Instability is suspected by regular cervical X-rays including flexion/extension views. If symptoms match the suspician of instability on films, that is when the speciality studies are ordered and reviewed.
Howard Head does have very good therapists for TOS but realize that TOS is one of the more difficult disorders to treat through physical therapy.
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.