Dysmenorrhea can be classified as either primary or secondary based on the absence or presence of an underlying cause. Secondary dysmenorrhea is dysmenorrhea which is associated with an existing condition.
The most common cause of secondary dysmenorrhea is endometriosis, which can be visually confirmed by laparoscopy in approximately 70% of adolescents with dysmenorrhea
Other causes of secondary dysmenorrhea include leiomyoma, adenomyosis, ovarian cysts, and pelvic congestion.
Unequal leg length might hypothetically be one of the contributors, as it may contribute to a tilted pelvis, which may cause lower back pain, which in turn may be mistaken for menstrual pain, as women with lower back pain experience increased pain during their periods.
Other skeletal abnormalities, such as scoliosis (sometimes caused by spina bifida) might be possible contributors as well.