Adjacent segment infection following instrumented fusion for lumbar degenerative disease: A case series of eight cases and review of literature

Background Adjacent segment infection (ASI) following instrumented lumbar fusion for lumbar degenerative disease(LDD) remains a rarely documented complication. While a few case reports have described this entity, to our knowledge this represents the first case series systematically characterizing ASI in the context of non-infectious lumbar degenerative disease. Methods This study analyzed 8 cases of ASI following instrumented lumbar fusion for LDD at a single institution, including 5 in-house cases (0.24% incidence among 2,075 surgeries) and 3 external referrals. Comprehensive data collection encompassed demographics, clinical presentation, comorbidities, inflammatory markers, multi-modal microbiological profiling, surgical parameters, infection timelines, and treatment outcomes. Results The cohort (median age 68.5 years, 6 males, 2 females) all presented with chronic back pain without fever, 62.5% exhibiting radiculopathy. Systemic inflammation markers showed universal ESR elevation, CRP elevation in 87.5%. Characteristic imaging findings revealed: All proximal pedicle screws demonstrated loosening signs, with halo signs universally present, cutting displacement occurred in 75%. ASI manifested at 2–58 months postoperatively (median 5.5 months), exclusively involving cranial adjacent segments (75% L1-L3). The pathogens were identified in all cases (including Mycobacterium tuberculosis, Moraxella osloensis, Prevotella bivia and Staphylococcus epidermidis ). Blood cultures were universally negative, while metagenomic next-generation sequencing (mNGS) detected pathogens in 62.5% and tissue cultures yielded pathogens in 50%. All patients underwent posterior-only approach debridement with fusion and instrumented revision. At a mean follow-up of 23 months, all patients demonstrated significant VAS score reduction and complete clinical resolution without recurrence. Conclusions ASI is relatively rare in clinical practice, predominantly manifesting as delayed-onset low-virulence infections. These patients frequently present with proximal instrumentation failure and demonstrate high failure rates with conservative management, thus early surgical intervention is strongly recommended. Trial registration Not applicable. This retrospective study did not require trial registration.