Comparison of Distal Spine Anchors and Distal Pelvic Anchors in Children with Hypotonic Neuromuscular Scoliosis Treated with Growth-friendly Instrumentation

Background: Lower preoperative pelvic obliquity (PO) and L5 tilt have been associated with good radiographic outcomes when the fusion ended short of the pelvis in children with neuromuscular scoliosis (NMS). Our purpose was to identify indications to exclude the pelvis in children with hypotonic NMS treated with growth-friendly instrumentation. Methods: This was a multicenter retrospective review. Children with spinal muscular atrophy and muscular dystrophy treated with dual traditional growing rod, magnetically controlled growing rod, or vertical expandable prosthetic titanium rib with minimum 2-year follow-up after the index surgery were identified. Results: A total of 125 patients met the inclusion criteria. Thirty-eight patients had distal spine anchors (DSAs) and 87 patients had distal pelvic anchors (DPAs) placed at the index surgery. Demographics and length of follow-up were similar between the groups but there was a greater percentage of DPA patients who were nonambulatory [79 patients (91%) vs. 18 patients (47%), P<0.0001]. Preindex radiographic measures were similar except the DSA patients had a lower PO (11 vs. 19 degrees, P=0.0001) and L5 tilt (8 vs. 12 degrees, P=0.001). Postindex and most recent radiographic data were comparable between the groups. There was no difference in the complication and unplanned returns to the operating room rates. Subanalysis of the DSA group based on ambulatory status showed similar radiographic measures except the ambulatory patients had a lower PO at all time points (preindex: 5 vs. 16 degrees, P=0.011; postindex: 6 vs. 10 degrees, P=0.045; most recent follow-up: 5 vs. 14 degrees, P=0.028). Only 1 ambulatory DSA patient had a PO ≥10 degrees at most recent follow-up compared with 6 nonambulatory DSA patients. Three (8%) DSA patients, all nonambulatory, underwent extension of their instrumentation to the pelvis. Conclusions: Pelvic fixation should be strongly considered in nonambulatory children with hypotonic NMS treated with growth-friendly instrumentation. At intermediate-term follow-up, revision surgery to include the pelvis was rare but DSAs do not seem effective at maintaining control of PO in nonambulatory patients. DSA and DPA were equally effective at maintaining major curve control, and complication and unplanned returns to the operating room rates were similar. Level of Evidence: Level III - therapeutic.