Spinal fusion became what has been termed the "gold standard" for the treatment of
mechanical low back pain, yet there was no scientific basis for this. Operations of fusion for
low back pain were initially done at the beginning of the last century for
back pain thought to be related to
congenital abnormalities or for past spinal
infection. The recognition of the disc as a cause of
sciatica, commonly associated with
back pain, and the recognition that a degenerate disc led to
abnormal movement suggested the concept that this
abnormal movement was the cause of
pain, and this
abnormal movement came to be called "instability". Much biomechanical expertise confirmed the fact that degenerate discs led to
abnormal movement, there were many hypothesis as to why this caused
pain. However clinical results of fusion for
back pain were unpredictable. The failure of
pedicle screws and cage fusion to improve the clinical results of fusion despite near 100% fusion success, and the introduction of "flexible stabilization" and artificial discs, which demonstrated that despite the often unpredictable movement permitted by of these devices, clinical success was similar to fusion, directed attention to the other role of the disc, that of load transfer, which these devices also affected. Abnormal load transfer was already known to be critical in other joints in the body and had led to the use of
osteotomy to realign joints. The relevance of load transfer to the future design of spinal implants used in the treatment of
low back pain is discussed, and some finite
element studies are reported demonstrating the likely effect of abnormal loading beneath an incompletely incorporated plate of an artificial disc, perhaps explaining in part the somewhat disappointing clinical results to date of the implantation of artificial discs.