Watchful waiting versus methylprednisolone or polidocanol injections as treatment of simple bone cysts

Aims Simple bone cysts (SBCs) are among the most prevalent benign cystic bone lesions in children. The use of watchful waiting as management is debated, as are the type and timing of injection therapy. This study aims to compare clinical outcomes of watchful waiting and delayed and immediate percutaneous procedures in children with SBCs, together with the efectiveness of methylprednisolone and polidocanol. Methods All eligible paediatric patients with SBCs and minimal one year of follow-up were included from our tertiary musculoskeletal oncology referral centre (January 2000 to December 2024). Outcomes of interest were cumulative incidence of (partial) healing (CI-Healing), cumulative incidence of failure (CI-Failure), and prognostic factors for healing and failure. For CI-Healing, competing risk analysis was performed with failure as the competing event. For CI-Healing and CI-Failure of methylprednisolone and polidocanol, landmark analysis was performed. Prognostic factors were estimated using a multivariate cause-specifc hazard model. Results In total, 160 paediatric patients with SBCs were included (mean age 8.7 years (SD 3.6); 128 (80%) males). Management consisted of watchful waiting (n = 41) and delayed (n = 86) or immediate (n = 33) percutaneous procedure. The median follow-up was 3.4 years (IQR 2.2 to 5.4). CI-Healing was signifcantly higher in immediate percutaneous procedures than in watchful waiting and delayed percutaneous procedures. Additionally, polidocanol performed signifcantly better than methylprednisolone regarding CI-Healing and CI-Failure. Lower limb localization was a signifcant negative prognostic factor for healing (cause-spe-cifc hazard ratio 0.38; 95% CI 0.18 to 0.82). Conclusion For treatment of SBCs, watchful waiting showed high chances of necessitating subsequent treatment, leading to lower CI-Healing and prolonged exposure to risk of failure. If treatment is required, polidocanol is a superior injectable compared with methylprednisolone, in terms of both healing and failure prevention.