I could theorize that cervical Spine Nerve Compression causes Shoulder Impingement but in practice, it would be exceedingly rare. Typically, a hooked acromion causes this. An easy way to disproved of this theory is to do a selective nerve root block of the C7 nerve. No temporary relief indicates the nerve is not involved.
Inability to lift the “arm up very high” is not a C7 nerve function but a C5 nerve function or a rotator cuff tear/inflammation.
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.