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Background: It is unclear whether the type of proximal anchor affects the spine length achieved with distraction-based surgeries in patients with nonidiopathic early-onset scoliosis (EOS). Since distraction may produce kyphosis, spine length should be assessed in the sagittal plane using the sagittal spine length (SSLcurved arc length of the spine in the sagittal plane). Our purpose was to determine if the type of proximal anchor in distractionbased surgeries will affect final spine length. Methods: Patients with nonidiopathic EOS treated with distraction-based systems (minimum 5 y follow-up, 5 lengthenings) were identified from 2 EOS registries. Radiographic analysis preoperative, postimplant (L1), and after each lengthening (L2-L5, L6-L10, L11-L15) was performed with the primary outcome of T1-S1 SSL. Results: We identified 126 patients-70 had rib-based implants (52 congenital, 9 syndromic, 9 neuromuscular) and 56 had spine-based implants (15 congenital, 29 syndromic, 12 neuromuscular) with preoperative age 4.6 years, scoliosis 75 degrees, and kyphosis 48 degrees. After initial correction (P < 0.05), scoliosis remained constant [58 degrees (13 to 104 degrees) at L11-L15] and kyphosis increased over time [38 degrees (9 to 108 degrees) at L1 to 60 degrees (17 to 134 degrees) at L11-L15] (P < 0.05). Preoperative SSL was higher in the spine-based group (29.6 cm) when compared with the rib-based group (25.2 cm) (P < 0.05). This difference was maintained after initial implantation (spine-based: 32.2 cm vs. rib-based: 26.7 cm, P < 0.05) and at final follow-up (spine-based: 37.0 cm vs. rib-based: 34.4 cm, P < 0.05). As preoperative SSL differed between groups, maximum SSL gains per interval were also normalized to preoperative SSL. There was no statistically significant difference between groups at L1, L2-L5, and L6-L10. However, at L11-L15, the rib-based group achieved a more relative increase in spine length compared with the spine-based group (45% vs. 31%, P < 0.05). Conclusion: At minimum 5 year follow-up, distraction-based surgeries increased spine length for patients with nonidiopathic EOS; regardless of proximal anchor type.

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