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Unicameral Bone Cyst

Last = Updated:=20 February 19, 2002
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Synonyms and related = keywords:=20 UBC, simple bone cyst, solitary bone cyst, bone cyst, = solitary=20 unicameral bone cyst, benign bone cyst, essential bone cyst=20 1

  AUTHOR INFORMATION=20 Section 1 of = 11   =20
Author=20 Information Introduction=20 Indications=20 Relevant=20 Anatomy And Contraindications Wo= rkup=20 Treatment=20 Complications=20 Outcome=20 And Prognosis Future=20 And Controversies = Pictures=20 Bibliography
Author: Charles=20 T Mehlman, DO, MPH, Director, Musculoskeletal = Outcomes=20 Research, Associate Professor, Division of Pediatric = Orthopaedic=20 Surgery, Cincinnati=20 Children's Hospital Medical Center

Charles T Mehlman, DO, MPH, is a member of the following = medical=20 societies: American Academy = of=20 Pediatrics, American Fracture=20 Association, American Medical=20 Association, American=20 Orthopaedic Foot and Ankle Society, American Osteopathic = Association,=20 Arthroscopy Association of = North=20 America, North = American Spine=20 Society, Ohio State = Medical=20 Association, Pediatric = Oncology=20 Group, Pediatric = Orthopaedic=20 Society of North America, and Scoliosis Research Society

Editor(s): Miguel A Schmitz, MD, = Consulting=20 Surgeon, Department of Orthopedics, Klamath Orthopedic and = Sports=20 Medicine Clinic; Francisco Talavera, PharmD, = PhD,=20 Senior Pharmacy Editor, Pharmacy, eMedicine; Sean P = Scully,=20 MD, PhD, Senior Associate Consultant, Department of = Orthopedics, Mayo Clinic of Rochester; Dinesh Patel, = MD, Assistant Clinical Professor of Orthopedic = Surgery,=20 Harvard Medical School; Chief of Arthroscopic Surgery, = Department of=20 Orthopedic Surgery, Massachusetts General Hospital; and=20 Harris Gellman, MD, Clinical Professor of=20 Orthopedic Surgery, University of Arkansas and University of = Miami;=20 Consulting Surgeon, Broward Hand Center =

A unicameral bone cyst (UBC) is = a=20 common benign fluid-filled lesion found almost exclusively in = children.=20 Much has been written about the diagnosis and management of these = lesions,=20 and evidence of a variety of successful treatment strategies can = be found=20 in the literature.=20

The orthopedic entity called a UBC is not believed to be a new=20 phenomenon. Lagier et al identified a UBC in the femur from the = remains of=20 a child from medieval times (Lagier, 1987). Virchow also = recognized such=20 bone cysts in humans in the late 1870s (Virchow, 1876).=20

In 1942, Henry Jaffe and Louis Lichtenstein published their = classic=20 paper concerning solitary UBC (Jaffe, 1942). In their article, the = authors=20 emphasized the distinctiveness of UBC by saying:=20

Solitary unicameral bone cyst is a lesion sui generis. = It=20 bears no relation whatever to giant cell tumor of bone, and in=20 particular it does not represent a cystic-healing phase of this = tumor.=20 Nor is it to be linked with enchondroma, fibroma or focus of = fibrous=20 dysplasia of bone that has undergone partial or extensive cystic = degeneration. Further, it should not be regarded as representing = cystic=20 expression of osteitis fibrosa, since to throw it into this = wastebasket=20 category (one which to us is also meaningless) is to obliterate = its=20 distinctiveness. Correspondingly, solitary unicameral bone cyst = ought no=20 longer to be classed as an expression of localized fibrocystic = disease=20 of bone or localized fibrous osteodystrophy=97likewise blanket=20 designations dating from a more primitive era of bone pathology. =

Despite abundant clinical confidence in managing these lesions, = many=20 basic questions still remain concerning the etiology and = pathophysiology=20 of UBCs.=20

This article offers a comprehensive review of the present state = of=20 knowledge of a UBC, highlighting aspects of its pathophysiology, = clinical=20 presentation, and the most commonly used treatment strategies.

History of the Procedure: For history of = surgical=20 procedures used to treat UBCs, see Surgical = therapy.

Problem: A UBC is a benign fluid-filled = radiolucent=20 lesion that may appear in virtually any bone, but, typically, it = is found=20 in either the proximal humerus or proximal femur. Illustrations of = such=20 lesions can be seen in Images=20 1-2. It often leads to thinning of adjacent areas of bone such = that=20 fracture or pain from microfracture may occur. When such cysts are = immediately adjacent to a growth plate, they are referred to as = active=20 cysts, and, when they have achieved some distance from the growth = plate,=20 they are considered to be latent cysts. This distinction has been = used in=20 the past, as it was believed to have prognostic significance. A = UBC=20 usually presents as a unifocal (one bone) problem, affecting = patients who=20 are skeletally immature.=20

The rarity of the lesion in adults supports a hypothesis of = spontaneous=20 resolution. In the absence of fracture through the cyst (or = impending=20 fracture), UBCs are asymptomatic. They are, at times, found=20 serendipitously when radiographs are taken for other reasons. In = the=20 absence of symptoms and in the absence of mechanical compromise of = the=20 involved bone (eg, extensive cortical thinning), no treatment may = be=20 necessary other than observation.=20

Treatment should be strongly considered for lesions that have = resulted=20 in fracture or marked weakening of bone. Some evidence exists that = spontaneous healing of a UBC may occur following fracture. Such = healing=20 occurs in only a minority of cases. Growth disturbance secondary = to a UBC=20 also is a concern (Stanton, 1998).=20

At least 2 case reports exist in which chondrosarcoma was found = to=20 arise within the same area of a previous histologically proven UBC = (Grabias, 1974). In a separate case, an 8-year-old boy was = reported to=20 sustain a pathologic fracture of the distal fibula that was = believed to=20 result from Ewing sarcoma infiltrating a UBC (Steinberg, 1985). = The=20 precise relationship between such rare instances of apparent = malignant=20 transformation and the thousands (if not millions) of UBCs that = have not=20 demonstrated such behavior remains unclear. At any rate, a UBC is = not=20 considered to be a malignant or premalignant lesion, and, as such, = routine=20 biopsy or other treatment of asymptomatic and nonproblematic = lesions based=20 on patient or family fear of cancer should not be undertaken.

Frequency: A UBC occurs most frequently in = children=20 aged 5-15 years, with an average age of approximately 9 years = (Capanna,=20 1996; Lokiec, 1998). Many authors consider cysts that present in = the first=20 decade of life to be more aggressive (Lokiec, 1998). A UBC affects = males=20 approximately twice as often as females (Campanacci, 1986; Neer, = 1966).=20 These lesions comprise approximately 3% of all bone tumors = (Oppenheim,=20 1984). A UBC probably represents the third or fourth most common = benign=20 bone tumor that the orthopedic surgeon confronts. The lesion may = occur in=20 conjunction with other benign bone tumors such as nonossifying = fibroma=20 (Godette, 1995).=20

By far, the most common location for the lesion is the proximal = humerus, followed by the proximal femur. The proximal humerus and = femur=20 together account for nearly 90% of all UBCs (Lokiec, 1998). = However,=20 virtually any bone may be affected, with the calcaneus being one = of these=20 notable alternate locations (Glaser 1999; Zenmyo, 2000; Chaudhary, = 2000;=20 Fikry, 1991).

Etiology: The specific etiology of a UBC has = not been=20 elucidated. Many theories have been proposed. One commonly quoted = theory=20 was proposed by Cohen in 1960. He studied the cyst fluid from 6 = children=20 undergoing treatment for UBCs and found 4 to resemble plasma and 2 = to=20 resemble blood. Cohen proposed that the principal etiological = factor is=20 blockage of the drainage of interstitial fluid in a rapidly = growing and=20 rapidly remodeling area of cancellous bone.=20

Chigira and a group of Japanese researchers studied the = internal=20 pressure of 7 patients with UBCs and found them to be higher (2-7 = mm Hg=20 range) as compared to contralateral normal bone marrow pressures = (Chigira,=20 1983). The partial pressure of oxygen found in the fluid from = these same=20 cysts was found to be impressively lower than venous or arterial = samples=20 taken at the same time. These authors suggested that venous = obstruction=20 within the bone appears to be a likely cause of such simple bone = cysts.=20

Such vascular theories have been supported by recent authors as = well=20 (Gebhart, 1996). Mirra has suggested that a UBC represents an area = of a=20 congenital rest of synovial tissue and has supported this by = demonstrating=20 both synovial type A (macrophagelike) and type B (fibroblastlike) = cells in=20 the lining of such cysts (Mirra, 1978). This description resembles = that of=20 an intraosseous synovial cyst. Yu et al also have demonstrated how = methylprednisolone influences the cellular physiology of synovial = cells in=20 culture, thus establishing a theoretic basis for steroid injection = treatments for a UBC (Yu, 1991).=20

In 1989, Shindel et al reported increased prostaglandin E2 = levels in=20 the cyst fluid from 7 of their patients and theorized that this = may help=20 explain the beneficial effect of steroid injection of such = lesions.=20 Gerasimov led a group of Russian researchers who stressed that the = fluid=20 from UBCs possesses increased lysosomal enzyme activity regardless = of the=20 UBCs' status as active or latent (Gerasimov, 1991). These authors=20 emphasized the role that such enzymatic activity might play in = permanent=20 corrosion of the cyst cavity, as well as increasing osmotic = pressure=20 within the cyst.=20

High levels of cytotoxic oxygen free radicals also have been = found in=20 the fluid from UBCs (Komiya, 1994). Such free radicals are = cytotoxic, and=20 they might be generated during the ischemic state following = blockage of=20 interstitial fluid drainage from UBCs. These Japanese researchers=20 suggested that such oxygen scavengers may contribute to the bone=20 destruction associated with UBCs. Reproduction of these results in = other=20 centers has not yet occurred.=20

In recent years, a group of Brazilian researchers have reported = specific genetic abnormalities in a pediatric patient with a UBC = of his=20 right distal femur. Vayego and her colleagues made their first = report in=20 1996. Cytogenetic analysis of the resected cyst initially = demonstrated=20 complex aberrations of chromosomes 4, 6, 8, 12, 16, and 21 = (Vayego, 1996).=20 Further study of the same patient (following bone cyst recurrence) = recently has revealed specific mutations associated with amino = acid=20 substitutions (arginine for tryptophane, arginine for serine)=20 (Vayego-Lourenco, 2001). Further study in this area clearly is = indicated,=20 and the potential for future gene-based therapies is seemingly = apparent.

Pathophysiology: Komiya and Inoue have the = only=20 longitudinal study (with serial radiographs over 6 y) that = documents the=20 development of a UBC over time. Initially, a small erosive lesion = of the=20 endosteal humeral metaphysis appeared, and, over time, the lesion=20 progressively enlarged into a typical UBC (Komiya, 2000). The = lesion=20 analyzed by these authors was somewhat unusual in that it was = located in=20 the distal humerus. In addition, the lesion appeared following = notation of=20 a previous UBC in the proximal aspect of the same bone.

Clinical: Most patients with a UBC present to = the=20 orthopedic surgeon after sustaining a pathologic fracture. Such = fractures=20 most commonly involve either the proximal humerus or the proximal = femur.=20 The events leading up to the fracture may vary from fairly = trivial, such=20 as throwing a ball, to more substantial, such as a hard fall while = playing=20 soccer. As with all patients who have sustained a fracture, a = careful=20 physical examination of the patient should include efforts to = exclude the=20 possibility of open fracture and neurocirculatory insult.=20

In other instances, patients may present to emergency = department=20 physicians, their primary care physicians, or orthopedic surgeons = for=20 other reasons, and radiographs obtained in the workup of other = complaints=20 may identify asymptomatic UBCs. Such incidental diagnosis of "a = bone=20 tumor" may be quite disconcerting to the child's parents and = family.=20 Random bone tumor discussion with such a child's family is=20 contraindicated. Medical personnel who eagerly deliver = well-intentioned=20 but inaccurate discussion of bone tumors often needlessly terrify=20 families.=20

In either of these scenarios, a review of the patient's past = history,=20 as well as their family's past history relative to fractures,=20 rheumatologic conditions, bone tumors, endocrine disease, and = cancer, is=20 appropriate. Physical examination of the patient also should = include a=20 screening examination of the axial skeleton and the uninvolved=20 extremities. Any other identified abnormalities may require = further plain=20 radiographs. Palpation of major lymph node areas, such as the = axillary and=20 inguinal fields, also is appropriate, as infection and malignancy = are part=20 of the differential diagnosis.

  INTRODUCTION = Section 2 of = 11   
Author=20 Information Introduction=20 Indications=20 Relevant=20 Anatomy And Contraindications Wo= rkup=20 Treatment=20 Complications=20 Outcome=20 And Prognosis Future=20 And Controversies = Pictures=20 Bibliography

The decision to pursue surgical=20 intervention in patients with UBCs is a highly individualized one. = An=20 asymptomatic lesion with satisfactory maintenance of cortical = thickness=20 may require only observation. A lesion with precarious cortical = thinning=20 (with or without insufficient pain) may demand surgical = intervention. In=20 addition, factors such as upper extremity (lower stress) versus = lower=20 extremity (higher stress) and younger children (more amenable to = cast=20 immobilization) versus older adolescents (less amenable to cast=20 immobilization) may strongly influence surgical decisions. Simple=20 treatment of the pathologic fracture may result in cyst resolution = in up=20 to 25% of cases (Farber, 1990).=20

Some authors have suggested the use of a cyst index aimed at = predicting=20 the future risk of pathologic fracture. In 1989, Andre Kaelin and = Dean=20 MacEwen discussed this concept. They defined their cyst index as = the area=20 of the UBC measured via its widest dimensions divided by the = diameter of=20 the diaphysis of the same bone (Kaelin, 1989). Based on their = statistical=20 analysis of 57 patients with UBCs, these authors recommended = mainly=20 observation for humeral cysts with an index of less than 4 and = femoral=20 cysts with an index of less than 3.5. When either of these = thresholds was=20 exceeded, stronger consideration regarding surgical intervention = was=20 believed to be appropriate.

  INDICATIONS = Section 3 of = 11   
Author=20 Information Introduction=20 Indications=20 Relevant=20 Anatomy And Contraindications Wo= rkup=20 Treatment=20 Complications=20 Outcome=20 And Prognosis Future=20 And Controversies = Pictures=20 Bibliography
=

Rele= vant=20 Anatomy: Anatomy relevant to UBCs mainly is that of the = proximal=20 humerus and proximal femur. Percutaneous approaches to the = proximal=20 humerus require the surgeon to avoid injury to the biceps tendon = as well=20 as the axillary nerve as it innervates the deltoid musculature. = The=20 standard delta-pectoral approach is the most common open surgical = approach=20 for proximal humeral lesions.=20

Key points of this approach include preservation of the = cephalic vein=20 as well as careful medial retraction of the conjoined tendon=20 (coracobrachialis and short head of biceps) to avoid injuring the=20 musculocutaneous nerve. Dissection in the region of the bicipital = groove=20 should be minimized, as this may injure the anterolateral = ascending branch=20 of the anterior humeral circumflex artery. This artery provides = the bulk=20 of the blood supply for the humeral head.

Contraindications: The main contraindication = for=20 surgical treatment of a UBC is a patient who otherwise meets = indications=20 for surgery but is unable to tolerate anesthesia. Another relative = contraindication for surgery is a patient with a small = asymptomatic latent=20 cyst with a low likelihood of pathologic fracture.

  RELEVANT ANATOMY AND = CONTRAINDICATIONS Section 4 of = 11   
Author=20 Information Introduction=20 Indications=20 Relevant=20 Anatomy And Contraindications Wo= rkup=20 Treatment=20 Complications=20 Outcome=20 And Prognosis Future=20 And Controversies = Pictures=20 Bibliography
Quick Find
Author=20 Information
Introduction
Indications
Relevant=20 Anatomy And Contraindications
Wo= rkup
Treatment
Complications
Outcome=20 And Prognosis
Future=20 And Controversies
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Bibliography

Click=20 for related images.

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Lab Studies:

  • The diagnosis of a UBC is strongly suspected based upon its = typical=20 radiographic appearance and is confirmed when appropriate cyst = fluid is=20 demonstrated. Specific laboratory tests are not a routine part = of the=20 workup of a UBC.

Imaging Studies:

  • Plain radiographs
    • Appropriate imaging studies for a UBC should always = include plain=20 radiographs.
    • The plain x-ray appearance of the lesion is virtually=20 diagnostic.
    • A particular radiographic sign (ie, fallen-fragment sign) = is, at=20 times, very helpful in the radiographic diagnosis of a UBC. = Reynolds=20 is credited with describing this sign in 1969 (Reynolds, = 1969).=20 Typically, the sign is identified when the patient with a UBC = presents=20 with a pathologic fracture. The interior of the bone cyst may = have=20 complete or nearly complete thin bony septations within the = cyst. At=20 the time of pathologic fracture, a portion of one of these = bony=20 segments actually may break free and float to the bottom of = the cyst.=20 This is possible because the UBC is fluid filled and is not a = solid=20 tumor. Some authors have altered the original description of = this sign=20 and referred to it as the fallen-leaf sign as they choose to = imagine=20 the broken fragment of bone gently wafting down from the top = of the=20 cyst to the bottom of the cyst as if it were a leaf slowly = falling to=20 earth from a tree. The fallen-fragment sign is found in = approximately=20 20% of patients who present with a pathologic fracture = secondary to=20 aUBC (Struhl, 1989).
  • Magnetic resonance imaging
    • If a UBC is in close proximity to a growth plate and = growth=20 impairment is a concern, magnetic resonance imaging (MRI) may = prove to=20 be quite helpful.
    • MRI should not be a routine part of the workup of a UBC. = Instead=20 it should be reserved for unusual or atypical situations. One = such=20 instance is a cyst where growth plate damage is a concern. = Several=20 authors have documented that such damage can occur about the = proximal=20 humeral growth plate.
    • Another situation in which preoperative MRI could be of = value is=20 in rare cases in which a more sinister diagnosis is suspected, = such as=20 in persons with pseudocystic osteosarcoma or low-grade central = osteosarcoma. In such instances, MRI is an appropriate part of = preoperative staging of such a tumor.
    • A UBC can produce a wide variety of appearances on MRI, = including=20 rather heterogenous fluid signals and even fluid-fluid levels = (a sign=20 much more commonly found in aneurysmal bone = cyst).
  WORKUP = Section 5 of = 11   
Author=20 Information Introduction=20 Indications=20 Relevant=20 Anatomy And Contraindications Wo= rkup=20 Treatment=20 Complications=20 Outcome=20 And Prognosis Future=20 And Controversies = Pictures=20 Bibliography

Medical therapy:=20 Nonoperative treatment of UBCs usually amounts to closed = fracture=20 care following pathologic fracture through the lesion. It has been = suggested that in as many as approximately 25% of cases, = spontaneous=20 healing of the cyst may occur following such pathologic fractures. = Not all=20 authors have reported such a high percentage of spontaneous = healing. Thus,=20 watchful waiting and routine fracture care only is not a = universally=20 accepted treatment option.

Surgical therapy: Surgical = therapy of=20 a UBC may be divided into open and percutaneous procedures. = Success of=20 such procedures has been quite varied, and the very definition of = success=20 also has varied from author to author.=20

In 1973, Neer and his coauthors stressed that reported = recurrence rates=20 in UBC surgery could be quite misleading if complete cyst = obliteration was=20 the criterion for success (Neer, 1973). They believed that true=20 recurrences were characterized by the cyst cavity reappearing and=20 enlarging, causing expansion and thinning of the cortex and the = threat of=20 fracture (Neer, 1973). The key aspects of the Neer rating system = for=20 purposes of evaluating treatment response (Neer, 1966) are as = follows:=20

Open techniques that have been reported include subtotal = resection with=20 and without bone grafting. Different bone grafting materials that = have=20 been used include autograft, allograft, demineralized bone matrix, = high=20 porosity hydroxyapatite bone grafting material, and = plaster-of-Paris=20 pellets.=20

Subtotal resection with and without grafting=20

In 1962, Fahey and O'Brien introduced a technique for UBC = treatment=20 that they referred to as subtotal resection and grafting (Fahey, = 1973).=20 The described technique involved subperiosteal exposure of the = cyst and a=20 portion of the adjacent normal bone followed by removal of two = thirds to=20 four fifths of the cyst. Cortical struts of bone graft harvested = from the=20 patient's iliac crest or tibia then were used to fill the defect.=20 Freeze-dried allograft also was used at times.=20

At an average of almost 4 years follow-up, Fahey and O'Brien = reported a=20 95% (19/20) success rate with their technique (using absence of = cyst as=20 their criterion). They considered the operation to be the = procedure of=20 choice for individuals with latent primary cysts and for persons = with=20 cysts that have recurred following conventional operation (Fahey, = 1973).=20 One patient required repeat grafting to achieve healing, and no = other=20 specific complications were reported with the technique.=20

In 1977, McKay and Nason reported on a similar subtotal = resection=20 approach to UBCs but without bone grafting. Their technique = yielded a 90%=20 (19/21) success rate (also defined as complete cyst obliteration) = (McKay,=20 1977). No infectious or neurocirculatory complications were = reported, but=20 they did identify 3 patients who suffered humeral growth = disturbances and=20 7 patients whose bones fractured during the procedure (although = this did=20 not substantively affect their later outcome).=20

Subtotal resection and bone grafting thus remains an option for = UBC=20 treatment. The procedure certainly carries with it a higher level = of=20 surgical morbidity than other procedures, and the surgeon's = enthusiasm for=20 the procedure may be directly proportional to the cyst's distance = from the=20 growth plate.=20

Curettage and bone grafting procedures have been used = extensively in=20 the treatment of a UBC.=20

Percutaneous treatment techniques=20

Interest in percutaneous treatment techniques for a UBC has = been rather=20 strong for the last 2 decades.=20

In 1974, Scaglietti introduced his procedure by which steroids = were=20 percutaneously instilled within UBCs (as well as other types of = bone=20 lesions) (Scaglietti, 1982). A minimum of 40 mg of = methylprednisolone=20 acetate was used for smaller cysts in young patients, and up to = 200 mg was=20 used for larger cysts in older patients (Scaglietti, 1982). The = described=20 technique included, on average, 3 or 4 injections in a period of = 12-20=20 months, but as many as 9 injections over 4 years were used = (Scaglietii,=20 1982).=20

Scaglietti reported complete healing of the bone cysts in 55% = of his=20 cases and 45% with some improvement, such as cortical thickening = within=20 the area of the cyst or areas of new bone formation within the = cyst=20 (Scaglietti, 1982). Twenty-four percent of his patients required = only one=20 injection, while 76% required multiple steroid injections. Image = 3=20 shows the typical appearance of fluid aspirated from UBCs.=20

Simple mechanical disruption of the cyst wall also has been=20 investigated as a treatment option for UBCs. Komiya and his = colleagues=20 called this trephination, and they reported good results in 10 of = 11 of=20 their patients. The technique consisted of aspiration of the cyst = until=20 venous hemorrhage became visible, perfusion of the cyst with = saline, and=20 cyst wall as well as proximal and distal medullary bone drilling = with a=20 Kirschner wire (Komiya, 1993). Chigira et al reported similar = success with=20 multiple drilling in 6 of 7 of their patients. Their technique = included=20 leaving the 2.0-mm Kirschner wires in place in some instances to = allow=20 drainage of the fluid through the cyst wall (Chigira, 1983).=20

Many other authors have reported their results and suggested=20 refinements of the percutaneous steroid technique. Rosenberg et al = emphasized the importance of eliminating fibrous or osseous septa = within=20 UBCs to facilitate bathing the entire lesion with the injected = steroids.=20 Capanna et al also pointed out that contrast examination allows = the=20 surgeon to identify noncontiguous septated areas of UBCs. Image = 4=20 illustrates intraoperative contrast evaluation of a UBC. This is = important=20 if optimizing the treatment response is desired (Capanna, 1984).=20 Injectable materials other than steroids, such as alcohol-based = fibrosing=20 agents, also have been suggested as treatment options for benign = bone=20 cysts (Adamsbaum, 1993; Garg, 2000).=20

Killian and his coauthors also have reported the use of = demineralized=20 bone matrix via a similar percutaneous technique. No steroids were = used.=20 Nine of their 11 patients demonstrated completely healed cysts at = 2-year=20 follow-up (Killian, 1998).=20

Recently, several authors have investigated the effectiveness = of=20 autologous bone marrow injection as a treatment for UBCs (Lokiec, = 1996;=20 Yandow, 1998). Spurred on by their earlier published work = (Wientroub,=20 1989), a group of Israeli researchers reported marked improvement = in=20 cortical thickness and cyst remodeling in 10 of their patients = following a=20 single bone marrow injection. Highlights of their technique = include the=20 following:=20

  • A single puncture into the cyst with a thin trocar or needle =

  • Aspiration of cyst fluid, which is sent for pathologic = analysis=20

  • Disruption of the lining and septations within the cyst = using the=20 trocar or needle=20

  • Contrast media examination (may be used)=20

  • Injection of autologous bone marrow aspirated from the iliac = crest=20 (average volume 25 cc)

All cysts healed completely with one procedure within 6-12 = months=20 (Lokiec, 1996).=20

Other authors (Yandow, 1998; Delloye, 1998) have demonstrated = similar=20 results with the percutaneous bone marrow injection procedure. = Yandow=20 noted that 10 of 12 of her patients with UBCs responded = satisfactorily to=20 the procedure, and Delloye et al had good results in 7 of their 8=20 patients. Kose and his fellow Turkish researchers evaluated the = outcome of=20 the autologous bone marrow procedure in 12 of their patients = (Kose, 1999).=20 Only 5 of 12 responded to the treatment, while 6 recurred and one=20 exhibited no response at all. These authors concluded that they = believed=20 the technique may be less effective in large cysts and in = multiloculated=20 cysts, and they recommended that the procedure be applied to = selected=20 patients only (Kose, 1999).=20

Comparative studies=20

Few comparative studies have been conducted regarding the = various=20 treatment alternatives for individuals with UBCs. Farber and = Stanton=20 performed a retrospective study of 36 patients with UBCs who were=20 surgically treated over a period of 45 years at the Alfred I. = DuPont=20 Institute (Farber, 1990). Curettage and bone grafting (with some = patients=20 receiving allograft and others receiving autograft) was associated = with a=20 53% (10/19) healing rate, while aspiration and injection with = steroid=20 yielded a 70% (12/17) success rate. Three of the 12 patients = required only=20 one injection. While this difference in overall healing rates = might appear=20 clinically significant, it was not statistically significant. The = authors=20 also did not explicitly define their criteria for success. The = authors=20 concluded that, because of similar healing rates and the lower = morbidity=20 of steroid injection, they favored this percutaneous approach over = traditional open curettage and bone grafting.=20

Oppenheim and Galleno reviewed 37 patients treated via open = surgical=20 techniques (35 curettage and bone grafting and 2 subperiosteal = total or=20 subtotal resection) versus 20 patients treated via steroid = injection. They=20 found a 38% recurrence rate and a 15% major complication rate in = their=20 open group, while the steroid injection group had only a 5% = recurrence=20 rate and a 5% major complication rate (Oppenheim, 1984). Although = not=20 calculated by the authors, this difference in recurrence rates is=20 statistically significant (P <0.02 via Fisher's exact = test).=20 These same authors used reconstitution of cortical thickness as = their=20 endpoint of healing rather than cyst obliteration.=20

Glaser and his colleagues have published a comparative study = focused on=20 calcaneal UBCs (Glaser, 1999). The calcaneus is a somewhat = uncommon site=20 (the third to sixth most common site for a UBC) for UBC (Moreau, = 1994;=20 Glaser, 1999). Glaser's multicenter study suggested that = percutaneous=20 steroid injection procedures were less effective in the calcaneal = lesions,=20 and they believed that curettage and bone grafting may be a more=20 predictable and successful procedure for simple bone cysts in this = location (Glaser, 1999).=20

Although not a new concept by any means (Imhauser, 1968), good = results=20 have been reported recently with flexible intramedullary nailing = of UBCs=20 in long bones (Roposch, 2000). Roposch and his coworkers reported = a 94%=20 (30/32) good response rate to flexible nailing of UBCs of the long = bones.=20 Complete cyst healing or healing with minor residual lucent areas = occurred=20 at an average of 36 months. Thus, this technique appears to = support the=20 compromised bone while the UBC follows its natural history and=20 spontaneously resolves. Some have stated that they believe such = flexible=20 nails allow continuous decompression of the UBC, with a resulting = decrease=20 in intralesional pressure (Roposch, 2000; Catier, 1981; Santori, = 1988.=20 Twenty-eight percent of patients required at least one further = operation=20 due to inadequate nail length in the face of continued bone growth = (Roposch, 2000).

  TREATMENT = Section 6 of = 11   
Author=20 Information Introduction=20 Indications=20 Relevant=20 Anatomy And Contraindications Wo= rkup=20 Treatment=20 Complications=20 Outcome=20 And Prognosis Future=20 And Controversies = Pictures=20 Bibliography

Injury to the growth plate = (physis)=20 may occur secondary to direct cyst expansion, pathologic fracture, = or=20 unintended mechanical disturbance during surgical intervention. = Direct=20 cyst expansion across the growth plate and into the epiphysis of = the=20 proximal humerus has been well documented by Gupta and Crawford = via MRI=20 (Gupta, 1996). Growth arrest also has been reported following = treatment=20 either by local injection of steroid or curettage and bone grating = (Stanton, 1998). Growth disturbance leading to angular deformity = or=20 disturbed longitudinal growth has been estimated to possibly occur = in=20 approximately 14% of cases (Lokiec, 1998). Steroid injection has = been a=20 successful treatment, even in the setting of cyst extension into = the=20 epiphysis (Malawar, 1982).

  COMPLICATIONS = Section 7 of = 11   
Author=20 Information Introduction=20 Indications=20 Relevant=20 Anatomy And Contraindications Wo= rkup=20 Treatment=20 Complications=20 Outcome=20 And Prognosis Future=20 And Controversies = Pictures=20 Bibliography

The overall outcome = and=20 prognosis of a UBC is good. The lesion is believed to resolve=20 spontaneously in most cases if given enough time. Cases that = present to=20 the orthopedic surgeon typically are patients who demonstrate a=20 combination of a cyst that has caused cortical thinning and the = right=20 stressful event, such as being tackled while playing football. In = general,=20 treatment may be summarized as doing nothing more than trying to = promote=20 natural healing. The flexible intramedullary nail studies = mentioned=20 earlier may do nothing more than mechanically support the bone = while the=20 natural healing process occurs.

  OUTCOME AND = PROGNOSIS=20 Section 8 of = 11   
Author=20 Information Introduction=20 Indications=20 Relevant=20 Anatomy And Contraindications Wo= rkup=20 Treatment=20 Complications=20 Outcome=20 And Prognosis Future=20 And Controversies = Pictures=20 Bibliography

Despite the = extensive=20 literature available on this common benign bone tumor called a = UBC, much=20 remains to be learned. As Bensahel has stated, "The solitary bone = cyst has=20 not revealed all its secrets" (Bensahel, 1998).=20

These and similar questions will require a far more coordinated = research effort than has been demonstrated in the past. A = multicenter=20 study just underway (a combined effort of the Shriner's Hospital = System=20 and the Pediatric Orthopaedic Society of North America) holds out = some=20 promise of refining the treatment approach to a UBC.

  FUTURE AND = CONTROVERSIES=20 Section 9 of = 11    =
Author=20 Information Introduction=20 Indications=20 Relevant=20 Anatomy And Contraindications Wo= rkup=20 Treatment=20 Complications=20 Outcome=20 And Prognosis Future=20 And Controversies = Pictures=20 Bibliography

  PICTURES = Section 10 of=20 11   
Author=20 Information Introduction=20 Indications=20 Relevant=20 Anatomy And Contraindications Wo= rkup=20 Treatment=20 Complications=20 Outcome=20 And Prognosis Future=20 And Controversies = Pictures=20 Bibliography
Caption: = Picture 1. Unicameral bone cyst. A large proximal = humeral=20 unicameral bone cyst demonstrates early cortical healing = following=20 pathologic fracture.
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Picture = Type:=20 X-RAY
Caption: = Picture 2. Unicameral bone cyst. A = large=20 unicameral bone cyst of the to pathologic fracture is = depicted. Note=20 the extension of the cyst into the region of the proximal = femoral=20 physis.
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3D"ClickeMedicine=20 Zoom View (Interactive!)
Picture = Type:=20 X-RAY
=
Caption: = Picture 3. Unicameral bone cyst. The typical appearance = of cyst=20 fluid is depicted. Initial aspiration often yields thin, = clear,=20 yellow fluid that rapidly becomes blood tinged. =
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3D"ClickeMedicine=20 Zoom View (Interactive!)
Picture = Type:=20 Photo
Caption: = Picture 4. Unicameral bone cyst. The double cannula = technique=20 demonstrates intraoperative use of contrast material for = evaluation=20 of cyst interior. In this case, a large partial septum = remains along=20 the inferior portion of the cyst.
3D"Click 3D"ClickView Full=20 Size Image
3D"ClickeMedicine=20 Zoom View (Interactive!)
Picture = Type:=20 X-RAY

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  • Catier P, Bracq H, Canciani JP, et al: [The treatment of = upper=20 femoral unicameral bone cysts in children by Ender's nailing = technique].=20 Rev Chir Orthop Reparatrice Appar Mot 1981; 67(2): 147-9[Medline].=20
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  BIBLIOGRAPHY = Section 11 of=20 11   =
Author=20 Information Introduction=20 Indications=20 Relevant=20 Anatomy And Contraindications Wo= rkup=20 Treatment=20 Complications=20 Outcome=20 And Prognosis Future=20 And Controversies = Pictures=20 Bibliography