Does metal plating reduce the degree of disc collapse following anterior spinal surgery

The Anterior Cervical Discectomy and Fusion (ACDF) is one of the most common operations utilised in treating cervical degenerative disc disease. This involves removal of an intervertebral disc and cartilage with surrounding bone removal to release compressed spinal nerves. Once the disc has been removed, an implant known as an ‘inter-body cage’ is introduced into the disc space to restore disc height with restoration of physiological alignment and create an environment to achieve bony fusion. Overall, this procedure aims to improve neck pain and nerve pain via neural decompression and improved stabilisation. One of the inherent problems with introducing an implant that is more resistant to compressive forces (i.e. an increased bulk modulus) when compared to vertebral bodies is subsidence. Subsidence involves the ‘sinking’ of an implant postoperatively into vertebral bodies over time. Radiologically, this is the distance measured between two vertebral bodies at the segment of interest. This can result in narrowing if the neural exit foramen and development of pathological alignment leading to recurrence of symptoms. Furthermore, adjacent levels are subjected to abnormal biomechanical stresses, ultimately leading to development of further issues. Early subsidence can also lead to increased mobility in the segment and lead to failure in fusion. Currently, there lacks consensus on the definition of subsidence, with reported parameters of radiological subsidence varying amongst publications, thus making comparison between studies difficult. Generally, it is accepted that subsidence has occurred when there is an absolute loss of 2-4mm in interbody height, or a 10% reduction in interbody height, when compared to cervical x-rays performed immediately postoperatively. Subsequent to the introduction of the ACDF utilising a standalone cage, the operation has been augmented by the addition of a metal, anterior cervical plate. By bridging the anterior aspect of a fused segment, this was shown to supplement the cage leading to increased fusion rates and better stability. However, some of the disadvantages associated with use of a plate included post-operative dislodgement, soft-tissue injury and dysphagia. Currently, there is no consensus over whether anterior cervical plating offers any added benefit, hence the need for this trial.