Successful treatment of unicameral bone cyst by single percutaneous injection of alpha-BSM

Unicameral bone cyst (UBC) is a benign bone lesion, recognized for its high rate of recurrence and need for repeat procedures to achieve healing. We hypothesized that the osteoconductive material apatitic calcium phosphate (alpha-BSM) could be effective in filling and stimulating resolution of UBC. The purpose of this study was to evaluate clinical and radiographic outcomes of UBC treated by a single injection of alpha-BSM.

Thirteen patients (6 male, 7 female) with a mean age of 10.5 years, underwent single percutaneous injection of alpha-BSM for presumed UBC. The aspiration of the cysts was followed by vigorous saline lavage using 2 wide bore needles to disrupt the cyst walls. alpha-BSM "paste" was then injected under fluoroscopic guidance. Radiographs were digitized to measure cystic area (millimeter squares) on 2 orthogonal views. Healing was rated according to a modified Neer outcome grading system. Nine of the 13 patients had had pathologic fractures in the past. Eleven of the 13 patients had had past unsuccessful treatment: multiple steroid injections in 6, curettage and bone grafting in 3, and bone marrow and demineralized bone matrix (Grafton) injection in 2.

Five cysts were grade 1 (healed 100%), 6 grade 2 (healed >50%), 2 grade 3 (healed <50% with increased cortical thickness), and none grade 4 (recurrence/enlargement). The average resolution of cystic area in 11/13 cysts was 85.7% at final follow-up of 35.8 months (P=0.0001) with 2.8 mm of average gain in cortical thickness (P=0.0018). None of the 13 lesions required an additional procedure or repeat injection. All patients were clinically asymptomatic at latest follow-up.

This is the first study quantifying cyst resolution objectively according to actual decrease in area (millimeter squares). A single injection of alpha-BSM is a safe, minimally invasive and efficacious method to treat UBC in the pediatric population.