Unicameral bone cysts of the proximal femur in skeletally immature patients: Do radiological parameters, pathological fracture, treatment method and recurrence affect the outcomes?

Unicameral bone cysts (UBC) are reported to be the underlying lesion in 40% of pathological femoral neck fractures in skeletally immature patients. They are typically asymptomatic and incidentally found on imaging. However, when symptomatic, it commonly may present with pathologic fracture that causes pain, swelling, or deformity. The purpose of this study was to assess the natural history of the pediatric proximal femoral unicameral bone cyst, risk factors for pathological fracture and recurrence. Medical records were retrospectively reviewed of patients with pediatric proximal femoral UBC’s who underwent surgery between 2004 and 2018. We included 51 consecutive patients with pediatric proximal femoral UBC (36 impending fractures/15 pathological fractures). The patients were evaluated regarding the localization of the UBC and the activity of the cyst. The cyst parameters were measured, and the patients were further assessed regarding the presence of pathological fracture and applied treatment. The pathological fracture group was compared to the impending fracture group using radiological cyst parameters, management options, healing, recurrences, and other related complications. The most commonly affected localizations were combined involvement of femoral neck and intertrochanteric (n=21) The number of latent lesions was 27 and active lesions were 24. The mean cyst index in our series was 3.8±1.2 (1.2-7.2). The cyst index in our series was correlated with pathological fractures. (p=0.048) There were significantly higher cyst index values in recurrent cases. (p=0.016) The cyst extension below the trochanter minor level was found as a risk factor for pathological fractures. (p=0.021) The most common treatment in our series was curettage, graft packing, and plate fixation with 27 patients. The treatment method showed no correlation with consolidation or recurrence rate. According to the healing criteria for UBC’s at final follow-up, 36 cysts were completely consolidated, 13 were evaluated as incomplete healing and two were persistent. The recurrence rate was significantly high in UBC’s who were operated on at <10 years of age (p=0.006). Accordingly, the active lesions were also significantly related to earlier recurrence (p=0.03). Although younger age, active cysts, and higher cyst index are shown as risk factors for recurrence, not for fracture in proximal femoral UBC’s. However, with age, the cyst relatively migrates to the weight-bearing intertrochanteric area, which may inevitably impose a major risk for pathological fractures. Ensuring stability with a plate even in impending fractures of the proximal femur may aid early mobilization and faster recovery. [ABSTRACT FROM AUTHOR]