Forty-two adult patients with low-grade single-level isthmic spondylolisthesis were randomized to undergo either posterolateral fusion (PLF, n=21) or posterior lumbar interbody fusion (PLIF, n=21). The primary outcome was the change in sagittal radiographic parameters, including spinopelvic and deformity indices. Secondary outcomes included correlations between radiographic changes and clinical outcomes assessed by the Oswestry Disability Index (ODI) and visual analogue scale (VAS). Follow-up was conducted over 24 months. Overall, the results of the study revealed that PLIF led to significantly greater correction in both spinopelvic and deformity parameters compared to PLF. However, both groups showed similar improvements in ODI and VAS. These findings suggest that although PLIF more effectively corrects spinal alignment, this radiographic advantage does not translate into superior short-term clinical outcomes.