What is the best treatment for a compression fracture to lumbar vertebrae?

Depends. It depends on the type and location of the fracture and the age of the patient. Often times, wearing a brace and avoiding strenuous activities will allow a compression fracture to heal in younger patients. In the elderly, if these measures fail, a kyphoplasty may be an option. Check out spine-health.Com.
Time. Compression fractures are very painful and time is the usual treatment. Pain medications and back braces also help. If the fracture is severe there are specialists who do procedures called 'vertebroplasty' where bone cement is injected into the vertebra surgically. It is very important to treat the underlying osteoporosis as well.