Bone cysts are benign lesions usually discovered in children from age of 5 to 15 years. Treatment options include observation, corticosteroid injection and surgery. Sometimes the risk of surgery is comparable to the likelihood of fracture without treatment. In orthopedic surgery, bone chips , various types of ceramics, natural and synthetized bone mineral hydroxyapatite and tricalcium phosphate, as well as numerous polymers and co-polymers of alfa-hydroxy acids are used to perform as an osteoconductive and rarely osteoinductive factor to help bone formation.Some evidence demonstrated that bone marrow mesenchymal stem cells deposited on the surface of this constructs enhance its osteogenic differentiation. In this study the investigators seeds cultured bone marrow derived mesenchymal stem cells on bone matrix, to evaluate its therapeutic potential in repairing unicameral or aneurysmal bone cyst.This composite is placed in the bone cyst after its curettage during a surgery.Post-operation assessment is done by X-Ray examination and MRI at 1, 2, 6, and 12 months after treatment.