Purpose: Spinal osteotomies are often essential in the treatment of congenital scoliosis. Risk factors for bleeding in these patients needing extracavitatory approaches, especially hidden blood loss, are sparsely investigated. We aimed to investigate the bleeding characteristics and hidden blood loss in paediatric patients undergoing spinal osteotomies for congenital scoliosis.

Methods: A retrospective analysis identified all patients with congenital scoliosis were retrospectively identified from the prospectively collected spine register from 2010 to 2022. Operative technique, perioperative laboratory results and imaging studies were extracted. The primary outcome was total blood loss including intraoperative, drain output and hidden blood loss.

Results: Fifty-seven children (32 boys) with a mean age of 8.3 years underwent spinal osteotomy for congenital scoliosis. Posterolateral hemivertebrectomy was sufficient in 34 (59%) patients, while vertebral column resection (VCR) was required in 23 patients. Total bleeding averaged 792 (523) ml accounting for 42% of the estimated blood volume. Hidden blood loss accounted for 40% of total bleeding and 21% of estimated blood volume with a mean of 317 (256) ml. VCR was associated with greater intraoperative and total bleeding than hemivertebrectomies (p = 0.001 and 0.007, respectively). After adjusting for patient weight and fusion levels, hidden blood loss was larger in hemivertebrectomies (4.18 vs. 1.77 ml/kg/fused level, p = 0.049). In multivariable analysis, intraoperative blood loss was inversely correlated with preoperative erythrocyte levels. Younger age was associated with significantly greater drain, hidden and total blood loss.

Conclusion: Hidden blood loss constitutes a significant portion (40%) of total bleeding in congenital scoliosis surgery. Younger age is a risk factor for bleeding and the hidden blood loss should be taken into consideration in their perioperative management.