Fusion cage with ipsilateral-impaction bone grafting in treating lumbar spinal stenosis combined with segmental instability

Background: This study investigates the feasibility and effectiveness of a fusion cage with ipsilateral-impaction bone grafting (IIBG) for treating lumbar spinal stenosis (LSS) combined with segmental instability. Methods: From January 2018 to December 2021, 282 LSS patients undergoing minimally invasive transforaminal lumbar interbody fusion (MIS-TLIF) at Union Hospital were enrolled (164 IIBG vs. 118 controls). The cohort comprised 97 males and 185 females (mean age 62.75 ± 6.88 years; body mass index [BMI] 24.02 ± 2.58 kg/m 2 ). Surgical levels included 218 single-level (L3–L4: 5, L4–L5: 113, L5–S1: 100), 42 double-level (L3–L5), and 22 multi-level (L3–S1) fusions. Visual analogue scale (VAS) and Oswestry disability index (ODI) were used to assess the severity of pain and spinal nerve function before surgery, as well as at one month, six months, and 12 months after surgery. Besides, the MacNab criteria were used to evaluate clinical efficacy at the last follow-up. Imaging indicators refer to the preoperative and postoperative ratio of intervertebral height and bone grafting area to vertebral body area. Fusion status was evaluated via the Bridwell Grade on 1-year computed tomography (CT). Results: The mean operative time was 94.11 ± 38.11 min (range 68–238 min), with an intraoperative blood loss of 90.82 ± 40.35 mL (range 20–150 mL). Follow-up visits were conducted among all 282 patients, with an average follow-up time of 22.44 ± 6.84 months (range 12–34 months). Preoperative VAS of lower back pain and lower limb pain was 6.99 ± 1.42 points and 7.80 ± 1.33 points, respectively, which showed statistical differences ( F = 2290.00, p < 0.001; F = 3307.17, p < 0.001) compared with postoperative results. The scores decreased to 2.20 ± 0.85 and 2.03 ± 0.84 at one month after surgery, 1.56 ± 0.60 and 1.51 ± 0.50 at six months after surgery, 0.89 ± 0.69 and 0.89 ± 0.69 at one year after surgery, and 0.85 ± 0.70 and 0.87 ± 0.69 at the last follow-up. ODI was 54.47 ± 2.89% (range 50%–59%) before surgery, 25.50 ± 2.88% (range 21%–30%) at one month after surgery, 15.02 ± 3.14% (range 10%–20%) at six months after surgery, 12.50 ± 1.71% (range 10%–15%) at one year after surgery, and 12.51 ± 1.71% (range 50%–59%) at the last follow-up; the difference was significant ( F = 734.432, p < 0.001). MacNab criteria indicated excellent outcomes in 209 cases, good outcomes in 58 cases, and fair outcomes in 15 cases, with excellent and good results of 92.74% among all 282 patients. Mean intervertebral height was 5.72 ± 1.39 mm (range 3.14–8.34 mm) before surgery, 13.21 ± 0.43 mm (range 12.46–13.98 mm) after surgery, and 11.62 ± 0.22 mm (range 11.10–11.99 mm) at the last follow-up; the difference was significant ( F = 6082.37, p < 0.001). Postoperative CT revealed that the bone grafting area (including cage) at the ipsilateral level accounted for 33.63 ± 3.42% (range 32.56%–39.02%) of the vertebral endplate area in the IIBG group, which was significantly different ( T = 31.35, p < 0.001) from the control group (22.83 ± 1.79%, range 18.57%–26.30%). CT at one year after surgery pointed out that significantly more patients in the IIBG group (91.5%, range 87.3%–95.7%) achieved successful fusion (Grade I or II in Bridwell) than the control group (76.53%, range 69.1%–83.9%), with a K value of 12.50 and a p value less than 0.001. Furthermore, a 3-year postoperative CT follow-up in a subset of patients consistently demonstrated more robust and extensive bridging bone formation across the entire disc space in the IIBG group, in contrast to the control group, where bridging bone was primarily confined within the cage windows. Besides, eight cases (4.8%) and 11 cases (9.3%) in the two groups appeared to have cage subsidence, but the difference was insignificant ( K = 2.03, p = 0.154). Three patients (1.0%) developed bone graft particles breaking through the anterior longitudinal ligament, but this did not cause vascular injury. Complications included CSF leakage (0.7%), pedicle screw misplacement (0.7%), and screw revision (0.3%). Conclusions: A fusion cage with ipsilateral impaction bone grafting ensures not only a large bone graft area outside the cage but also a shorter bone bridging distance between endplates and denser impaction of bone graft particles. Thus, this technique appears to be a safer impaction bone grafting method that provides a better environment for intervertebral fusion.