Abstract: OBJECTIVE:  With the development of the lumbar pedicle internal fixation system, lumbar posterior fusion has been widely used in the treatment of degenerative diseases of the lumbar spine. Adjacent segment degeneration is one of the long-term complications after lumbar fusion. There are many risk factors affecting postoperative adjacent segment degeneration, some of which are still controversial, so it is necessary to conduct systematic analysis. Thus, this study investigated the risk factors of adjacent segment degeneration after posterior lumbar fusion.
METHODS: A comprehensive computer search was conducted for PubMed, The Cochrane Library, Embase, CNKI, Wanfang, and VIP database. The major orthopedic journals with high impact factors in and outside China were manually searched. The search term mainly included “lumbar fusion”, “adjacent segment degeneration”, “factors”, “ASD” and “risk factors”. The search period was from the database inception to March 2020, including the single-factor or multi-factor analysis of adjacent segment degeneration after lumbar posterior fusion. Literature quality was strictly evaluated using NOS scale after literature was screened according to inclusion and exclusion criteria. The primary outcome measure was age ≥ 60 years. Secondary outcome measures included: gender (female), smoking history, body mass index, osteoporosis, preoperative presence of adjacent segment degeneration, surgical approach of posterior lumbar interbody fusion, fusion segment > 1, laminectomy, and floating fusion. Among them, body mass index was a continuous variable index, and the rest were binary variables. Relevant data were extracted and statistically analyzed using Revman 5.3 software.
RESULTS: (1) A total of 18 literatures were included, among which 14 were of high quality, 4 were of medium quality, 17 were case control studies, and 1 was retrospective cohort study. A total of 568 patients with adjacent segment degeneration after lumbar posterior fusion were included, and 2 936 patients in the control group were included. (2) Age ≥ 60 years (OR=2.59, 95%CI:1.83-3.67), P < 0.000 01), smoking history (OR=1.63, 95%CI(1.17-2.26), P=0.004], body mass index (OR=3.54, 95%CI: 2.67-4.41), P < 0.000 01), preoperative presence of adjacent segment disc degeneration (OR=3.68, 95%CI: 2.85-4.76), P < 0.000 01), fusion segment > 1 (OR=1.82, 95%CI: 1.39-2.38), P < 0.000 1) were strongly correlated with adjacent segment degeneration after posterior lumbar fusion. (3) Age ≥ 60 years (OR=2.62, 95%CI:1.71-4.02, P < 0.000 01), preoperative presence of adjacent segment intervertebral disc degeneration (OR=4.45, 95%CI:3.08-6.44), P < 0.000 01), and fusion segment > 1 (OR=1.56, 95%CI:1.06-2.31), P=0.03] were independent risk factors for adjacent segment degeneration after lumbar posterior fusion.  
CONCLUSION: The gender, osteoporosis, operation method, laminectomy, and floating fusion had no obvious correlation with adjacent segment degeneration. However, the above conclusions need to be verified by large-sample and high-quality clinical studies.

Key words: bone, lumbar spine, degeneration, osteoporosis, risk factors, lamina, fixation, complications, meta-analysis