Background and Objectives: Symptomatic adjacent segment degeneration (ASD) with lumbar spinal canal stenosis (LSCS) is a common complication after spinal intervention, particularly interbody fusion. Stand-alone posterior expandable cages enable interbody fusion with preservation of the previous operation site, and screw-related complications are avoided. Thus, the aim of this study was to investigate the clinicoradiologic outcomes of stand-alone posterior expandable cages for ASD with LSCS. Materials and Methods: Patients with persistent neurologic symptoms and radiologically confirmed ASD with LSCS were evaluated between January 2011 and December 2016. The five-year follow-up data were used to evaluate the long-term outcomes. The radiologic parameters for sagittal balance, pain control (visual analogue scale), disability (Oswestry Disability Index), and early (peri-operative) and late (implant) complications were evaluated. Results: The data of 19 patients with stand-alone posterior expandable cages were evaluated. Local factors, such as intervertebral and foraminal heights, were significantly corrected (p < 0.01 and p < 0.01, respectively), and revision was not reported. The pain level (p < 0.01) and disability rate (p < 0.01) significantly improved, and the early complication rate was low (n = 2, 10.52%). However, lumbar lordosis (p = 0.62) and sagittal balance (p = 0.80) did not significantly improve. Furthermore, the rates of subsidence (n = 4, 21.05%) and retropulsion (n = 3, 15.79%) were high. Conclusions: A stand-alone expandable cage technique should only be considered for older adults and patients with previous extensive fusion. Although this technique is less invasive, improves the local radiologic factors, and yields favorable clinical outcomes with low revision rates, it does not improve the sagittal balance. For more widespread application, the strength of the cage material and high subsidence rates should be improved.