Muscles that spasm are a functional aspect of lower back disorders and cannot be “seen” on an MRI or X-ray (unless there is an antalgic list which would be evident on standing X-rays). Muscle spasms are typically a result of back disorders and not a cause. Muscles spasms are a result of instability as a protective mechanism or nerve irritation that induces the spasm.
There are rare insertional tendonitis issues (like tennis elbow of the back) such as ischial tuberosity tendonitis but in the erector spinae group (back muscles), this is exceedingly rare.
Donald Corenman, MD, DC is a highly-regarded spine surgeon, considered an expert in the area of neck and back pain. Trained as both a Medical Doctor and Doctor of Chiropractic, Dr. Corenman earned academic appointments as Clinical Assistant Professor and Assistant Professor of Orthopaedic Surgery at the University of Colorado Health Sciences Center, and his research on spine surgery and rehabilitation has resulted in the publication of multiple peer-reviewed articles and two books.