“…Endometriosis of the skeletal muscular system (ESMS) is defined as the presence of endometrial glands or stromal cells in skeletal muscles, bones, or joints. To date, beyond the head muscles, cases with ESMS have been reported in the trunk muscles, extremities muscles, pelvis muscles, and limb joints, including the trapezius muscle [ 9 ], deltoid muscle [ 10 , 11 ], rectus abdominis [ 12 – 39 ], obliquus externus abdominis [ 40 , 41 ], pyramidalis [ 42 ], psoas major muscle and iliopsoas muscle [ 43 – 47 ], piriformis muscle [ 48 – 51 ], internal obturator muscle [ 52 , 53 ], gluteus muscle [ 54 – 59 ], Levator ani and coccygeus [ 60 , 61 ], vastus lateralis muscle [ 62 – 65 ], thigh adductor muscle and gracilis [ 66 ], biceps femoris muscle [ 67 , 68 ], soleus and gastrocnemius [ 69 ], shoulder joint [ 70 ], wrist joint [ 71 ], and knee joint [ 72 , 73 ]. ESMS has highly variable manifestations due to the heterogeneity of lesion location; the symptoms are usually atypical, the pain is often not proportional to the size of the lesion, and sometimes ESMS does not coexist with pelvic endometriosis, which may lead to misdiagnosis or delayed diagnosis, prolonged therapy, or impaired function of the patients [ 4 ].…”