In children, a condition occurs called pseudosubluxation of C2 on C3. This is due to two circumstances. One is that the osseous structures have not fully formed and the cartilaginous structures do not show up on an X-ray film (the facets are less angulated than the adult). In addition, the ligaments are more lax than in an adult. Subluxation of 4mm is within normal limits for a child.
If he does not complain of significant neck pain, the popping is probably a facet suction release as is the typical chiropractic adjustment.
I cannot comment on Ligaplex II as it has been a long time since I reviewed Standard Process products.
Generalized strengthening maneuvers would be a good idea but do not load the neck with weights at this time. He is simply too young with open growth plates.
Since the X-rays are within normal limits, I would just follow him listening to his complaints only as no further X-rays are necessary in regards to C2-3.
Dr. Corenman
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.