gave physicians new diagnostic tools, revealing the intervertebral disc as a source for back pain in some cases. in 1938, orthopedic surgeon joseph s. barr reported on cases of disc-related sciatica improved or cured with back surgery. as a result of this work, in the 1940s, the vertebral disc model of low back pain took over, dominating the literature through the 1980s, aiding further by the rise of new imaging technologies such as ct and mri. the discussion subsided as research showed disc problems to be a relatively uncommon cause of the pain. since then, physicians have come to realize that it is unlikely that a specific cause for low back pain can be identified in many cases and question the need to find one at all as most of the time symptoms resolve within 6 to 12 weeks regardless of treatment. society and culture low back pain results in large economic costs. in the united states, it is the most common type of pain in adults, responsible for a large number of missed work days, and is the most common musculoskeletal complaint seen in the emergency department. in 1998, it was estimated to be responsible for $90 billion in annual health care costs, with 5% of individuals incurring most (75%) of the costs. between 1990 and 2001 there was a more than twofold increase in spinal fusion surgeries in the us, despite the fact that there were no changes to the indications for surgery or new evidence of greater usefulness. further costs occur in the form of lost income and productivity, with low back pain responsible for 40% of all missed work days in the united states. low back pain causes disability in a larger percentage of the workforce in canada, great britain, the netherlands and sweden than in the us or germany. in the united states, low back pain is highest of years lived with disability (ylds) rank, rate, and rercentage change for the 25 leading causes of disability and injury, between 1990 and 2016. workers who experience acute low back pain as a result of a work injury may be asked by their employers to have x-rays. as in other cases, testing is not indicated unless red flags are present. an employer's concern about legal liability is not a medical indication and should not be used to justify medical testing when it is not indicated. there should be no legal reason for encouraging people to have tests which a health care provider determines are not indicated. research total disc replacement is an experimental option, but no significant evidence supports its use over lumbar fusion. researchers are investigating the possibility of growing new intervertebral structures through the use of injected human growth factors, implanted substances, cell therapy, and tissue engineering.