chondral lesions in the patellofemoral joint are the most common cause for acute pain at the anterior aspect of the knee .
when the fissure is located at the medial retro patellar aspect and a plica mediopatellaris exists , it is assumed that the fissure is caused by the plica as incision injury so that the removal of the plica is indicated to prevent further cartilaginous incision injuries .
there are cartilage specific gradient echo sequences like the 2d multiple - echo data image combination sequence ( medic ) which are used in musculoskeletal imaging to delineate cervical disc herniation , tiny ligaments such as the scapholunate ligament , labrum injuries such as the bankart lesion , calcific deposits like in tendinitis calcarea or loose bodies in the joint .
this sequence is used to determine the thickness of the cartilage and can be performed in 3d to quantify and map the volume of the cartilage . on the other hand ,
there are spin echo sequences which in contrast to the gradient echo - sequence better demarcate bone marrow edema when fat suppressed . in addition
, these sequences provide a kind of indirect arthrography due to the high contrast between cartilage and surrounding fluid .
thus , the short - tau inversion recovery sequence ( stir ) seems to be the optimal sequence to demarcate both , tiny cartilaginous fissures and bone marrow edema as their consequence .
the medic has been only absolutely assessed but not relatively to other sequences schmid mr et al . .
thus , the purpose of our study was to determine the value of the 2d multiple - echo data image combination sequence relative to the short - tau inversion recovery sequence regarding the depiction of chondral lesions in the patellofemoral joint .
during a period of 6 month patients with acute pain at the anterior aspect of the knee , joint effusion and suspected chondral lesion in the patellofemoral joint underwent mri including axial medic and stir imaging .
mri was performed on a 70  cm open bore and 125  cm short 1.5 t scanner ( magnetom espree , siemens healthcare , erlangen , germany ) using a circular polarized knee coil .
only patients with chondral lesions in the patellofemoral joint on at least one mri sequence were elected for sequence comparison .
the medic and stir sequence were quantitatively compared regarding the patella cartilage - to - effusion contrast - to - noise ratio ( cnr ) . for that purpose the mean signal intensity ( si ) of retropatellar cartilage and effusion as well as the standard deviation ( sd ) of air were measured by standardized region - of - interest ( roi ) measurement at the level of the chondral lesion with 36  mm diameter depending on the thickness of the retropatellar cartilage .
the standard deviation of air served as noise , so that cnr was calculated according to the formula : cnr :  =  ( sicartilage  sieffusion)/sdair the medic and stir sequence were qualitatively compared by two radiologists with 2 and 6 years experiences in musculoskeletal imaging who independently scored the depiction of the chondral lesion on a 3-point scale ( 1  =  not depicted ; 2  =  blurred depicted ; 3  =  clearly depicted ) .
the comparison in objective cnr and subjective rating was performed by the wilcoxon - mann - whitney - test using a p - value less than 0.05 as level of significance .
inter - observer agreement was analyzed with cohen  analysis using the four categories in agreement : fair (   =  0.210.40 ) , moderate (   =  0.410.60 ) , substantial (   =  0.610.80 ) , almost perfect (   =  0.811.00 ) .
the medic and stir sequence were quantitatively compared regarding the patella cartilage - to - effusion contrast - to - noise ratio ( cnr ) . for that purpose the mean signal intensity ( si ) of retropatellar cartilage and effusion as well as the standard deviation ( sd ) of air were measured by standardized region - of - interest ( roi ) measurement at the level of the chondral lesion with 36  mm diameter depending on the thickness of the retropatellar cartilage .
the standard deviation of air served as noise , so that cnr was calculated according to the formula : cnr :  =  ( sicartilage  sieffusion)/sdair
the medic and stir sequence were qualitatively compared by two radiologists with 2 and 6 years experiences in musculoskeletal imaging who independently scored the depiction of the chondral lesion on a 3-point scale ( 1  =  not depicted ; 2  =  blurred depicted ; 3  =  clearly depicted ) .
the comparison in objective cnr and subjective rating was performed by the wilcoxon - mann - whitney - test using a p - value less than 0.05 as level of significance .
inter - observer agreement was analyzed with cohen  analysis using the four categories in agreement : fair (   =  0.210.40 ) , moderate (   =  0.410.60 ) , substantial (   =  0.610.80 ) , almost perfect (   =  0.811.00 ) .
30 of 58 patients ( male : female , 21:9 ; age : 44    12 yrs ) revealed cartilage lesions ( fissures , n  =  5 ( fig . 1 , fig .
6 ) ; osteoarthritis , n  =  3 ) and were included in this study .
the stir - sequence was significantly ( p  <  0.001 ) superior to the medic - sequence regarding both , the patella cartilage - to - effusion cnr ( mean cnr : 232    61 vs. 40    16 ) as well as the depiction of chondral lesion ( mean score : 2.83    0.4 vs. 1.75    0.7 ) with substantial inter - observer agreement in the rating of both sequences (   =  0.76 - 0.89 ) .
our results show that the stir - sequence is significantly superior to the medic - sequence regarding the depiction of chondral lesions in the patellofemoral joint ( fig . 1 , fig . 2 , fig . 3 , fig .
thus , the stir - sequence should be preferred over the medic - sequence for the depiction of chondral lesions in the patellofemoral joint .
although the medic - sequence provides a higher spatial resolution ( 0.5    0.4  mm vs. 0.7    0.6  mm ) ( tab .
3 ) or delamination ( fig . 6 ) . due to the high prevalence of mediopatellar plica in up to 80% of cases   and its association with cartilage damage ,  
in contrast to the medic - sequence the stir- sequence also depicts reactive edemas in the bone marrow as indirect sign of cartilage stress or damage ( fig .
3 ) . furthermore , edema depiction facilitates the assessment of severity , acuteness and consequence of cartilage stress or damage ( fig .
3 ) . also , the stir - sequence gave better depiction of the liquid film under the delamination , highlighting this pathology ( fig .
both , the objective analysis and subjective analysis with substantial inter - observer agreement accordingly confirm the superiority of the stir - sequence .
we saw no advantage for the t2 * -weighting of the medic - sequence in the depiction of chondral lesions in the patellofemoral joint . on the medic the cartilage signal was homogeneous in every case thus any inner inhomogeneity reflecting pressure
the medic - sequence may be superior to the stir - sequence in the depiction of loose bodies in the joint due to its higher ( not saturated ) contrast between fat in tissue and bone .
however , in the one case with a loose body in the patellofemoral joint there was no difference in the depiction of the loose body between the medic and stir - sequence .
there was also no difference in the depiction of the plica mediopatellaris , which is anyway also and even better depicted on the sagittal fat - saturated t2  w sequence in the protocol of the entire knee .
a mixed t1/t2 * -weighted so - called double - echo steady state ( dess ) sequence has also been proposed as a cartilage specific sequence .
the dess - sequence is currently being used in the osteoarthritis initiative to assess the cartilage of the knee joint . regarding the cartilage - to - effusion contrast there seems to be no significant difference between the medic- and dess - sequence .
also used the model of the patellar cartilage to evaluate the diagnostic value of the dess - sequence and found that the dess - sequence was inferior to the conventional t2  w spin echo ( se)-sequence . both , the medic- and dess - sequence provide less contrast than the stir - sequence for both , bone edema and cartilage injuries .
thus , the stir - sequence combines the advantage of indirect arthrography with delineation of subchondral edema .
however , the medic and dess 3d - sequences provide mapping of the cartilage volume with the intention to facilitate the prevention of osteoarthritis , thus providing prophylactic meaning .
in contrast , the stir - sequence depicts focal damage of the cartilage and bone marrow edema as causes of pain .
if other prior performed sequences reveal an effusion as indirect sign of damage we therefore prefer the stir - sequence to better depict the cause for the effusion . in the younger patient group ( here with a mean age of 44    12  years ( range : 2168 years ) ) with acute pain and effusion in the pfj in particular , the stir - sequence seems to be more helpful in directing therapy decisions as the pretest - probability cause of pain and effusion is less likely to be chronic .
we did not compare the stir sequence with the fat - saturated t2w or pd sequences because the stir - fat saturation is known to optimally depict bone edema , which seems crucial to indicate lateral release or any other surgical procedure to prevent or treat osteoarthritis . in this manner , the knee protocol ( table 1 ) also includes the maximum of bone edema - to - bone contrast .
thus , for the benefit of non - invasiveness we compared the sequences regarding the cartilage - to - effusion cnr and depiction of lesion and not regarding their accuracy in the lesion detection .
but the significant superiority of the stir over the medic sequence in both , the objective and subjective analysis is so clear that it seems not likely that the lack of a standard of reference biases the message of the study .
the stir sequence should be preferred over the medic sequence for the depiction of chondral lesions in the patellofemoral joint .
the stir sequence should be preferred over the medic sequence for the depiction of chondral lesions in the patellofemoral joint .
there is no actual or potential conflict of interest in relation to this article ( no disclosures).the work has not been published beforeno funding was received for this work.this paper describes the author own work.it is not under consideration elsewhere , and all authors have read and approved the manuscript .
there is no actual or potential conflict of interest in relation to this article ( no disclosures).the work has not been published before no funding was received for this work .
it is not under consideration elsewhere , and all authors have read and approved the manuscript .
 purposeto determine the value of the 2d multiple - echo data image combination ( medic ) sequence relative to the short - tau inversion recovery ( stir ) sequence regarding the depiction of chondral lesions in the patellofemoral joint.materials and methodsduring a period of 6 month patients with acute pain at the anterior aspect of the knee , joint effusion and suspected chondral lesion defect in the patellofemoral joint underwent mri including axial medic and stir imaging 
 . patients with chondral lesions in the patellofemoral joint on at least one sequence were included . 
 the medic and stir sequence were quantitatively compared regarding the patella cartilage - to - effusion contrast - to - noise ratio ( cnr ) and qualitatively regarding the depiction of chondral lesions independently scored by two radiologists on a 3-point scale ( 1  =  not depicted ; 2  =  blurred depicted ; 3  =  clearly depicted ) using the wilcoxon - mann - whitney - test . for the analysis of inter - observer agreement 
 the cohen 's weighted kappa test was used.results30 of 58 patients ( male : female , 21:9 ; age : 44    12 yrs ) revealed cartilage lesions ( fissures , 
 n  =  5 including fibrillation ; gaps , n  =  15 ; delamination , n  =  7 ; osteoarthritis , n  =  3 ) and were included in this study . 
 the stir - sequence was significantly ( p  <  0.001 ) superior to the medic - sequence regarding both , the patella cartilage - to - effusion cnr ( mean cnr : 232    61 vs. 40    16 ) as well as the depiction of chondral lesion ( mean score : 2.83    0.4 vs. 1.75    0.7 ) with substantial inter - observer agreement in the rating of both sequences (   =  0.760.89).conclusionfor the depiction of chondral lesions in the patellofemoral joint , the axial stir - sequence should be chosen in preference to the axial medic - sequence . 
Introduction
Materials and methods
Objective/quantitative Comparison
Subjective/qualitative Comparison
Statistical analysis
Results
Discussion
Conclusion
Conflict of Interest Statement