Incidence of the Crankshaft Phenomenon in Thoracic Congenital Early-Onset Scoliosis Patients Followed Until Skeletal Maturity

BACKGROUND AND OBJECTIVES: Patients who undergo posterior spinal fusion (PSF) surgery before puberty are at high risk of experiencing the crankshaft phenomenon. Currently, there are no studies reporting the incidence of crankshaft phenomenon in a highly homogeneous cohort of patients with thoracic congenital early-onset scoliosis (CEOS) who were followed up to skeletal maturity. The aim of this study was to reveal the real incidence and identify the risk factors associated with the crankshaft phenomenon in CEOS patients who underwent pedicle screw fixation and PSF before the pubertal growth spurt and to explore surgical strategies aimed to prevent this phenomenon. METHODS: Patients who underwent pedicle screw fixation and PSF before the pubertal growth spurt and were followed up until skeletal maturity were enrolled. Coronal and sagittal radiological parameters were evaluated before surgery, immediately after surgery and at the final follow-up. The incidence and risk factors of the crankshaft phenomenon were evaluated according to different parameters. RESULTS: Eighty-one patients (31 men and 50 women) were enrolled, with a mean follow-up time of 97.36 ± 33.03 months (60-192 months). The mean age was 7.24 ± 2.53 years (2-10 years) preoperatively and 15.40 ± 2.07 years (14-25 years) at the last follow-up. The overall incidence of the crankshaft phenomenon was 32.10% (26/81), and 12 of the patients (46.15%) required revision surgery. The incidence of the crankshaft phenomenon significantly increased with the age 5 years and younger (odds ratio = 3.402, P = .038) and number of fused segments <5 (odds ratio = 3.662, P = .028). CONCLUSION: The incidence of the crankshaft phenomenon may have been underestimated before this point, and skeletal maturity could determine the real incidence of the crankshaft phenomenon. The incidence could be as high as 32.10% in thoracic CEOS populations. A younger age (≤5 years old) and short segmental fusion (<5 segments) can help predict the crankshaft phenomenon in thoracic CEOS patients.