Response to Letter to the Editor Regarding “Safety and Efficacy of Magnetically Controlled Growing Rods for Early-Onset Scoliosis in the Era of Disease-Modifying Therapies: Mid-Term Results in a Homogeneous Cohort of Spinal Muscular Atrophy Type I Patients”

We welcome the opportunity to address the insightful inquiries raised by Dr. Skaggs and colleagues regarding our recent study on magnetic controlled growing rod (MCGR) constructs in patients with Spinal Muscular Atrophy (SMA). To clarify our patient demographics, no individuals in our cohort experienced a loss of ambulatory status following pelvic instrumentation because all patients had severe, genetically confirmed SMA Type I and were strictly non-ambulatory prior to surgical intervention. The introduction of disease-modifying therapies (DMTs) has radically reshaped the natural history and survival rates of SMA Type I, allowing these children to achieve unprecedented motor milestones; however, they remain highly susceptible to aggressive early-onset scoliosis combined with profound neuromuscular pelvic obliquity. In this specific non-ambulatory clinical landscape, extending spinal instrumentation to the pelvis remains a biomechanical necessity to establish a stable and symmetric sitting foundation, ensure uniform weight distribution, and prevent severe, posture-induced truncal decompensation. Furthermore, when assessing functional mobility and ambulatory decline in stronger SMA variants (Types II and III), it is essential to distinguish surgical biomechanics from the confounding bias of natural, time-dependent disease progression mismatched with adolescent weight gain. While preserving lumbosacral motion remains ideal for pre-operative ambulatory patients, an MCGR construct extended to the pelvis provides predictable coronal alignment and spinal growth accommodation safely for non-ambulatory SMA Type I sitters within the modern post-DMT era. Key concepts • In our cohort of patients with Spinal Muscular Atrophy (SMA) Type I, no cases of ambulatory loss were observed following pelvic fixation because all individuals were strictly non-ambulatory prior to spinal surgery. • The integration of modern disease-modifying therapies (DMTs) has dramatically improved the long-term survival and motor milestones of children with SMA Type I, although aggressive early-onset scoliosis with severe pelvic obliquity remains a frequent structural complication. • Extending spinal instrumentation to the pelvis is a biomechanical necessity in non-ambulatory SMA Type I sitters to establish a stable sitting foundation, ensure balanced weight distribution, and prevent severe posture-induced truncal decompensation. • Evaluating ambulatory status post-surgery requires careful stratification by specific SMA subtype and ongoing DMT timeline to avoid the significant confounding bias introduced by natural, time-dependent neuromuscular disease progression.