Look at those poor little chameleons! I hope you can help them!
The idea is to increase availability and absorption of calcium into the blood and then draw it back into the bones. This will mean that the chameleon needs to have enough D3 either produced from exposure to UVB or sunlight and/or from supplements to be able to use the calcium. The problem comes with figuring out how much is enough regarding supplements. All I can say is that any chameleons that I have had over the years that I have treated for MBD have not been given extra D3 from supplements...just extra calcium. I am not a vet...this information comes from personal experience and from what I have read and learned from my vets.
Calcium injections can be given by a vet and then when the calcium levels are high enough in the blood, an injection of calcitonin can be given which draws the calcium back into the bones quickly.
Here's a site that talks about it...
"TREATMENT AND DIAGNOSIS
Treatment for MBD in chameleons must address several issues. The first is to correct proper nutrition. A varied diet of gut-loaded insects that are dusted regularly with calcium, especially for hatchlings and juveniles, is extremely important. Avoid biasing the diet with insects with a poor Ca

ratio. Additionally, add appropriate UV lighting, and correct husbandry practices.
http://www.adcham.com/html/veterinary/mbd-fractures-kramer.html
Treatment (under a veterinarian's supervision) generally involves administering medications which may include oral or injectable calcium, injectable vitamin D3, and/or calcitonin. Symptoms and specific medical problems will need to be addressed on a case-by-case basis, and may include procedures such as tube-feeding, correction of dehydration, or fracture stabilization. Be very careful handling patients with MBD as their bones are very fragile and subject to further injury if mishandled. Radiographs (X-rays) are useful to assess bone density and confirm suspicion of MBD, and measuring blood calcium and phosphorus levels can also aid diagnosis and help guide therapy. Those chameleons that recover from MBD and regain strong solid bones will probably still retain some hint of bumps or bends in the legs, which represent healed fractures. These animals can however go on to lead good quality lives. Sometimes other skeletal abnormalities may persist including general stunting, shortening of the mandible or maxilla, and spinal deviations. In general, MBD is a treatable disease if diagnosed and treated early."