Journal of Pediatric Orthopedics2:71-79 © 1982Raven Press, New York

Unicameral Bone Cyst with Epiphyseal Involvement:Clinicoanatomic Analysis

*Martin M. Malawer and tBruce Markle

Departments of "'Orthopedic Surgery and tRadiology, Children's Hospital National Medical Center and GeorgeWashingfOl7 University School of Medicine, washington, D.C.

Summary: Epiphyseal involvement of a unicameral bone cyst (UBC) is rare.This anatomic setting represents a distinct clinical and radiographic entity. Thisstudy reports a new case and analyzes the clinical and biological behavior ofseven additional UBCs with epiphyseal involvement from the literature. Wereport the first successful treatment of this variant with methylprednisoloneacetate. The average age was 20.1 years with a male to female ratio of 1.3: 1.Anatomic location: proximal femur (4), proximal humerus (2), and proximaltibia (2). Both age and location were atypical when compared to the classicmetaphyseal location. Radiographically, all lesions presented a characteristicinvolvement of the epiphysis and metaphysis in various proportions. Theepiphyseal plates were judged closed versus open in 50%, respectively.Follow-up ranged from 9 months to 3 years. Six cases healed following a singlecurettage (three with and three without bone graft). There were no late compli-cation of fracture, deformity, shortening, or avascular necrosis. Recurrencewas 0%. No secondary procedures were required. We conclude the age, loca-tion, and radiographic appearance is atypical and diagnosis is difficult, but thebiological behavior is less agressive and the prognosis more favorable than thetypical, metaphyseal UBC. Curettage with or without bone graft has a highsuccess rate. We recommend aspiration and intralesional methylprednisoloneas the initial management. We hypothesize that epiphyseal UBCs have a betterprognosis than metaphyseal location alone due to the older age, atypical loca-tion, and the potential of the epiphysis to reossify. Key Words: Epiphysis-Unicameral bone cyst-Methylprednisolone acetate-Proximal humerus-Proximal femur-Benign bone tumor (childhood).

Unicameral bone cyst (UBC) is a benign lesionfound in the long tubular bones of children and ad-olescents. Classically, they originate in themetaphysis, abut the growth plate, and later mayinvolve the diaphysis. This results from the con-tinued longitudinal bone growth of the epiphysisbeyond the site ofthe cyst (11). UBCs rarely involvethe epiphysis. Jaffee first decribed UBC, noting a

Dr. Malawer is Consultant at the Surgery Branch, NationalCancer Institute, N.I.H., Bethesda, Maryland.

Address correspondence and reprint requests to Dr. MaJawerat Department of Orthopedics/Oncology Section, Children'sHospital National Medical Center, III Michigan Avenue, .W.,Washington, D.C. 20010.

single example of epiphyseal involvement in a 42-year-old man (11). Cohn reported three cases ofUBC that had evidence of penetration of the physisat surgery (6). Other reports of epiphyseal involve-ment by UBC, including treatment and results, havebeen described (2,3,7,10,18,22). We have recentlytreated a solitary bone cyst with extensive epiph-yseal involvement in the proximal femur of a 14-year-old boy. Treatment consisted of biopsy, aspi-ration, and injection of methylprednisolone acetate.Curettage or bone grafting was not performed. Thepurpose of this paper is to report this case and toreview the literature.

A review of the literature has revealed a total of

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72 M. M. MALAWER AND B. MARKLE

seven cases of UBC with epiphyseal involvement(Table I) (2,3,7,10,11,18,22). All of these reportshave been of isolated cases (1942-1980). To ourknowledge, this study is the first report to analyzethe overall manifestation and behavior of unicam-eral bone cysts with epiphyseal involvement (EUBC).This paper presents a retrospective analysis of theabove cases in order to answer the following ques-tions:

I. What are the clinical and radiographic char-acteristics of UBCs with epiphyseal extension?

2. What is the clinical significance (biological be-havior) regarding growth disturbance, deformity,recurrence, and avascular necrosis?

3. What is the appropriate clinical managementof this rare variant?

CASE REPORT

A 14-year-old male complained of exercise-related pain in the right hip for 3 months not re-sponsive to salicylates. There were no other mus-culoskeletal or constitutional complaints. Therewere no cutaneous abnormalities. Physical exami-nation showed that both legs were of equal leglengths without atrophy. The gait was normal; theTrendelenburg test was negative. The range ofinternal and external rotation on the right hip waslimited by 30°. The remainder of the musculo-skeletal examination was normal. Laboratory

studies, including CBC, serum electrolytes, calciumphosphorus, and serum alkaline phosphatase werewithin normal limits.

Radiographic Evaluation

Radiographs of the right hip (Fig. l) demonstratedan extensive radiolucent defect of the femoral neckand capital femoral epiphysis, partly circumscribedby a narrow margin of sclerosis. The cortex showedthinning but no expansion, cortical breakthrough,periosteal reaction or fracture. The femoral neckwas of normal length without deformity. Theacetabulum, pelvis, and joint space were normal.

A 99'J'c-MDP bone scan (Fig. 2) revealed no in-creased uptake in the lesion, but a subtle decreasein the femoral neck. There was normal activity inthe growth plates (signifying an open, active growthplate) without evidence or hyperemia or soft tissueextension.

Computed tomography (Fig. 3) showed a lucent,nonexpansile lesion of the femoral head and neckwithout extraosseous extension or matrix forma-tion, with an internal absorption coefficient of fluid.The combined radiographic studies suggested anonagressive lesion. The preoperative differentialdiagnoses included atypical UBC, atypical chon-droblastoma, giant cell tumor, unusual aneurysmalbone cyst, or eosinophilic granuloma.

TABLE 1. Epiphvse al unicamera! bone C.I'SI: literature review

Location Rx Status CommentReference Age/sex

Relationshipto epiphyseal Status of

plate plate

Closed

Metaphyseal!epiphyseal

Closed

MetaphyseaJ/ Openepiphyseal

Metaphyseal! Closedepiphyseal (tomograms)

Metaphyseall Closedepiphyseal

Epiphyseal Open

II 42/M Distal femur

10 6.5/F Proximal tibia

221F Proximal femur

22 Proximal tibial(entire ~)

15.3/F Proximal humerus(entire VI)

241M Proximal humerus

18

7 171M Proximal femur

Malawer and 141M Proximal femurMarkley (1982)

Metaphyseal! Openepiphyseal

Curettage:bone graft

Curettage:no graft

Curettage:bone graft

Curettage:no graft

Curettage;no graft

Curettage;bone graft

Healed 3 years, No shortening,FROM" no deformity

Healed 18 rnos,no Fx·

FROM 9 mos,healed

Healed (80%),2 years

Healing 6 mos, Initially presentedasymptomatic with articular collapse and

early degenerative change

2 em shortening

Intralesionalmethylprednisolonealone; no curettageor graft

FROMhealed (80%)2 years

Pressure, 16 em H20(pulsatile)

a FROM. full range of motion.• Fx. fracture.

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UNICAMERAL BONE CYST WITH EPIPHYSEAL INVOLVEMENT

,B

Operative Procedure and Histology

The femoral neck was approached through ananterolateral incision. An I8-gauge needle was in-serted into the lesion, and clear, yellow fluid wasaspirated. Manometric measurements showed 16cm H20 pressure. Pulsation of the column syn-chronized with the patient's pulse. A Valsalva ma-neuver was performed, and a direct variation of thepressure was noted. Biopsy of the wall through alimited 0.5 x 0.5 em window in the anterior cortexconfirmed a cystic cavity with no underlying pri-mary neoplasm.

Histologically, the lining showed islands of acel-lular eosinophilic material, interspersed by a thinfibrous stroma containing a few vessels (Fig. 4).There were no giant cells, histiocytes, or hernosid-

R

FIG. 2. Coned down, pinhole collimator views of 99mTc-MDPbone scan of the hips, in frontal projection, show normallinear areas of increased activity at the open growth platesof the femoral heads (straight arrow). greater trochanters(small arrowhead), and at the triradiate cartilates (largearrowhead). Despite the uncertain status of the growth plateby radiography, this scan demonstrates an active physealmechanism within the lesion. Note the subtle photon defi-cient area of the right femoral neck corresponding to the cyst(curved arrow).

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FIG. 1. Initial anteroposterior (A) andlateral (B) radiographs demonstrate anextensive, well marginated, lytic de-fect of the femoral head and neck.The cortices of the femoral neck arethinned. The joint space and acetabu-lum are normal. The overall shape andsize of the femoral head are normal.There is no pathological fracture. Notethe extensive metaphyseal and epiph-yseal involvement without deformity.

erin. The clinical and histological diagnosis of UBCwas based on the finding of a cavity containing yel-low fluid lined by a thin fibrous membrane. Curet-tage and bone graft were not performed. Methyl-prednisolone acetate, 240 mg, was instilled underdirect vision via the cortical window, and thewound was closed. The dose was determined by theamount required to fill the cyst cavity.

RESULTS AND FOLLOW-UP

Postoperatively, the patient was maintainednonweight bearing for 6 weeks. Full weight bearingwas begun at 2 months. Twenty-four months fol-lowing surgery, he was fully ambulatory and par-ticipating in all activity. Examination of the hipshowed a full range of motion and a normal gait.

Radiographic Evaluation

Radiographs were obtained at 2 months, 6months, 8 months, 12 months (Fig. 5), and 18months (Fig. 6) after surgery. Serial radiographsshowed rapid thickening of the bony cortex andsecondarily progressive centripedal ossification.Heterotopic bone formation in the abductor mus-cles was noted and considered secondary to thesurgery. Twelve months after surgery, 80% of thedefect had reossified. There was complete reossifi-cation of the epiphysis and remodeling of the calcar,with premature obliteration of the epiphyseal plateand subsequent femoral neck shortening (decreasearticular trochanteric distance) but without defor-mity or avascular necrosis and with maintenance ofa normal joint space (Fig. 6A).

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74 M. M. MALA WER AND B. MARKLE

3A,8

FIG. 3. Computed tomography scans at the level of the capital epiphysis (A) and at the level of the femoral neck (8). Apart from asolitary central calcification, no osseous or cartilaginous matrix is present. There is no soft tissue mass. The cortex of the femuris thinned but intact. The joint space and acetabulum are normal. Note the surrounding zone of reactive sclerosis indicating abenign lesion.

Comment

In planning the treatment of this lesion, thepreoperative radiographic evaluation was importantin demonstrating the limits of the lesion and its

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...-- , ,fit,

-,

I

II , .

FIG. 4. Histologic section of the bone cyst lining shows anamorphous, eosinophilic extracellular material and a cellularcomponent composed of mature fibrocytes. No osseous orcartilaginous matrix is present. There is no evidence of giantcells, chondroblasts, or inflammation.

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nonaggressive character. The unusual, extensiveinvolvement of the epiphysis made a specific diag-nosis difficult, even though many of the lesion'scharacteristics suggested a bone cyst. Additionalpossible diagnoses included chondroblastoma, giantcell tumor, eosinophilic granuloma, aneurysmalbone cysts, or a well healed infection (21). The"cold" character on radionuclide bone scan arguedagainst fibrous dysplasia (9). An intraosseouslipoma should have shown a typical low attenuationvalue by computed tomography. A bone cyst wasultimately diagnosed by the finding of a cystic cav-ity, containing clear yellow fluid, and Linedby a thinfibrous membrane.

CLINICOANATOMIC ANALYSIS ANDLITERATURE REVIEW

An extensive review of the literature noted sevencases in addition to the present case of UBC withepiphyseal involvement (Table 1). We analyzed theage, sex, location, treatment, rate of recurrence,and deformity in order to determine the clinicalbehavior and the appropriate management of thivariant.

Age and Sex Distribution

Age at the time of diagnosis ranged from 6.5 to 42years with an average of 20.1 years. Males outnum-bered females 4:3. The average age was notablyhigher than those reported of classic metaphy eallesions (1,2,4,10,14-16,19).

UNICAMERAL BONE CYST WITH EPIPHYSEAL INVOLVEMENT

Location of Lesion

There were four (50%) femoral, two (25%) proxi-mal humeral, and two (25%) proximal tibial lesions.This is an unusual distribution. Neer reported a re-verse ration of 2: 1, proximal humerus:proximalfemur, in a review of250 simple bone cysts (17). Hefound the tibia to be a rare site (less than 4%). Twoof eight cases of EUBCs involved the tibia.

Radiological Relationship and Status of Physis

All lesions (except Case 7) involved the metaphy-sis and epiphysis. The degree of involvement variedfrom predominantly metaphyseal to equivalent de-grees of epiphyseal and metaphyseal involvement.

Four of the seven cases (Cases 1,3,5, and 6) werein older individuals whose epiphyseal plates wereclosed. Three reported cases (Cases 2, 4, and 7) inaddition to our case (Case 8) had an open physis. Inone case, the epiphyseal plate was obliterated bythe lesion and the effects of old trauma.

Treatment and Results

Follow-up ranged from 9 months to 3 years. Re-sults of the earliest case (Case I) were not reported.

Six of the remaining cases reviewed were treatedwith curettage, three with and three without bonegrafting. All lesions healed. Bone grafting did notoffer any apparent advantage. There were no differ-ences between those with open or closed epiphysesregarding final outcome, irrespective of treatment.There were no recurrences, late fractures, defor-mity, avascu lar necrosis, or secondary proceduresrequired. No patient developed leg-length discrep-ancy. Humeral shortening in Case 5 was attributedto old trauma. Case 7, a femoral head lesion, pre-senting with subarticular collapse and early de-generative changes, was cured with curettage andbone graft. This was the only case of articular col-lapse. Thus, open epiphyseal plates did not appearto increase the incidence of late complications.

DISCUSSION

Unicameral bone cysts are classically metaph-y eal and adjacent to the physis in origin but maylater involve the diaphysis. Seventy percent willremain juxta-epiphyseal (17). The epiphysis israrely involved. This study reports one new case of

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a UBC with epiphyseal involvement and retrospec-tively analyzed seven cases from the literature.

Clinical Considerations

The average age of patients with UBC in tubularbones is 9 to 15 years (1,3,4,10,14,16,19,20) with amale to female ratio of2 to 3: 1. In the present series,the average was older, 20 years, and the male to fe-male ratio was decreased to 1.3:1. The proximalhumerus and proximal femur (2: 1) are the mostcommon sites representing 75% of most large series. Incontrast, the present series showed four femoraland two proximal humeral lesions, a reverse of theexpected ratio. In addition, two patients (Cases 3and 4) had proximal tibia lesions, whereas tibial le-sions were much less common in other series. Neernoted that less frequent locations were characteris-tically found in adults (19). Boeseker et al. foundno proximal tibia lesion in 145simple UBC reviewed(3). He noted only one UBC with epiphyseal involve-ment in a review of the 145 UBCs seen at the MayoClinic during a 47 year period. Therefore, we con-cluded that the age, sex, and anatomic location ofEUBCs are atypical and do not lead to a correctdiagnosis from clinical or radiographic criteria alone.Surgery is necessary to establish the correct diag-nosis. Aspiration is a simple diagnostic technique.

Biological Activity and HemodynamicConsiderations

Biological and hemodynamic correlates of "ac-tivity" in addition to radiological location have beendescribed by Enneking (8) (1977). Latent cysts werecharacterized by a pressure on manometric mea-surement equal to venous pressure (6-10 cm H20)with a nonpulsatile column. Our hemodynamicmeasurements correspond to an active cyst (16 emH20 and pulsatile). This is the first reported pres-sure determination of a EUBC. Cohen (6) (1977)briefly reported three proximal femoral lesions withapparent perforation of the physis at surgery, but nofurther clinical or hemodynamic data were given.While one can speculate that increased cyst pres-sure may cause local erosion of the epiphyseal platewith subsequent epiphyseal extension, we suspectthis is not the main determinant, since most activecysts (therefore increased pressure) (8) do not clini-cally involve the epiphysis. Epiphyseal involvementhas been postulated to result from trauma to the

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76 M. M. MALAWER AND B. MARKLE

SA,B

SC,D

SE,F

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UNICAMERAL BONE CYST WITH EPIPHYSEAL lNVOLVEMENT

5G,H

77

FIG. 5. Serial postoperative radiographs at 2, 3, 6, and 10 months following cyst aspiration and steroid injection demonstrate thepattern of centripedal reossification. The initial stage shows amorphous ossification, which faintly outlines the radiolucent cystlining (open arrow, 3 months). Progressive ossification of this matrix provides substantial thickening of the bony cortex in bothfemoral neck and in the epiphysis (arrows). This continues centrally, slowly obliterating the cavity, i.e., endosteal new boneformation and not central ossification of the lesion.

growth plate with secondary extension (18). Thiscannot be substantiated by this review. The pul-satile, elevated pressure measurement we obtainedmay suggest a vascular etiology. Previously venousobstruction had been proposed by Cohen (5,6).Johnson suggested an etiology related to a smallangiomyxofibrillar lipoma (12).

Role of Methylprednisolone

Recurrence following curettage of UBC haveranged from 17 to 50% (17). Specifically, UBCs of

the proximal femur are difficult to treat and oftenresult in growth disturbance and pathologic frac-tures with subsequent coxa vara and ischemic ne-crosis (J 3). Boeseker (1968) noted a 28% recurrencerate of proximal femoral UBCs (3). Thus, we choseto treat our patient with aspiration and methylpred-nisolone as described by Scaglietti et al, (19) in orderto avoid this anticipated high rate of morbidity andrecurrence.

Scaglietti et aJ. (1979) reported 72 bone cyststreated by topical injection of methylprednisolone(19). Seventy-two percent of the lesions involved

6A,B

FIG. 6. Postoperative result at 18 months. Finalpostoperative anteroposterior (A) and lateral (B)radiographs demonstrate a small residual centralradiolucency, but significant reconsitution of thenormal bony architecture of the femoral head,neck, and calcar has been achieved without defor-mity, shortening, or avascular necrosis. Note thepremature obliteration of the physis and the resul-tant decrease in articular trochanteric distancesecondary to the healing (reossification) of thephysis.

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78 M. M. MALA WER AND B. MARKLE

the humerus or proximal femur. Radiographic find-ings showed reconstitution of the cortical bone ofthe cyst wall (similar to our patient). Progressiveformation of new bone was noted at 6 months withopacification of the cyst cavity. Complete oblitera-tion of the cavity took 3 years. The epiphysis, un-like in our patient, usually continued normal growth,and Scaglietti stressed that no damage to the epiph-yseal cartilage resulted from injection of steroids.We hypothesize the premature closure of the epiph-yseal plate in the present case was due to the heal-ing process, i.e., reossification of the involved phy-sis and epiphysis (Fig. 6).

Scaglietti noted in all cases with a positiveradiological response that no fracture occurred. Nopatient required surgical treatment. Our patient sim-ilarly showed a good response, with early thicken-ing of the cortical walls and opacification of thecavity with resultant early ambulation and mainte-nance of a good range of motion (Fig. 5).

CONCLUSIONS

Unexpectedly, all six reported cases in the pres-ent series healed with a single curettage (with orwithout bone graft). More importantly, there wereno late sequelae offracture, deformity (except Case7), or avascular necrosis. Joint destruction and re-currence was not a problem. Interestingly, thestatus of the physis (open or closed) did not influ-ence the final outcome.

EUBC is a rare lesion and may be difficult todiagnose. The differential diagnosis should includechondroblastoma, giant cell tumor, eosinophilicgranuloma, intraosseous lipoma, and aneurysmalbone cyst (21). We believe that the clinical behaviorof a EUBC is to heal with simple curettage. Theexpected tendency for recurrence, deformity, andavascular necrosis is less than we anticipated. Wehypothesize that these lesions have a better prog-nosis than metaphyseal location alone due to theolder age of these patients (a good prognosticator insimple UBC), their atypical locations, and the in-creased potential of the epiphysis to reossify. Webelieve EUBCs represent a distinct clinicoanatomicentity with a less aggressive behavior and a morefavorable prognosis than the classic, metaphysealUBC, although its etiology is unknown. Furtherhemodynamic evaluation of both the metaphysealand epiphyseal variant is warranted and may eluci-date an underlying mechanism of epiphyseal exten-IOn.

SUMMARY

This paper reports a new case of a unicameralbone cyst with epiphyseal involvement and reviewsseven cases from the literature. The clinical andbiological behavior were analyzed.

1. An exact radiologic diagnosis is difficult.Radiologic imaging aids by demonstrating a nonag-gressive, solitary osseous lesion confined to bone.Aspiration is recommended as a simple confirma-tory diagnostic technique.

2. UBC (epiphyseal valiant) presents in an olderage group, often after epiphyseal closure, withoutexpansion or cortical destruction and involves boththe metaphysis and epiphysis.

3. These lesions are less aggressive than themetaphyseal UBC and can be expected to heal withsimple curettage, with or without bone graft.

4. There is a low morbidity following curettage.Postoperative fracture, deformity, and avascularnecrosis did not occur.

5. We recommend intralesional methylpred-nisolone acetate following aspiration with protec-tive bracing as the initial management and wouldreserve curettage for recurrent lesions or for diag-nosis when aspiration is nonconfirmatory.

Acknowledgment. We wish to acknowledge the con-tribution of Karen Harris in preparation of the manu-script and Dr. Lee Haacker in patient contribution.

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