Unicameral Bone Cysts: Review of Etiopathogenesis and Current Concepts in Diagnosis and Management

Abstract

Objective: This article aims to review the epidemiology, etio-pathogenesis and updates in clinical diagnostics and management of unicameral bone cysts (UBC).

Methods: A computerized literature search using Cochrane database of systematic reviews, EMBASE and PubMed was performed. MeSH (Medical Subject Headings) terms used in searches included the following sub-headings: "unicameral bone cyst", "epidemiology", "etiology", "pathogenesis", "diagnosis", "management" and "surgery". Studies were analyzed based on clinical relevance for the practicing orthopedic surgeon.

Results: UBC accounts for 3% of all bone tumors and is asymptomatic in most cases. Nearly 85% of cases occur in children and adolescents, with more than 90% involving the proximal humerus and proximal femur. Despite multiple theories proposed, the exact etiology is still unclear. Diagnosis is straightforward, with radiographs and MRI aiding in it. While non-surgical treatment is recommended in most cases, in those warranting surgery, combined minimal-invasive techniques involving decompression of cyst and stabilization have gained importance in recent times.

Conclusion: There is variation in the diagnosis and treatment of UBCs among surgeons. Due to the vast heterogeneity of reported studies, no one method is the ideal standard of care. As most UBCs tend to resolve by skeletal maturity, clinicians need to balance the likelihood of successful treatment with morbidity associated with procedures and the risks of developing a pathological fracture.

Study design: Review Article.

Keywords: Current concepts; Cyst decompression; DBM; Diagnosis; MRI; Management; Steroids; Unicameral bone cyst.

Fig. 1

Radiograph demonstrating a centrally located lytic lesion in the calcaneum a with corresponding MRI sequence showing high signal intensity, b with homogenous intensity throughout the cyst suggestive of a UBC. Pathologic fracture of a UBC in the humerus shaft in a 9-year-old girl, c, d with the ‘fallen leaf/fragment’ sign on the radiograph. Histology showed fragments of multinucleated giant cells with focally loose fibroblasts (e) seen in UBC

Fig. 2

Pathological fracture through UBC in the humerus (a, b) was managed conservatively. Follow-up radiographs at 6 weeks (c, d) showing callus formation. Radiographs taken at 6 months of follow-up show complete union and adequate remodeling (e, f)

Fig. 3

Pathological fracture of the humerus (a, b) with deformity due to UBC in a 10-year-old boy, which was managed with IM flexible nailing (c, d) and resulted in union at 6 months with the healing of cyst (e, f)

Fig. 4

Proximal femoral fracture (a–c) due to UBC with loss of lateral wall integrity in a 6-year-old boy managed with curettage, allograft packing, and internal stabilization (d, e). Screws in the femoral head were not passed through the physis to avoid growth arrest problems. Complete union and resolution of the cyst were followed by implant removal (f)

Fig. 5

UBC in the humeral shaft with pain (a, b) on presentation in a 6-year-old girl was managed with curettage and allograft packing (c, d). At 1-year follow-up, there was evidence of recurrence with cortical thinning on radiographs and increased pain (e, f). Cyst decompression with flexible IM nail (g) was combined with steroid injection to achieve healing and resolution of the cyst (h)

Fig. 6

Illustrative algorithm depicting the diagnosis and management of suspected UBC lesions. Note: The decision on internal stabilization varies depends mainly on the anatomical location of the lesion