Upper Limb Rehabilitation Using Non-invasive Spinal Cord Stimulation

This test will be used to assess the hand function in participants, particularly their grasping ability and object manipulation. This includes two components: prehension ability (PA) and prehension performance (PP).

PA evaluates the capacity to perform different grasp patterns, including cylindrical, lateral pinch, and tip pinch grasps. Each hand is assessed separately and scored on a scale from 0 to 4, with 4 being the normal voluntary control of the wrist and fingers during grasp execution.

PP assesses the ability to complete functional tasks requiring grasp, manipulation, and release of objects of various shapes and sizes. Each hand is evaluated separately, and task performance is scored from 0 to 5, with 5 being the most successful task completion using the intended grasp pattern.

Higher total scores indicate better hand function and prehension ability.

The subtest has excellent test-retest reliability (ICC = 0.93-0.98) and excellent inter-rater reliability (ICC = 0.95-0.96).

This will be used to assess the sensory level of the participant by evaluating the ability to feel stimuli and to differentiate between sharp and dull sensations (pinprick test) on specific regions of the skin corresponding to spinal nerve segments.

The summed sensory scores (light touch + pinprick) have good to excellent inter- and intra-rater reliability. So, we will use the summed scores. The test has good validity for classifying lesion level and severity, moderate for predicting function, and has limited sensitivity (not sensitive to subtle changes) compared to electrophysiological or quantitative tests.

Light touch and pinprick sensation are first demonstrated on the participant's cheek. The participant, seated with eyes closed, is tested using light touch with tissue or cotton (assessing large A fibers) and pinprick with a pin or toothpick (assessing smaller A-delta and C fibers for superficial pain) at six test sites. The sensation is reported by them.

This will be used to quantify and to assess the sensory function, particularly for detecting areas of sensory loss or abnormal sensation (neuropathic pain). This test has high validity and inter-and intra tester reliability in participants with chronic cervical spinal cord injury.

The test is conducted using Semmes-Weinstein monofilaments. With eyes closed, the participant is asked to report whether they can feel the pressure when a monofilament is applied to different regions of the upper limb. The threshold at which the stimulus is perceived is recorded (5.88, 5.07, 4.56, 4.08, 3.22). Specific regions are assessed depending on the nerve: the pulp of the middle finger for the median nerve, the pulp of the little finger for the ulnar nerve, the first dorsal space of the hand between the thumb and index finger and the lateral epicondyle at the extensor compartment for the radial nerve, and the deltoid region for the axillary nerve.

This will be used to assess grip and pinch strength which are used in daily tasks involving hand function. The Pinch strength test has good to excellent reliability for neurological conditions and has strong to very strong correlations with grip strength. It has a good validity.

The Grip strength has an excellent test-retest reliability in SCI. It shows a very high intra- and inter-rater reliability if standardized protocols (same dynamometer, position, instructions) are followed. It has a good validity.

Grip strength is measured using a dynamometer, with the participant seated and the elbow flexed at 90 degrees. The participant must squeeze the device as hard as possible for 3 trials; the average of these trials is calculated. Pinch strength is measured using a pinch gauge, where the participant pinches an object between the thumb and index finger with maximum effort. Again, the average of 3 trials is taken.

This test is used to the assess the ability to sense the position of the limbs in space, important for evaluating proprioceptive deficits that can affect balance and coordination.

It has a moderate overall and inter-rater reliability and depends strongly on the therapist's technique. Intra-rater reliability is better but is variable as participants can have fatigue or guess. Test-retest reliability is lower than that of dermatomes or motor scores.

It has a limited validity; construct validity is supported and concurrent validity shows moderate correlation with function; criterion validity is limited.

The participant is blinded while the therapist moves their upper limb (shoulder, elbow, and wrist) to a specific position and asks them to replicate the position with the opposite limb or to report the position. Results are reported as the difference between the actual and replicated positions.

This test is used to assess the ability to perform smooth, controlled movements, critical for fine motor tasks (e.g. writing, buttoning a shirt).

Its reliability is generally low to moderate: intra-rater reliability is variable as it depends on the therapist scoring, inter-rater reliability is moderate at best, and test-retest reliability is limited since coordination can fluctuate with fatigue, spasticity, or attention.

Validity is also limited, with moderate construct validity, low to moderate concurrent validity, and limited criterion validity.

The standard finger-to-nose test is used: the participant is asked to touch a target with the index finger and then their nose, repeating the movement five times at a fast but comfortable pace. The therapist observes for tremors, uncoordinated movements, delays, and scores performance using a 12-point scale per side that considers precision, fluidity, arm movement, and trunk stability.

TEPs will be measured through single-pulse transcutaneous spinal stimulation (tSCS). The cathode (Dura stick plus double wire, Dura stick, USA) will be positioned at the midline over C4-T1 and anode over the external part of the clavicles (TENS electrodes, ROHVEMJ). Single-pulse tSCS will be delivered using a constant-current stimulator (DS8R, Digitimer, UK) with monophasic square-wave pulses of 1ms at a frequency of 0.2Hz to induce TEPs. Responses will be recorded from surface electromyography. Stimulation intensity will be gradually increased from 0 to evoke a potential in all, or in the maximum number of upper limb muscles recorded. Two of the outcome measures will be for each muscle: the motor threshold, i.e., the lowest intensity inducing 5/10 stimulation responses; and the recruitment curve. The third measure will include amplitude, latency, and duration of the TEP at 120% of the motor threshold, determined for the myotome that showed the smallest response.

This neurophysiological assessment will be done to test if there are neuroplastic changes because of the ABT + tSCS training. TMS will be applied to the primary motor cortex (M1) over the representation area of the contralateral bicep brachii muscle (this is the target muscle). A figure-8 shaped coil will deliver the magnetic field to activate motor nerves, leading to the activation of the target muscle. This response will be recorded painlessly using surface electromyography electrodes placed over the targeted muscle. Four 5-minute stimulation sets, each separated by 2-minute rest periods, will be conducted. The entire evaluation, including setup, will take approximately one hour. The responses evoked by TMS, that is, the motor evoked potentials, (MEPs) will be compared across the 3 time frames in each group. Quantitative parameters will include MEP amplitude (magnitude), and latency, serving as indicators of cortico-spinal excitability changes pre- and post-intervention.

This test will also be done for neuroplastic evaluation. SSEPs are time-locked EEG responses reflecting sensory pathway conduction from peripheral nerves to the somatosensory cortex. Participants will be comfortably seated in a chair. For each arm, the median nerve will be stimulated using surface electrodes placed near the wrist to elicit upper-limb SSEPs. EEG will be recorded with a 32-channel cap (Brain Vision Recorder 2.0) following the 10-20 system, referenced to Fz. During a 10-minute session for each arm, 1800 stimuli (3 Hz, 0.001 s duration) will be delivered at 5% of the maximal flexor carpi radialis response. EEG signals will be sampled at 5000 Hz and analyzed in BrainVision Analyzer using filtering and averaging. Primary regions of interest include C3/C4 and adjacent electrodes (Cz, C1/2, FCz). The expected SSEPs are N20 (~20 ms) and P25 (~25 ms). The presence, amplitude, and latency of the N20-P25 complex will serve as measures of somatosensory pathway excitability.