The neck can only influence the patellar reflexes by increasing the response (this due to cord compression and myelopathy) in a condition called hyperreflexia. If the patellar reflex is diminished, this is typically due to compression of the nerve root (new or old), injury to the tendon (prior knee surgery, fracture or tendon rupture) or aging (causes all reflexes to diminish over time).
MS will cause patchy increased reflexes but also a slew of other symptoms. Do not be too concerned with the return of normal reflexes after having increased reflexes and an ACDF for a large cervical hernation. I think that is a good sign.
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.