The silent segment speaks: functional and clinical impact of concomitant spondylolysis in adolescent idiopathic scoliosis. Retrospective cohort study.

Abstract

While adolescent idiopathic scoliosis is often asymptomatic, emerging evidence indicates that low back pain may affect a subset of patients, challenging the traditional notion of AIS as a painless deformity. This study investigates the prevalence and clinical relevance of spondylolysis in surgically treated AIS patients, highlighting it as a potentially underrecognized factor contributing to persistent symptoms and less favorable outcomes. A retrospective cohort study was conducted involving 160 AIS patients (median age: 15 years; 81.3% female) who underwent posterior spinal fusion between 2015 and 2022 with a minimum follow-up of 2 years, thereby ensuring methodological consistency with standard reporting guidelines. Patients were stratified into two groups based on the presence or absence of bilateral pars interarticularis defects, confirmed via X-ray, CT and MRI. Clinical assessments included Visual Analog Scale (VAS) for pain and Scoliosis Research Society-22 (SRS-22) scores. Radiological evaluations encompassed MRI (T2 signal loss, Modic changes), CT (sclerosis), and radiography. Surgical variables such as operative time, intraoperative blood loss, and incidence of distal junctional kyphosis (DJK) were recorded. Concomitant spondylolysis was observed in 7.5% of AIS patients, highlighting its clinical significance. Patients with spondylolysis demonstrated significantly worse postoperative outcomes. VAS scores remained elevated postoperatively (median: 6(95% CI 5.5-6) vs. 3(95% CI 3-4)), with no meaningful pain improvement (p = 0.738). SRS-22 pain and activity domain scores were significantly lower in the spondylolysis group (p < 0.001). Radiologically, all spondylolysis patients exhibited structural degeneration (T2 attenuation, Modic changes, CT sclerosis), which was absent in controls (p < 0.001). The presence of pars defects correlated with greater apical vertebral rotation (p = 0.028), increased blood loss (p = 0.010), and a markedly higher incidence of DJK (33% vs. 0%, p < 0.001). Delta analysis of SRS-22 scores confirmed diminished postoperative gains in pain (p < 0.001), activity (p = 0.003), and total score (p = 0.021) for patients with spondylolysis. This study establishes spondylolysis as a clinically impactful comorbidity in adolescent idiopathic scoliosis, associated with increased postoperative pain, dysfunction, and distal junctional complications. Routine preoperative identification and tailored surgical strategies are warranted. By positioning pars defects as modifiable risk factors, our findings support a paradigm shift toward biomechanically-informed, individualized approaches in AIS surgical planning and long-term management.