A retrospective comparative study of postoperative sagittal balance in isthmic L5–S1 spondylolisthesis using single segment or two-segment pedicle screw fixation

OBJECTIVE: To compare the radiographic parameters and clinical outcomes of isthmic L5–S1 spondylolisthesis with single segment or two-segment pedicle screw fixation. METHODS: Between January 2018 and January 2019, a total of 76 patients with isthmic L5–S1 spondylolisthesis were included in this study. All patients were treated with varying numbers of pedicle screw fixation with single-segment fusion during posterior lumbar interbody fusion (PLIF). Patients were divided into two groups, based on the number of pedicle screws placed during fixation, namely, 4 screws (4S) group and 6 screws (6S) group. Subsequently, the sagittal balance parameters were measured, which included slippage degree (SD), lumbar lordosis (LL), segmental lordosis (SL), pelvic incidence (PI), pelvic tilt (PT), sacral slope (SS), and sagittal vertical axis (SVA). Clinical functional outcomes were assessed using the visual analog scale (VAS) for back pain and the oswestry disability index (ODI) scores. RESULTS: The 4S group comprised of 10 males and 27 females, with a median age of 55.2 ± 10.8 years old and a mean follow-up of 16.95 ± 4.16 months. The 6S group comprised of 14 males and 25 females, with a median age of 58.1 ± 7.5 years old and a median follow-up of 17.33 ± 3.81 months. No significant differences were evident in all preoperative parameters between both groups. In contrast, the postoperative LL, SL, PT, SS, and SD values increased significantly, compared to the preoperative values in both groups (all P < 0.05). At the last follow-up, the 6S group exhibited better correction in LL, SL, and PT, relative to the 4S group (all P < 0.05). A significant SD difference was observed between both groups at all points post surgery (P < 0.05). The postoperative slip correction rate was significantly larger in the 6S group, compared to the 4S group (P < 0.05). The postoperative VAS and ODI scores of both groups improved significantly, when compared to the preoperative scores (both P < 0.05). However, there were no significant differences in the ODI and VAS scores between the two groups at all time points. CONCLUSIONS: The clinical outcomes of both approaches appeared to be satisfactory. In terms of short-term outcomes, the 6S group exhibited better spinal sagittal restoration and stability than the 4S group.