Spinal fusion for lumbar instability : Does it have a scientific basis?

The validity of spinal fusion for lumbar instability is considered. Some difficulty lies in the interpretation of the term instability. The differing interpretations in the clinical, radiologic, and biomechanical contexts are discussed. These interpretations may only be reconciled if the confusion between hypermobility and instability is removed and some recourse is made to soft tissue integrity. Fusion is considered in the context of the functioning spine as a whole. Although the aim of the surgery is usually to produce a solid arthrodesis, some studies show that this can compromise the functioning of the rest of the spine. Furthermore, there is some evidence that pseudarthrosis itself may not be detrimental. Dynamic imaging offers the potential for improved diagnosis and assessment, but further work is needed to pave the way for better selection criteria and treatment strategies.