Osteoporosis and Mechanical Failure After Long-Segment Fusion for Degenerative Lumbar Scoliosis: A Systematic Review of Direct and Indirect Evidence.

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.

STUDY DESIGN: Systematic review using Synthesis Without Meta-analysis (SWiM).

LEVEL OF EVIDENCE: 3.