I'm wondering if your doc used a smaller scanning unit - there are portable types that won't cover the lumbar spine. Here's a good link to read about the procedure:
http://www.radiologyinfo.org/content/dexa.htm
Dr. Bertagnoli does the scans prior to surgery - and the equipment does cover the lumbar spine. I had another scan in the states post-op - everything, including my Prodisc levels, were scanned, but the Prodisc levels weren't read as part of the overall score.