en جراحی زانو Knee surgery پژوهشی Research Article <div style="text-align: justify;">Alkaptonuria is a rare inborn metabolic disease, in which an enzymatic deficiency accumulates alkapton in different tissues, causing darkness and injury, especially in spine and large cartilages, called ochronosis. The urine darkness can be a key to early diagnosis in childhood, but some cases are missed until adulthood and gradual damage to cartilages causes disability and impairs the patients&rsquo; quality of life. Here, a 49-year old male patient is presented with a 2 week history of left knee pain and swelling, who underwent arthrotomy, and the macro- and microscopic evaluation revealed ochronosis, superimposed by septic arthritis. Diagnosis of this rare disease should be considered in differential diagnoses of common joint disorders, like septic arthritis and osteoarthritis, so that appropriate management of the disease can prevent further damages.</div> Alkaptonuria, Ochronosis, Infectious arthritis 41 46 http://jros.iums.ac.ir/browse.php?a_code=A-10-663-1&slc_lang=en&sid=1 Morteza Nakhaee Amroodi drmnakhaei@gmail.com 10031947532846003762 10031947532846003762 Yes Bone and Joint Reconstruction Research Center, Shafa Orthopedic Hospital, Iran University of Medical Sciences,Tehran, Iran. Abolfazl Bagherifard bagherifd@gmail.com 10031947532846003763 10031947532846003763 No Bone and Joint Reconstruction Research Center, Shafa Orthopedic Hospital, Iran University of Medical Sciences,Tehran, Iran. Mahmoud Jabalameli jabalamelimd@yahoo.com 10031947532846003764 10031947532846003764 No Bone and Joint Reconstruction Research Center, Shafa Orthopedic Hospital, Iran University of Medical Sciences,Tehran, Iran. Mostafa Salehpour salehpour.m@gmail.com 0078607183 10031947532846003765 No Bone and Joint Reconstruction Research Center, Shafa Orthopedic Hospital, Iran University of Medical Sciences,Tehran, Iran. Shoeib Majdi shoeibmajdi@gmail.com 10031947532846003766 10031947532846003766 No Bone and Joint Reconstruction Research Center, Shafa Orthopedic Hospital, Iran University of Medical Sciences,Tehran, Iran.