Adjacent Segment Degeneration After Posterior Lumbar Fusion: A Minimum Five-year Follow-up

[Objective] A minimum5-year follow-up for radiologic outcome measuresthat were used to determine a lumbar fusion’s contribution to degenerative changes inadjacent segments. To investigate the mechanism and risk factors of adjacent segmentdegeneration.[Methods] From July2003to July2005,156patients who underwent lumbarfusion because of lumbar degeneration and have more than5years of follow-up wereevaluated. Male90cases，female66cases, aged28～74years old, with a mean value of50.5±5.4years old. Above60years old have54cases. No internal fixation in59cases,97cases of internal fixation (fixed-segment L4-L5,34cases; L5-S1,21cases; L3-4-5,14cases;L4-5-S1,28cases. single segment fusion55cases, multiple segment fusion42cases). All cases were collected clinical history and X-ray, CT/MRI and to find theadjacent segment of the incidence, the site and forms of observation after lumbarfusion. According to the literature, we think that the height of inter-vertebral spacestenosis﹥20%,or dynamic displacement﹥3mm or the rostra vertebral slip morethan10%width can be regarded as ASD.[Results] The patients were followed up for a mean of75.6±7.4months (60～96months).The incidence of ASD was12.8%(20/156) in all patients, and16casesoccurring at the cephalic adjacent segment，4cases occurring at the caudal adjacentsegment. The male incidence rate of ASD was13.3%(12/90),12.1%(8/66)forfemale, between them the rate of ASD has no significant difference （P=0.823﹥0.05）.The incidence rate of ASD was14.8%(8/54) in the patients over60years and11.7%(12/102) in the other ones, there was no difference in statistics（P=0.769﹥0.05）. Preoperative adjacent segment degeneration patients with the imaging on ASD26.7%(16/60)is higher than the no degenerations (4.2%4/96)（P=0.003﹤0.05）.The incidence rate of ASD was17.5%(17/97)in the patients with internal fixation and5.1%(3/59) in no ones, there was an important significance in statistics（P=0.024﹤0.05）, and multiple segment fusion will increase the rate of ASD, there was asignificance in statistics between the multiple and single segment fusion（P=0.049﹤0.05）.[Conclusions] The changes of the original structure, the stability of bonedestruction and adjacent biomechanical will lead to the occurrence of ASD. Thecranial adjacent segment has a more rate to degeneration than the caudal. The use ofspinal internal fixation will inevitably accelerate the occurrence of ASD, and with theincrease of the fusion segment the trend will also increase, especially when theadjacent segment have degeneration itself the rate of ASD increase is more obvious.