Long-term growth and risk factors for crankshaft phenomenon following posterior hemivertebra resection with mono-segment fusion in congenital early-onset scoliosis.

BACKGROUND

Congenital early‑onset scoliosis (CEOS) resulting from hemivertebra presents critical challenges in pediatric orthopedics due to asymmetric spinal growth and progressive deformity. While posterior hemivertebra resection (HVR) with mono-segment fusion has demonstrated efficacy in correcting spinal deformities, the long-term growth patterns of vertebral structures and risk factors for the crankshaft phenomenon remain poorly characterized. This study uniquely investigates differential growth trajectories in the anterior and middle spinal columns between patients with and without postoperative crankshaft phenomenon, while identifying modifiable surgical risk factors.

METHODS

We retrospectively analyzed 31 CEOS patients (age < 10 years) with single hemivertebra undergoing single‑stage posterior HVR and mono‑segment fusion between 2003 and 2019. Radiographic parameters were vertebral body height (VBH), interpedicular length (IPL), and anteroposterior diameter of the vertebral body (VBAP) measured preoperatively and at final follow‑up. Vertebral rotation was graded by the Nash‑Moe method. The crankshaft phenomenon was defined as a progression of ≥ 10° in either the Cobb angle or the rib-vertebra angle difference (RVAD). Statistical comparisons employed Welch's t‑test and Fisher's exact test, while multivariate logistic regression evaluated potential risk factors.

RESULTS

The mean age at surgery for all patients was 4.66 ± 1.94 years, and the mean follow‑up duration was 8.35 ± 2.82 years. The crankshaft phenomenon occurred in 29.0% (9/31) of patients, with all affected individuals demonstrating grade II or III vertebral rotation versus none in the non‑crankshaft group (p < 0.001). Although VBH, IPL, and VBAP increased significantly in all vertebrae (p < 0.05), there were no significant differences between the crankshaft and non‑crankshaft groups in terms of final follow‑up values, absolute growth, or growth rate. Multivariate analysis identified incomplete hemivertebra resection as the predominant risk factor (OR = 18.85, 95% CI: 2.65-251.66, p = 0.002).

CONCLUSIONS

In CEOS patients treated with posterior HVR and mono‑segment fusion, VBH, IPL, and VBAP increased significantly in both the crankshaft and non‑crankshaft groups; however, aside from more pronounced vertebral rotation in the crankshaft cohort, there were no significant differences between the two groups in terms of final follow‑up measurements, absolute growth, or growth rates. Complete resection of the hemivertebra is essential to minimize the risk of crankshaft phenomenon in these patients. A meticulous surgical technique and vigilant long‑term surveillance are recommended to minimize the likelihood of the crankshaft phenomenon.

TRIAL REGISTRATION

This study is a retrospective analysis and was not prospectively registered.