Unfortunately, adding a fusion to a preexisting one is somewhat common. The same genetics that existed to allow the fuzed level to wear out initially and need a fusion still exists. When the next level wears out, it is called adjacent segment disease (ASD) This disorder is so common, it does have a name. Normally, the level that wears out is the very next level. It is more uncommon that the level 2 levels away wears out. L2-3 is separated from L4-5 by L3-4.
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.