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Unicameral bone cysts (UBC) or simple/solitary bone cysts are benign fluid filled cavities that enlarge over time, resulting in thinning of the bone. Usually these cysts are reported in the metaphyseal areas of long bones with open physes. 85% of UBCs occur almost exclusively in children and adolescents. UBCs are more aggressive in the first decade of life and correspondingly the recurrence rate for these patients is four times that for adolescents. The proximal humerus and femur account for almost 90% of these cases. UBCs are classified as active when they are within 1 cm of the physis and latent as they progress to a diaphyseal location. Differential diagnoses for UBC include aneurysmal bone cyst, fibrous dysplasia, enchondroma, and intraosseous ganglia. By the time of skeletal maturity most UBCs tend to resolve. Nonoperative treatment may be a viable option for many patients with small or symptomatic lesions. Interventions include steroid injection, open curettage and bone grafting, decompression and percutaneous injection of marrow or graft substitutes.

BACKGROUND Deformity and growth arrest of the humerus in children may result as sequelae of proximal humerus fractures and unicameral bone cysts, or as complications of their treatment. As approximately 80% of the growth of the humerus arises from the proximal physis, the resultant upper limb-length discrepancy can be substantial. Benefits to lengthening the shortened arm have been previously demonstrated with the use of external fixation devices. To our knowledge, no reports have been published on the use of intramedullary implants for this purpose. METHODS A 15-year-old girl with humeral shortening secondary to proximal humeral growth disturbance following treatment for a unicameral bone cyst was treated with humeral osteoplasty and gradual lengthening with an off-label use of a fully implantable motorized intramedullary lengthening nail. A varus proximal humeral deformity and lateral starting point allowed for avoidance of the rotator cuff insertion. RESULTS Humeral lengthening (5 cm) was achieved at 9 weeks, with bony union at 7 months, and hardware removal at 9½ months. Shoulder and elbow motion was maintained during and after treatment. CONCLUSIONS This is the first case report of humeral lengthening using a fully implantable motorized intramedullary lengthening nail. Although some technical limitations remain when compared with other methods, the procedure was well tolerated throughout the course of treatment. LEVEL OF EVIDENCE Level IV-case report.

Unicameral bone cysts are benign bone lesions that are often asymptomatic and commonly develop in the proximal humerus and femur of skeletally immature patients. The etiology of these lesions remains unknown. Most patients present with a pathologic fracture, but these cysts can be discovered incidentally, as well. Radiographically, a unicameral bone cyst appears as a radiolucent lesion with cortical thinning and is centrally located within the metaphysis. Although diagnosis is frequently straightforward, management remains controversial. Because the results of various management methods are heterogeneous, no single method has emerged as the standard of care. New minimally invasive techniques involve cyst decompression with bone grafting and instrumentation. These techniques have yielded promising results, with low rates of complications and recurrence reported; however, prospective clinical trials are needed to compare these techniques with current evidence-based treatments.

The aim of this study was to determine the benefits of cystography in the management of a simple bone cyst, its implication in the final result of the treatment after corticoid intracystic injections, and the presence of secondary effects. We retrospectively reviewed 42 patients diagnosed with a simple bone cyst. Cystography was performed before the corticoid injection. The presence or absence of loculation intracyst and the existence and number of venous outflows were determined. According to the venous drainage, cysts were classified as type 0 when a venous outflow did not exist and as type 1 when there was a rapid venous outflow (

BACKGROUND: There is a variety of treatment modalities for unicameral bone cysts, with variable outcomes reported in the literature. Although good initial outcomes have been reported, the success rate has often changed with longer-term follow-up. We introduce a novel, minimally invasive treatment method and compare its clinical outcomes with those of other methods of treatment of this lesion. METHODS: From February 1994 to April 2008, forty patients with a unicameral bone cyst were treated with one of four techniques: serial percutaneous steroid and autogenous bone-marrow injection (Group 1, nine patients); open curettage and grafting with a calcium sulfate bone substitute either without instrumentation (Group 2, twelve patients) or with internal instrumentation (Group 3, seven patients); or minimally invasive curettage, ethanol cauterization, disruption of the cystic boundary, insertion of a synthetic calcium sulfate bone-graft substitute, and placement of a cannulated screw to provide drainage (Group 4, twelve patients). Success was defined as radiographic evidence of a healed cyst or of a healed cyst with some defect according to the modified Neer classification, and failure was defined as a persistent or recurrent cyst that needed additional treatment. Patients who sustained a fracture during treatment were also considered to have had a failure. The outcome parameters included the radiographically determined healing rate, the time to solid union, and the total number of procedures needed. RESULTS: The follow-up time ranged from eighteen to eighty-four months. Group-4 patients had the highest radiographically determined healing rate. Healing was seen in eleven of the twelve patients in that group compared with three of the nine in Group 1, eight of the twelve in Group 2, and six of the seven in Group 3. Group-4 patients also had the shortest mean time to union: 3.7 ± 2.3 months compared with 23.4 ± 14.9, 12.2 ± 8.5, and 6.6 ± 4.3 months in Groups 1, 2, and 3, respectively. CONCLUSIONS: This new minimally invasive method achieved a favorable outcome, with a higher radiographically determined healing rate and a shorter time to union. Thus, it can be considered an option for initial treatment of unicameral bone cysts. LEVEL OF EVIDENCE: Therapeutic Level III. See Instructions to Authors for a complete description of levels of evidence. ORIGINAL ABSTRACT CITATION: “Treatment of Unicameral Bone Cyst. A Comparative Study of Selected Techniques” (2010;92:855-62).

Unicameral bone cysts are benign lesions that usually spontaneously regress with skeletal maturity; however, the high risk of pathologic fractures often justifies treatment that could reinforce a weakened bone cortex. Various treatments have been proposed but there is no consensus regarding the best procedure.We compared the healing rates and failures of two methods of cure based on multiple injections of corticosteroid or a single injection of demineralized bone matrix (DBM) in association with bone marrow concentrate (BMC).We retrospectively reviewed 184 patients who had one of the two treatments for unicameral bone cysts with cortical erosion. Clinical records were reviewed for treatment failures and radiographs for healing in all patients. The minimum followup was 12 months for the Steroids Group (mean, 48 months; range, 12-120 months) and 12 months for the DBM + BMC Group (mean, 20 months; range, 12-28 months).After one treatment we observed a lower healing rate of cysts treated with multiple injections of steroids compared with the healing after the first injection of DBM + BMC (21% versus 58%, respectively). At last followup, 38% healed with steroids and 71% with DBM + BMC. The rate of failure after one steroid injection was higher than after a single injection of BDM + BMC (63% versus 24%, respectively). We observed no difference in fracture rates after treatment between the two groups.A single injection of DBM added with autologous bone marrow concentrate appears to provide a higher healing rate with a lower number of failures compared with a single injection of steroids.

Background There is a variety of treatment modalities for unicameral bone cysts, with variable outcomes reported in the literature. Although good initial outcomes have been reported, the success rate has often changed with longer-term follow-up. We introduce a novel, minimally invasive treatment method and compare its clinical outcomes with those of other methods of treatment of this lesion. Methods From February 1994 to April 2008, forty patients with a unicameral bone cyst were treated with one of four techniques: serial percutaneous steroid and autogenous bone-marrow injection (Group 1, nine patients); open curettage and grafting with a calcium sulfate bone substitute either without instrumentation (Group 2, twelve patients) or with internal instrumentation (Group 3, seven patients); or minimally invasive curettage, ethanol cauterization, disruption of the cystic boundary, insertion of a synthetic calcium sulfate bone-graft substitute, and placement of a cannulated screw to provide drainage (Group 4, twelve patients). Success was defined as radiographic evidence of a healed cyst or of a healed cyst with some defect according to the modified Neer classification, and failure was defined as a persistent or recurrent cyst that needed additional treatment. Patients who sustained a fracture during treatment were also considered to have had a failure. The outcome parameters included the radiographically determined healing rate, the time to solid union, and the total number of procedures needed. Results The follow-up time ranged from eighteen to eighty-four months. Group-4 patients had the highest radiographically determined healing rate. Healing was seen in eleven of the twelve patients in that group compared with three of the nine in Group 1, eight of the twelve in Group 2, and six of the seven in Group 3. Group-4 patients also had the shortest mean time to union: 3.7 +/- 2.3 months compared with 23.4 +/- 14.9, 12.2 +/- 8.5, and 6.6 +/- 4.3 months in Groups 1, 2, and 3, respectively. Conclusions This new minimally invasive method achieved a favorable outcome, with a higher radiographically determined healing rate and a shorter time to union. Thus, it can be considered an option for initial treatment of unicameral bone cysts.

Bone tumors are rare in children. Most bone tumors tend to involve the areas of fastest growth. Lower extremity tumors are more common than upper extremity ones, however upper extremity bone tumors do occur and can have a negative impact in the child's activities. Luckily, most bone tumors seen in children are benign and can be effectively treated by means of observation or local control by surgery. In this article we review and discuss the diagnosis and management of the most common pediatric benign bone tumors seen in the upper extremities including unicameral bone cyst, aneurysmal bone cyst, fibrous cortical defect, non-ossifying fibroma, osteochondroma, osteoid osteoma and enchondroma.

BACKGROUND Unicameral bone cyst (UBC) is a benign bone lesion, recognized for its high rate of recurrence and need for repeat procedures to achieve healing. We hypothesized that the osteoconductive material apatitic calcium phosphate (alpha-BSM) could be effective in filling and stimulating resolution of UBC. The purpose of this study was to evaluate clinical and radiographic outcomes of UBC treated by a single injection of alpha-BSM. METHODS Thirteen patients (6 male, 7 female) with a mean age of 10.5 years, underwent single percutaneous injection of alpha-BSM for presumed UBC. The aspiration of the cysts was followed by vigorous saline lavage using 2 wide bore needles to disrupt the cyst walls. alpha-BSM "paste" was then injected under fluoroscopic guidance. Radiographs were digitized to measure cystic area (millimeter squares) on 2 orthogonal views. Healing was rated according to a modified Neer outcome grading system. Nine of the 13 patients had had pathologic fractures in the past. Eleven of the 13 patients had had past unsuccessful treatment: multiple steroid injections in 6, curettage and bone grafting in 3, and bone marrow and demineralized bone matrix (Grafton) injection in 2. RESULTS Five cysts were grade 1 (healed 100%), 6 grade 2 (healed >50%), 2 grade 3 (healed

We determined the role of mechanical decompression in the resolution of unicameral bone cyst. A total of 69 children with unicameral bone cysts were treated either by (i) open curettage and bone grafting, (ii) steroid injection or (iii) cannulated screw insertion. During a mean follow-up of 69 months (range, 12-58), the cysts were evaluated by radiological criteria. The healing rates in the three groups were 25, 12 and 29% after the first treatment, and a further 50, 19 and 65% after the second. The study has demonstrated the advantages of the decompression technique for unicameral bone cysts over other treatment modalities studied.

Several treatment options exist for unicameral bone cysts (UBCs), including observation, steroid injection, bone marrow injection, and curettage and bone grafting. These are all associated with high recurrence rates, persistence, and occasional complications. Newer techniques have been described, most with variable success and only short follow-up reported. Because of these factors, a new minimally invasive percutaneous technique was developed for the treatment of UBCs in children. Twenty-eight children with UBCs who underwent percutaneous intramedullary decompression, curettage, and grafting with medical-grade calcium sulfate (MGCS) pellets by the senior author (J.P.D.) between April 2000 and April 2003 were analyzed as part of a pediatric musculoskeletal tumor registry at a large tertiary children's hospital. Four patients were lost to follow-up, and the remaining 24 patients had an average follow-up of 21.9 months (range 4-48 months). Twelve patients were followed for at least 24 months. Six of the 24 children had received previous treatment of their UBC, most often at an outside institution. Follow-up was performed through clinical evaluation and radiographic review. Postoperative radiographs at most recent follow-up showed complete healing, defined as more than 95% opacification, in 22 of 24 patients (91.7%). One patient (4.2%) demonstrated partial healing, defined as 80% to 95% opacification. One patient had less than 80% radiographic healing (4.2%). All 24 patients returned to full activities and were asymptomatic at most recent follow-up. The only complication noted was a superficial suture abscess that occurred in one patient; this resolved with local treatment measures. The new minimally invasive technique of percutaneous intramedullary decompression, curettage, and grafting with MGCS pellets demonstrates favorable results with low complication and recurrence rates compared with conventional techniques. The role of intramedullary decompression as a part of this percutaneous technique is discussed.

Humeral shaft fractures constitute only 3% of fractures in children younger than age 16 years. They are most common in children younger than 3 and older than 12 years old. They can be classified according to the fracture pattern, location, and tissues damaged. Fractures resulting from minor trauma may be caused by an occult unicameral bone cyst. Each age group requires different diagnosis, treatment, and prognosis. Fractures at birth are seen mostly with macrosomic and breech presentation. In children younger than 3 years, humeral fractures often are linked to child abuse. In those older than 10 years, fractures are related to direct or indirect trauma. Sports activities have been reported also to cause injuries in skeletally immature patients. Most humeral fractures are controlled nonoperatively; however, potential operative indications include open fractures, multiple trauma, bilateral injuries, compartment syndromes, pathological fracture, significant nerve injuries, and inadequate closed reduction.

Although benign bone neoplasms are relatively uncommon in children and adolescents, their discovery can produce great angst among providers and parents. In most but not all instances, imaging studies can indicate the likely benign nature of the tumor and allay fears. The clinical presentation, imaging, and contemporary management of five common types of tumor or tumor-like conditions of bone commonly seen in children and adolescents are reviewed: nonossifying fibroma, unicameral bone cyst, aneurysmal bone cyst, fibrous dysplasia, and exostosis.

Simple bone cyst (SBC) is an enigma to the radiologist, pathologist and the orthopaedic surgeon. The etiology of this asymptomatic lesion that frequently causes pathological fracture is still unknown. It is probably self limited in nature, seen in children but rare among adults. The biological behavior is unpredictable as is the clinical course in various anatomical sites. This reflects on the high recurrence rate that has been associated with various treatment modalities. The clinical, radiological and biological features are discussed together with comparative review of treatment options from resection, curettage, and bone grafting to steroid injection and the latest experience of the use of percutaneous autologous marrow grafting in SBC.

Documented epiphyseal extension of a solitary unicameral bone cyst in the presence of an open physis is extremely rare3,15. Epiphyseal extension by such cysts has been noted on plain radiographs3, on computed tomography15, and intraoperatively10. We report an unusual case of a skeletally immature child in whom magnetic resonance imaging clearly demonstrated extension of a solitary bone cyst into the proximal humeral epiphysis. The portions of the cyst in the epiphysis and metaphysis communicated through a defect in the physis that was probably due to erosion by the cyst. Progressive limb-shortening developed. The purpose of the current report is to describe the natural history and pathogenesis of physeal involvement by a unicameral bone cyst. A fourteen-year-old boy was seen in the emergency room of the Children's Hospital Medical Center in Cincinnati with a history of a twisting injury of the right arm. He had been managed for a pathological fracture of the humerus on the same side when he was nine years old. Roentgenograms made at that time had revealed a fracture through a unicameral bone cyst (Figs. 1-A and 1-B). He had had no specific problems since that time except that the right arm was noticeably shorter than the left. Figs. 1-A through 1-F: Roentgenograms and magnetic resonance images of a boy who had a unicameral bone cyst. Fig. 1-A: Roentgenogram, made when the patient was nine years old, showing a pathological fracture through a typical unicameral bone cyst in the proximal part of the humerus. The cyst abuts the physis and extends one to five centimeters from it. There is a small area where the cyst wall forms an interface with the physis. The growth plate otherwise appears intact, and the fracture does not extend to the physis. …

The calcaneus is an uncommon site for a unicameral bone cyst. However, because of the concentration of forces through the heel, such cysts are usually symptomatic and require treatment. Because of the lack of attention paid to calcaneal unicameral bone cysts, as well as the controversy concerning their appropriate treatment and ultimate outcome, a retrospective study of our experience was undertaken. Over a 15-year period, we treated six children with calcaneal unicameral bone cysts. The diagnosis was confirmed pathologically at the time of treatment for all six. The most common presenting complaint was heel pain upon weight-bearing, secondary to microfracturing of the cyst. Although conservative treatment, which entailed casting and sponge fillers in the shoes, was attempted for most patients, none responded to this form of management. One child had three separate injections of methylprednisolone acetate without any radiographic or clinical change in the cyst, which ultimately required curettage and bone grafting. Bone grafting with either autogenous or allograft bone was successful in eradicating the cyst in all six patients, with no symptoms of recurrence at an average follow-up of 4 years. No resultant treatment complications were encountered. Unicameral bone cysts of the calcaneus, when symptomatic, respond well to curettage and bone grafting, and this type of treatment is recommended.

We present a case of unicameral bone cyst with fluid-fluid levels evaluated with CT and MRI. A literature review revealed that fluid levels within aneurysmal bone cysts, giant cell tumors, chondroblastomas, and tel-angiectatic osteosarcomas have been described.

Unicameral bone cysts (UBCs) were first described by Virchow in 18761. They are commonly found in the proximal part of the humerus in males between eleven and twenty years of age2,3. While some cysts are discovered incidentally after radiographs are taken for other reasons, most patients present with arm pain, with or without fracture through the cyst2. In clinical situations consistent with UBC of the proximal part of the humerus, radiographs are sufficient for diagnosis, and additional imaging usually is not recommended4. The patient and his parents were informed that data concerning the case would be submitted for publication, and they provided consent. A nine-year-old boy had experienced left shoulder pain after playing football. Because the pain had persisted, his primary care provider had obtained a radiograph; this radiograph had demonstrated a cystic lesion of the proximal part of the left humerus without fracture (Fig. 1). Subsequent magnetic resonance imaging (MRI) had been consistent with a benign bone cyst, which was likely a UBC (Fig. 2), without an associated soft-tissue mass. He had been referred to an orthopaedic oncology surgeon for management, and he had been followed for six months as the pain resolved. Fig. 1 At presentation, the anteroposterior radiograph was consistent with a UBC. Coronal short tau inversion recovery ( Fig. 2-A ), coronal T1-weighted ( Fig. 2-B ), coronal T2-weighted ( Fig. 2-C ), and sagittal T2-weighted ( Fig. 2-D ) MRI at presentation did not show a soft-tissue mass. Fig. 2-A Fig. 2-B Fig. 2-C Fig. 2-D Twelve months after the original presentation, the arm pain had returned. After repeat radiographs had confirmed an unchanged benign bone cyst, surgical aspiration and injection of autograft bone marrow and demineralized allograft bone matrix had been performed. At the time of contrast dye injection into the cyst, intraoperative fluoroscopy had not shown a noteworthy soft-tissue mass, thus confirming the diagnosis of UBC (Fig. 3). Fig. 3 Intraoperative fluoroscopic image of the humerus. Twelve months after the injection, follow-up radiographs had shown healing of the cyst. The patient …

Simple bone cysts were treated by trepanation. The technique consists of drainage of cyst fluid, lavage of the cystic cavity with saline, and the making of multiple drilling holes through the cortical and the medullary bone of the cyst wall. Injection of corticosteroid was omitted. In 11 cases treated by this method, the clinical outcome was good. Biochemical analyses of the cyst fluid showed bone-resorptive factors, i.e., prostaglandins, interleukin 1, proteolytic enzymes. Electrophoretic analysis of proteolytic enzymes in polyacrylamide gel containing sodium dodecyl sulfate and polymerized gelatin showed proteins with molecular weights of about 130,000, 92,000, 72,000, and lower than 50,000. Increase in such bone-resorbing activities seems to be one of the causative factors in simple bone cysts. The technique was effective in decompressing the internal pressure of the cysts, improving the blood flow through the medullary bone of the cyst wall, stimulating the periosteum to induce bone formation, and eliminating bone destruction.

Unicameral bone cyst fluid possesses N-acetyl-beta-D-glucosaminidase, beta-glucuronidase, PZ-peptidase, cathepsin D, acid phosphatase, N-acetyl-beta-D galactosaminidase, and beta-galactosidase activities. The activities of lysosomal enzymes in the cyst fluid are, as a rule, higher than in the serum, whereas the total protein content is lower. The content of collagen degradation products in the cyst fluid is higher compared to the serum. In bone cavity wall tissues, the collagen content is decreased. Adenosine 3':5'-cyclic phosphate and cyclic guanosine 3,5'-monophosphate accumulate in the cyst cavity. However, in some cases, there is no correlation among the activities of lysosomal enzymes in the cyst fluid, blood serum, and cyst wall tissues. The ratios of lysosomal enzyme activities in the cyst fluid differ from those in the cyst wall tissues, cultured skin fibroblasts, and blood polymorphonuclear leucocytes. The lack of coincidence of enzymatic spectra of the cyst fluid, wall tissues, and serum is suggestive of the diversity of ways of lysosomal enzyme enter the cyst cavity, i.e., blood, cyst fluid cells, and cyst cavity walls. The cysts with different locations (i.e., active and latent cysts) have similar lysosomal lytic potentials. The presence in the cyst cavity of extracellular lysosomal enzymes and collagen degradation products testifies to the permanent corrosion of the cyst cavity walls from the inside as well as to the increase in the osmotic pressure of the cyst fluid. Lysosome destruction should be regarded as an important pathogenetic factor that requires surgical or pharmacologic correction or both in the course of bone cyst management.

Summary An 8-year-old boy sustained a fracture of the distal fibula. The fracture resulted from Ewing's sarcoma infiltrating a unicameral bone cyst. Ewing's sarcoma has not previously been described in association with a unicameral bone cyst.

Twenty cases of calcaneal solitary bone cyst were evaluated. The typical lesion had a pathognomonic roentgenographic appearance. Eleven patients were treated by curetting and bone-grafting, and there were no recurrences. The cysts in patients followed non-operatively usually did not heal, but were asymptomatic and did not enlarge. A recommendation for non-operative management is made for most cases because the cysts are frequently painless and not likely to fracture.

A series of 175 unicameral bone cysts is presented. The pathogenesis of the lesion and the results of treatment differed depending upon the specific bone involved. It is our opinion that prompt surgical treatment to establish an accurate histological diagnosis and to reinforce the involved segment of bone against fracture by thoroughly evacuating the cavity and filling it with bone grafts is a more satisfactory treatment than watchful waiting. A persistent and static roentgenographic defect after surgery should not be considered a clinical failure if adequate bone strength is present. A second operation is indicated only for an enlarging cyst with the threat of fracture. In this series of 129 primary operations, the incidence of re-operation was 30 per cent in the proximal end of the humerus, 17 per cent in the proximal end of the femur, 1 1 per cent in the proximal end of the tibia, and nil in most of the other less frequent locations. In retrospect, a number of second procedures were considered unnecessary since they were performed for asymptomatic and static roentgenographic defects associated with sufficient bone strength to prevent fracture. True recurrence followimug surgical treatment is significantly more frequent in patients under ten years of age. Age is a more reliable prognostic criterion than the proximity of the cyst to the epiphyseal plate when assessing the likelihood of recurrence after surgical treatment.

Twenty cysts were treated by excision of most of the cyst wall, including bone, and grafting with struts of autologous or homologous bone. Eleven cysts were in the active phase and nine were in the latent. All but one was cured without recurrence, and that cyst healed after a second operation. The ages of the patients with active cysts ranged from four and a half to ten years; one patient was twelve years old. Data on twenty other patients, some treated by curettage and bone-grafting and some (six) in whom early healing followed fracture, are also given.

Cyst fluid of six simple cysts of bone was aspirated and determinations of electrolytes and protein content made. In four of the cysts the fluid resembled plasma. In two others it resembled blood. A theory of etiology of simple cysts is suggested in which the principal etiological factor is blockage of the drainage of interstitial fluid in a rapidly growing and rapidly remodeling area of cancellous bone.

Certain conclusions may be drawn from this case concerning the role of the epiphyseal plate in solitary bone cysts. 1. Apparently the cysts are usually delimited by the cartilage plate from extension into the epiphysis, but this rule is not infallible, and one must not be guided by this finding alone in arriving at a preoperative diagnosis. 2. A defect in the cartilage plate may not limit growth in the area of the defect unless the peripheral portion of the plate—that adjacent to the cortex—is also destroyed. 3. Curettage and filling the cavity with bone chips, as reported by numerous authors 1-5. 7, arrests the progress of the lesions and results in the cavity being filled with normal-appearing bone. Even when a cavity is packed, so that the bone crosses into the epiphyseal area through a defect in the epiphyseal-cartilage plate, it probably will not arrest normal bone growth.

The roentgenographic findings in unicameral bone cyst may be difficult to differentiate from a solid tumor of bone. When present, the fallen fragment sign may aid in determining the roentgenographic diagnosis of unicameral bone cyst. In this finding, with a pathologic fracture a fragment of cortical bone may become dislodged and gravitate to the dependent portion of the unicameral bone cyst. Two examples of the fallen fragment sign demonstrate the displacement of a fragment of cortical bone to the dependent portion of the cystic cavity.

Unicameral bone cysts are rarely observed in the foot. A histologically proven unicameral bone cyst occurred in the talus of a three-year-old boy. Six additional cases in the world literature are cited to illustrate the therapeutic and diagnostic problems encountered with this lesion.

Extremely favorable results are obtained with the use of microcrystals of methylprednisolone acetate for treatment of bone cysts. These results have led to a complete suspension of surgical treatment of bone cysts since 1974. On the basis of these results with corticosteroids, a surgical procedure that involves an incision at the fracture location and bone graft inserted is not indicated. Results following surgery indicate a recurrence rate of approximately 25% to 30%. Since we are as yet unable to explain the mechanism by which the local injection of MPA promotes bone replacement of the cyst, the present observations only reaffirm the hypothesis (presented in our early publications) that the corticosteroid exerts a destructive action on the pathological tissue of the lesion, thus favoring a progressive process of repair. We consider this explanation valid even for lesions, e.g., eosinophilic granulomas and nonossifying fibromas, in which this method of treatment has had varying degrees of success.

This is a case report of a 21 year old man with a unicameral bone cyst of the scapula. The occurrence here, as in other flat bones, is rare. The unusual location presents a diagnostic problem, but as in other flat bones, the prognosis after treatment by bone grafting is very good.

Unicameral bone cysts of the scapula have been reported mainly in adult patients. The atypical location of the unicameral bone cyst in a 12-year-old girl presented a diagnostic dilemma. Curettage proved to be an effective method for both diagnosis and treatment of this benign lesion.