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BACKGROUND: The optimal timing of cranioplasty (CP) following decompressive craniectomy (DC) for the management of traumatic brain injury (TBI) remains debated. Prior studies comparing early CP (EC) and late CP (LC) report conflicting outcomes, compounded by inconsistent timing thresholds and limited attention to effect modifiers such as implant material. OBJECTIVE: To perform a systematic review and meta-analysis comparing outcomes of EC (≤ 90 days) versus LC (> 90 days) after DC for TBI, with particular evaluation of ultra-EC (< 35 days) and implant material. METHODS: MEDLINE, Embase, and CENTRAL were electronically searched from inception to April 2025, supplemented by manual screening of references and grey literature. Randomised and observational studies comparing EC and LC in adult TBI patients were included. Primary outcomes of interest were overall complications, reoperation, and functional outcomes. Secondary outcomes included hydrocephalus, shunt dependence, extra-axial collections, infection, haematoma, bone resorption, seizures, mortality, and operative time. Risk of bias was assessed with ROBINS-I and RoB 2 tools, and certainty of evidence with GRADE. Pooled risk ratios (RRs) and mean differences (MDs) were calculated using random-effects meta-analysis. RESULTS: Eighteen studies (n = 2226) were included. Overall complications did not differ between EC and LC, though autologous/allogenic EC carried higher risk (RR = 1.92; P = 0.02). Reoperation was significantly higher in mixed-materials EC cohorts (RR = 2.98; P = 0.02). No difference was observed in functional outcomes. Ultra-EC was associated with a lower risk of postoperative hydrocephalus (RR = 0.31; P = 0.005), while shunt dependence showed no significant difference. No significant differences were observed in extra-axial collections, infection, haematoma, bone resorption, seizures, or mortality. Operative time was shorter with EC (MD = -23.94 min; P = 0.0008), with the greatest reductions in ultra-EC (MD = -42.43 min; P < 0.00001). These findings are based largely on observational data with low-moderate certainty and should be interpreted cautiously. CONCLUSIONS: CP timing alone does not determine safety or efficacy, with risks varying substantially by implant material. Outcomes are critically modified by implant material and perioperative context. Ultra-EC may confer operative and physiological advantages without excess infection or mortality, particularly with synthetic implants, whereas early autologous or allogenic reimplantation carries higher risk of complications and reoperations. These findings argue for moving beyond a simplistic early-versus-late dichotomy and instead shifting towards material- and patient-specific strategies. Harmonised definitions and material-stratified prospective trials incorporating long-term functional outcomes are essential to establish evidence-based guidelines.
Thamilmaran et al. (Thu,) studied this question.