we measured the height of the lesion by using the lesion s arc (  ) obtained from the difference between the angle of flexion at the beginning of the lesion and the angle of flexion at the end of the lesion . these records must be taken the same way for each arthroscopy and for each investigator . the lower limb was placed in an arthroscopic leg holder with the thigh horizontal ; the standard 4.5-mm arthroscope ( 30 tip angulation , wide - angle lens ) was introduced through a portal inferolateral or inferomedial to the patella . for the reference position , the scope was placed on the homolateral anterior meniscal horn , pointed horizontally toward the damaged condylar , and remained solidly against the tibia during movements . the knee was completely extended and gently flexed to 120 , the reading being done on the equator of the screen . when the anterior edge of the lesion appeared , the flexion angle of the knee was recorded visually on the lateral side of the limb ( a ) , and then , when the posterior edge of the lesion was on the equator of the screen , the second angular position was recorded ( b ) ( fig . the lesion s arc was obtained by the difference (  ) between these two positions ( b  a ) . the angles of flexion a and b give information regarding the anterior - posterior location of the condylar lesion . arthroscopic measurement of the angle of the lesion in the laboratory : on the equator of the screen , the anterior border of the lesion is at 30 ( a ) and the posterior border is at 70 ( b ) . we validated this principle in the anatomical laboratory at the university of rennes , france . in the first series , the donor ages were 51 , 62 , 64 , 72 , and 77 years , with no degenerative knees on radiograph . the thigh was securely fixed in a leg holder with the leg free of flexion / extension movement . 4 quadrangular artificial lesions , grade 3c on the icrs scale , were carried out with a curette , under scope view , by an investigator not involved in the work . two lesions were created on the medial and two on the lateral condyles  thus 4 defects in 1 knee and 20 defects in the first series . each lesion had been randomly evaluated using the lesional arc checked visually by 2 trained surgeons in arthroscopy ( jcl : observer 1 , hr : observer 2 ) . each measurement was randomly repeated after an interval of 1 hour , thus evaluating the intra- and interinvestigator reliability . then we did a second series of 20 defects in 5 other knees ( 54 , 56 , 63 , 78 , 89 years old ) , 1 month later , and as before , all the specimens had a bmi below 35 . again the flexion angles of the knees were measured using a goniometer solidly fixed on the lateral side of the thigh and the leg , the center of the goniometer superimposed on the epicondylar ( fig . were then disarticulated , and the true lesion arc was checked with a goniometer to assess the validity of the arthroscopic measurements . the center of the goniometer was superimposed on top of the epicondylar , and the lesion arc was read between the condylo - trochlear line ( point 0 ) and the posterior condyle ( point 90 ) . each actual lesion s arc directly measured on the disarticulated knee was compared with the previous results obtained by the 2 arthroscopists . second series : lateral view of the knee with the goniometer fixed on the lateral side of the knee . the lesion s arc (  ) obtained experimentally has to be converted into height ( mm ) for a clinical application . for this , we determined , from 30 lateral x - rays in scale 1/1 , 5 standard profiles with an increase of 3 mm . for each lateral x - ray , we defined the condylar center according to the methodology of grood and suntay for the description of the kinematics of bones . then we measured the length of the arc of flexion from 0 ( condylo - trochlear point ) to 90 and the length of each arc of 10 by using the orthogon software ( agfa healthcare , greenville , sc ) ( fig . 3 ) . thus , we could obtain an abacus for the calculation of the height of the lesion ( mm ) for these 5 standard profiles ( a to e ) . on x - ray , the center of the circle inscribed in the profile of the medial condyle allows an arc to be defined from 0 to 90 , with each arc length of 10 measured with the orthogon software . thus , we could obtain an abacus for the calculation of the height of the lesion ( mm ) for 5 standard profiles ( a to e ; see also fig . . the intraobserver reliability of the measurements of these angles was conducted using the bland and altman test limit of agreement ( see figs . 4 and 5 ) . the principle of the bland and altman test is to compare the difference between a pair of measurements ( e.g. , between 2 observers or between an observation and a reference ) against their mean values . if the measurements are comparable , the differences should be small , be centered around 0 , and show no systematic variation with the mean of the measurement pairs . for the analysis of agreement between 2 investigators , we chose the kappa coefficient . analyses of reproducibility within the observers for the 2 techniques were tested with all angular measurements of each anterior and posterior limit of the lesions ( i.e. , 2 per lesion ) . these measurements were transformed into categorical data for kappa agreement by rounding up the value to intervals of 10 ranging from 0 to 90 ( 010 , 1120 , 2130 , etc . ) , which seemed to be an  acceptable error margin  within the experience of the investigators . as each lesion was widened by the instrument once during the experiment , only half of the lesions were available for reading after disarticulation of the knee . the kappa coefficient calculated between the measurements of the 2 investigators is .66 , indicating poor agreement . the kappa coefficient calculated between the measurements of the 2 investigators is .78 , indicating good agreement . we measured the height of the lesion by using the lesion s arc (  ) obtained from the difference between the angle of flexion at the beginning of the lesion and the angle of flexion at the end of the lesion . these records must be taken the same way for each arthroscopy and for each investigator . the lower limb was placed in an arthroscopic leg holder with the thigh horizontal ; the standard 4.5-mm arthroscope ( 30 tip angulation , wide - angle lens ) was introduced through a portal inferolateral or inferomedial to the patella . for the reference position , the scope was placed on the homolateral anterior meniscal horn , pointed horizontally toward the damaged condylar , and remained solidly against the tibia during movements . the knee was completely extended and gently flexed to 120 , the reading being done on the equator of the screen . when the anterior edge of the lesion appeared , the flexion angle of the knee was recorded visually on the lateral side of the limb ( a ) , and then , when the posterior edge of the lesion was on the equator of the screen , the second angular position was recorded ( b ) ( fig . the lesion s arc was obtained by the difference (  ) between these two positions ( b  a ) . the angles of flexion a and b give information regarding the anterior - posterior location of the condylar lesion . arthroscopic measurement of the angle of the lesion in the laboratory : on the equator of the screen , the anterior border of the lesion is at 30 ( a ) and the posterior border is at 70 ( b ) . we validated this principle in the anatomical laboratory at the university of rennes , france . in the first series , the donor ages were 51 , 62 , 64 , 72 , and 77 years , with no degenerative knees on radiograph . all the specimens studied had a body mass index ( bmi ) below 35 . the thigh was securely fixed in a leg holder with the leg free of flexion / extension movement . 4 quadrangular artificial lesions , grade 3c on the icrs scale , were carried out with a curette , under scope view , by an investigator not involved in the work . two lesions were created on the medial and two on the lateral condyles  thus 4 defects in 1 knee and 20 defects in the first series . each lesion had been randomly evaluated using the lesional arc checked visually by 2 trained surgeons in arthroscopy ( jcl : observer 1 , hr : observer 2 ) . each measurement was randomly repeated after an interval of 1 hour , thus evaluating the intra- and interinvestigator reliability . then we did a second series of 20 defects in 5 other knees ( 54 , 56 , 63 , 78 , 89 years old ) , 1 month later , and as before , all the specimens had a bmi below 35 . the flexion angles of the knees were measured using a goniometer solidly fixed on the lateral side of the thigh and the leg , the center of the goniometer superimposed on the epicondylar ( fig . all 10 knees ( 5 in each series ) were then disarticulated , and the true lesion arc was checked with a goniometer to assess the validity of the arthroscopic measurements . the center of the goniometer was superimposed on top of the epicondylar , and the lesion arc was read between the condylo - trochlear line ( point 0 ) and the posterior condyle ( point 90 ) . each actual lesion s arc directly measured on the disarticulated knee second series : lateral view of the knee with the goniometer fixed on the lateral side of the knee . the lesion s arc (  ) obtained experimentally has to be converted into height ( mm ) for a clinical application . for this , we determined , from 30 lateral x - rays in scale 1/1 , 5 standard profiles with an increase of 3 mm for each lateral x - ray , we defined the condylar center according to the methodology of grood and suntay for the description of the kinematics of bones . then we measured the length of the arc of flexion from 0 ( condylo - trochlear point ) to 90 and the length of each arc of 10 by using the orthogon software ( agfa healthcare , greenville , sc ) ( fig . thus , we could obtain an abacus for the calculation of the height of the lesion ( mm ) for these 5 standard profiles ( a to e ) . on x - ray , the center of the circle inscribed in the profile of the medial condyle allows an arc to be defined from 0 to 90 , with each arc length of 10 measured with the orthogon software . thus , we could obtain an abacus for the calculation of the height of the lesion ( mm ) for 5 standard profiles ( a to e ; see also fig . the intraobserver reliability of the measurements of these angles was conducted using the bland and altman test limit of agreement ( see figs . 4 and 5 ) . the principle of the bland and altman test is to compare the difference between a pair of measurements ( e.g. , between 2 observers or between an observation and a reference ) against their mean values . if the measurements are comparable , the differences should be small , be centered around 0 , and show no systematic variation with the mean of the measurement pairs . for the analysis of agreement between 2 investigators , we chose the kappa coefficient . analyses of reproducibility within the observers for the 2 techniques were tested with all angular measurements of each anterior and posterior limit of the lesions ( i.e. , 2 per lesion ) . these measurements were transformed into categorical data for kappa agreement by rounding up the value to intervals of 10 ranging from 0 to 90 ( 010 , 1120 , 2130 , etc . ) , which seemed to be an  acceptable error margin  within the experience of the investigators . as each lesion was widened by the instrument once during the experiment , only half of the lesions were available for reading after disarticulation of the knee . the kappa coefficient calculated between the measurements of the 2 investigators is .66 , indicating poor agreement . the kappa coefficient calculated between the measurements of the 2 investigators is .78 , indicating good agreement . for the first series of tests , 20 artificial lesions were evaluated without a goniometer ( table 1 ) : the range for the 95% limit of agreement for the intraobserver analysis showed confidence intervals from 21.82 to 22.32 for observer 1 and 19.36 to 16.36 for observer 2 . means of differences were respectively 0.25 and 1.5 , which shows little bias . in each case , agreement was good . study without the goniometer note : cm1 = first lesion in the medial condyle ; cm2 = second lesion in the medial condyle ; cl1 = first lesion in the lateral condyle ; cl2 = second lesion in the lateral condyle . observer 1 , 1st = first registration by observer 1 ; observer 1 , 2nd = second registration by observer 1 ; observer 2 , 1st = first registration by observer 2 ; observer 2 , 2nd = second registration by observer 2 . for the second series , 20 artificial lesions were evaluated with a goniometer ( table 2 ) . we found a confidence interval from 8.9 to 8.1 and 6.94 to 7.94 for observers 1 and 2 , respectively . as the confidence interval was narrower with series with the goniometer for the 2 observers , we can approximately say that intraobserver reproducibility error was smaller with the goniometer . study with the goniometer note : cm1 = first lesion in the medial condyle ; cm2 = second lesion in the medial condyle ; cl1 = first lesion in the lateral condyle ; cl2 = second lesion in the lateral condyle . observer 1 , 1st = first registration by observer 1 ; observer 1 , 2nd = second registration by observer 1 ; observer 2 , 1st = first registration by observer 2 ; observer 2 , 2nd = second registration by observer 2 . for the series without the goniometer , kappa coefficient was evaluated at 0.66 , which could be classified as poor concordance . calculation for the series with the goniometer showed the kappa coefficient at 0.78 , with concordance between observers for this series thus being good . comparison to anatomical lesions , available only for half of the measurements , showed for both observers , for the first series , without goniometer , a 95% confidence interval from 27.69 to 21.32 and the mean of these differences around 3.19 ( fig . agreement was good , and bias was small . with the goniometer , in the second series , the confidence interval of the mean limits of agreement was from 16.69 to 10.81 ( fig . compared to anatomical lesions , we can hypothesize that reproducibility errors were lower with than without the goniometer . measurement of the lesion arc , without using the goniometer , after disarticulating the knee . measurement of the lesion arc , when using the goniometer , after disarticulating the knee . these results show that intra- and interobserver reliability and concordance between observers of reading angular limits of chondral lesions were better with the goniometer . the use of the abacus is relatively easy from the lesional arc and a strict x - ray profile of the patient s knee . the height or longitudinal dimension in millimeters of the lesion is obtained by subtraction of angle b and angle a on the abacus . for example , in the case of a lesion extending from 20 to 60 on a condyle sized c , the length of the arc  is 44  14.6 = 29.4 mm ( see fig . ( a ) abacus for calculating lesion height based on condyle size ( a to e ) and lesion arc . ( b ) lateral x - rays of the 5 knees sized from a to e. for a scale 1/1 , the d segment has to measure 12 mm long . the patient s x - ray ( scale 1/1 ) is superimposed on the drawing to determine its size relative to the standard 5 sizes ( a to e ) . the main result of this work is to propose a method for measuring the height of condylar chondral lesions under arthroscopy from a lesion s arc defined by its anterior and posterior limits . for wilson et al . , the arthroscopic estimate of the extent of a lesion is considered the  gold standard ,  but for oakley et al . , it can contain considerable errors . several authors have suggested their own techniques but without experimental validation of their accuracy . the determination of the surface area in the case of a focal defect is important for the choice of treatment ( microfracture , osteochondral graft , chondrocyte implantation ) . in the case of knee osteoarthritis , it is more important to know the percentage of cartilage damage compared to the total surface of the knee cartilage than in a localized lesion . in this instance , the french arthroscopic society composite scoring system proposed by ayral et al . in 1993 it is based on the combination of the beguin and locker classification for the severity and the percent area estimates for the size ; each compartment ( medial or lateral femorotibial , femoropatellar ) has a score between 0 ( normal cartilage ) and 100 points ( major chondropathy ) . the intraobserver reliability of percent area estimates was evaluated by examination of arthroscopic video recordings and was found to be good , but interobserver reliability was poor , explaining why a single trained observer is used to reread the videos . hunt s score also uses an evaluation system in percentage terms of each functional lesioned zone , but even the author states that the reliability and accuracy are both insufficient . these 2 composite scores require recording percent area estimates for each grade of chondropathy . in a plastic knee model , oakley et al . found that the accuracy and reliability of arthroscopic percent area estimates on the femoral surfaces were generally poor , and there was a clear trend to poorer reliability with larger lesions . it appears to us to be difficult in daily practice , as well as inaccurate for femoral condyles , due to their convexity and their large surface area . the use of variable - angle elongated probes especially designed for measurement of lesion diameter is one possible approach that has not been evaluated to date , to our knowledge . we have no direct experience of the commercially available flexible intra - articular rulers ( arthrex , naples , fl ) , and although their use is a possibility , they are actually single - use instruments . however , there are no data regarding reliability and validity of arthroscopic methods of localization ( e.g. , comparison of arthroscopy and anatomic dissection ) . our experimental study led to the development of an abacus based on radiological findings and arthroscopic measurements of the lesion arc . in the operating room , the width or transverse dimension is measured by a long graduated hook ( 0 - 20 mm ) inserted through the homolateral portal . the depth is estimated with a short angulated probe , of known size , according to the icrs score in 4 grades , and the height is obtained from the lesion s arc with the table ( fig . the lesion surface , similar to a quadrangular dome , is obtained by the following formula : width  radius    /180 . this formula does not take into account the spiral in the center of the curvature ( evolved fick curve ) . in practice , we can simply multiply the width by the height to calculate the lesion surface area assimilated to a rectangle after having chosen the exact size of the patient femur by superimposing a printout of figure 8b on the lateral x - ray ( scale 1/1 ) . figure 8c shows the superimposition of patient x - ray and trace d which best fits this case . the recording of the lesion s arc can also be used to locate the lesion on the icrs map . the location of the condylar lesion between 0 and 90 can be plotted on the 3 areas : anterior , middle , and posterior . there are two limitations of the work : first , we did not measure the height of the lesion in millimeters after dislocating the knees to validate the abacus , only the lesion arc . this was because we did not have at our disposal at that time a flexible and curved ruler , for example , those manufactured by the orteq ( london , uk ) . the technique of measuring the lesion s arc is reproducible , with care taken to respect the conditions required when taking records and using a standard goniometer , solidly fixed on the lateral side of the knee . care must be taken not to move the stationary arms of the goniometer when taking readings . by using the x - ray lateral view of the knee with the abacus , we can obtain the height , and a simple formula allows the calculation of the size of the lesion ( width  height ) . preoperatively , the three - dimensional mr mapping of cartilage surface will permit the accurate measurement of focal defects , but arthroscopy remains the standard for assessing small or superficial lesions and the physical properties of cartilage . we propose a simple , reliable method to measure the height of a condylar lesion with the lesion s arc during arthroscopy . this method provides the height of the lesion from a simple - to - use abacus .
purpose : to present a new method of arthroscopic measurement of the surface and location of condylar lesions.methods:we propose measuring the height of the condylar lesion by using the lesion s arc (  ) obtained from the difference between the angle of flexion at the beginning of the lesion and the angle of flexion at the end of the lesion . 
 the first goal of the study was to determine the intra and inter reliability of the lesion s arc . 
 experiment 1 : 20 deep lesions were evaluated using the lesional arc by two arthroscopists . experiment 2 : in a second series of 20 lesions , the flexion angles of the knees were recorded using a goniometer . all 10 knees ( 5 in each series ) were then disarticulated and the true lesion arc was checked with a goniometer to assess the validity of the scopic measurements . the second goal was to obtain the height of the lesion from the lesion s arc . 
 the lesion arc  of the condylar is converted into height ( millimeters ) on the basis of a table obtained from 5 standard profiles of the lateral x - ray of the knee.results:experiment 1 : the intra observer reliability was good but the inter observer reliability was poor . 
 experiment 2 : the intra and inter observers reliability were good . on the anatomic control after disarticulating the knee , 
 the confidence interval was narrower when using the goniometer.conclusions:we propose a simple , reliable method to measure the height of a condylar lesion with the lesion s arc during arthroscopy .