Recent advances in design and actuation have led to important improvements in prosthetic limbs. However, these devices lack a means for providing direct sensory feedback, requiring users to infer information about limb state from pressure on the residual limb. Lack of sensation limits their ability to control the prosthesis and leads to slow gait and increased risk of falling. There is also evidence that lack of sensory feedback contributes to phantom limb pain (PLP), and that electrical stimulation at the dorsal root ganglia (DRG) can reduce PLP. The primary objective of this study is to use commercially available, FDA-cleared spinal cord stimulator (SCS) leads to test the effects of electrical stimulation of the DRG and dorsal rootlets (DR) as a means of restoring naturalistic sensation (e.g. pressure, movement), reducing PLP, and improving gait function in transtibial amputees. We will use stimulation to (1) produce sensations of pressure and joint movement, (2) reduce PLP, (3) evoke patterns of muscle activity that mimic automatic responses that occur normally during standing and walking, and (4) improve postural stability when standing and walking with a sensorized prosthesis.
Aim 1 : Use stimulation of the DRG/DR to generate naturalistic sensations of pressure and joint movement, localized to the amputated limb, and achieve a clinically relevant reduction in phantom limb pain To provide intuitive feedback, evoked sensations should be perceived as originating in the amputated limb and should feel naturalistic. A concomitant reduction in PLP may also have important effects on quality of life. We will perform detailed psychophysical testing in which stimulation parameters are varied while study participants are asked to report information about the evoked sensation (e.g. location, modality, naturalness) and the effects on PLP.
Aim 2 : Characterize the motor responses in the intact and amputated limbs evoked by DRG/DR stimulation and their relationship to stimulation parameters Bilaterally coordinated reflexes play an important role when responding to unexpected perturbations like slips and trips. Additionally, the transitions between phases of gait are largely mediated by reflexive responses to sensory input from the legs. For a prosthesis to restore the full capabilities of the amputated limb during standing and walking, the ability to evoke and precisely control these patterns of reflexive activity will be critical. We will record electromyogram (EMG) signals from the limbs during standing and walking while varying stimulus patterns and quantify the relationships between stimulation parameters and evoked reflexive responses. Understanding these relationships will aide in the programming of stimulation patterns for functional prosthesis use.
Aim 3 : Decrease postural sway and increase gait stability by providing sensory feedback via DRG/DR stimulation To quantify the functional impact of sensory restoration on prosthetic limb usage, we will instrument each participant's prosthetic limb with a pressure sensitive insole and joint angle sensors, and use signals from these devices to modulate stimulation. We will perform a battery of posture and balance measures, and we will track changes in functional prosthesis usage after a 7-day take-home trial of the device.
The impaired sensory function that results from lower-limb amputation often causes reduced balance control, an increased risk of falling, and severe phantom limb pain. Electrical stimulation of the nerves in the lower back, near the spinal cord, known as dorsal root ganglia and dorsal rootlets, may reduce phantom limb pain and generate naturalistic sensations of touch and limb movement. We will examine the effects of these sensations on phantom limb pain, motor responses, balance control and functional use of a prosthesis in individuals with transtibial amputation.
