Posterior deformity correction and internal fixation for sagittal imbalance due to spontaneous fusion in lumbar spondylolisthesis: A case report.

RATIONALE: Lumbar spondylolisthesis (LS) with spontaneous fusion (SF) accompanied by sagittal imbalance (SI) poses a practical decision-making challenge in surgical planning. Here, we present a trauma-associated case of lumbar spondylolisthesis with SF and SI, and outline a reproducible, evidence-informed framework for surgical management. PATIENT CONCERNS: A 57-year-old patient developed low back pain after trauma. Lumbar computed tomography (CT) showed L4 anterolisthesis with bilateral pars interarticularis defects. Despite standardized conservative treatment, the back pain progressed, with forward trunk inclination of approximately 40° and concomitant left lower-limb weakness. DIAGNOSIS: Lumbar spondylolisthesis with nerve root impairment. INTERVENTIONS: After over 20 years of conservative treatment, the symptoms did not achieve meaningful improvement; the patient's back pain progressively worsened, with forward trunk inclination of approximately 40° and progressive weakness of the left lower limb. The patient ultimately underwent pedicle screw instrumentation. OUTCOMES: The procedure was uneventful; the patient remained on bed rest for 3 days and was discharged on postoperative day 12. LESSONS: LS with SF and SI is encountered clinically but remains under-specified for surgical decision-making; importantly, when LS and SI coexist, symptoms are not invariably attributable to the slipped level - marked forward stooping may instead reflect ligamentum flavum hypertrophy, nerve-root entrapment, adhesions, or other adjacent-level pathology. In selected patients, LS with SI does not require reduction of the slipped vertebra; surgical objectives can be achieved by decompression of the symptomatic level(s) and restoration of segmental lordosis to re-establish global alignment.