DiagnosisSymptomatic popliteal sesamoid (cyamella)DiscussionSesamoid bones, the ossification of cartilage remnantswithin muscles and tendons, are quite common near joints,including the knee [1] and facilitate the biomechanicaltranslation of tendons at sites of mechanical stress byreducing pressure over bones, redirecting force vectors atsites of tendon angulation, and reducing friction.Oftenasymptomatic,sesamoidbonescanalsobethecauseof considerable pathology, particularly in the lower extremity[2]. The popliteal sesamoid (cyamella, popliteal fibula,fabella distalis) is present in the majority of primates but isuncommon in humans [3]. It has been described as bothwithin the popliteus muscle (distal to the knee joint line) andin the vicinity of the myotendinous junction (proximal to theknee joint line). Recognition of this sesamoid is important sothat it is not mistaken for a fracture, osteochondral fragment,heterotopic ossification, or tumor [4–6].Isolated case reports have also described the poplitealsesamoid as a purported cause of lateral knee pain,swelling, and restricted range of motion [4, 7]. There hasbeen a case report of a giant, hypertrophied poplitealsesamoid in an osteoarthritic knee, felt to cause locking [5].Gur et al. described the radiographic, CT, and MRappearance of an incidentally occurring popliteal seasamoidthat demonstrated a low signal periphery on T1 and T2 spinecho and T2* gradient echo imaging compatible withcortical bone and CT findings indicating marrow fat [6].There have, to date, been two case reports ofsymptomatic popliteal sesamoids. Mishra et al. describeda patient with lateral pain and inability to extend his kneefollowing basketball injury. The authors proposed thatthe patient dislocated and subsequently spontaneouslyreduced his popliteus tendon and sesamoid. Arthroscopyconfirmed an inflamed/thickened popliteus tendon withinthe femoral hiatus. The patient recovered withoutincident [7].Benthien et al. described a recreational athlete whocomplained of several weeks of posterior, lateral knee painand restricted extension in the absence of trauma. Radio-graphs demonstrated a popliteal sesamoid in the region ofthe popliteus myotendinous junction (above the joint line).MRI demonstrated normal marrow signal, without edema.The appearance of the popliteus tendon was not reported.The patient completely recovered following physicaltherapy and was asymptomatic at 1 year [4].This case demonstrates MRI findings suggesting symp-tomatology: bone marrow edema-like signal within thesesamoid itself and the adjacent femoral condyle. Periten-dinous soft tissue and subtendinous bone marrow edema-