ochronosis is seen mostly in adults and peaks in the forth decade . with increasing age complaints of hip , although ochronotic pigmentation of tissues , black discoloration of urine due to sodium hydroxide ( naoh ) , degenerative arthropathy of large joints are classical findings , definitive diagnosis is made with quantitative detection of homogentisic acid in the urine and detection of ochronotic pigmentation in the histopathologic examination of tissue biopsies . in this paper we present a case complaining of knee pain and having arthroscopically detected black discoloration of menisci and cartilage which led us to the biopsy and further laboratory tests and finally diagnosed as ochronosis . a forty two year - old male admitted to our outpatient clinic with right knee pain and clicking on exertion for two years . there was pain on the lateral joint line by palpation and mc murray test was positive . x - ray revealed arthrosis in the lateral tibiofemoral and patellofemoral joint spaces . magnetic resonance imaging ( mri ) of the right knee revealed effusion , partially torn anterior cruciate ligament , thickening of quadriceps tendon . there were 3  cm    2  cm in diameter outerbridge stage 4 chondral defect in patellar joint surface and medial femoral condyle . 1 ) . acl was partially torn but the posterior cruciate ligament ( pcl ) was intact . arthroscopic view of the lateral joint space revealed a large , yellow and black colored grade 4 chondral defect in the lateral tibial condyle . lateral meniscus was thickened , black colored at the inferior surface and torn ( fig . biopsy was taken from the black colored areas of femoral condyle ( fig . 3a and b ) . we have done further investigation with the suspect of ochronosis because of the black discoloration of tissues seen in the arthroscopic intervention . urine was normal in color but when treated with sodium hydroxide ( naoh ) color of the urine became darker ( fig . the patient is under follow up by cardiology for valvular insufficiency and orthopedics for ochronotic arthropathy . it was first described by virchow in a postmortem examination of a 67 year - old patient in 1866 . it is characterized by deposition of ochronotic pigment in the tissues due to homogentisic oxidase enzyme deficiency in the tyrosine metabolism . ochronotic pigment can accumulate in hyaline cartilage , tendon , skin , teeth , nail , sclera , tympanic membrane , heart valves , renal tubular cells , duramater , pancreas and walls of great arteries . ochronosis is easily recognized with ochronotic pigmentation of tissues , degenerative arthropathy , especially in large joints and dark discoloration of urine because of alcalinisation . all patients in the literature were examined with knee arthroscopy with different reasons and the diagnosis of ochronosis is made through a further investigation of the intraarticular tissues because of the black discoloration . as in the other cases , black discoloration of cartilage and meniscal tissues moreover , we detected osteoarthritis and vacuum phenomenon in the intervertebral joints , arthrosis of large joints like hip , knee and glenohumeral joints and increased homogentisic oxidase in urine . unlike other cases we detected thickening of quadriceps tendon and asymptomatic supraspinatus tear in the mri and mitral valve insufficiency as an extraarticular finding . increasing homogentisic acid levels in the blood and resulting accumulation in tissues become symptomatic especially in the forth decade along with decreasing renal functions . in ochronotic arthropathy , articular cartilage becomes more sensitive to mechanic stresses causing fragmentation and resulting in nonspecific tenosynovitis . high grade glenohumeral arthropathy is very rare but must be kept in mind in ochronotic arthropathy . homogentisic acid polyphenol oxidase enzyme , which is located especially in tendons and ligaments , produces free radicals through oxidation and causes tendon and ligament ruptures . mri of our patient revealed partial rupture of acl , a thickened quadriceps tendon and asymptomatic rupture of supraspinatus tendon . high dose ascorbic acid ( 100  mg / kg ) may reduce hga excretion in the urine but does not prevent development of arthropathy . because the modalities addressing the cause of the disease are unclear , treatment of ochronotic arthropathy is symptomatic . nonsteroid antiinflammatory drugs and preparates containing glucosamine and chondroitin sulphate , intraarticular hyaluronic acid and steroid injections , arthroscopic debridement and arthroplasty are the treatment options . arthroscopy is helpful in diagnosis of ochronotic arthropathy and may lead to further investigation and treatment of concomitant pathologies . written informed consent was obtained from the patient for publication of this case report and case series and accompanying images . a copy of the written consent is available for review by the editor - in - chief of this journal on request . adnan kara : study concept or design , data collection , data analysis or interpretation , writing the paper . hasan basri sezer : writing the paper.bekir eray kilinc : writing the paper.metin uzun : writing the paper.key learning pointochronosis is a rare disease affecting connective tissues . arthroscopy is helpful in diagnosis of ochronotic arthropathy and may lead to further investigation and treatment of concomitant pathologies . arthroscopy is helpful in diagnosis of ochronotic arthropathy and may lead to further investigation and treatment of concomitant pathologies . arthroscopy is helpful in diagnosis of ochronotic arthropathy and may lead to further investigation and treatment of concomitant pathologies .