Comprossion of the cord is called spinal cord compression. Compression of 30% of the canal can cause myelopathy but not always. I have seen myelopathy with only 10% cord compression and no myelopathy with 50% compression. Nonetheless,I would be concerned with a 30% canal compression for both myelopathy and the chance of a central cord injury.
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.