IntroductionInitially described by Jaffe and Lichtenstein in 1942Common in first two decades of the life, the rarity of thelesion in the adults suggests that spontaneous healing occurs.
PathogenesisHypothesized that the cyst forms as a response to venousocclusion in the intramedullary spaceConsidered them to be intraosseous synovial cystsDysplastic areas, which they believed developed in responseto trauma
PathologyAn area of fusiform expansionPeriosteum lifts away easily and underlying bone is egg-shellthin, semitranslucent,bluish and easily penetrated.
Histologic examinationThe cyst walls arelined with a fibrousmembrane, withoccasional giantcells
The fluid within the cyst has beenanalyzed and shown to contain highlevels of oxygen-free-radicalscavengers, prostaglandins(prostaglandin E2), interleukin-1, andproteolytic enzymes
These substances, which cause bone resorption, may play a rolein the formation and growth of cysts.The cyst fluid has a lower total protein content than serum buthigher levels of protein-bound hydroxyproline, lactate, andalkaline phosphatase.
Vascular occlusion theoryThe pressures within a cyst are elevated above venouspressuresif radiopaque dye is injected into the cyst with enoughpressure, the dye can be extruded into the venous system ofthe limb. Reestablishing these outflow channels may assist inthe involution of the cyst
simply lowering the interstitial pressure by multipleperforations may cause cyst involution
Clinical FeaturesAge- younger patientsSex- M:F 2:1Most common site-the proximal femur, followed by the proximalhumerusMany cysts are immediately adjacent to, and appear to involve,the epiphyseal growth plate
The area is slightly warm and swollenThe symptoms of unicameral bone cysts are most oftenbrought on by traumaWhen fractures do become evident, they rarely involve thegrowth plate itself
Cysts progress from active to quiescent to an involutionalstage in the course of their natural historyThe difficulty for the clinician is to assess the current stage ofthe cyst at the time of diagnosis
RadiographsRadiographs usually reveal a nondisplaced or minimallydisplaced fracture through an area of very thin, expandedcortical bone
Fallen leaf signOccasionally, a fragment of the cyst wall has fractured andfallen into the fluid cavity
The corticalfragment becomesdislodged from themargin at the timeof fracture andliterally floats to thebottom of the cystic structure.
MRIMagnetic resonance imaging most accurately delineates thecentral fluid collection
D.D.Aneurysmal bone cystFibrous dysplasiaEnchondromaEosinophilic granulomaGCT
TreatmentDifficult to decide whether the cyst is in the active, latent, orinvolutional StageUnless there is a tremendous amount of cortical thinning,there may not be a comparable decrease in strength as a cystexpands the cortical margins
It may be reasonable to choose close observation rather thana surgical procedureIf the cyst is active and obviously enlarging duringobservation (3 to 6 months), treatment may be appropriate
Exceptionlarge cyst involves the subtrochanteric region of the femurEarly treatment may be needed to avoid fracture
Injection TechniquesInjecting methylprednisolone into the cyst under fluoroscopiccontrol while using radiopaque dye to confirm entry into the cystAspiration of the cyst is done prior to injectionThe level of PGE2 in cyst fluid is reduced after injection ofmethylprednisolone
Advantageous by decreasing the morbidity due to a majorsurgical procedureRecurrence rates of 15% to 88% after an average of threeinjections
Surgical TechniquesResection or curettage plus bone grafting has been employedas the definitive treatment for unicameral bone cysts
TechniqueA cortical window is made, which allows access to the entirecontents of the cavityThe clear fluid should be removed, and the fibrous membranecuretted from the cyst wall
Autologous bone marrow, allograft, demineralized bone matrix(DBM), and other bone substitute materials have been usedsuccessfullyThus sparing the patient the morbidity of an autograft harvestingsiteAllograft bone chips have proved effective in the treatment ofcysts
Calcium sulfate in the form of plaster of paris has been usedwith a good success rate and a low recurrence rate