Working Diagnosis:
Unicameral bone cyst

Treatment:
Sclerotherapy with doxycycline and bone grafting

Outcome:
Athlete cleared to return to play after 8 weeks of activity restriction

Author's Comments:
Unicameral bone cysts (UBC) are benign, fluid filled lesions with a fibrous lining.[1] The most common locations are the proximal humerus and femur. Rarely, they can also occur in the pelvis (2%).[2,3] UBCs commonly present with pathologic fracture, pain, or changes in range of motion. On X ray, UBCs appear as well marginated lytic lesions with or without reactive sclerosis.[2] In general, UBCs can either be observed with serial X rays every 4 to 6 months or treated with steroid injections, injection of demineralized bone matrix, or curettage with bone graft. Overall, active treatment has improved outcomes over conservative treatment.[4] However, there is not conclusive evidence to support one treatment over the other.[4] One case series of UBCs of various locations showed a median return to sport time of 3 months after curettage, decompression, and injection of calcium sulfate/phosphate composite.[5]

Editor's Comments:
In this case study, a 15 year old male presented with bilateral knee pain, which gradually developed while playing basketball and football. Despite attempts at self care with ice, stretching, and ibuprofen, his symptoms persisted, limiting his athletic performance. The patients history of intermittent knee pain without trauma, combined with physical examination findings, suggested a non traumatic etiology. The workup revealed a rare diagnosis of a unicameral bone cyst (UBC) in the pelvis, confirmed by MRI and biopsy. UBCs are benign lesions typically found in long bones and rarely can occur in the pelvis. They can cause pain and impaired function, particularly in active individuals. In this case, the patient was treated with sclerotherapy and bone grafting, leading to a successful return to sports after a period of activity restriction. This case underscores the importance of considering rare diagnoses in young athletes with persistent pain, as well as the effectiveness of active treatment options like sclerotherapy in promoting recovery and return to play.

References:
1. Tis J. Nonmalignant bone lesions in children and adolescents. UpToDate. 2023.
2. Biermann JS. Common benign lesions of bone in children and adolescents. J Pediatr Orthop. 2002;22(2):268-73.
3. Abdelwahab IF, Hermann G, Norton KI, Kenan S, Lewis MM, Klein MJ. Simple bone cysts of the pelvis in adolescents. A report of four cases. J Bone Joint Surg Am. 1991;73(7):1090-4.
4. Kadhim M, Thacker M, Kadhim A, Holmes L, Jr. Treatment of unicameral bone cyst: systematic review and meta analysis. J Child Orthop. 2014;8(2):171-91.
5. Gentile JV, Weinert CR, Schlechter JA. Treatment of unicameral bone cysts in pediatric patients with an injectable regenerative graft: a preliminary report. J Pediatr Orthop. 2013;33(3):254-61.

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