Oral Presentation 50th International Society for the Study of the Lumbar Spine Annual Meeting 2024

INTRODUCTION

Proximal junctional kyphosis and failure (PJK/F) is a common complication in adult spinal deformity (ASD) surgery, and osteoporosis is considered as a risk factor for PJK/F. Hounsfield units (HU) are obtained using computed tomography (CT), and it has been demonstrated that HU could be used as an alternative bone strength assessment method for DXA. Studies have demonstrated that surgery itself cause bone loss after surgery. However, those population was patients undergoing decompression alone and/or short-segment fusion surgery. The effect of long-instrumented fusion on regional bone quantity in the adjacent vertebrae and the association between postoperative bone loss and the occurrence of PJK/F remains unclear. This study aimed to investigate the influence of long thoracolumbar fusion with pelvic fixation on regional bone density, measured in HU, at the adjacent vertebrae, and to evaluate the association between the bone loss and the incidence of PJK/F.

METHODS

The records of patients who underwent long thoracolumbar fusion defined as fusion including pelvis to T10 or above, between 2016 and 2022 for ASD were retrospectively reviewed. According to the institutional protocol, all patients underwent routine CT scans preoperatively and typically within 1–2 weeks postoperatively. Postoperative changes in HUs in the vertebrae at one or two levels above the upper instrumented vertebra (UIV+1, UIV+2) were measured. HU measurements were performed using an elliptical region of interest in the trabecular bone on the axial plane. Three axial slices were chosen per vertebra (upper 1/4, middle, lower 1/4), and the mean values of all three measurements were utilized. The pre- and postoperative HU values were compared. We also included patients who underwent a single-level posterior lumbar interbody fusion surgery between 2018 and 2022 as a control group. Furthermore, the presence of PJK/F within two years was investigated, and HU changes were compared between the PJK/F and control groups. For statistical analysis, the paired t-test was used to compare pre- and postoperative measurements. Fisher’s exact test for categorical variables and Student’s t-test or Mann-Whitney U test for continuous variables were used. Statistical significance was set at p<0.05.

RESULTS

A total of 127 patients were included in the final analysis (45 long fusion; 73.9 ± 5.6 years, 82 PLIF; 72.5 ± 9.29 years). Postoperative CT scan was performed at a median of 3.0 [1–7] and 4.0 [1–7] days postoperatively. In both groups, HU in UIV+2 demonstrated a significant decrease postoperatively. (P=0.034) Regarding the comparison between long fusion and PLIF group, there is no significant background difference between two groups. UIV+1 and UIV+2 decreased to a larger extent in the long fusion group, although not significantly so. In the patients with PJK/F, HU values in UIV+1 and UIV+2 demonstrated significantly more decrease compared to those in the non-PJK/F counterpart.

CONCLUSION

Lumbar spinal fixation negatively affected the regional HU values at adjacent levels immediately after surgery in long thoracolumbar fusion with pelvic. Among the long fusion group patients, PJK/F patients showed greater bone loss at UIV+1 and UIV+2. Further research is required to prevent postoperative bone loss and subsequent PJK/F.