Background: Steroid injection is a common method in the treatment of unicameral bone cysts (UBC). In this study, the relationship between the clinical results and inflammatory molecules' levels in the cyst fluid was evaluated after three repeated steroid injections in UBC subjects.

Methods: Twenty-one patients diagnosed with UBC were treated with methylprednisolone acetate (MPA) injections. Patients were given three injections, each containing MPA, 6-8 weeks apart. Plain radiographs were obtained and cyst healing was evaluated according to modified Neer classification. Cyst fluid samples were taken. Samples were taken at first and last operations and were studied using the ELISA method to examine IL-1β, PGE2, MMP-1, and VEGF-A levels.

Results: There were 17 and 4 cases localized to the humerus and femur, respectively. The mean follow-up period was 36.9 months. Complete recovery was achieved in 13 patients (61.9%) receiving MPA. Four patients (19%) recovered with residual lesions. One patient (4.7%) did not respond to steroid injections at all. In three patients (14.2%) the cyst recurred. Results were satisfactory in 17 patients (80.9%) and totally unsuccessful in 4 patients (19%). IL-1β, PGE2, and MMP-1 levels in cyst fluid were not affected by injection (p > 0.05), but VEGF-A levels decreased significantly with cyst healing (p = 0.01).

Conclusion: Steroid injection is a good choice in the treatment of UBC because of its less aggressive and relatively good outcome. It may be considered to evaluate the response to treatment by performing biomarker monitoring especially VEGF-A in repeated injections.

Level of evidence: Level II study.

Keywords: Bone cysts; Fractures; Interleukin-1beta; Matrix Metalloproteinase1; Methylprednisolone; Prostaglandins; Spontaneous; Vascular endothelial growth factor A.