IntroductionInitially described by Jaffe and Lichtenstein in 1942Common in first two decades of the life, the rarity of the lesion in the adults suggests that spontaneous healing occurs.
PathogenesisHypothesized that the cyst forms as a response to venous occlusion in the intramedullary spaceConsidered them to be intraosseous synovial cystsDysplastic areas, which they believed developed in response to trauma
PathologyAn area of fusiform expansionPeriosteum lifts away easily and underlying bone is egg-shell thin, semitranslucent,bluish and easily penetrated.
Histologic examinationThe cyst walls are lined with a fibrous membrane, with occasional giant cells
The fluid within the cyst has been analyzed and shown to contain high levels of oxygen-free-radical scavengers, prostaglandins (prostaglandin E2), interleukin-1, and proteolytic enzymes
These substances, which cause bone resorption, may play a role in the formation and growth of cysts.The cyst fluid has a lower total protein content than serum but higher levels of protein-bound hydroxyproline, lactate, and alkaline phosphatase.
Vascular occlusion theoryThe pressures within a cyst are elevated above venous pressuresif radiopaque dye is injected into the cyst with enough pressure, the dye can be extruded into the venous system of the limb. Reestablishing these outflow channels may assist in the involution of the cyst
simply lowering the interstitial pressure by multiple perforations may cause cyst involution
Clinical FeaturesAge- younger patientsSex- M:F 2:1Most common site-the proximal femur, followed by the proximal humerusMany 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 often brought on by traumaWhen fractures do become evident, they rarely involve the growth plate itself
Cysts progress from active to quiescent to an involutional stage in the course of their natural historyThe difficulty for the clinician is to assess the current stage of the cyst at the time of diagnosis
RadiographsRadiographs usually reveal a nondisplaced or minimally displaced fracture through an area of very thin, expanded cortical bone
Fallen leaf signOccasionally, a fragment of the cyst wall has fractured and fallen into the fluid cavity
The corticalfragment becomes dislodged from themargin at the timeof fracture andliterally floats to thebottom of the cystic structure.
MRIMagnetic resonance imaging most accurately delineates the central fluid collection
D.D.Aneurysmal bone cystFibrous dysplasiaEnchondromaEosinophilic granulomaGCT
TreatmentDifficult to decide whether the cyst is in the active, latent, or involutional StageUnless there is a tremendous amount of cortical thinning, there may not be a comparable decrease in strength as a cyst expands the cortical margins
It may be reasonable to choose close observation rather than a surgical procedureIf the cyst is active and obviously enlarging during observation (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 fluoroscopic control 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 of methylprednisolone
Advantageous by decreasing the morbidity due to a major surgical procedureRecurrence rates of 15% to 88% after an average of three injections
Surgical TechniquesResection or curettage plus bone grafting has been employed as the definitive treatment for unicameral bone cysts
TechniqueA cortical window is made, which allows access to the entire contents of the cavityThe clear fluid should be removed, and the fibrous membrane curetted from the cyst wall
Autologous bone marrow, allograft, demineralized bone matrix (DBM), and other bone substitute materials have been used successfullyThus sparing the patient the morbidity of an autograft harvesting siteAllograft bone chips have proved effective in the treatment of cysts
Calcium sulfate in the form of plaster of paris has been used with a good success rate and a low recurrence rate