Total Disc Replacement (TDR) in Adult Spinal Deformity

Adult spinal deformity is a highly complex set of conditions. While we often associate this term with thoracolumbar disease, it is important to remember that it also includes the cervical spine. To be even more complete, any loss of ‘normal’ spinal alignment or motion can and should be considered a deformity. Our native spine is constantly moving and takes on various configurations as we perform our daily activities. Having a distorted or biomechanically abnormal segment generates a deformity in this segment (primary disease) and results in forced compensation—and hence another deformity—in another part of the spine (secondary disease). If left uncorrected over a period of time, this compensating segment may become rigid, resulting in it being converted into another segment with primary disease. In the strictest sense, any form of surgical fusion thus also constitutes a deformity on the basis of immobilising a normally mobile segment of the spine. Indeed, we are often inclined to accept this as a trade-off for achieving symptom relief in many patients. Surgical fusion results in a fixed alignment, which may be appropriate in one posture but will invariably introduce abnormal alignment in another posture. The authors recommend the use of the term ‘spinal realignment’ in fusion surgery, rather than ‘deformity correction’. In essence, fusion surgeries are deformity-generating rather than deformity-correcting, considering their effect on spinal mobility. Under the aforementioned strict criteria, TDR is the only way capable of truly correcting a deformed spine due to its ability to reshape the spine and adapt to physiological spinal movement.