The cyamella, a lost sesamoid: Normal variant or posterolateral corner anomaly?

Abstract

Cyamella, an accessory sesamoid ossicle of the popliteus in the region of the proximal myotendinous junction, is an extremely unusual finding, with a paucity of current published literature describing its MR appearance. In this case study, we describe MRI findings in a 44-year-old female presenting with pain after a stretching workout. Bone edema in the cyamella, edema in the myotendinous portion of the popliteus, and pericapsular edema at the posterolateral corner were identified. While commonly seen in certain mammalian species, cyamella is rare in humans. The upright walking posture of humans requires posterolateral corner structures to play a greater role in structural support and weight-bearing. We hypothesize that the cyamella, while intrinsic to certain mammalian species, may interfere with these biomechanical functions in upright walking posture, thereby predisposing to isolated injury of the posterolateral corner in humans.

Sesamoids in tetrapods: the origin of new skeletal morphologies

“…Some studies are devoted to particular clinical syndromes, such as the accessory navicular syndrome (Bernaerts et al, ). Khanna & Maldjian () described the absence of sesamoids, in their case of the cyamella, Duarte et al . () provided an account of a giant cyamella causing lateral knee pain, and Corvalan, Tang & Robinson () discuss the cyamella, and lateral and medial fabella in humans, highlighting the low prevalence of the cyamella.…”

Giant cyamella: a rare sesamoid bone

“…Most sesamoid bones are located in the lower limbs ( 2 ) . Embryologically, sesamoid bones are generally more common in the fetus; with skeletal growth and bone maturation, many sesamoid bones fuse ( 2 , 3 ) . In humans, the largest sesamoid bone is the patella ( 2 ) .…”

“…Although the cyamella is common in other primates, it is quite rare in humans, and, when it occurs, it can articulate with the lateral condyle of the tibia and be quite near the head of the fibula ( 3 , 4 ) . However, it does not have a well-defined function ( 6 ) .…”

“…However, it does not have a well-defined function ( 6 ) . It resides as an accessory ossicle in the popliteal tendon itself or at the intersection between the tendon and the muscle ( 6 , 7 ) ; its size can vary considerably ( 3 ) , and it should be clearly distinguished from free bodies, calcifications, osteophytes, and the fabella, as well as from osteochondromatosis ( 3 ) and avulsion of the popliteal tendon ( 7 ) .…”

“…A diagnosis of cyamella can be established through various imaging modalities, such as X-ray, computed tomography, and MRI ( 3 ) . On T1-, T2-, and T2*-weighted MRI scans, a cyamella appears as an ossicle with low signal intensity along its borders ( 6 ) .…”