The cranioplasty equation: the influence of biomaterials, surgical timing, and frailty on optimising success.

Cranioplasty outcomes are influenced by multiple perioperative factors, yet the interplay between frailty, surgical timing, and material selection remains incompletely understood. This study aimed to characterise the independent and combined effects of these variables on postoperative complications. We conducted a retrospective study of 315 patients undergoing cranioplasty following decompressive craniectomy between January 2014 and June 2024. Patients were stratified by preoperative frailty using the modified frailty index (mFI: not frail [0], pre-frail [1-2], frail [≥ 3]), timing of reconstruction (early < 90 days, late ≥ 90 days), and implant material (autologous bone graft, synthetic, titanium). Primary outcomes included bone flap depression, skin erosion, infection, postoperative haemorrhage, and new-onset seizures. Cox proportional hazards modelling and multiple logistic regression analyses were performed to identify independent predictors of complications. The cohort comprised 242 males and 73 females with mean age 44.4 years and mean follow-up of 884 days. Increased frailty was associated with higher risk of bone flap depression (HR = 2.091) and postoperative seizures (HR = 1.311). Early cranioplasty resulted in shorter median length of stay (3 vs. 5 days, p = 0.002) but marginally increased seizure risk. Late reconstruction was associated with increased skin erosion risk (HR = 1.018). Both synthetic (HR = 2.065) and titanium (HR = 2.778) materials demonstrated significantly higher infection rates compared to autologous bone grafts. Titanium implants also carried increased seizure risk (HR = 1.801) and longer hospital stays. Reoperation rates were higher in frail patients (HR = 1.891) and those receiving synthetic implants (HR = 1.405). On multiple logistic regression, synthetic (OR = 2.42) and titanium (OR = 3.875) cranioplasties were independently associated with increased infection risk. Increased time to cranioplasty was independently associated with higher odds of skin erosion (OR = 1.002 per day) and bleeding (OR = 1.002 per day), but reduced odds of seizures (OR = 0.998 per day). Cranioplasty outcomes are shaped by the interplay between preoperative frailty, surgical timing, and implant material. These findings support the integration of frailty assessment, timing optimisation, and individualised material selection into a comprehensive preoperative risk-stratification framework.