Dynamic spring-mediated cranioplasty in a rabbit model

Research progress and perspective of metallic implant biomaterials for craniomaxillofacial surgeries

Craniomaxillofacial bone serves a variety of functions. However, the increasing number of cases of craniomaxillofacial bone injury and the use of selective rare implants make the treatment difficult, and the cure rate is low. If such a bone injury is not properly treated, it can lead to a slew of complications that can seriously disrupt a patient's daily life. For example, premature closure of cranial sutures or skull fractures can lead to increased intracranial pressure, which can lead to headaches, vomiting, and even brain hernia. At present, implant placement is one of the most common approaches to repair craniomaxillofacial bone injury or abnormal closure, especially with biomedical metallic implants. This review analyzes the research progress in the design and development of degradable and non-degradable metallic implants in craniomaxillofacial surgery. The mechanical properties, corrosion behaviours, as well as in vitro and in vivo performances of these materials are summarized. The challenges and future research directions of metallic biomaterials used in craniomaxillofacial surgery are also identified.

The History of Spring-Assisted Surgery Implementation into the Treatment Algorithm for Craniofacial Deformities

Spring-assisted surgery has been a part of the craniofacial surgeon's armamentarium for more than 2 decades now. The development and implementation of this technique will be reviewed as well as the evolution of spring surgery at Wake Forest University.

Syndromic Craniosynostosis

Management strategies for syndromic craniosynostosis patients require multidisciplinary subspecialty teams to provide optimal care for complex reconstructive approaches. The most common craniosynostosis syndromes include Apert (FGFR2), Crouzon (FGFR2), Muenke (FGFR3), Pfeiffer (FGFR1 and FGFR2), and Saethre-Chotzen (TWIST). Bicoronal craniosynostosis (turribrachycephaly) is most commonly associated with syndromic craniosynostosis. Disease presentation varies from mild sutural involvement to severe pansynostoses, with a spectrum of extracraniofacial dysmorphic manifestations. Understanding the multifaceted syndromic presentations while appreciating the panoply of variable presentations is central to delivering necessary individualized care. Cranial vault remodeling aims to relieve restriction of cranial development and elevated intracranial pressure and restore normal morphology.

Physico-chemical and Histomorphometric Evaluation of Zinc-containing Hydroxyapatite in Rabbits Calvaria

The aim of this study was to characterize the physico-chemical properties and bone repair after implantation of zinc-containing nanostructured porous hydroxyapatite scaffold (nZnHA) in rabbits' calvaria. nZnHA powder containing 2% wt/wt zinc and stoichiometric nanostructured porous hydroxyapatite (nHA - control group) were shaped into disc (8 mm) and calcined at 550 °C. Two surgical defects were created in the calvaria of six rabbits (nZnHA and nHA). After 12 weeks, the animals were euthanized and the grafted area was removed, fixed in 10% formalin with 0.1 M phosphate buffered saline and embedded in paraffin (n=10) for histomorphometric evaluation. In addition, one sample from each group (n=2) was embedded in methylmethacrylate for the SEM and EDS analyses. The thermal treatment transformed the nZnHA disc into a biphasic implant composed of Zn-containing HA and Zn-containing β-tricalcium phosphate (ZnHA/βZnTCP). The XRD patterns for the nHA disc were highly crystalline compared to the ZnHA disc. Histological analysis revealed that both materials were biologically compatible and promoted osteoconduction. X-ray fluorescence and MEV-EDS of nZnHA confirmed zinc in the samples. Histomorphometric evaluation revealed the presence of new bone formation in both frameworks but without statistically significant differences (p>0.05), based on the Wilcoxon test. The current study confirmed that both biomaterials improve bone repair, are biocompatible and osteoconductive, and that zinc (2wt%) did not increase the bone repair. Additional in vivo studies are required to investigate the effect of doping hydroxyapatite with a higher Zn concentration.

Development and characterization of elastic nanocomposites for craniofacial contraction osteogenesis

Development of resorbable elastic composites as an alternative means to apply contractive forces for manipulating craniofacial bones is described herein. Composites made from the biodegradable elastomer, poly (1,8-octanediol co-citric acid) (POC), and hydroxyapatite (nHA) with a 200 nm diameter (0-20% loadings) were created to develop a material capable of applying continuous contractive forces. The composites were evaluated for variation in their mechanical properties, rate of degradation, and interaction of the hydroxyapatite nanoparticles with the polymer chains. First, an ex vivo porcine model of cleft palate was used to determine the rate of cleft closure with applied force. The closure rate was found to be 0.505 mm N(-1) . From this approximation, the ideal maximum load was calculated to be 19.82 N, and the elastic modulus calculated to be 1.98 MPa. The addition of nHA strengthens POC, but also reduces the degradation time by 45%, for 3% nHA loading, compared to POC without nHA. X-ray diffraction data indicates that the addition of nHA to amorphous POC results in the formation of a semicrystalline phase of the POC adjacent to the nHA crystals. Based on the data, we conclude that amongst the 0-20% nHA loadings, a 3% loading of nHA in POC may be an ideal material (1.21 MPa elastic modulus and 13.17 N maximum load) to induce contraction forces capable of facilitating osteogenesis and craniofacial bone repair.

Comparison of spring-mediated cranioplasty to minimally invasive strip craniectomy and barrel staving for early treatment of sagittal craniosynostosis

The treatment of sagittal craniosynostosis has evolved from early strip craniectomy to total cranial vault remodeling and now back to attempts at minimally invasive correction. To optimize outcomes while minimizing morbidity, we currently use 2 methods of reconstruction in patients younger than 9 months: spring-mediated cranioplasty (SMC) and minimally invasive strip craniectomy with parietal barrel staving (SCPB). The purpose of this study was to compare the safety and efficacy of the 2 methods. Hospital records of our first 7 SMCs and our last 7 SCPBs were analyzed for demographics, the type of operation performed, estimated blood loss, transfusion requirements, operative time, length of stay in the intensive care unit, length of hospital stay, preoperative cephalic index, postoperative cephalic index, and complications. The techniques were then compared using analysis of variance.All 14 patients successfully underwent cranial vault remodeling with significant improvement in cephalic index. Demographics, length of stay in the intensive care unit (P = 0.15), preoperative cephalic index (P = 0.86), and postoperative cephalic index (P = 0.64) were similar between SMC and SCPB. Spring-mediated cranioplasty had statistically significantly shorter operative time (P = 0.002), less estimated blood loss (P < 0.001), and shorter length of hospital stay (P = 0.009) as compared with SCPB. Complications included 1 spring dislodgment in an SMC that did not require additional management and 1 undercorrection in the SCPB group. Both SMC and SCPB are safe, effective means of treating sagittal craniosynostosis. Spring-mediated cranioplasty has become our predominant means of treatment of scaphocephaly in patients younger than 9 months because of its improved morbidity profile.

Time-dependent perioperative anesthetic management and outcomes of the first 100 consecutive cases of spring-assisted surgery for sagittal craniosynostosis

BACKGROUND

  The anesthetic risks and outcomes of the first 100 consecutive spring-assisted surgeries (SAS) for cranial expansion from a single institution are reported. The effect of number of procedures was also tested on hematocrit postoperative day 1 (POD1), anesthesia time, and surgery time of the first procedure.

METHODS

  The records of 100 consecutive patients undergoing SAS were reviewed. Anesthesia management and related complications are presented. Time series linear regression analysis was performed on hematocrit POD1, anesthesia time, and surgery time of the first procedure.

RESULTS

  The average age of the first insertion procedure was 4.4 and 9.0 months for the second removal procedure. Two patients were inadvertently extubated during positioning. Thirty-eight children had a decrease in blood pressure >20% from baseline. No child was admitted to the intensive care unit. No patient received any blood or blood product transfusion. Anesthesia time, surgery time, and hematocrit POD1 were correlated with procedure number or experience.

CONCLUSIONS

Changes in anesthetic management resulted from changing the procedure. The reduction in volume resuscitation reduces the need for invasive monitoring. Facility and comfort with the surgical procedure increase with time and number of procedures performed. This experience further reduces blood loss and risk of transfusion.

The biomechanical characteristics of cranial sutures are altered by spring cranioplasty forces

BACKGROUND

The mechanical properties of the pediatric craniofacial complex allow dissipation of spring cranioplasty forces. Springs do not fully expand in situ and continue to transmit a continuous force until removal. The authors wished to investigate whether ongoing forces altered the biomechanical characteristics of cranial sutures.

METHODS

Thirty New Zealand White rabbits were divided into five groups: spring expansion for 4, 7, and 10 weeks; early spring removal at 4 weeks followed by monitoring for 3 weeks; and a control group (n = 6 each). Cranial expansion was monitored using cephalometry. The left coronal suture then underwent load-displacement testing in a dynamometer.

RESULTS

Relapse of cranial expansion was observed following early spring removal (mean, 6 percent; p = 0.017). Cranial suture thickness was significantly correlated to the length of spring insertion. Load displacement curves of sutures in all groups initially exhibited classic viscoelastic behavior. The treatment group developed intrasutural weakening before failure that was not observed in controls. The peak load before failure as a percentage of that observed in controls was 31 percent in the 4-week group (p = 0.001), 35 percent in the 7-week group (p = 0.000), and 45 percent in the 10-week group (p = 0.023).

CONCLUSIONS

Cranial suture compliance is modified in the presence of continuous spring cranioplasty forces. Thickening of the coronal sutures, which have been expanded in a shear-like manner, increases their three-dimensional surface area and may contribute to the relative lack of relapse observed after early spring removal.

Spring-assisted surgery-a surgeon's manual for the manufacture and utilization of springs in craniofacial surgery

BACKGROUND AND PURPOSE

Spring-assisted surgery has been used for the treatment of craniofacial deformities since its 1997 inception in Sweden by Dr Lauritzen (Scand J Plast Reconstr Surg Hand Surg 1998;32:331-338). Initial applications have focused on the treatment of patients with single-suture craniosynostosis. Recently, indications and applications have expanded to include patients with syndromic craniosynostosis, multiple-suture synostosis, and midface hypoplasia. The advancement of spring-assisted surgery in this country has been hindered by the need for patient-specific spring fabrication because few surgeons understand how to make the springs for each application. We will review our spring design and treatment algorithms to facilitate wider use of this innovative treatment modality.

METHODS

This is a retrospective institutional review board-approved analysis of the spring design for our first 90 cases of spring-assisted surgery used to treat sagittal synostosis at the North Carolina Center for Cleft and Craniofacial Deformities. Outcome analysis was done to generate a treatment algorithm based on diagnosis, patient age, spring design, number of springs, spring force and expansion, and clinical outcome.

RESULTS

Ninety children with sagittal craniosynostosis (64 males, 26 females) were treated during an 8-year period (2001-2009) with spring-assisted surgery. Mean age at treatment was 4.4 months and mean age at spring removal was 8.8 months. Mean number of springs used was 2 (range, 1-3). Mean spring force used in sagittal synostosis was 5.5-9.5 (range) for the anterior spring and 5.5-9.5 (range) for the posterior spring with a mean posttreatment expansion of 6.65 cm. Analysis of the results shows that spring force and expansion required for optimal correction is dependent on the age at surgery, type of the deformity, and severity of the deformity. Specifically, the younger the child, the weaker the spring needed for surgical correction. General principles for spring application for scaphocephaly include (1) the longer the anterior posterior dimension of the skull deformity, the more likely a third spring is necessary; (2) the narrower the posterior occiput, the stronger the posterior spring required; and (3) if a postcoronal band is seen in the calvarium, a stronger anterior spring is needed.

CONCLUSIONS

Long-term experience with spring-assisted surgery has facilitated the development of standardized, reproducible techniques allowing spring design modifications to optimize clinical outcome.

Adaptation of the cranium to spring cranioplasty forces

BACKGROUND

During spring-assisted cranioplasty, the spring transmits forces through adjacent cranium. We have previously demonstrated that the ectocranial-endocranial thickness of cranial sutures increases significantly over time in the presence of continuous spring forces. We wished to investigate if cranial bone showed similar adaptational responses.

METHODS

New Zealand white rabbits were randomized into a treatment group [a spring was placed across a posterior frontal suture (PFS) suturectomy and a control group (PFS suturectomy)]. Animals (n = 6) were euthanized from each group at 4, 7, and 10 weeks, respectively. A sham group (n = 6) was euthanized at 10 weeks. Frontal bone thickness was recorded at five reproducible anatomical points on the frontal bone. Histological analysis of the bone architecture was performed.

RESULTS

Frontal bone thickness was significantly greater than controls at all five sites at weeks 7 and 10. There were multiple significant differences between the 4-, 7-, and 10-week groups with each site progressively thickening over time. Histological analysis revealed a uniform increase in thickness of the endocranial and ectocranial cortical bone in the treatment groups.

CONCLUSIONS

Cranial bone adapts to the presence of continuous spring cranioplasty forces by progressively thickening over time. This property is beneficial in craniosynostosis cases with very thin and poor quality bone and may partly explain the observed lack of spring erosion through bone.

Do expansile cranial springs erode through the cranium?

Expansile cranial springs are used in selected cases of craniosynostosis. The spring exerts moderate force against the relatively thin skull. We investigated whether the spring erodes through the bone and the clinical significance of any erosion relative to the cranial expansion achieved.

METHODS

New Zealand white rabbits (n = 10) underwent sagittal suturectomy and spring insertion. Amalgam markers were placed perpendicular to the expected direction of suture erosion. A control group (n = 10) underwent suturectomy. Radiological evaluation was performed for 7 weeks to check for migration of the spring foot.

RESULTS

The mean cranial thickness was 1.4 mm at the site of spring insertion. This compared with 1.8 mm in 7 children undergoing spring cranioplasty. The mean spring force was 9.4 N. In sagittal synostosis, the mean spring force used is 7 to 10 N.The cranial width increased 11.02 mm in the spring treatment group compared with 0.23 mm in the control group (P < 0.001). Spring erosion occurred in 4 (20%) of the 20 spring ends. Mean spring erosion for the treatment group was 0.18 mm. This was 3.2% of the mean increase in cranial width. The maximum percentage spring erosion versus cranial expansion in an individual rabbit was 14.17%. There was no statistical difference in cranial expansion between the rabbits in whom bone erosion did and did not occur.

CONCLUSIONS

The degree of spring force required to effectively expand the cranium may cause bone erosion in some individuals. This degree of spring erosion was of minimal clinical significance in this animal model.

Superelastic NiTi springs for corrective skull operations in children with craniosynostosis

This paper concerns the formation and characterization of superelastic springs and rings of NiTi alloys for long-term skull correction. Superelastic properties of the rings were induced in the process of ageing of the already formed rings which cause hardening of parent phase by the precipitation of coherent Ni(4)Ti(3) particles. The efficacy of the worked out springs and rings were successfully proved in several clinical applications.

Dynamic Spring Mediated Cranioplasty in an Experimental Model With Resorbable Foot Plates

Craniofacial surgery continues to be progressive in its approach to maximize function and aesthetic appearance while minimizing risks and complications. Dynamic springs are one way to minimize invasiveness while achieving favorable results. The purpose of this study was to show the safety and efficacy of dynamic springs with resorbable foot plates for treatment of metopic suture abnormalities in a swine model. The study population consisted of twelve 20 kg Chester swine. The swine were divided into two treatment groups: four in the sham surgery group and eight in the stainless steel spring group. Postoperative analysis consisted of evaluation of the skull growth over time and integrity of the foot plates and underlying dura. The swine, killed at 8 weeks, were examined for spring location in the foot plates, ease of removal of the spring, and postmortem histologic analysis of the bone growth. No morbidity or mortality occurred in the immediate perioperative period secondary to the surgery. Postmortem histologic analysis revealed no infections or complications related to the surgery. Statistical analysis using a mixed linear model with an unstructured variance-covariance matrix was fit. In conclusion, this study confirms the efficacy and safety of the spring-mediated cranioplasty at the metopic suture with use of resorbable foot plates in a swine model.

Calvarial bone healing under spring distension at continuous forces

The aim of the present study was to evaluate in young animals the dynamics of calvarial bone healing when exposing a bone defect to continuous forces for up to 13 weeks. Six-week-old rabbits after a sagittal suture strip craniectomy were randomized for either of the following protocols: (1) no spring was applied (n = 7); (2) a titanium-molybdenum alloy (TMA) lower-force spring was inserted across the craniectomy gap (n = 9); (3) a stainless steel (SS) higher-force spring was applied (n = 8), or (4) sham operation (n = 8). Results showed that the surgically created calvarial bone gap was after 3 weeks kept widened both when a spring of lower force (TMA) and when a spring exerting a higher force (SS) was applied. At 6 weeks, none of the rabbits of the spring-exposed (2 and 3) groups had any bone bridging the gap, while bone bridging was visible in animals of the 2 groups (1 and 4) lacking springs. Strikingly enough, in both spring-treated groups, the surgically created defect was still after 13 weeks incompletely bridged by bone, interposed by connective tissue, most evidently in those exposed to higher forces (SS). In contrast, a normal sagittal suture enclosed by lamellar bone was seen in both the sham and the strip groups. We conclude that exposing a surgically created calvarial bone defect to continuous mechanical forces delayed the bridging of the bone defect by at least 13 weeks, even if the force exerted by either spring was very low. In any case, when a higher force (SS group) was applied, the bone reunion was efficiently prevented. No side effects were recognized.

Spring-Mediated Cranial Reshaping For Craniosynostosis

The evolution of modern craniofacial surgery has come full circle from the early strip craniectomies to the complete calvarial remodeling and now back to attempts at minimally invasive surgical interventions. The goal of the craniofacial surgeon has always been the correction of form and function with minimization of associated morbidity and mortality. Particularly problematic has been the ability to maintain the anatomical correction beyond the result seen on the operating room table secondary to changes with growth. The ability to improve the clinical result in a growing and developing child has been the impetus for dynamic treatment modalities. Dr Claes Lauritzen's pioneering work in this area has been particularly successful using internal springs to correct craniofacial deformities. The purpose of this study is to assess this treatment modality clinically in terms of safety and efficacy and to develop a methodology for the spring formation that would be easily reproducible. This is an institutional review board-approved prospective study of 15 children (11 male, 4 female) with non-syndromic sagittal suture synostosis. All patients were treated with a sagittal strip craniectomy and placement of 2 omega-shaped stainless steel springs at a mean age of 3.9 months. Patients were followed clinically and with cephalograms; after reossification of the intervening bone, the springs were removed at a mean age of 8.2 months. The mean force applied at initial placement of the springs was 6.9 N, and the mean spring deflection at formation was 6.87 cm. All patients completed the study protocol without any significant morbidity or any mortality. Perioperative variables, including blood loss, transfusion rate, operative time, intensive care unit stay, hospital stay, and hospital charges, were all significantly less (P < 0.05) in this study group compared with children with the same diagnosis treated with cranial vault reshaping during the same period. Furthermore, the preoperative mean cephalic index of 64.3 corrected to 77.6 after surgery and was maintained over time. Spring-mediated cranial reshaping is efficacious and safe for the treatment of sagittal synostosis. Long-term study of cranial development and clinical morphology are ongoing to validate further the effectiveness of this treatment modality.

Advances in Craniosynostosis Research and Management

The purpose of the present paper is to analyze the most recent advances in the field of craniosynostosis basic and clinical research and management, and to give an overview of the more frequently adopted surgical strategies. After reviewing some basic concepts regarding normal craniofacial embryology and growth, aetiopathogenesis of craniosynostosis and craniofacial dysostosis, classification and diagnosis and historical evolution of surgical treatment, the authors elaborate on a selection of topics that have modified our current understanding of and therapeutical approach to these disease processes. Areas covered include advances in molecular biology and genetics, imaging techniques and surgical planning, resorbable fixation technology, bone substitutes and tissue engineering, distraction osteogenesis and the spring-mediated cranioplasties, resorbable distractor devices, minimally invasive surgery and in utero surgery. A review of the main subtypes of craniosynostosis and craniofacial dysostosis is presented, including their specific clinical features and a commentary on the presently available surgical options.

Surgical advancement influences perioperative care: a comparison of two surgical techniques for sagittal craniosynostosis repair

Methods for surgical correction of sagittal craniosynostosis have progressed. The hypothesis is that advances in surgical interventions for craniosynostosis affect perioperative anesthetic care. We reviewed the records of eight children who underwent cranial vault reconstruction (CVR) and nine who underwent spring-mediated cranial expansion (SME) for sagittal craniosynostosis. We compared the data from the CVR procedure to data from the combined procedures for SME (insertion and removal of springs). Anesthesia times were similar between the CVR (4 h 24 min) and the combined SME (4 h 27 min) groups, whereas surgical times were different between the CVR (3 h 25 min) and combined SME groups (2 h 21 min) (P = 0.002). Length of stay was 4.1 days for the CVR group (confidence interval [CI], 3.8-4.4 days) versus 3.1 days (CI, 2.9-3.4 days) in the combined SME group (P = 0.0001). Blood loss was significantly less in the combined SME group at 48 mL (CI, 29-83 mL) compared with the CVR group at 291 mL (CI, 230-352 mL). All eight patients in the CVR group received blood with a mean of 1.4 U (range, 1-2 U). No SME patient received any blood products. The reduction in blood loss with this new surgical treatment is significant for the patient in reducing blood transfusion and for the anesthesiologist in reducing concerns of volume resuscitation.