Predictive factors for recurrence of simple bone cyst of the proximal humerus.

To evaluate factors predictive of recurrence following curettage of simple bone cysts (SBCs) in the proximal humerus. Records of 29 male and 3 female patients aged 3 to 22 (mean, 11) years who underwent curettage with or without bone grafting for a solitary SBC in the proximal humerus were reviewed. The appearance, size, location, activity level, and fracture pattern of each cyst were recorded. The cyst index indicated the risk of refracture. Recurrence was defined as a refracture or enlargement of the cyst. 31 patients presented with a pathological fracture. The main symptoms were pain (n=30), loss of function (n=22), and mass/swelling (n=15). 25 patients gave a history of trauma. The duration of symptoms was less than one month. 10 patients had recurrence after a mean of 10 (range, 4-27) months; 5 were refractures and another 5 were enlargement of the cysts. Six were treated conservatively and eventually healed, whereas 4 underwent further curettage. Factors predictive of recurrence were patient age 5 years or younger (p=0.014), right-sided cyst (p=0.01), larger cyst (p=0.039), multilocular cyst (p=0.004) and unimpacted fracture (p=0.04). Recurrence was not related to gender, cyst location, or cyst activity level. Most SBCs heal even if the fracture is treated expectantly. SBCs should be left alone unless symptomatic. If curettage is performed, grafts or bone substitutes should be used. More aggressive treatment might be necessary for unimpacted fractures to minimise the risk of recurrence.