Adaptation of the cranium to spring cranioplasty forces

What is the Role of Force in Correcting Scaphocephaly Through Spring-Mediated Cranial Vault Expansion for Sagittal Craniosynostosis?

OBJECTIVES

Spring-mediated cranial vault expansion (SMC) may enable less invasive treatment of sagittal craniosynostosis than conventional methods. The influence of spring characteristics such as force, length, and quantity on cranial vault outcomes are not well understood. Using in vivo and ex vivo models, we evaluate the interaction between spring force, length, and quantity on correction of scaphocephalic deformity in patients undergoing SMC.

METHODS

The authors retrospectively studied subjects with isolated sagittal craniosynostosis who underwent SMC between 2011 and 2019. The primary outcome measure of in vivo analysis was head shape determined by cephalic index (CI). Ex vivo experimentation analyzed the impact of spring length, bend, and thickness on resultant force.

RESULTS

Eighty-nine subjects underwent SMC at median 3.4 months with median preoperative CI 69% (interquartile range: 66, 71%). Twenty-six and 63 subjects underwent SMC with 2 and 3 springs, with mean total force 20.1 and 27.6 N, respectively (P < 0.001).Postoperative CI increased from 71% to 74% and 68% to 77% in subjects undergoing 2- and 3-spring cranioplasty at the 6-month timepoint, respectively (P < 0.001). Total spring force correlated to increased change in CI (P < 0.002). Spring length was inversely related to transverse cranial expansion at Postoperative day 1, however, directly related at 1 and 3 months (P < 0.001). Ex vivo modeling of spring length was inversely related to spring force regardless of spring number (P < 0.0001). Ex vivo analysis demonstrated greater resultant force when utilizing wider, thicker springs independent of spring arm length and degree of compression.

CONCLUSIONS

A dynamic relationship among spring characteristics including length, bend, thickness, and quantity appear to influence SMC outcomes.

A review of the management of single-suture craniosynostosis, past, present, and future

BACKGROUND

Craniosynostosis is a condition in which 2 or more of the skull bones fuse prematurely. The spectrum of the disorder most commonly involves the closure of a single suture in the skull, but it can also involve syndromic diagnoses in which multiple skull bones and/or bones outside of the cranium are affected. Craniosynostosis can result in cosmetic deformity as well as potential limitations in brain growth and development, and the neurocognitive impact of the condition is just starting to be studied more thoroughly. Our knowledge regarding the genetics of this condition has also evolved substantially. In this review, the authors explore the medical and surgical advancements in understanding and treating this condition over the past century, with a focus on how the diagnosis and treatment have evolved.

METHODS

In this review article, the authors, who are the leaders of a craniofacial team at a major academic pediatric hospital, focus on single-suture craniosynostosis (SSC) affecting the 6 major cranial sutures and discuss the evolution of the treatment of SSC from its early history in modern medicine through the current state of the art and future trends. This discussion is based on the authors' broad experience and a comprehensive review of the literature.

SUMMARY

The management of SSC has evolved substantially over the past 100 years. There have been major advances in technology and medical knowledge that have allowed for safer treatment of this condition through the use of newer techniques and technologies in the fields of surgery, anesthesia, and critical care. The use of less invasive surgical techniques along with other innovations has led to improved outcomes in SSC patients. The future of SSC treatment will likely be guided by elucidation of the causes of neurocognitive delay in these children and assessment of how the timing and type of surgery can mitigate adverse outcomes.

Assessment of spring cranioplasty biomechanics in sagittal craniosynostosis patients

OBJECTIVE 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. METHODS 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. RESULTS Stiffer springs were implanted in older patients (p < 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 < 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. CONCLUSIONS 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.

Cranial bone structure in children with sagittal craniosynostosis: Relationship with surgical outcomes

BACKGROUND

While spring-assisted cranioplasty has become a widespread technique to correct scaphocephaly in children with sagittal synostosis, predicting head shape changes induced by the gradual opening of the springs remains challenging. This study aimed to explore the role of cranial bone structure on surgical outcomes.

METHODS

Patients with isolated sagittal synostosis undergoing spring-assisted cranioplasty at GOSH (London, UK) were recruited (n = 18, age: 3-8 months). Surgical outcome was assessed by the change in cephalic index measured on 3D head scans acquired before spring insertion and after their removal using a 3D handheld scanner. Parietal bone samples routinely discarded during spring-assisted cranioplasty were collected and scanned using micro-computed tomography. From visual assessment of such scans, bone structure was classified into one- or three-layered, the latter indicating the existence of a diploë cavity. Bone average thickness, volume fraction and surface density were computed and correlated with changes in cephalic index.

RESULTS

Cephalic index increased for all patients (p < 0.001), but individual improvement varied. Although the patient age and treatment duration were not significantly correlated with changes in cephalic index, bone structural parameters were. The increase of cephalic index was smaller with increasing bone thickness (Pearson's r = -0.79, p < 0.001) and decreasing bone surface density (r = 0.77, p < 0.001), associated with the three-layered bone structure.

CONCLUSIONS

Variation in parietal bone micro-structure was associated with the magnitude of head shape changes induced by spring-assisted cranioplasty. This suggests that bone structure analysis could be a valuable adjunct in designing surgical strategies that yield optimal patient-specific outcomes.

Safety of Open Cranial Vault Surgery for Single-Suture Craniosynostosis: A Case for the Multidisciplinary Team

INTRODUCTION

Single Suture Craniosynostosis (SSC) occurs in 1 in 2,500 live births and is the most common type of craniosynostosis treated in most centers. Surgical treatment has evolved over the past century and open techniques are tailored to the specific suture type. Additionally, the concept of multi-disciplinary team care has proliferated and is becoming the standard of care for SSC. The combination of these evolutions, we believe, has improved the safety of cranial vault surgery for SSC.

METHODS

A retrospective review of patients participating in the Infant Learning Project at Seattle Children's Hospital who underwent cranial vault surgery for treatment of SSC between 2002 and 2006 was performed. Pre-operative assessment, surgical techniques, anesthetic and intraoperative events and both intra-operative and post-operative adverse events were analyzed.

RESULTS

Eighty eight patients fulfilled the inclusion criteria (42 sagittal, 23 metopic, 19 unicoronal, 4 lambdoid). Length of procedure varied (FOA 5.2 hrs, modified pi 2.5 hrs, total vault 4.9 hrs and switch cranioplasty 4.6 hrs), as did transfusion amount (FOA 385 mL, modified pi 216 mL, total vault 600 mL, switch cranioplasty 207 mL) although 99% of patients received a transfusion of some sort. There were no deaths and no major intraoperative complications. Minor events include; ET tube malposition (1), desaturation (1), acidosis (1), hypothermia (9), coagulopathy (2), Hct < 25 (55). Average hospital stay was 3.4 days with no major post-operative complications. One patient was readmitted to the ICU and 1 had a scalp hematoma, but no patients returned to the operating room within 6 months after surgery.

DISCUSSION

The surgical treatment of SSC has evolved from lengthy, risky procedures to become almost routine at most craniofacial centers. Additionally, the care for patients with SSC has evolved from a single provider to a multidisciplinary team concept based around protocols for workup, delivery of anesthesia, streamlined surgical procedures and post-operative care and assessment. This evolution has given open cranial vault surgery for SSC an acceptable safety profile.