Beware of open triradiate cartilage: 1 in 4 patients will lose > 10° of correction following posterior only fusion

Purpose: As 2-year follow-up may not be sufficient to assess the risk of curve progression following fusion in immature patients with adolescent idiopathic scoliosis (AIS), this study reports on 5-year outcomes of AIS patients, factoring in maturity and surgical approach, to determine whether immature patients are at risk of continued curve progression beyond 2 years. Methods: A multicenter database was reviewed for AIS patients who underwent spinal fusion with pedicle screw fixation and who had both 2 and 5-year follow-up. Radiographic and SRS-22 scores were compared between three groups: open triradiate cartilage-posterior fusion (OTRC-P), OTRC-combined anterior/posterior fusion (OTRC–APSF), and closed TRC (CTRC, matched to OTRC-P group). Results: 142 subjects were included (67 OTRC-P, 8 OTRC–APSF, 67 CTRC). Main curve type (p = 0.592) and size (p = 0.117) were not different between groups at all timepoints. Compensatory curve size was similar at all timepoints for OTRC-P and CTRC, with a slight increase for OTRC–APSF from immediate postoperative to 5 years. At 5 years, OTRC-P had > 10° loss of correction in 25% of patients, which was greater than in the CTRC (6%) and OTRC–APSF (0%) groups (p = 0.002). No significant differences were found in loss of correction of the compensatory curve or in SRS-22 scores between groups. Conclusions: Compared to those with CTRC and those treated with anterior/posterior fusion, patients with OTRC treated with posterior fusion had an increased risk of main curve progression greater than 10°, with some continued loss of correction after 2 years. This did not appear to affect patient-reported outcomes.