Osteoporosis and Mechanical Failure After Long-Segment Fusion for Degenerative Lumbar Scoliosis: A Systematic Review of Direct and Indirect Evidence.
STUDY DESIGN Systematic review using Synthesis Without Meta-analysis (SWiM). OBJECTIVE To synthesize evidence on osteoporosis and mechanical outcomes after fusion for degenerative lumbar scoliosis (DLS) and related adult spinal deformity (ASD), and appraise perioperative teriparatide or romosozumab. SUMMARY OF BACKGROUND DATA DLS-specific long-fusion evidence is sparse; much literature comprises related ASD or indirect short-segment/mixed-fusion cohorts. METHODS PubMed, Embase, CENTRAL, and Web of Science were searched through January 31, 2026, with a focused PubMed verification audit during revision. PROSPERO registration on April 22, 2026 followed the search; post-registration eligibility and analysis deviations are disclosed. Core DLS evidence required explicit long-segment fusion or ≥4 fused/instrumented levels; a stricter ≥5-vertebrae subset was examined. Adjusted estimates were reported per study without pooling. Risk of bias used QUIPS, RoB 2, or ROBINS-I; certainty used GRADE. RESULTS Twenty-one index primary reports informed the synthesis; eight were core DLS long-fusion reports; one overlapping companion was linked to its index cohort. Of eight core reports, five showed adverse adjusted associations, one was adjusted-null, and two were mixed across bone measures. The strict ≥5-vertebrae subset contained three adverse reports. Direct estimates included osteoporosis OR 8.19 (95% CI, 2.40-27.97) for screw loosening, S1 VBQ OR 4.565 (1.430-14.568) for PJK, osteoporosis OR 6.713 (1.667-27.031) for mechanical complications, and lumbosacral HU OR 0.941 (0.906-0.977) for distal instrumentation problems. Two reports had internally inconsistent regression tables; unsafe numeric effects were not extracted. Cohort overlap, heterogeneous measures/endpoints, and indirect evidence precluded pooling; three anabolic studies did not establish a DLS-specific class effect. CONCLUSIONS Most core DLS reports linked lower bone quality to mechanical complications, but retrospective design, probable cohort overlap, measure-dependent null findings, and reporting defects make certainty very low. No pooled DLS-specific magnitude is justified. Effects on final alignment and disability remain unresolved, and perioperative anabolic therapy is promising but not definitive. LEVEL OF EVIDENCE 3.