Long-Term Minimum Clinically Important Difference in Health-Related Quality of Life Scores After Instrumented Lumbar Interbody Fusion for Low-Grade Isthmic Spondylolisthesis

BACKGROUND: Despite its growing popularity, no comparative studies have explored the minimum clinically important difference (MCID) of health-related quality of life scores following lumbar interbody fusion (LIF) performed on a single-level adult low-grade isthmic spondylolisthesis (LGIS). OBJECTIVE: The purpose of this study is to investigate factors related to MCID of health-related quality of life scores following instrumented LIF performed on a single-level adult LGIS. METHODS: Consecutive patients who underwent instrumented LIF for single-level LGIS were reviewed. The inclusion criteria were adult patients who underwent L4-5 or L5-S1, underwent anterior lumbar interbody fusion or transforaminal lumbar interbody fusion with a posterior screw fixation, and had a minimum 36-month postoperative follow-up period. MCID was defined as having an improved score of visual analog scale (VAS) back and leg pain >3 and Oswestry Disability Index (ODI) >12. Patients were subdivided into groups named "achievement" (A) and "nonachievement" (N) depending on their postoperative MCID for each health-related quality of life score category. RESULTS: One-hundred and five patients met the inclusion criteria. The overall achievement of MCID for VAS back, leg, and ODI was 80%, 73.3%, and 82.9%. MCID-VAS leg and ODI were less achieved at the L5-S1 level than at the L4-5 level. Postoperatively, disk height was higher and segmental lordosis (SL) was lower in group A of MCID-VAS leg. SL was lower in group A of MCID-ODI. CONCLUSIONS: We postulate that excessive SL does not affect lumbar lordosis; rather, it can result in lowering posterior disk height. The decrease in posterior DH may lead to a decreased foraminal height that, in turn, can lead to nerve root compression. Proper restoration of disk height and bone fusion is more important than restoration of more segmental lordosis or slip reduction for isthmic spondylolisthesis.