The nerves that run through the spine pass through a cavity called the spinal canal.
The cavity is surrounded by the vertebral body, intervertebral disc, posterior longitudinal ligament from the front, and the ligamentum flavum from the back.
When the spinal canal becomes narrow due to age-related deformation of the bone / intervertebral disc, lumbar compression fracture, herniated disk, posterior longitudinal ligament sclerosis, fat and cholesterol adhesion, sports injury (lumbar spinal separation), etc., the nerve is compressed. And the symptoms appear.
Numbness and pain from the lower back to the buttocks and legs and weakness in the lower limbs are observed.
You may not complain of back pain, so you may not think it is the cause.