Editorial Non-fusion surgeries of the cervical spine

Anterior spinal fusion is one of the most commonly performed procedures of the cervical spine for traumatic, degenerative, or malignant conditions that require excision of intervertebral discs or vertebral bodies. Autogenous bone grafting has been shown to have a 95% or greater fusion rate for single-level surgery. The introduction of artificial spacers or bone substitutes has reduced the problem of donor-site pain, and anterior cervical plating has claimed further enhancement of fusion rate and obviated the need for postoperative external immobilisation. Despite these satisfactory outcomes, spinal fusion, at least theoretically, adds extra stress to the adjacent segments and may accelerate degeneration. On the other hand, it has also been argued that adjacent segment degeneration is merely part of the natural history of the disease in genetically predisposed individuals. 1,2 Nevertheless, preservation of motion of the functional spinal unit after disc excision or non-fusion surgeries remains a reasonable goal. The idea of replacing the intervertebral disc is not new. In the past 50 years, over 100 designs ranging from a simple metallic ball to complex composite polymers with different metal backings have been reported. Most are used for the lower lumbar spine, which is the most common site of degenerative disc disease as a cause of low back pain. With better understanding of the biomechanics and kinematics of the functional spinal unit, modern designs are more sophisticated and better resemble the natural mechanics. Although the short-term results appear satisfactory, medium-and long-term results are not yet available. It is ironic that the best clinical outcome actually occurred in segments that went into spontaneous fusion, making the artificial disc a very expensive intervertebral spacer for fusion. 3 Some prospective randomised controlled trials claimed superior results from artificial disc replacements, but the control group consisted of stand-alone intervertebral cages that are notorious for producing the worst results. Conditions in the cervical spine are inherently less hostile than in the lumbar region. The size of the disc, the loading forces involved, the facet joint anatomy, and the kinematics are all very different from the lumbar segments, which should render disc replacement theoretically more successful. Indeed, in recent years the number of reports in the literature on the cervical spine is catching up with that of the lumbar spine. In general, around 5º to 7º of segmental motion can be preserved but whether this is the reason for the paucity of observed adjacent segment degeneration remains …