Dingjun Hao, Baorong He, Liang Yan. Hong Hui Hospital, Xi an Jiaotong University College. of Medicine, Xi an, Shaanxi , China

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1 Xi an Hong Hui Hospital Xi an, Shaanxi, China The difference of occurring superior adjacent segment pathology after lumbar posterolateral fusion by using two different pedicle screw insertion techniques in 9-year minimum follow-up Dingjun Hao, Baorong He, Liang Yan Hong Hui Hospital, Xi an Jiaotong University College of Medicine, Xi an, Shaanxi , China

2 ABSTRACT PURPOSE Lumbar fusion surgery is a widely accepted treatment for lumbar diseases, such as lumbar stenosis, trauma, tumor and spondylolisthesis. Fusion and clinical success rates have increased due to improvements in instrumentation and bone graft material. In contrast, numerous complications and problems of fusion surgery have been reported, with ASD being one of the most important. The aim of the prospective study was to test the hypothesis that different pedicle screw insertion positions would increase the likelihood of superior adjacent segment degeneration (ASD).

3 METHODS This prospective study included 210 patients with low-grade isthmic spondylolisthesis (IS). From January 1999 to December 2003, patients were randomized underwent posterolateral fusion (PLF) using two different pedicle screw insertion positions. The patients were followed up postoperatively and were assessed with regard to radiological and clinical outcomes. Radiologic outcomes were assessed mainly on the basis of disc degeneration, facet joint degeneration and bone fusion. Clinical outcomes were evaluated mainly with use of visual analog scale (VAS) for pain and the Oswestry Disability Index (ODI).

4 RESULTS 178 of 210 (84.7%) patients were available for at least 9-year radiological and clinical follow-up data: 85.3% (87/102) patients in Group A and 84.3% (91/108) patients in Group B. At the last follow-up, bone fusion was achieved in all patients. ASD was proven in 110 (61.8%) of 178 patients. The incidences of radiographic and symptomatic ASD were 57.9% (103/178) and 3.9% (7/178), respectively. The incidence of ASD in Group B was significantly lower than Group A. Results of clinical outcomes showed lower VAS and ODI scores in two groups compared with those preoperative, but Group B had greater improvement on the ODI scores compared with Group A in patients with ASD.

5 CONCLUSIONS The degeneration of superior adjacent segment is closely related to the position of the pedicle screws during lumbar fusion surgery. The position of the pedicle screw farther from the facet joint surface can reduce the degeneration of superior adjacent segment. Key words: posterolateral fusion; adjacent segment degeneration; pedicle screw insertion; prospective

6 Figures and Tables Figure 1. The entry point of two different methods marked on the posterior vertebral cortex. Left point (black point) represents Magerl s entry point. Right point (red point) represents Du s entry point.

7 Figure 2. The axial CT scans. A represents Du s method, B represents Magerl s method. Magerl s method needs more lateral and steeper angles for insertion. CT indicates computed tomography.

8 Table 1. Characteristics of the patients Group A Group B P Value Number of patients (n) Sex (M/F) 34/53 37/ Age (years) 46.1± ± Mean follow-up(months) 118.8± ± Mean body mass index (kg/m 2 ) 24.2± ± Clinical symptoms Back pain Radiculopathy Both Fusion level L L5-S Table 2. Clinical and functional outcomes Preoperative postoperative P Value ODI 57.4± ±14.6 <0.001 VAS (back) 8.2± ±1.6 <0.001 VAS (leg) 7.4± ±1.6 <0.001 ODI, Oswestry Disability Index; VAS, Visual Analog Scale.

9 Table 3. Comparison of postoperative clinical and functional outcomes between different groups Overall Overall ASD non-asd P Value Group A Group B P Value (n=110) (n=68) (n=87) (n=91) ODI 23.4± ± ± ± VAS (back) 2.0± ± ± ± VAS (leg) 2.1± ± ± ± ODI, Oswestry Disability Index; VAS, Visual Analog Scale; ASD, adjacent segment degeneration. Table 4. Comparison of clinical outcome by ODI score Group A Group B P Value All patients 24.3± ± Patients with ASD 28.6± ±11.4 <0.001 Patients without ASD 23.5± ± ODI, Oswestry Disability Index; ASD, adjacent segment degeneration.

10 Disclosure of Conflicts of Interest We certify that all our affiliations with or financial involvement in, within the past 3 years and foreseeable future, any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript are completely disclosed.