Autofusion in early-onset scoliosis growing constructs: occurrence, risk factors, and impacts

Autofusion (AF) during growing rod (GR) instrumentation for early-onset scoliosis (EOS) has been reported, but AF incidence, causation, and clinical implications remain unknown. This article aims to (1) quantify frequency and severity of AF, (2) determine risk factors for AF, and (3) assess the influence of AF on final curve correction and spinal lengthening.

EOS patients were prospectively enrolled (2016-2021). Patients underwent evaluation, GR implantation, lengthenings, and posterior spinal fusion (PSF). Cobb angle and spinal length measurements were collected. AF was assessed and graded, with grades I-II being low-grade and III-V being high-grade. Exposure analysis quantified risk factors' impact via odds ratios and Pearson regression correlates. Statistical significance was p ≤ 0.05 or ≥ 0.95.

28 patients, with variable EOS diagnoses, were included. On average, GR were implanted at 8.54-year-old and lengthened over 4.66 years. 53.6% of patients received magnetically controlled GR (MCGR) and 46.4% traditional GR (TGR). The average construct bridged 13.4 levels. Over the lengthening period, for all indications, patients averaged 2.9 total open procedures. Curves corrected from 68.5º preoperatively to 35.3º after index GR to 35.6º after PSF. Spinal length increased from 30.0 cm preoperatively to 33.9 cm after index GR to 39.5 cm after PSF. AF grading was: 28.6% Grade I, 25.0% Grade II, 17.9% Grade III, 25.0% Grade IV, and 3.6% Grade V. Idiopathic EOS tended to have lower AF grades (p = 0.37). AF risk factors included GR age < 8 (10.4×, p = 0.01), any interval open procedures (6.3×, p = 0.05), and residual curve > 30º after index GR (13.7×, p = 0.02). Protective factors included preoperative spinal length of > 30.0 cm (0.11×, p = 0.01) and index MCGR (0.16×, p = 0.03). Maintenance of Cobb angles from index GR through PSF was relatively better in low-grade patients (p = 0.08). Spinal length gained was no different between low- and high-grade AF (p = 0.50).

This largest-to-date evaluation found AF is nearly ubiquitous in GR constructs, but with variable severity. Both risk factors and protective factors coincide with AF. Ultimately, even in high-grade AF, curve correction was maintained, and spinal lengthening was achieved.

Level II-prospective cohort study.