Article: http://www.dailymail.co.uk/health/article-2589710/Boy-11-grows-six-inches-height-surgeons-inserted-MAGNETS-twisted-spine-stretch-out.html

Obviously this surgery is only currently used to straighten a crooked spine for corrective purposes. I'm sure the surgery could be arranged to elongate an already straight spine if the surgeon were so inclined. You'd be working around the CNS, and if you damage anything there, you'd paralysed for life. The prospect of this becoming cosmetic would most likely be reserved for surgeons the ranks of Dr. Sarin and patients as overzealous as Sysop. But if this were to become feasible, then it would enable an individual to overcome discrepancies in leg/torso proportions. 2.5in in the tibia, 3in in the femur and 2-6in (don't know the prospective range of the spine) in the spine would be quite the feat to achieve.