Assessment of spring cranioplasty biomechanics in sagittal craniosynostosis patients

Abstract

<jats:sec><jats:title>OBJECTIVE</jats:title><jats:p>Scaphocephaly secondary to sagittal craniosynostosis has been treated in recent years with spring-assisted cranioplasty, an innovative approach that leverages the use of metallic spring distractors to reshape the patient skull. In this study, a population of patients who had undergone spring cranioplasty for the correction of scaphocephaly at the Great Ormond Street Hospital for Children was retrospectively analyzed to systematically assess spring biomechanical performance and kinematics in relation to spring model, patient age, and outcomes over time.</jats:p></jats:sec><jats:sec><jats:title>METHODS</jats:title><jats:p>Data from 60 patients (49 males, mean age at surgery 5.2 ± 0.9 months) who had received 2 springs for the treatment of isolated sagittal craniosynostosis were analyzed. The opening distance of the springs at the time of insertion and removal was retrieved from the surgical notes and, during the implantation period, from planar radiographs obtained at 1 day postoperatively and at the 3-week follow-up. The force exerted by the spring to the patient skull at each time point was derived after mechanical testing of each spring model—3 devices with the same geometry but different wire thicknesses. Changes in the cephalic index between preoperatively and the 3-week follow-up were recorded.</jats:p></jats:sec><jats:sec><jats:title>RESULTS</jats:title><jats:p>Stiffer springs were implanted in older patients (p &lt; 0.05) to achieve the same opening on-table as in younger patients, but this entailed significantly different—higher—forces exerted on the skull when combinations of stiffer springs were used (p &lt; 0.001). After initial force differences between spring models, however, the devices all plateaued. Indeed, regardless of patient age or spring model, after 10 days from insertion, all the devices were open.</jats:p></jats:sec><jats:sec><jats:title>CONCLUSIONS</jats:title><jats:p>Results in this study provide biomechanical insights into spring-assisted cranioplasty and could help to improve spring design and follow-up strategy in the future.</jats:p></jats:sec>

Spring assisted cranioplasty: A patient specific computational model

“…In 2008, SAC was introduced at Great Ormond Street Hospital for Children (GOSH), London, UK, with a different distractor design (Figure 2a) [24] compared to that proposed by Lauritzen [8,25] and a standardized surgical procedure in order to ensure result reproducibility [26].…”

“…Three different spring models (S10, S12 and S14) are available with same geometry, but different wire size (1.0, 1.2 and 1.4 mm respectively) hence varying stiffness (0.17, 0.39 and 0.68 N/mm respectively, Figure 2b) [26]. At GOSH, SAC is used for correction of After surgery, patients are followed up with x-rays at day 1 (FU1) and after three weeks (FU2), before spring removal is carried out approximately 3-6 months from insertion.…”

A population-specific material model for sagittal craniosynostosis to predict surgical shape outcomes

“…1b). Further clinical details about the SAC procedure can be found in previous publications from our group (Borghi et al 2017a(Borghi et al , 2018Rodgers et al 2017).…”

“…As in a previous work from our group (Borghi et al 2018), a viscoelastic material model was adopted to mimic the skull reshaping both on-table and over time, due to skull-spring interaction (Davis 2010;Zhang et al 2016;Borghi et al 2017a): where α ∞ and α i are the relative moduli, τ i are the time constants, G(t) is the instantaneous shear modulus and G 0 is the shear modulus at the beginning of the relaxation (t = 0). A bone relaxation modulus scale constant was introduced to account for different relaxation properties of the pediatric bone, compared to adult calvarium:…”

Editorial. “Horses for courses”

“…Children (GOSH) group on the use of springs in the management of craniosynostosis. 1 This group has been using the spring-assisted cranioplasty technique since 2008, and this is a welcome opportunity to review the progress they have made in applying the minimally invasive surgery and taking advantage of bone-fluid physiology in the correction of scaphocephaly. The focus of their paper is spring biomechanics and kinematics (a separate manuscript that describes the clinical outcomes in 100 consecutive cases of nonsyndromic scaphocephaly has been accepted for publication).…”