Musculoskeletal Strain or Sprain: This is often the most common cause of shoulder girdle and spine pain, along with leg spasms, due to overuse, poor posture, or direct injury. The symptoms can radiate or refer pain to different areas, including the legs, due to the complex innervation of the spine and surrounding muscles.

Herniated Disc: A herniated disc in the cervical or lumbar spine can cause pain in the shoulder girdle, spine, and radiate down to the legs, accompanied by muscle spasms. The pain and spasms are due to nerve compression or irritation.
Degenerative Disc Disease: Similar to a herniated disc, degenerative disc disease can cause chronic pain in the spine and shoulder girdle, with occasional radiation to the legs and associated muscle spasms.
Fibromyalgia: Although more generalized, fibromyalgia can present with widespread musculoskeletal pain, including the shoulder girdle and spine, and may be accompanied by leg spasms due to muscle tension.

Cauda Equina Syndrome: A serious condition that occurs when the nerves in the spinal canal are compressed, leading to pain, numbness, and weakness in the legs, as well as potential bladder and bowel dysfunction. It requires immediate medical attention.
Spinal Stenosis: Narrowing of the spinal canal can compress the spinal cord or nerves, leading to pain, weakness, and spasms in the legs, which can be exacerbated by standing or walking.
Multiple Sclerosis: An autoimmune disease that affects the brain and spinal cord, leading to a wide range of neurological symptoms, including pain, spasms, and weakness in various parts of the body, including the legs.

Ehlers-Danlos Syndrome: A group of disorders that affect connective tissues supporting the skin, bones, blood vessels, and many other organs and tissues, which can lead to musculoskeletal pain, joint hypermobility, and potentially leg spasms.
Neuromyelitis Optica: An autoimmune disorder that primarily affects the optic nerve and spinal cord, leading to vision loss and spinal cord damage, which can cause severe pain and spasms in the legs among other symptoms.
Spinal Tumors: Both benign and malignant tumors can compress nerves, leading to pain, weakness, and spasms in the legs, along with shoulder girdle and spine pain if the tumor is located in the cervical or upper thoracic spine.