks after the end of the intervention

McGill Short Form Questionnaire (Melzack, 1987): a series of 4-point scales assessing 15 characteristics of pain (e.g., throbbing, shooting, cramping, etc.). It generates separate scores for Sensory, Affective, and Total pain (maximum 78 points), and correlates strongly with the well-known long form of the questionnaire

baseline, pre-intervention; immediately after the end of the intervention; 1 week after the end of the intervention; 8 weeks after the end of the intervention

average pain intensity since the previous intervention on an 11-point numerical rating pain scale; (0 - minimum score/no pain; 10 maximum score/pain as bad as participants can imagine); higher scores indicate higher level of pain (worse outcome)

The Frenchay Activities Index (FAI) (Holbrook et al., 1983):1983): a scale measuring the physical function and daily activity that has excellent reliability in subjects with lower-limb amputation in predicting quality of life (Asono et al., 2008). 0 minimum score - 45 maximum score; higher scores indicate more daily activities (better outcome).

baseline, pre-intervention; immediately after the end of the intervention; 1 week after the end of the intervention; 8 weeks after the end of the intervention

The 12-Item Short Form Health Survey (SF-12) (Ware et al., 1996): a brief measure of quality of life and functional capacity that has been validated in patients with amputation and PLP (Padovani et al., 2015; Chen et al., 2012; Pape et al., 2010). 0 minimum score - 100 maximum score. Higher scores indicate lower physical and mental health (worse outcome).

baseline, pre-intervention; immediately after the end of the intervention; 1 week after the end of the intervention; 8 weeks after the end of the intervention

The Pain Interference Scale from the Brief Pain Inventory (BPI) (Cleeland & Ryan, 1994): this assesses the degree to which pain interferes with daily activities using a 0-10 numeric rating scale. 0 minimum score - 10 maximum score. Higher scores indicate higher pain interference (worse outcome).

baseline, pre-intervention; immediately after the end of the intervention; 1 week after the end of the intervention; 8 weeks after the end of the intervention

The Hospital Anxiety and Depression Scale (HADS) (Zigmond & Snaith, 1983):1983): the HADS is a 14- item measure assessing both depressive and anxiety symptoms. In addition to providing separate scores for anxiety and depression, the HADS also provides a measure of global negative affect. 0 minimum score - 42 maximum score. Higher scores indicate more depression and anxiety (worse outcome)

baseline, pre-intervention; immediately after the end of the intervention; 1 week after the end of the intervention; 8 weeks after the end of the intervention

The 13-item Pain Catastrophizing Scale (Sullivan et al., 1995): this scale investigates pain catastrophizing, which has been highly associated with pain severity and disability after amputation (Hanley et al., 2004; Whyte & Carroll, 2004; Jensen et al., 2002). 0 minimum score -52; Higher scores indicate higher tendency to catastrophizing (worse outcome)

baseline, pre-intervention; immediately after the end of the intervention; 1 week after the end of the intervention; 8 weeks after the end of the intervention

Insomnia Severity Index (Bastien et al., 2001): this is a 7-point scale that measure insomnia, a symptom associated with PLP (Durmus et al., 2015). 0 minimum score - 28 maximum score; higher scores indicate more insomnia (worse outcome)

baseline, pre-intervention; immediately after the end of the intervention; 1 week after the end of the intervention; 8 weeks after the end of the intervention

Technology Acceptance Scale (Morris et al., 1997): this is a 7-point scale that measure level of acceptance of the VR system. 0 minimum score - 133 maximum score; higher scores indicate low level of acceptance (worse score)

System Usability Scale (SUS) (Brooke, 1996); Scale measuring the usability of each game; minimum score 10 - maximum score 50. Higher scores indicate less usability (worse outcome).

Brief Slater-Usoh-Steed Presence Questionnaire (Usoh et al., 2000; Slater et al., 1998; 1994). 7 minimum score - 42 maximum score. Higher scores indicate more presence in the VR (better outcome

The Modified Limb Deficiency and Phantom Limb Questionnaire (Goller et al., 2013): this questionnaire assesses prosthesis type and usage and non-painful phantom limb experiences, including perceived position (e.g., telescoping) and ability to move the phantom. In addition to providing useful descriptive information, prosthesis use and telescoping will be used in the adaptive randomization algorithm to assign subjects to treatments.

baseline, pre-intervention; immediately after the end of the intervention; 1 week after the end of the intervention; 8 weeks after the end of the intervention

visual analogue scale that evaluates treatment satisfaction (Robinson et al., 2004; Smith et al., 2005); 0 minimum score - 10 maximum score; Higher scores indicate more treatment satisfaction (better outcome)

Inclusion Criteria: Age 18 - 100 years Capacity to provide Informed Consent Unilateral above or below knee amputation more than 3 months prior to enrollment Absence of cognitive impairment, operationally defined as a Montreal Cognitive Assessment score of 18 or greater Pain averaged over the preceding 1 month in the phantom limb rated as greater than 4 on a scale of 0-10. Exclusion Criteria: History of significant medical or neurological disorder such as stroke or moderate to severe traumatic brain injury (operationally defined as loss of consciousness for more than 30 minutes) History of significant or poorly controlled psychiatric disorders Current significant depression or anxiety as judged by the Hospital Anxiety and Depression Scale (HADS) (Zigmond & Snaith, 1983). Current abuse of alcohol or drugs, prescription or otherwise Nursing a child, pregnant, or intent to become pregnant during the study

After de-identification, individual participant data to be shared will include descriptors of clinical status (e.g., time since amputation, level of amputation), background test battery results, and outcome measures results.

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