The impact of diabetes mellitus on outcomes following cervical spine surgery: a qualitative systematic review

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Background: Evidence regarding diabetes mellitus (DM) and outcomes following cervical spine surgery is conflicting, complicating counseling about perioperative risk and expected functional benefit. This review synthesizes associations between diabetes, glycemic control, complications, and functional recovery to inform individualized risk assessment.Methods: The MEDLINE (PubMed), Scopus, and the EMBASE databases were searched for studies published from January 1, 2000, through April 7, 2026, using terms related to diabetes, cervical spine surgery, and postoperative outcomes. Eligible studies evaluated adults undergoing cervical spine surgery and compared clinical or functional outcomes between diabetic and non-diabetic patients or among diabetes subgroups. Reviews, nonclinical studies, uncontrolled case reports, and non-English publications were excluded. Study characteristics, demographics, and outcomes were extracted using a standardized form. Risk of bias was assessed using the Quality In Prognosis Studies (QUIPS) tool. Findings were synthesized narratively across functional outcomes, perioperative complications, and glycemic control; heterogeneity in study designs, diabetes definitions, procedures, and outcome measures precluded meta-analysis.Results: Twenty-four studies reported more than 2.1 million patients, predominantly in retrospective cohorts; 21 studies were classified as Level III and three as Level II evidence. Diabetes definitions varied, including binary diagnosis, insulin dependence, and glycemic control. Increased perioperative complications and longer hospitalization were reported particularly in patients with poorly controlled or insulin-dependent diabetes. Elevated hemoglobin A1c (HbA1c) was associated with infection and poorer outcomes, although reported thresholds varied. Functional findings were inconsistent: diabetic patients frequently had worse baseline neurologic status, but many studies reported comparable postoperative improvement. Predominantly retrospective evidence and substantial clinical heterogeneity limited causal interpretation.Conclusions: The evidence suggests that elevated perioperative risk can coexist with meaningful functional improvement in patients with diabetes undergoing cervical spine surgery. Counseling should distinguish complication risk from expected functional benefit and consider glycemic control and disease severity. The available evidence does not establish a universal cervical surgery-specific HbA1c threshold or demonstrate that preoperative glycemic optimization causally improves outcomes.