Unicameral Bone Cyst

B. Alami-Harandi MD, E. Navab-Sheikholeslami MD, M. Seghatchian MD, M. Nowroozi MD

Shariati Hospital, Tehran, Iran

Key Words · Bone cyst · bone-graft · injection of hydrocortisone in bone cyst · recurrent bone cyst

Introduction

Unicameral bone cyst (UBC), solitary or simple bone cyst, comprise about 3% of biopsied primary bone tumors. It was recognized as an entity apart from other cystic lesions of the bone by Bloodgood in 1910¹. Jaffe and Lichtenstein gave a detailed discussion of the lesions in 1942².

Unicameral bone cysts usually occur in children and adolescents, most often in boys and almost always in cylindrical bone, predominantly the proximal ends of the femur and humerus. Opinions differ as to the method of treatment for these cysts. The lesion is often first seen with fracture through the cyst and with subsequent healing of the fracture the cyst may fill up. The established method of treatment for these cysts is curettage and bone graft. Campanacci et al. in 1977 and Scaglietti in 1979 reported the successful treatment of UBC by injecting methyl prednisolone into the cyst.^3,4 Since that time, topical injection into the cyst has become a routine method of treatment in many centers. The success rates of curettage and bone graft or injection with methyl-prednisolone are approximately the same.

We reviewed the results of two methods of treatment (surgical and injection) in UBC in 30 patients referred to our department.

Materials and Methods

Between 1993-1997, 30 patients with UBC of the proximal end of the humerus were admitted to the Shariati Hospital and Imam Khomeini Hospital for treatment. Diagnosis of these patients was made by histological examination of the curreted material in surgical cases and x-ray findings and the appearance of the fluid drained from the cyst in injected cases.

Suspicious cases and patients who were initially treated in other centers and had recurrence were excluded from this study as were patients with hyperparathyroidism and diabetes.

In the patients who were treated surgically, the cyst was exposed with an antero-lateral deltopectoral approach. After vertical incision over the periosteum, evaluation was carried out taking care to avoid fracturing the eggshell wall of the cyst. A window was opened in the cyst and after aspiration of the fluid, the wall of the cyst was curreted with care to avoid damage to the growth plate and fracturing the cyst wall. After curettement of the cyst wall and irrigation, the cyst was packed with cancellous bone graft taken from iliac bone.

In patients who were treated with injection, with the aid of an image intensifier, two needles were inserted into the cyst, one for injection and the other for the release of fluid. In cases where the cyst wall was thin, the needle was introduced easily, but if the cyst wall was thick, the needle was introduced with a cannulated needle after drilling. Depending on the size of the cyst, 40-120 mg of methyl-prednisolone was injected. X-rays were taken 1 to 2 months after the procedure and if the cavity persisted or minimal improvement noted, the injection was repeated three times.

Of 30 patients, 14 were treated surgically (group A) and 16 by injection (group B). Follow up of the patients was every 2 weeks in the first month and every other month thereafter.

Results

Of 30 patients, 19 were boys and 11 girls. Group A consisted of 9 boys and 5 girls with an average age of 11.4 years. Group B consisted of 10 boys and 6 girls with an average age of 8-10 years. Average time of surgery in group A was 69 minutes and treatment duration in group B was 31 minutes.

Average bleeding for group A patients was 242 cc. However, none of the patients required blood transfusion. No bleeding was seen in group B patients.

One case of deep infection was noted in group A but no infection was present in group B patients. Two patients had keloid formation in the surgical group and 4 patients had temporary flushing in the injected patients that disappeared without treatment.

The healing time after the surgical procedure was 8-15 months with an average of 11.6 months whereas healing time in the injected group was 15-18 months with an average time of 13.9 months. The difference in healing time was not clinically important, overall the healing rate in surgical patients was 85.7% and in injected patients 75%. [Figures 1, 2]

Discussion

Successful treatment of UBC by injecting methyl-prednisolone into the cyst was first reported by Campanacci, et al. in 1977 and subsequently by

Scaglietti in 1979.^3,4 In a later paper, Scaglietti reported in 1982 that 55% of cysts treated by injection were totally eradicated with 45% showing some persistence, especially in older children. One injection was adequate in 24% of cases with 76% requiring further treatment. Oppenheim and Galleno reported a 40%-75% success rate after injection whereas Scaglietti reported a 96% success rate in his first report.⁵ Campanacci compared the results of curettage and bone graft with methyl-prednisolone injection and found that the results were the same. Subsequent papers have reported more or less the same results as above.⁶

The reason for the difference between the results is probably due to the age of the patients, site of the cyst and the distance between the cyst and growth plate. In more recent years, injection of autogenous bone marrow has been recommended by some authors, but the results have not been completely evaluated.

The reason for the effectiveness of the method is not well understood. Ponner believes that the introduction of a needle into the cyst causes bleeding which in turn may cause bone formation and healing. Cohen suggests that obstruction of the venus system and inadequate drainage of interstitial fluid of the growing bone will cause cyst formation.⁷ Connolly and Shindell showed that there is increased prostaglandin in the cyst fluid and injecting methyl prednisolone into the cyst will reduce prostaglandin and cause healing.^8,9

In our study, of 30 patients with UBC of the proximal end of the humerus who were treated with curettage and bone graft we had an 85.7% success rate. In patients treated with injection, 75% healed. There was no complication in the injected group whereas there was one case of infection and 2 cases of keloid formation in the surgical group.

Taking into consideration that the results from the two groups were more or less the same and that injection of the cyst is a minor procedure which can be performed ambulatory with almost no complication, we consider it better to treat UBC of the upper limb by injection of methyl-prednisolone. Curettage and bone grafts or other procedures may be reserved for unresponsive cases.

In regard to the risk of impending fracture of the cyst, injection should not be performed in the treatment of UBC of the lower limbs. It is better in our opinion to treat them with curettage and bone graft with or without fixation.

References

1 Bloodgood JC. Benign bone cysts, osteitis fibrosa, giant cell sarcoma and bone aneurysm of long pipe bone. Ann Surg 1910;52:145-89.

2 Jaffe HL, Lichtenstin L. Solitary unicameral bone cyst with emphasis on the roentgen picture: the pathological appearance and pathogenesis. Arch Surg 1942;44:1004-25.

3 Campanacci M, DeSessa L, Scaglietti S. Method of conservative treatment of simple bone cysts with local injection of methyl prednisolone acetate. Ital J Orthop Traumatol 1977;3:64-7.

4 Scaglietli O, Marchtli PG. The effects of methyl prednisolone acetate in treatment of bone cysts. JBJS 1979; 61(B):200-4.

5 Oppenheim WL, Galleno H. Operative treatment versus steroid injection in management of unicameral bone cyst. J Pediatr Orthop 1984;4:1-7.

6 Campanacci M, Capanna R. Unicameral and aneurysmal bone cysts. Clin Orthop 1986;204:25-36.

7 Cohen J. Simple bone cyst. Studies of cyst fluid in six cases with theory of pathogenesis. J B J S 1960;42(A):604-16.

8 Shindell R, Connolly F. Prostoglanding levels in unicameral bone cyst treated by corticosteroid injection. J Pediatr Orthop 1987;7:210-12.

9 Shindell R, Huurman WW, Lipiello L, Connolly JF, et al. Prostaglandin levels in unicameral bone cyst treated by intralesional steroid injection. J Pediatr Orthop 1989;9:516-9.

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