Assistance provided by Nanni Allington MD.
- Discussion:
- a membrane lined cavity containing a clear yellow fluid.
- occurrs most often in children 4-10 years of age;
- lesions remain asymptomatic unless complicated by fracture.
- they enlarge during skeletal growth and become inactive, or latent, after skeletal maturity.
-
active cysts:
- develop in patients under 10 years of age;
- cyst arises adjacent to growth plate & may grow to fill most of metaphysis;
- bone may be slightly expanded w/ thin cortical shell;
- it will continue to enlarge during observation;
- may cause pathologic fracture;
-
passive cysts:
- patients are usually over 12 years of age;
- cysts cease to expand;
- become increasingly separated from growth plate (more than 1-2 cm);
- have thicker bony wall than active lesions;
- may show evidence of healing or ossification
- less likely to result in frx;
- Location:
- lesion appears to arise from the growth plate & in early stages, lesion is lies adjacent to growth plate;
- typically the simple bone cyst will have a central location, whereas an
ABC will have a slightly eccentric location;
- predilection for the metaphysis of long bones;
-
proximal humerus (50% of cases)
-
proximal tibia;
-
proximal femur (40%)
- foot:
- ref:
Clinical Relevance of Calcaneal Bone Cysts: A Study of 50 Cysts in 47 Patients.
- Radiographs:
- show a central, well marginated & symmetric
radiolucent defect in metaphysis;
- usually no bony separations or loculations;
- may appear to have a slightly ballooned w/in the metaphysis;
- metaphyseal bone does not remodel normally, & metaphysis is broader than normally seen but not broader than with width of
epiphyseal plate;
- thin rim of non reative bone borders the unicameral bone cyst;
- when cyst becomes latent, epiphysis grows away from the lesion;
-
diff dx:
-
fibrous dysplasia;
- monostotic fibrous dysplasia is usually eccentric rather than central and diaphyseal rather than metaphyseal;
- periosteal reaction is greater in fibrous dysplasia than simple bone cyst;
-
aneurysmal bone cyst;
- metaphysis is expanded, with marked cortical thinning that predisposes to fracture;
- enlarge metaphysis to greater than width of the epiphyseal plate;
- Histologic Examination:
- active cyst have a mesothelial membrane lining thin margin of bone;
- inner wall of bone adjacent to membrane may be lined by osteoclasts;
- between membrane & osteoclasts is a layer of areolar tissue containing fibroblastic and multinucleated giant cells;
Treatment:
- goal of treatment is prevention of
pathologic fracture;
- conventional teaching is that the cyst will heal and resolve if a fracture occurs thru the cyst;
- this has been called into question w/ some estimates that cyst healing occurs in less than 10% fractures;
- simple cysts are treated with curettage and bone grafting;
- recurrence is high for active cysts (50%) & low for latent cysts (10%);
- alternative treatments:
-
steroids:
- 80-200 mg of
methylprednisolone infused into cavity;
- in the study by A. Hashemi-Nejad, 32 patients with unicameral cysts received multiple intralesional steroid injections;
- earliest time to healing was 3 months;
- at median review of 5 years, 13% of cysts had healed, 62% were paritally visible but sclerotic, 12.5% were visible but opaque, and 12.5% were clearly visible;
- healing response to intralesional steroids was unpredictable and was incomplete even after multiple injections;
- failure in wt bearing bones was high;
- authors questioned whether the results of the treatment were a result from multiple drill holes rather from the steroid;
- references:
- Incomplete healing of simple bone cysts after steroid injections. A. Hashemi-Nejad and WG Cole. JBJS Vol 79-B. No 5. Sep. 1997. p 727.
-
Simple bone cysts. The effects of methylprednisolone on synovial cells in culture.
-
autologous bone marrow injection:
- references:
- Simple bone cysts treated by percutaneous autologous marrow grafting. F Lokiec et al. JBJS Vol 78(6)-B. 1996-Nov. p 934-937
-
multiple drill holes:
- references:
- Simple bone cysts treated by multiple drill holes: 23 cysts followed 2-10 years. T. Shinozaki et al. Acta Orthop Scand. Vol 67. 1996. p 288-290.
- Radiological evidence of healing of a simple bone cyst after hole drilling. Arch Orthop Trauma Surg. Vol 105. 1986. p 150-153.
Solitary unicameral bone cyst: treatment with freeze-dried crushed cortical-bone allograft. A review of one hundred and forty-four cases.
Simple bone cyst. Treatment by trepanation and studies on bone resorptive factors in cyst fluid with a theory of its pathogenesis.
Unicameral bone cyst.
The fallen fragment sign in unicameral bone cyst.
Packing with high-porosity hydroxyapatite cubes alone for the treatment of simple bone cyst.
Unicameral bone cyst (simple bone cyst). JT Makley and MJ Joyce. Orthop. Clinics of North America. Vol 20. 1989. p 407-415.
Pathologic fractures secondary to unicameral bone cysts. JL Ahn and JS Park. Int Orthop. Vol 18. 1994. p 20-22.
Epiphyseal involvement of simple bone cysts.
