Review Article Unicameral Cysts: General Characteristics and Management Controversies

Abstract Juan Pretell-Mazzini, MD Unicameral bone cysts are benign bone lesions that are often Robert Francis Murphy, MD asymptomatic and commonly develop in the proximal humerus and of skeletally immature patients. The etiology of these lesions Indranil Kushare, DNB, DOrtho remains unknown. Most patients present with a pathologic John P. Dormans, MD fracture, but these cysts can be discovered incidentally, as well. Radiographically, a unicameral appears as a radiolucent From the Department of Orthopaedic lesion with cortical thinning and is centrally located within Surgery, Musculoskeletal Oncology Division, University of Miami, Jackson the . Although diagnosis is frequently straightforward, Memorial Hospital, Miami, FL management remains controversial. Because the results of (Dr. Pretell-Mazzini), the Department various management methods are heterogeneous, no single method of Orthopaedic Surgery, University of Tennessee, Campbell Clinic, has emerged as the standard of care. New minimally invasive Memphis, TN (Dr. Murphy), the techniques involve cyst decompression with bone grafting and Division of Orthopaedic Surgery and instrumentation. These techniques have yielded promising results, Sports Medicine, Children’s National Medical Center, Washington, DC with low rates of complications and recurrence reported; however, (Dr. Kushare), and the Division of prospective clinical trials are needed to compare these techniques Orthopaedic Surgery, The Children’s Hospital of Pennsylvania, with current evidence-based treatments. Philadelphia, PA (Dr. Dormans). Dr. Murphy or an immediate family member serves as a board member, nicameral bone cysts (UBCs) are we offer a comprehensive review of owner, officer, or committee member benign, fluid-filled cavities that the current knowledge of UBCs based of the American Academy of U Orthopaedic Surgeons. Dr. Dormans develop in tubular and flat (eg, on a MEDLINE literature search of or an immediate family member humerus, femur). These cysts tend to articles on etiology, pathophysiol- serves as a board member, owner, expand and weaken the local bone, ogy, clinical presentation, radiologic officer, or committee member of the but they are not true neoplasms. In assessment, and the most commonly Société Internationale de Chirurgie 1 Orthopédique et de Traumatologie 1876, Virchow first described these used management strategies. We (SICOT) USA, the Scoliosis Research lesions as cystic structures caused by selected articles based on their clinical Society, the SICOT Foundation, and abnormalities in local circulation.2 importance for the practicing ortho- the World Orthopaedic Concern. UBCs are also known as simple or paedic surgeon. Neither of the following authors nor any immediate family member has solitary bone cysts. They occur almost received anything of value from or has exclusively in children and adoles- stock or stock options held in cents (up to 85% of cases),2,3 with Etiology a commercial company or institution a reported peak between ages 3 and related directly or indirectly to the subject of this article: 14 years and the average age at The etiology of UBCs is currently Dr. Pretell-Mazzini and Dr. Kushare. diagnosis being 9 years.4 These lesions unknown. Historically, these lesions J Am Acad Orthop Surg 2014;22: represent approximately 3% of all were thought to be a pathologic 295-303 bone tumors and occur more com- response to bone trauma5 or an in- monly in boys than in girls (2:1).1,4 traosseous synovial cyst6 that devel- http://dx.doi.org/10.5435/ JAAOS-22-05-295 The clinical characteristics, diag- oped as a result of venous obstruction nosis, and management of UBCs have that led to intramedullary accumula- Copyright 2014 by the American Academy of Orthopaedic Surgeons. been well described; however, man- tion of interstitial fluid and cavity agement remains controversial. Here, formation.7,8

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Figure 1

A, Low-power view of a frozen section of fragments of trabecular bone with marrow elements and tissue demonstrating chronic inflammation, granulation tissue, hemosiderin-laden macrophages, and multinucleated giant cells in a 14-year-old boy who was referred for right shoulder pain during activity (hematoxylin-eosin stain). B, AP radiograph of the right humerus demonstrating a centrally located lytic lesion within the medullary cavity and thinned cortices. No cortical destruction, fracture, malalignment, or periosteal reaction was detected. C, Sagittal short-tau inversion recovery MRI sequence demonstrating the lesion with high signal intensity. D, Coronal T1-weighted magnetic resonance image of the humerus demonstrating the cyst, with low signal intensity and homogeneous intensity present throughout the cyst cavity.

of long bones. In one study, the regarding radiation exposure in chil- Pathology proximal humerus and proximal dren, CT is typically reserved for le- femur were the most commonly sions in areas that are not easily In general, the gross pathology of affected sites (.90%).10 However, viewed on plain radiography and a UBC demonstrates a singular fluid- the cysts can develop in other areas when there is concern regarding the filled cavity. In some cases, multi- of the axial and appendicular skele- structural integrity of a weight- locular lesions are present. The bony ton, including, but not limited to, the bearing area. On MRI, UBCs typi- architecture surrounding the cyst is calcaneus, pelvis, and spinous pro- cally demonstrate low signal intensity nonreactive and otherwise unremark- cesses.11-13 on T1-weighted sequences and high able. Microscopic and histologic signal intensity on T2-weighted and analysis shows a fibrous tissue mem- short tau inversion recovery sequences brane, with occasional giant cells (Figures 1, C and D). Compared with present (Figure 1, A). The biochemical Radiologic Evaluation plain radiography, T1-weighted MRI composition of the fluid within the is superior for predicting fracture cysts contains high levels of prosta- Traditionally, plain radiography has risk.14 Cystography can also be used glandins and other enzymes.9 been used to diagnose and monitor UBCs, but advanced imaging has to aid the diagnosis and management 8,15 become more popular as the tech- of these lesions. Clinical Presentation nology has improved. On plain radi- ography, UBCs appear as lytic, Clinical presentation depends on expansile lesions within the medul- Differential Diagnosis whether a is pres- lary cavity of a long bone. The cortex ent. If the cyst is discovered inciden- is thinned but typically is not com- Primary differential diagnoses for tally, the patient may not have any promised (Figure 1, B). Rarely, UBC include complaints or physical manifestations. a UBC can develop in the diaphyseal (ABC), fibrous dysplasia, enchon- However, in the setting of pathologic portion of long bones and is known droma, and intraosseous ganglia. fracture, patients typically present as a latent cyst. Careful inspection of radiography with pain, swelling, and erythema and Advanced imaging has proved use- coupled with knowledge of the may present with deformity. ful for confirming diagnosis of a UBC, defining radiologic features of each of Typically, UBCs are located at the especially in unusual areas such as these lesions will assist the clinician in proximal end of the medullary canal the pelvis. Because of the concern making an accurate diagnosis. An

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Table 1 Summary of Clinical Outcomes of Injections Used to Manage Unicameral Bone Cysts Initial Healing Recurrence Study No. of Patients Type of Injection Rate (%) Rate (%) Level of Evidence

Cho et al23 25 DBM 76 8 III Chang et al24 79 ABM: 14, steroid: 65 ABM: 43, steroid: 51 NA III Rougraff and Kling25 23 ABM and DBM 69 21.7 IV Di Bella et al26 184 ABM and DBM: 41, ABM and DBM: 58, NA III steroid: 143 steroid: 21 Thawrani et al27 13 a-BSM 38.5 0 IV

ABM = autologous bone marrow, a-BSM = apatitic calcium phosphate bone substitute material, DBM = demineralized bone marrow, NA = not available

ABC is a lytic, intramedullary bone Successful management of a UBC healing is characterized by ,80% lesion, with eccentric expansion and results in a healed bone with normal opacification of the cyst with no a transverse diameter that is wider than mechanical and anatomic axes that cortical thickening. the epiphyseal plate. MRI is helpful for can withstand functional activity. delineating double-density fluid levels Nonsurgical treatment is recom- Medical Therapies and septations, which are much more mended when UBCs are discovered The theoretical use of diphospho- common in cases of ABC than in those incidentally in asymptomatic patients nates and botulinum toxin for of UBC.16 Monostotic fibrous dys- and there is no substantial decrease in management of UBCs has been plasia has the radiographic appear- the strength of the affected bone to investigated in some basic science ance of ground glass (typically caused warrant invasive intervention. It is research.21,22 However, there are no by cystic degeneration), which is reasonable to treat these patients with established or recommended med- a hallmark feature that distinguishes it close observation unless the affected ical or noninterventional treat- from a UBC. Enchondromas are well- bone is at risk of pathologic fracture. ments for this condition. defined, radiolucent intramedullary In patients with a pathologic fracture lesions that may be associated with of the upper extremity associated thinning and expansion of the cortex; with a UBC, initial nonsurgical Injection Techniques however, they are more commonly treatment with immobilization for 4 Several agents have been used for found in short tubular bones of the to 6 weeks is appropriate. intralesional injection of UBCs, hands and feet. Typically, intra- Although a healed bone constitutes with heterogeneous results reported osseous ganglia are small radiolucent successful management of a UBC, no (Table 1). Scaglietti28 first described lesions that are oftendiscoveredinci- standard definition of healing exists. the use of methylprednisolone in- dentally in the epiphysis and sub- Spontaneous healing occurs in jections in patients with UBCs and chondral region.17-19 ,10% of patients with a UBC as reported “favorable” results in 90%. a result of traumatic decompression However, radiographic assessment of the cyst caused by pathologic showed that several of the treated Management fracture.2 We use a clinical radio- cysts were clinically stable but not graphic tool to assess UBC healing.20 completely healed, and these cysts Strategies for management of UBCs The parameters include cyst opaci- were reported as favorable results. have evolved over the years. Cur- fication on plain radiography, Subsequent studies have failed to rently, management methods include thickening of the cortices, and pain reproduce these findings, even fol- injection, decompression, and com- status of the patient. We define lowing multiple steroid injections and bined surgical techniques. Although complete healing as .95% opacifi- anesthetics; recurrence rates of 15% no single, superior management cation of the cyst with cortical to 88% have been reported after method has emerged, treating clini- thickening and no pain. Partial an average of three injections.29,30 cians must consider and select the healing is defined as .80% to 95% Because of its osteogenic potential, appropriate option for each patient opacification of the cyst with or with- autologous bone marrow (ABM) has to optimize care. out cortical thickening. Incomplete been used to stimulate healing of

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UBCs. Although some studies have Figure 2 reported higher success rates with ABMthanwithsteroids(52%versus 23%, respectively) and a lower recur- rence rate (13% versus 42%, respec- tively),23 other studies found no advantage with the use of ABM.15,24 Rougraff and Kling25 combined the osteogenic potential of ABM with the osteoinductive/osteoconductive properties of demineralized bone marrow (DBM) to treat 23 patients with UBCs. They found that this injection regimen demonstrated a higher healing rate than did steroid injection (58% versus 21%, respec- tively) and a lower failure rate (24% versus 63%, respectively).26 In a study of 13 patients with UBCs treated with an injection of an osteoconductive A, AP radiograph of the humerus showing a pathologic fracture through apatitic calcium phosphate bone sub- a unicameral bone cyst in a 13-year-old boy who reported pain and functional stitute, complete healing rates were limitation after trivial trauma. He was treated with immobilization for a 6-week period before surgery. B, Postoperative AP radiograph of the humerus following comparable to those of other modal- percutaneous curettage, intramedullary decompression, and insertion of ities (eg, minimally invasive techni- osteoset pellets. C, AP radiograph of the humerus obtained at 2-year follow-up ques), with no recurrence reported.27 demonstrating complete healing of the cyst. The results of these studies must be interpreted with caution because the Risk factors for pathologic fracture graft bone grafting, healing rates outcome variables are not standard- associated with UBC include a cyst were as low as 25% to 36%, and only ized. Furthermore, agents such as with a transverse diameter that is improved marginally (37% to 50%) ABM and DBM are not radiopaque, .85% of the diameter of the affected even after a repeat procedure was making follow-up radiographic stud- bone and a cyst wall that is ,0.5 mm performed35,36 (Table 2). The use of ies difficult to interpret. Although the thick.32-34 A wide variety of surgical calcium sulfate pellets for grafting use of biologic and synthetic injections procedures has been proposed for yielded a better healing rate (66%) have yielded promising results, addi- management of active lesions. Histor- than did bone grafting; however the tional large, long-term studies are ically, curettage and bone grafting has rate of recurrence remains high required to prove the superiority of been the definitive open procedure for (25%).37 these agents over steroids. management of UBC. However, innovative techniques have been Decompression Techniques described recently, including decom- Surgical Techniques Based on Cohen’s7 hypothesis in pression (with no instrumentation left Surgical treatment is indicated for which venous obstruction leads to in- in place), instrumentation (eg, cannu- symptomatic patients with an obvious tramedullary accumulation of inter- lated screws, flexible intramedullary or suspected pathologic fracture,31 stitial fluid that results in cavity nails), and combined methods. those with cyst enlargement during the formation, a UBC can be decom- observation period, or those with cysts pressed by violating the wall of the cyst located in bones that have a risk of Curettage and Bone Grafting and draining its contents, allowing pathologic fracture (eg, proximal Although this technique has been the native marrow to enter the cavity. femur).1,2 In a study of 55 patients with classic management method for Decompression can be achieved using UBCs, 91% percent initially presented UBCs, recent studies do not support needles, curets, or implants (eg, intra- with pathologic fractures.20 Of these, the use of this modality. Studies that medullary nails, cannulated screws, 32 patients (58%) presented with compared various methods of man- Kirschner wires). In a study of 12 macrofractures and 18 (33%) pre- aging these cysts have reported that, UBCs, Gebhart and Blaimont44 sented with microfractures (Figure 2). following open curettage and allo- described a decompression technique

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Table 2 Summary of Outcomes for Surgical Management of Unicameral Bone Cysts No. of Healing Recurrence Level of Study Patients Technique Graft Material Rate (%) Rate (%) Evidence

Mik et al20 55 Percutaneous curettage, Calcium sulfate pellets 80 0 IV decompression with a flexible IM nail Brecelj and 8 Open curettage and bone 50% glucose and bone 25 NA III Suhodolcan35 grafting allograft Sung et al36 34 Open curettage and bone Corticocancellous 36 NA III graft allograft bone chips Hou et al37 12 Open curettage and grafting Calcium sulfate pellets 66 25 III 12 Percutaneous curettage; Calcium sulfate pellets 91.6 NA III ethanol injections; IM decompression, grafting, and placement of a cannulated screw for continuous decompression Canavese et al38 10 Disruption of cyst walls with None 70 NA III percutaneous curettage de Sanctis and 47 Decompression with None 65.9 0 IV Andreacchio39 a flexible IM nail Masquijo et al40 48 Decompression with None 54.2 8.33 IV a flexible IM nail Glanzmann and 22 Decompression with None 72.7 9 IV Campos41 a flexible IM nail Kanellopoulos 9 Decompression with DBM/iliac crest bone 77 0 IV et al42 a flexible IM nail marrow Dormans et al43 24 Percutaneous curettage, Calcium sulfate pellets 91.7 0 IV decompression with a flexible IM nail

DBM = demineralized bone marrow, IM = intramedullary, NA = not available

in which saline was injected at high medullary nails, healing rates of up to outcomes. Dormans et al43 described speed with alternate aspiration of cyst 73% were reported at 2- to 10-year the use of a minimally invasive tech- fluid. The authors reported that 11 follow-up, with recurrence rates of nique that consists of percutaneous cysts went on to heal. In a recent ,10%.39-41 In a study of nine pa- intramedullary decompression, curet- comparative study of management of tients with UBCs treated with flexible tage, and grafting with medical-grade UBCs with percutaneous curettage, intramedullary nails and an injection calcium sulfate pellets. First, cystog- steroid injection, or autologous bone of DBM/iliac crest bone marrow, raphy was performed with aspiration marrow injection, simple cyst decom- cysts healed completely in 7 patients of cystic fluid and injection of dye into pression with percutaneous curettage (77%), with no recurrence re- the cyst (Figure 3, A). After the dye had better healing rates than did ster- ported.42 Although the overall results was injected, percutaneous curet- oid or bone marrow injections (70%, of treatment with intramedullary tage of the cyst lining was per- 41%, and 21%, respectively).38 nails is impressive, clinicians must formed with a pituitary rongeur Most of the recent literature on recognize that this technique requires and angled curets (Figure 3, B). decompression of bone cysts with a second surgery to remove the nails. Excised tissue was sent for frozen implants focuses on the use of intra- section when the findings were equiv- medullary nails alone or in combina- Combined Techniques ocal. After curettage, intramedullary tion with DBM injection. In three Some authors have proposed com- decompression was performed using large series of patients with UBC bining mechanical techniques with an angled curet or a flexible intra- treated solely with flexible intra- biologic agents in an effort to improve medullary nail (Figure 3, C). Finally,

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Figure 3

A though C, Fluoroscopic images of the right proximal humerus in a 14-year-old boy with a unicameral bone cyst and a 2-month history of pain. A, Following cyst aspiration, dye was injected into the cyst. Note the homogeneous distribution of dye. A biopsy of the cyst wall was performed and sent for frozen section. B, Curettage was performed and the lining of the cyst wall was removed. C, The cyst was decompressed with a flexible intramedullary nail. D, Postoperative AP radiograph of the humerus demonstrating the final reconstruction following placement of medical-grade calcium sulfate pellets in the cavity.

medical-grade calcium sulfate pellets remaining membrane lining of the were inserted into the cyst, com- active cyst. A 4.5-mm cannulated Management of Pathologic pletely filling the cavity (Figure 3, D). screw was then inserted for contin- Fractures Associated At a mean follow up of 21.9 months uous decompression. The authors With UBCs (range, 4 to 48 months), complete reported a partial or complete heal- Pathologic fractures of the proximal healing (defined as opacification of ing response in 11 patients, but 1 had femur associated with UBCs can lead .95% of the cyst with cortical a subtrochanteric femoral fracture 2 to serious complications, including thickening) was reported in 22 pa- months after initial treatment. varus malunion, osteonecrosis of the tients (91.7%). In a study of 55 pa- Intramedullary decompression, which femoral head, and growth arrest of tients with UBCs treated with this allows for the introduction of native technique, Mik et al20 reported that, bone marrow cells into the cyst, is part the proximal femoral physis. Typi- at a mean follow-up of 37 months of both of these combined techniques. cally, these fractures are treated with 32 (range, 24 to 70 months), 44 patients Inouropinion,thisstepiscriticalfor internal fixation. 32 (80%) had a partial (cyst opacifica- successful healing. In addition, the Dormans and Pill classified tion of 80% to 90%, with or without radiopaque nature of calcium sulfate management of pathologic proximal cortical thickening) or complete pellets that are placed in the cystic femoral fractures associated with healing response after initial surgery, cavity is helpful for radiographic UBCs into six types based on the with a cumulative healing rate of follow-up. Because UBCs are radio- location and size of the cyst and the 100% after three procedures. lucent, a treated cyst that remains presence or absence of the lateral Hou et al37 described the use of unhealed will appear as a radiolu- buttress (Figure 4). Type IA fractures a similar technique to treat 12 pa- cent area on radiography. Radi- have a cyst of moderate size in the tients with UBCs. In addition to opaque agents such as calcium middle of the femoral neck. Ade- curettage, intramedullary decom- sulfate pellets integrate with bone in quate bone is present in both the pression, and bone grafting with time and, when a recalcitrant cyst or femoral neck and lateral proximal calcium sulfate, the authors injected recurrence is suspected, these agents femur (lateral buttress) to permit a 95% ethanol solution into the cyst serve as contrast to better assess these curettage and bone grafting followed cavity three times to kill the lesions. by fixation with cannulated screws.

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Figure 4

Illustrations demonstrating a classification system for management of pathologic pediatric fractures of the proximal femur associated with bone cysts. A, In type IA, a cyst of moderate size is present in the middle of the femoral neck. The lateral buttress is intact, and sufficient bone is available in the femoral neck and lateral proximal femur to allow fixation with cannulated screws. B, In type IB, a large cyst is present at the base of the femoral neck. The lateral buttress is compromised; therefore, the use of a pediatric hip screw and side plate should be considered. Types IIA (C) and IIB (D) are characterized by a large lesion in the femoral neck. E, In type IIIA, the lateral buttress is present, and cannulated screws can be used to stabilize the fracture. F, In type IIIB, the loss of the lateral buttress requires the use of a pediatric hip screw and a side plate for fixation following curettage and bone grafting.

In type IB fractures, a large UBC is physis is closing or closed. After successful treatment is the age of the present at the base of the femoral curettage and bone grafting are per- patient; patients older than 10 years neck. Although adequate bone is formed, cannulated screws can be heal at a higher rate (90%) than do available in the femoral neck, the use used for fixation of type IIIA fractures. younger patients (60%), no matter of a pediatric hip screw and side plate However, because of the loss of the what treatment regimen is used.32 should be considered rather than lateral buttress in type IIIB fractures, Alternatively, a lesion located ,2cm cannulated screw fixation because of a pediatric hip screw and side plate from the physis may be a risk factor the loss of the lateral buttress. A large should be used after curettage and for recurrence.45 The risk of recur- lesion is present in the femoral neck in bone grafting rather than fixation rence, however, may be related to type IIA and IIB fractures. Fixation with cannulated screws. Postoperative the treatment modality used rather with cannulated screws is not an immobilization with a spica cast is than the location of the lesion. Sur- option because of the lack of sufficient recommended for younger patients. geons are likely to be less aggressive bone beneath the physis. when the cyst is closer to the physis Two alternative management op- to avoid the potential for physeal tions are available for these fracture Prognosis damage. types. The first method involves curettage and bone grafting followed Although most UBCs resolve by the by insertion of smooth parallel pins time the patient reaches skeletal Complications across the physis. The second method maturity, patient age and the location requires the patient to be treated in of the cyst within the physis are pre- The most common complications traction (with subsequent application dictors of successful treatment that associated with management of UBCs of a spica cast) until the fracture heals; may aid clinicians in counseling pa- are potential embolization of the in- curettage and bone grafting can then tients and their families about the jected material (eg, steroid, bone mar- be performed. In types IIIA and IIIB, expected clinical course. For some row aspirate), local reactions to the the lateral buttress is present and the authors, the only predictor of material used to fill the cyst cavity,

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pathologic fracture, and growth dis- contents. In this article, reference 15 12. Hammoud S, Weber K, McCarthy EF: 46 Unicameral bone cysts of the pelvis: A study turbances. MacDonald et al noted an is a level II study. References 14, 23, of 16 cases. Iowa Orthop J 2005;25:69-74. exaggerated inflammatory response 24, 26, 29, 35-38, and 45 are level III 13. Tsirikos AI, Bowen JR: Unicameral bone following the use of recombinant bone studies. References 4, 6, 8-13, 16, cyst in the spinous process of a thoracic morphogenetic protein in patients with 20, 25, 27, 28, 30, 33, 34, 39-44, vertebra. J Spinal Disord Tech 2002;15(5): recalcitrant UBCs. Yandow et al47 and 46-48 are level IV studies. Ref- 440-443. used a precordial Doppler to evaluate erences, 2, 3, 5, 7, 17-19, 21, 22, 31, 14. Pireau N, De Gheldere A, Mainard- patients treated with steroid and bone and 32 are level V expert opinion. Simard L, Lascombes P, Docquier PL: Fracture risk in unicameral bone cyst: Is marrow injections and noted systemic References printed in bold type are magnetic resonance imaging a better physiologic changes associated with predictor than plain radiography? Acta those published within the past 5 years. 2011;77(2):230-238. these injections, including decreased Orthop Belg 1. Virchow R: On the formation of bony cysts, 15. Wright JG, Yandow S, Donaldson S, end-tidal CO2 and changes in heart in Uber die Bildung von Knochencysten. Marley L; Simple Bone Cyst Trial Group: A rate and blood pressure. Berlin, Germany, SB Akad Wiss, 1876, pp randomized clinical trial comparing As previously noted, fractures of 369-381. intralesional bone marrow and steroid the proximal femur are worrisome injections for simple bone cysts. J Bone 2. Wilkins RM: Unicameral bone cysts. JAm Joint Surg Am 2008;90(4):722-730. because of the potential for varus Acad Orthop Surg 2000;8(4):217-224. 16. Sullivan RJ, Meyer JS, Dormans JP, malunion, femoral head osteone- 3. Biermann JS: Common benign lesions of Davidson RS: Diagnosing aneurysmal and crosis, and growth arrest of the bone in children and adolescents. J Orthop unicameral bone cysts with magnetic Pediatr 2002;22(2):268-273. proximal femoral physis. In addition, resonance imaging. Clin Orthop Relat Res 1999;(366):186-190. growth arrest associated with UBC is 4. Boseker EH, Bickel WH, Dahlin DC: A clinicopathologic study of simple more common than generally appre- 17. Tahririan M, Motiffard M: Unicameral unicameral bone cysts. Surg Gynecol bone cyst of the proximal tibia in a five ciated and can present as limb-length Obstet 1968;127(3):550-560. year old girl. J Res Med Sci 2012;17(1): discrepancy, premature physeal clo- 5. Jaffe HL, Lichtenstein L: Solitary 104-107. sure, and deformity. In a study of 51 unicameral bone cyst: With emphasis on the 18. Remotti F, Feldman F: Nonneoplastic consecutive patients with UBCs of the roentgen picture, the pathologic lesions that simulate primary tumors of appearance and the pathogenesis. Arch 48 bone. Arch Pathol Lab Med 2012;136(7): humerus, 10% had growth arrest. Surg 1942;44:1004-1025. 772-788.

6. Mirra JM, Bernard GW, Bullough PG, 19. Gereige R, Kumar M: Bone lesions: Benign JohnstonW,MinkG:Cementum-like and malignant. Pediatr Rev 2010;31(9): Summary bone production in solitary bone cysts 355-362, quiz 363. (so-called “cementoma” of long bones): The natural history of UBCs indicates Report of three cases. Electron 20. Mik G, Arkader A, Manteghi A, microscopic observations supporting Dormans JP: Results of a minimally that they will resolve once the patient a synovial origin to the simple bone cyst. invasive technique for treatment of reaches skeletal maturity. Therefore, Clin Orthop Relat Res 1978;(135): unicameral bone cysts. Clin Orthop Relat 295-307. Res 2009;467(11):2949-2954. clinicians must balance the likelihood of successful treatment with the mor- 7. Cohen J: Etiology of simple bone cyst. 21. Yu J, Chang SS, Suratwala S, Chung WS, J Bone Joint Surg Am 1970;52(7): Abdelmessieh P, Lee HJ, Yang J, Lee FY: bidity associated with different man- 1493-1497. Zoledronate induces apoptosis in cells from agement options and the risk and fibro-cellular membrane of unicameral 8. Ramirez A, Abril JC, Touza A: Unicameral consequences of pathologic fracture. bone cyst (UBC). J Orthop Res 2005;23(5): bone cyst: Radiographic assessment of 1004-1012. Observation may be appropriate for venous outflow by cystography as a prognostic index. J Pediatr Orthop B 22. Namazi H: Practice pearl: A novel use of many patients with these bone cysts. 2012;21(6):489-494. botulinum toxin for unicameral bone cyst In cases that warrant intervention, Ablation. Ann Surg Oncol 2008;15(2): 9. Komiya S, Minamitani K, Sasaguri Y, 657-658. high success rates have been achieved Hashimoto S, Morimatsu M, Inoue A: with aggressive procedures that Simple bone cyst: Treatment by trepanation 23. Cho HS, Seo SH, Park SH, Park JH, involve cyst aspiration, curettage and and studies on bone resorptive factors in Shin DS, Park IH: Minimal invasive surgery cyst fluid with a theory of its pathogenesis. for unicameral bone cyst using bone grafting, and decompression. Clin Orthop Relat Res 1993;(287): demineralized bone matrix: A case series. However, levels of evidence for stud- 204-211. BMC Musculoskelet Disord 2012;13:134. ies that support different management 10. Campanacci M, Capanna R, Picci P: 24. Chang CH, Stanton RP, Glutting J: options for UBC remain low. Unicameral and aneurysmal bone cysts. Unicameral bone cysts treated by injection Clin Orthop Relat Res 1986;(204):25-36. of bone marrow or methylprednisolone. J Bone Joint Surg Br 2002;84(3):407-412. 11. Dormans JP, Dormans NJ: Use of References percutaneous intramedullary 25. Rougraff BT, Kling TJ: Treatment of active decompression and medical-grade calcium unicameral bone cysts with percutaneous sulfate pellets for treatment of unicameral injection of demineralized bone matrix and Evidence-based Medicine: Levels of bone cysts of the calcaneus in children. autogenous bone marrow. J Bone Joint evidence are described in the table of Orthopedics 2004;27(1 suppl):s137-s139. Surg Am 2002;84(6):921-929.

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