Elevated B12 in the absence of supplements can be due to some
serious illnesses.

This article discusses some:
http://www.ncbi.nlm.nih.gov/pmc/arti...480434/?page=1
This link explains how bacterial overgrowth in the bowel may cause elevated B12 levels:
http://www.yourhealthbase.com/vitamin_B12.html#overload

Ensure Plus has 1.5 mcg of cyanocobalamin (supplements have much higher doses than this amount).
http://www.nutritiondata.com/facts/d...roducts/7708/2

At Nutritiondata.com here are some examples of broth:
http://www.nutritiondata.com/facts/s...gravies/1230/2
http://www.nutritiondata.com/facts/s...gravies/1030/2
both show no B12 content.
I'd have to have the ingredients from your particular broth source...it may be medically fortified, and if so I would suspect it similar to Ensure.

I don't see getting high serum readings from this intake.
Your reading is not that "high" compared to studies, which typically go over 2000-3000.

In fact, if you have intact intrinisic factor still, you are absorbing the small amounts of cyanocobalamin from your Ensure drink efficiently.
This suggests you don't have pernicious anemia or autoimmune dysfunctions at the parietal cell level.

If you are having a spinal fusion? Zinc and protein are the most critical nutrients for that. Calcium, Vit D, magnesium, B12 (which you already have), and trace elements like boron, manganese are typically recommended --the same as for osteoporosis treatments.
Avoidance of smoking, NSAIDs, steroids will help with fusion of bone.