Application of computer assisted three-dimensional simulation operation and biomechanics analysis in the treatment of sagittal craniosynostosis

Evaluating mechanical benefit of wedge osteotomies in endoscopic surgery for sagittal synostosis using patient-specific 3D-printed models

PURPOSE

Endoscopically assisted sagittal strip craniotomy with subsequent cranial orthosis is a frequently used surgical approach for non-syndromic sagittal synostosis. Originally, this technique involved a wide sagittal strip craniectomy with bilateral wedge osteotomies. More recent studies suggest omitting wedge osteotomies, achieving similar outcomes. The controversy surrounding wedge osteotomies and our efforts to refine our technique led us to create models and evaluate the mechanical impact of wedge osteotomies.

METHODS

We conducted a 3D-print study involving preoperative CT scans of non-syndromic scaphocephaly patients undergoing minimally invasive-assisted remodelation (MEAR) surgery. The sagittal strip collected during surgery underwent thickness measurement, along with a 3-point bending test. These results were used to determine printing parameters for accurately replicating the skull model. Model testing simulated gravitational forces during the postoperative course and assessed lateral expansion under various wedge osteotomy conditions.

RESULTS

The median sagittal strip thickness was 2.00 mm (range 1.35-3.46 mm) and significantly positively correlated (p = 0.037) with the median force (21.05 N) of the 3-point bending test. Model testing involving 40 models demonstrated that biparietal wedge osteotomies significantly reduced the force required for lateral bone shift, with a trend up to 5-cm-long cuts (p = 0.007). Additional cuts beyond this length or adding the occipital cut did not provide further significant advantage (p = 0.1643; p = 9.6381).

CONCLUSION

Biparietal wedge osteotomies reduce the force needed for lateral expansion, provide circumstances for accelerated head shape correction, and potentially reduce the duration of cranial orthosis therapy.

Computer-Assisted Design and Manufacturing Assists Less Experienced Surgeons in Achieving Equivalent Outcomes in Cranial Vault Reconstruction

PURPOSE

The purpose of this study was to assess whether long-term outcomes were equivalent between computer-assisted design and manufacturing (CAD/CAM) -assisted cranial vault reconstruction performed by an inexperienced surgeon, with fewer years of surgical experience, and traditional reconstruction performed by senior surgeons with many decades of experience.

METHODS

An Institutional Review Board-approved retrospective cohort study was performed for all patients with nonsyndromic craniosynostosis between the ages of 1 month to 18 years who received primary, open calvarial vault reconstruction at the Johns Hopkins Hospital between 1990 and 2017. The primary outcome variable was the Whitaker category (I-IV) for level of required revision at the 2-year follow-up visit. Secondary outcomes included estimated blood loss, length of stay, operative time, and postoperative complications. CAD/CAM-assisted surgery was considered noninferior if the proportion of cases requiring any revision (Whitaker II, III, or IV) was no more than 10% greater than the proportion in the traditional surgery group with multivariate logistic regression analysis. t tests and fisher exact tests were used for secondary outcomes.

RESULTS

A total of 335 patients were included, with 35 CAD/CAM-assisted reconstructions. CAD/CAM-assisted reconstruction was noninferior to traditional after accounting for patient demographics, type of surgery, and experience level of the plastic surgeon. The traditional group required revision more frequently at 29.0% compared to CAD/CAM at 14.3%. Secondary outcomes were not significantly different between groups, but CAD/CAM had significantly longer average operative times (5.7 hours for CAD/CAM, 4.3 hours for traditional, P < 0.01).

CONCLUSION

CAD/CAM technology may lower the learning curve and assist less experienced plastic surgeons in achieving equivalent long-term outcomes in craniofacial reconstruction.

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

Sagittal craniosynostosis consists of premature fusion (ossification) of the sagittal suture during infancy, resulting in head deformity and brain growth restriction. Spring-assisted cranioplasty (SAC) entails skull incisions to free the fused suture and insertion of two springs (metallic distractors) to promote cranial reshaping. Although safe and effective, SAC outcomes remain uncertain. We aimed hereby to obtain and validate a skull material model for SAC outcome prediction. Computed tomography data relative to 18 patients were processed to simulate surgical cuts and spring location. A rescaling model for age matching was created using retrospective data and validated. Design of experiments was used to assess the effect of different material property parameters on the model output. Subsequent material optimization-using retrospective clinical spring measurements-was performed for nine patients. A population-derived material model was obtained and applied to the whole population. Results showed that bone Young's modulus and relaxation modulus had the largest effect on the model predictions: the use of the population-derived material model had a negligible effect on improving the prediction of on-table opening while significantly improved the prediction of spring kinematics at follow-up. The model was validated using on-table 3D scans for nine patients: the predicted head shape approximated within 2 mm the 3D scan model in 80% of the surface points, in 8 out of 9 patients. The accuracy and reliability of the developed computational model of SAC were increased using population data: this tool is now ready for prospective clinical application.

An Overview of Modelling Craniosynostosis Using the Finite Element Method

Craniosynostosis is a medical condition caused by the early fusion of the cranial joint. The finite element method (FEM) is a computational technique that can answer a variety of "what if" questions in relation to the biomechanics of this condition. The aim of this study was to review the current literature that has used FEM to investigate the biomechanics of any aspect of craniosynostosis, being its development or its reconstruction. This review highlights that a relatively small number of studies (n = 10) has used FEM to investigate the biomechanics of craniosynostosis. Current studies set a good foundation for the future to take advantage of this method and optimize reconstruction of various forms of craniosynostosis.