A rare case of chronic pain and atraumatic inability to flex the knee: Evidence of a unilateral accessory popliteus muscle

The literature describes a few case reports of bilateral accessory popliteus muscle, a rare variant of the popliteus muscle. We report a case of a 24-year-old male patient with acute pain and inability to flex the left knee, without a traumatic event. Additionally, the patient reported mild sensitive symptoms in the left calf region and no pain in the right knee. The patient underwent a series of other examinations which culminated in a Magnetic Resonance Imaging (MRI) that showed an accessory popliteus muscle. The comparative study of the contralateral knee showed no evidence of this anatomic variant.