Study of an Intrathecal Port and Catheter System for Subjects With Spinal Muscular Atrophy

Inclusion Criteria: 1. Subject is 3 years or older 2. Subject diagnosed with SMA who are candidates for Spinraza treatment as indicated in its label 3. Subject resistant to lumbar puncture (LP), where resistance is defined as: 1. Subject with respiratory issues or other comorbidities who is at an increased risk for complications due to the need for repeat anesthesia and imaging radiation exposure to safely perform LP; or 2. Subjects for whom the treating physician determines implantation of the ThecaFlex DRx™ System is otherwise in the subject's best interest 4. Subject has been prescribed nusinersen via chronic intrathecal bolus administration in accordance with the drug labeling and first port access of the ThecaFlex DRx system is planned within 2 weeks of implantation 5. Subject, per Investigator discretion, is able to undergo a percutaneous or open surgical procedure for index port and catheter implantation where at least 7 cm of the ThecaFlex DRx system catheter will be placed intrathecally 6. Subject (or subject's legally authorized representative) is willing and able to provide written informed consent; and 7. Subject and parent/caregiver able and willing to complete all clinical investigation procedures, measurements, and visits. Exclusion Criteria: 1. Subject meets any of the contraindications for use of the ThecaFlex DRx™ System as outlined in the ThecaFlex DRx™ System Instructions for Use 2. Presence or history of (\< 6 months prior to the procedure): an implanted microinfusion pump, intrathecal catheter, or other intrathecal drug delivery devices/component, or implanted shunt for drainage of cerebrospinal fluid (CSF), or reservoir in the CSF space (note: any ThecaFlex Port and Catheter System must not be placed in the same location as a previous indwelling port and catheter) 3. Subject is pregnant or nursing or plans to become pregnant during the course of the clinical investigation 4. Any condition or event, which in the opinion of the Investigator may adversely affect the safety and effective implantation and use of the ThecaFlex DRx™ system or confound the clinical investigation, including: 1. Severe structural impediment that may preclude safe implantation of the catheter and port 2. Major medical events within 60 days prior to screening; or 3. Relevant surgeries (e.g., head and neck, back, etc.) within 60 days prior to screening or planned during the duration of the clinical investigation 4. Space-occupying lesion with mass effect 5. Posterior fossa mass 6. Arnold-Chiari malformation 7. Coagulation abnormalities and/or thrombocytopenia 8. Insufficient or inadequate skin or underlying fat to adequately protect the port or enough surface area to allow the skin to close safely 5. Subject is contraindicated for administration of nusinersen per its approved labeling 6. History of intrathecal granuloma formation 7. History of bacterial meningitis or aseptic meningitis within 6 months of screening 8. History of tumors or other spinal abnormalities documented by magnetic resonance imaging (MRI) or computed tomography (CT) that would interfere with the catheter implantation procedures or CSF circulation 9. History of hydrocephalus 10. Diagnosed degenerative muscular disease other than SMA 11. History of depression, cognitive impairment, or another psycho-behavioral problem that in the opinion of the Investigator may preclude safe participation in the clinical investigation and 12. Serious medical condition that, in the opinion of the investigator, may lead to reduced life expectancy beyond 12 months. 13. Subject is involved in another Investigation Device Exemption Study.