PURPOSE:
The purpose of this study was to evaluate whether simple bone cysts (SBC) resolve with age.

METHODS:
Twenty four subjects with SBC who participated in a prior randomized clinical trial but had not healed at trial conclusion were evaluated for cyst healing. The following clinical and radiographic data were evaluated: age, sex, pain (Visual Analogue Scale), functional health (Short Form 36), subsequent fracture, involved bone, cyst area (cm), distance from physis (cm), endosteal thickening (yes/no), scalloping (no new scalloping/new scalloping), opacity/radiolucency (as is), loculation (yes/no), trabeculation (yes/no), tubulation (yes/no), transition zone (sharp/wide), geographic borders (geographic nonpermeative/nongeographic permeative), radiodense rim (>50%/no rim), and growth plate status (open/closed). Cyst healing was graded as: 1-cyst clearly visible; 2-cyst visible but multilocular and opaque; 3-sclerosis around or within a partially visible cyst; or 4-complete healing with obliteration of cyst. Healing was defined as grade 4.

RESULTS:
Of 24 subjects, 15 (63%) were male, 18 (75%) cysts were located in the humerus, and 4 (25%) in the femur. Patients were followed for 7.0±1.0 years following initial treatment with a mean age at follow-up of 17.2±3.2 years and 14 (87%) of growth plates were closed. Pain was minimal (0.6/10), function was high (91/100), and none of the patients had experienced subsequent fractures. Although distance from physeal scar had increased (P< 0.0001), cyst area reduction (P< 0.1) and overall cyst healing (P< 0.2) had not changed. Of the 24 subjects, none were graded as healed at time of follow-up. Of the remaining radiographic variables, only decreased loculation (P< 0.02) and increased endosteal thickening (P< 0.04) showed significant changes.

CONCLUSION:
Despite the assumption that most SBC will resolve with skeletal maturity, this study indicates that none of the cysts were graded as completely healed although 87% of growth plates were closed.

SIGNIFICANCE:
Growth plate closure may not signify healing of SBC and although symptoms and fractures are rare, further studies are needed to follow patients with SBC through early adulthood.





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