osteochondral lesions involve the articular cartilage and underlying subchondral bone , and most often affect the knee and the talus ( 1 ) .
osteochondral lesions of the femoral head are uncommon , and few studies have reported the imaging findings of such lesions . since this condition occurs in relatively young patients , and osteochondral damage puts joints at high risk of subsequent degeneration ( 2 ) , timely recognition of this disorder is important for proper treatment . herein , we review previous literature related to osteochondral lesions of the femoral head and 796report a case in which lesion involving the bilateral femoral heads was observed .
this lesion manifested as subchondral cysts according to the initial radiography images , and led to further evaluation by computed tomography ( ct ) arthrography and immediately obtained magnetic resonance imaging ( mri ) scan that revealed overlying articular cartilage defects .
a 20-year - old female patient was referred to our hospital from a local hospital .
her chief complaint was pain in both hips along with severe right side pain of approximately 2 months duration .
notably , however , she had been a taekwondo athlete in high school for several years . on clinical examination ,
plain radiography of the hip showed well - defined subchondral radiolucent lesions with a subtle sclerotic rim in the superior portion of the right femoral head ( fig .
the acetabuli in both sides of the hip displayed mild dysplasia with lower limit of normal ( center - edge angle , 24 - 25 degrees ) .
no signs of degeneration , such as joint space narrowing or juxta - articular sclerosis , were observed , except for subtle osteophyte around the head - neck junction of the right femur .
deformations of the femoral head , such as flattening , or the presence of crescent signs were also absent .
based on imaging findings , a provisional diagnosis of avascular necrosis with subchondral cysts could not be excluded . to further investigate the lesion ,
1b , c ) revealed several subchondral cysts that were hypointense on the t1-weighted images ( repetition time [ tr]/echo time [ te ] , 374/20 ) and hyperintense on the t2-weighted fat - suppressed images ( tr / te , 1500/29 ) .
the overlying portion in this region revealed a focal articular cartilage defect measuring about 10  15 mm in size , consistent with an osteochondral lesion .
no surrounding bone marrow edema was observed , and no cartilage damage was noted on the opposite site of the acetabulum .
the scintigraphy scan with 99 m technecium methylene diphosphonate showed no increased activity in the femoral head .
on arthroscopy , chondral damage was noted in the superior portion of the femoral head .
follow - up plain radiography of the hip performed about a year later revealed subchondral cysts in the superior portion of the left femoral head ( fig .
the patient reported no incidence of trauma in the meantime , other than mild hip discomfort .
1f ) scans of the left hip also showed several subchondral cysts , measuring about 14  13 mm in size , with associated overlying articular cartilage loss .
retrograde inspection of previous hip mri scans performed at the local referral hospital 2 months before the first visit to our hospital revealed lesions of the left femoral head with abnormal signal intensity , including hypointensity on the t1-weighted images and hyperintensity on the t2-weighted images ( fig .
this led us to hypothesize that the subchondral cyst lesion had progressed from a pre - existing lesion already present one year before .
the chondral defect was confirmed by arthroscopy and core decompression with a bone graft was performed , as had been done for the right side .
osteochondral lesions involve articular cartilage and the underlying subchondral bone , and mainly affect the knee and the talus ( 1 ) .
osteochondral lesions of the femoral head are rare and the prevalence is unclear ( 3 ) .
detailed reports of the imaging findings of such lesions are also quite limited . therefore , osteochondral lesions of the femoral head can be easily overlooked , unless radiologists are suspicious of osteochondral lesions that develop in the femoral region .
furthermore , osteochondral lesions of the femoral head are known to cause joint degeneration ( 2 ) .
we diagnosed the osteochondral lesion by identifying the accompanying overlying articular cartilage defects by ct arthrography and mri , which were performed for further evaluation .
we excluded a diagnosis of avascular necrosis due to the absence of a double line sign or a crescent sign of the femoral head on mri .
moreover , no signs indicative of primary osteoarthritis , such as joint space narrowing or juxta - articular sclerosis in both the acetabulum and femoral head , were observed .
the causes of osteochondral lesions have not yet been elucidated , and are likely to be multifactorial ( 4 ) .
one of the well - known causes of the osteochondral lesion of the femoral head is legg - calv - perthes disease . in this secondary lesion
, however , separated subchondral bone with articular cartilage from the joint surface is the main feature , which is different than our case .
other etiologies of osteochondral lesions in the hip include previous infection , genetics , ischemia or trauma ( 5 , 6 ) .
many studies have reported damages incurred by repetitive traumas ( 7 , 8 , 9 ) .
( 10 ) reported normal plain radiographic finding but mri detection of a subchondral lesion in an athlete with continuous hip pain , and suggested that although an athlete may not recall a specific incidence of past trauma , shearing injury of the cartilage by subluxation during joint rotation or impact damage caused by forces exerted by jumping could have occurred .
( 7 ) demonstrated that osteochondritis dissecans of the elbow can result from articular cartilage damage inflicted by repeated trauma .
nakamura et al . ( 6 ) reported an osteochondral lesion of the femoral head believed to have originated from repeated impact and high axial loads in a fencer .
our patient was previously an athlete , and so could have developed the osteochondral lesions by repetitive trauma , despite the lack of recollection of any particular past trauma .
( 10 ) also reported abnormal bone marrow signals from an osteochondral lesion on the femoral head .
this lesion exhibited hypointensity on the t1-weighted images and hyperintensity on the t2-weighted images , along with cartilage surface irregularities of the medial portion . in our case , although the cartilage surface irregularities were not immediately apparent from the previous mri scans taken at the local referral hospital , lesions displaying hypointensity on the t1-weighted images and hyperintensity on the t2-weighted images were present in the left femoral head .
an articular cartilage defect lesion accompanied by subchondral cysts was found about a year later , similar to the lesion previously observed on the right femoral head .
we concluded that an osteochondral lesion was already present at the time of the previous mri scan , and that this lesion progressed to the lesion with subchondral cysts .
it may often be necessary to distinguish osteochondral lesions from avascular necrosis in differential diagnoses .
the articular cartilage of the femoral head has been shown to be unaffected in the majority of cases of avascular necrosis , whereas this cartilage is often damaged in osteochondral lesions . moreover ,
avascular necrosis of the femoral head manifests itself as a somewhat broader lesion , often accompanied by serpiginous , low signal lines or crescent signs ( 11 ) . on the other hand ,
osteochondral lesions often reveal smaller - sized areas with wedge - shaped signal abnormalities , or a narrow inlet with deep nest - shaped lesions , as seen in this case ( 12 , 13 ) .
patient age , in particular being younger , is also helpful in distinguishing this condition from avascular necrosis ( 10 ) .
10 ) are thought to be indicative of lesions in the acute or subacute stage . in the chronic stage , however , a progressed degenerative bony lesion in the form of subchondral cysts , as seen in our case , or perhaps even a sclerotic change exhibiting hypointensity on the t1- and t2-weighted images , may be observed ( 6 ) . although some authors have reported that high uptake on the scintigraphy represents inflammation or lesion healing , no increased uptake was observed in our case , probably because the lesions are in the chronic stage .
in addition , young patients , especially those with a previous trauma or a history of being an athlete , are potential candidates for osteochondral lesions .
radiologists should look for bony lesions associated with articular cartilage defects in the femoral head , which could be indicative of an osteochondral lesion , similar to the lesions that are known to occur in the knee or the talus .
 osteochondral lesions of the femoral head are uncommon and few studies have reported their imaging findings . 
 since joints are at risk of early degeneration after osteochondral damage , timely recognition is important . 
 osteochondral lesions of femoral head may often be necessary to differentiate from avascular necrosis . here , we report a case of osteochondral lesions on bilateral femoral heads . 
 this lesion manifested as subchondral cysts in initial radiographs , which led to further evaluation by computed tomography arthrography and magnetic resonance imaging , which revealed overlying cartilage defects . 