Abstract: Reconstruction of Secondary Calvarial Defects with Ex-Situ Split Calvarial Bone Grafts

INTRODUCTION: Reconstruction of secondary calvarial defects continues to represent a challenge, amid unresolved debates regarding the optimal material and technique. Autologous reconstruction presents the advantages of biocompatibility, biointegration, and growth potential at the expense of donor site morbidity and possible resorption. Therefore, we investigated the outcomes of skull reconstruction with split calvarial bone graft (SCBG) over a 35-year period, analyzing risk factors for poor outcomes and changes in graft thickness. METHODS: A retrospective chart review of patients who underwent cranioplasty with SCBG superior to the supraorbital margin between 1982 and 2016 was performed. Complications were divided into minor and major, with major requiring reoperation. Changes in graft thickness were analyzed using follow-up CT and MRI scans; bone thickness contralateral to the donor site was used as a reference point to approximate the initial donor bone thickness and served as the denominator to calculate all ratios. RESULTS: Forty patients with an average age of 33.2 years, cranial defect size 68cm2, mean follow-up of 27.6 months were included. The majority of patients (85%) had significant comorbidities or risk factors; 43% experienced infection of a bone flap or alloplastic material prior to SCBG, and 68% of patients underwent an average of 2.2 prior skull reconstruction procedures. Minor or major complications occurred in 37.5% of the cases, with 27.5% experiencing a major complication requiring a second operation to treat most commonly resorption (4/11; 36%), irregularities (3/11; 27%), or infection (2/11; 18%). Patients with ≥1 comorbidity (OR=2.12; p=0.04) or a smoking history (OR=6; p=0.02) were more likely to experience a complication. Prior infection did not increase the likelihood of complication (p=0.80). Mean radiographic follow-up was 11.9 ± 10.9 years. Within the first year after SCBG, the mean ratio of the recipient-graft to the original donor bone thickness was 0.47 ± 0.11 and 0.52 ± 0.04 for the donor site. These ratios remained stable throughout the follow-up period at 0.48 ± 0.17 and 0.57 ± 0.10, respectively (p>0.05). CONCLUSION: Skull reconstruction with SCBG in the setting of significant comorbidities and risk factors yields a high first-attempt success rate (72.5%), with good longevity, biocompatibility, and biointegration. All cases of major resorption occurred early, while the long-term follow-up of SCBG thickness demonstrates permanence with no significant remodeling altering graft thickness.