الفهرس 
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Abstract
The term “adjacent segment degeneration” is used to describe radiographic changes seen at levels adjacent to a previous spinal fusion procedure
On the other hand, the term “adjacent segment disease” is used to refer to the development of new clinical symptoms that correspond to radiographic changes adjacent to the level of a previous spinal fusion.
Based on radiographic analysis and several investigators have argued that the degeneration of adjacent segment after spinal fusion is nothing more than the normal degenerative process rather than a consequence of biomechanical stresses.
Several other clinical studies have further corroborated a trend of increasing adjacent segment degeneration with older age. Osteoporosis also has been reported as a potential risk factor for adjacent segment degeneration by several investigators
Although the exact mechanism remains uncertain, altered biomechanical stresses appear to play a key role in the development of adjacent segment degeneration .
The diagnosis of symptomatic adjacent segment disease was based on both newly developed clinical symptoms and radiological lesions. The clinical symptoms referable to the adjacent levels were defined as low back pain and/or radiculopathy which caused the deterioration of JOA score during follow-up. Plain radiographs, CT, myelographs, and MRI were used for the radiological evaluation.
The upper and lower adjacent lesions should be checked. The existence of disc herniation, lumbar stenosis, or severe disc degeneration must be examined.
Because arthrodesis is a standard procedure for various disorders, preventive strategies should be considered for patients at high risk of adjacent segment disease.
Although the development of adjacent segment disease has been biomechanically and clinically studied, the actual indications for further surgical treatment of adjacent disease should be based on the same principles as the original surgery. Because there will be a subset of patients that naturally undergo progressive disc degeneration and aging, the majority of patients with junctional radiographic evidence of disc degeneration will need no treatment or continued conservative treatment.
Most patients with predominant adjacent level disease complaining of low back pain which can be managed successfully by non-operative treatment modalities. The decision to proceed with repeat surgical intervention must be carefully considered. The clinical examination findings and radiological pathoanatomy must be correlated to develop an effective preoperative plan.
A common and challenging manifestation of ASD is spinal stenosis at the segment cranial to a previous decompression and fusion. As part of the overall surgical plan, an initial consideration is whether the previously operated area needs to be revised.
Areas of residual or recurrent stenosis that could contribute to the patient’s clinical complaints should be addressed at the time of there operation. Likewise, a suspected pseudoarthrosis should be formally explored. Since both of these require additional time and attention intraoperatively, advanced planning will promote efficient execution of the surgical plan. The manufacturer of previously placed instrumentation should be identified either from the original operative notes or from close inspection of the radiographs so that proper removal devices can be guaranteed.
The presence of a spondylolisthesis combined with stenosis at the adjacent segment should prompt strong consideration of extending the fusion. Retrolisthesis, rotatory listhesis, or substantial hypermobility on flexion-extension films may also warrant extension of the fusion.
Nowadays many surgeons routinely extend the fusion at the time of decompression for junctional stenosis even in the absence of evidence of instability, as its motion can be considered one of the root causes of ASD. Others, however, have reported that decompression alone in this setting can be effective. Patients are typically advised of an increased risk of dural tear compared with the risk of the index procedure.
Concerns that fusion may increase the biomechanical stresses imposed on neighboring unfused lumbar segments have led some investigators to pursue an alternative strategy of so called dynamic stabilization. A number of different dynamic stabilization systems have been developed that utilize different biomechanical principles to address the pathoanatomy thought to cause clinical syndromes such as back pain and neurogenic claudication.