Neuromodulation to Reduce Muscle Stiffness Following Spinal Cord Injury

People with spinal cord injuries may experience muscle tightness or uncontrollable spasms. This study is being conducted to investigate whether transcutaneous spinal stimulation can improve these symptoms. Transcutaneous spinal stimulation is a non-surgical intervention by applying electrical currents using skin electrodes over the lower back and belly.

The investigators want to see how well the intervention of transcutaneous spinal stimulation performs by testing different levels of stimulation pulse rates. Also, transcutaneous spinal stimulation is compared to muscle relaxants such as baclofen and tizanidine, commonly given to people with spinal cord injuries, to reduce muscle stiffness and spasms. By doing this, the investigators hope to discover if transcutaneous spinal stimulation similarly reduces muscle spasms and stiffness or if combining both methods works best. This could help improve treatment options for people with spinal cord injuries in the future.

The primary questions to be addressed are whether the intervention reduces muscle stiffness and spasms and alters spinal reflexes:

* Using a 100-Hz (a measure of frequency) transcutaneous spinal stimulation is better than using a 50-Hz.
* Transcutaneous spinal stimulation at 50 Hz differs from a single dose of baclofen.
* Transcutaneous spinal stimulation at 50 Hz differs from a single dose of tizanidine.
* Combining the 50 Hz stimulation with either baclofen or tizanidine decreases spasticity more than just taking the medicine alone.

Participants will visit the Methodist Rehabilitation Center in Jackson, Mississippi, six times over a period of 3 to 5 weeks. During the first visit, the overall health and motor and sensory functions will be assessed following a spinal cord injury. For the next five visits, participants will take a study medication (tizanidine, baclofen, or a placebo). After an hour, they will receive a continuous 30-minute transcutaneous spinal stimulation at either 50 Hz, 100 Hz, or sham. The spinal reflexes and clinical assessments will be evaluated before, during, and after each intervention.

Eligibility Criteria:
Inclusion criteria:

* Age 18 years or older
* History of spinal cord injury
* Time since diagnosis longer than six months
* Presence of spasticity in the lower limbs (≥ 3 on the Numerical Rating Scale of Spasticity Severity \[range from 0 to 10\])
* If needed, agreement to reduce antispastic medication

Exclusion criteria:

* Neurological level of spinal cord injury below T11
* Ventilatory-dependent
* Change in neurological status over the past 2 months
* Rigidity, contraction, or passive range of motion of less than 40 deg in both knee joints
* Botulinum toxin injections in lower extremities in the previous 3 months before enrollment
* Systolic blood pressure at rest lower than 90 mm Hg
* Implanted active devices (e.g., intrathecal baclofen pumps)
* Passive implants (plates, screws) between T11 and L2 vertebras
* Skin conditions precluding placement of electrodes
* Pressure ulcers stage 2 or higher on the gluteal area or lower extremities
* Receiving antibiotics for infections
* Pregnancy
* Difficulty following instructions
* Participation in another study with investigational drugs or devices within the 30 days preceding and during the present study
* Other medical risks/contraindications as determined by the study physicians