Spring-Assisted Correction of Hypotelorism in Metopic Synostosis

A critical eye on metopic craniosynostosis: A retrospective study assessing orbital dysmorphology as a marker of disease

This investigation sought to ascertain whether orbital morphology could predict genuine metopic craniosynostosis (MCS). The study retrospectively analyzed preoperative three-dimensional computed tomography (3D-CT) scans of patients who underwent surgical correction for MCS. MCS severity was evaluated using the interfrontal angle (IFA). Orbital dysmorphology was assessed based on multiple angles, including supraorbital notches and nasion (SNS), infraorbital foramina and nasion (INI), zygomaticofrontal suture-supraorbital notch-dacryon (ZSD), and orbital long axis (OLA). Results were juxtaposed against age/gender-matched controls and individuals with non-synostotic metopic ridge (MR). The study included 177 patients: 68 MCS, 35 MR, and 74 control subjects. All orbital measurements exhibited significant differences across groups. IFA demonstrated a strong association with all orbital measurements, particularly SNS (B = 0.79, p < 0.001). SNS showed the highest area under the curve among orbital measurements (0.89). Using a 95% sensitivity threshold, the optimal diagnostic angle for SNS was 129.23° (specificity 54%, sensitivity 96%). These findings suggest a correlation between orbital dysmorphology and trigonocephaly severity. The observed dysmorphology manifested in a superomedially accentuated rotational pattern. Importantly, SNS angle predicted MCS, with an angle greater than 130° indicating <5% likelihood of MCS diagnosis. The simplicity of measuring SNS angle on any 3D-CT scan highlights its practical use for assisting with MCS diagnosis.

Validating the Supraorbital Notch-Nasion-Supraorbital Notch Angle as a Marker for Metopic Craniosynostosis Severity

OBJECTIVE

Metopic craniosynostosis (MCS) can be difficult to differentiate from metopic ridge (MR) or normal frontal morphology. This study assess whether the supraorbital notch-nasion-supraorbital notch (SNS) angle can help identify MCS.

METHODS

Records of 212 patients with preoperative three-dimensional computed tomography scans were examined. The SNS angles, surgeon craniofacial dysmorphology rankings, and CranioRate metopic severity scores (MSSs) were compared with the Spearman rank correlation coefficient. Receiver operating characteristic (ROC) curves with Youden J-statistic and cross-validation of regression models assessed the ability of these measures to predict surgery.

RESULTS

A total of 212 patients were included, consisting of 78 MCS, 37 MR, and 97 controls. Both the mean SNS angle (MCS: 111.7 ± 10.7 degrees, MR: 126.0 ± 8.2 degrees, controls: 130.7 ± 8.8 degrees P < 0.001) and MSS (MCS: 5.9 ± 2.0, MR: 1.4 ± 1.9, controls: 0.2 ± 1.9, P < 0.001) were different among the cohorts. The mean SNS angle (111.5 ± 10.7 versus 129.1 ± 8.8, P < 0.001) was lower in those who had surgery and CranioRate score (5.9 ± 2.1 versus 0.8 ± 2.2, P < 0.001) was higher in those who underwent surgery. SNS angles were positively correlated with surgeon craniofacial dysmorphology rankings ( r = 0.41, P < 0.05) and CranioRate MSS ( r = 0.54, P < 0.05). The ROC curve requiring high sensitivity revealed an SNS angle of 124.8 degrees predicted surgery with a sensitivity of 88.7% and a specificity of 71.3%. A ROC curve using the CranioRate MCC values ≥3.19 predicted surgery with 88.7% sensitivity and 94.7% specificity.

CONCLUSION

Orbital dysmorphology in patients with MCS is well captured by the supraorbital-nasion angle. Both the SNS angle and CranioRate MSS scores accurately predict surgical intervention.

Three-Dimensional Analysis and Surgical Planning for Open Correction of Trigonocephaly

SUMMARY

Metopic craniosynostosis results in trigonocephaly, characterized by a triangular forehead with metopic ridge, bitemporal pinching, and narrow-set eyes with recessed lateral orbital rims. Surgical management is controversial but may include open expansion and vault remodeling, to enhance neurocognitive and aesthetic outcomes. This article and video vignette depict the diagnosis and treatment of metopic craniosynostosis, demonstrating the senior author's open approach, three-dimensional virtual surgical planning, and technical steps.

Photogrammetric evaluation of corrective surgery for trigonocephaly

The aim of this study was to capture preoperative, postoperative, and follow-up head shapes of male trigonocephaly patients who underwent fronto-orbital remodelling (FOR), using three-dimensional (3D) photography. Fifty-seven male infants with metopic synostosis operated on using standardized FOR during a 5-year period were included. All measurements were compared with those of an age-matched healthy control cohort (n = 253 for early postoperative comparison, n = 43 for the 1-year follow-up comparison) to determine the effect of FOR at 14 days and at 1 year post-surgery. Intracranial volume, frontal angle, nasofrontal angle, interfrontoparietal-interparietal ratio, and inter-orbital distances were measured 1 day preoperatively, 14 days and 1 year postoperatively. Mean age at surgery was 9.7 ± 1.1 months. Prior to surgery, boys with metopic synostosis showed a reduced intracranial volume (-7.0%, P < 0.001), frontal angle (-10.2%, P < 0.001), interfrontoparietal-interparietal ratio (-4.9%, P < 0.01), and orbital distances (-6.5%, P < 0.001) compared to the reference group, but values did not differ significantly from the specific control group after surgery (all P> 0.05). This was consistent by the time of the follow-up examination. Corrective surgery should therefore aim to achieve volume expansion and correction of the deformity. Furthermore, 3D photogrammetry provides a valuable alternative to computed tomography scans in the diagnosis of metopic synostosis, significantly reducing the amount of radiation exposure to the brain.

Why do metopic sutural synostoses angulate? The concept of nasion sutural complex and its implication on the management of hypotelorism-early results and proof of concept

OBJECT

Angulation at the suture is a hallmark of metopic synostoses amongst all craniosynostoses. No other sutural synostoses demonstrate angulation at synostoses consistently. We look into the possible aetiology and the implication of the understanding in the treatment goals of trigonocephaly. We hypothesise that the nasal bone and nasofrontal suture viz. "nasion sutural complex" are involved in trigonocephaly along with the well-accepted role of metopic suture. We propose that it is the angulation at this junction which leads to trigonocephaly and its secondary features.

MATERIALS AND METHODS

The study included seven infants, who underwent correction for trigonocephaly at our paediatric craniofacial division at Amrita Institute of Medical Sciences and Research Centre, Kochi, India, between the period July 2015 to March 2018. The cohort included were infants with trigonocephaly who had CT head for diagnosis. We analysed the multidimensional CT (MDCT) of these infants and compared to an equal number of age-matched controls. The controls were infants with other forms of sutural synostosis with metopic uninvolved and normal infants where MDCT was done for other reasons. Sutural characteristic at the nasion and metopic suture recorded in comparison with an equal number of age-matched controls. We performed spring cranioplasty for three infants after metopic suturectomy, extending the release beyond the nasion sutural complex, placing springs to distract the suture. The infants who underwent spring cranioplasty were followed up for the aesthetic outcome. Remaining infants of the study underwent standard frontorbital correction for metopic craniosynostoses.

RESULTS

We could demonstrate a fusion of nasofrontal and nasal suture in all cases (n = 7) of trigonocephaly included in the study on MDCT and intraoperatively. We performed spring cranioplasty for three infants (n = 3/7), where we released the internasal suture. At 3 months follow-up, along with correction of the angulation, the hypotelorism improved significantly. Other infants in the study (4/7) underwent classical frontorbital advancement.

CONCLUSIONS

Fusion of nasion sutural complex along with metopic sutures may explain the angulation in trigonocephaly. We propose that all minimally invasive techniques for correction of trigonocephaly and associated hypotelorism should consider this fact for an improved outcome.

Spring-Assisted Surgery in the Treatment of Complex Craniosynostosis

Multisutural nonsyndromic craniosynostosis is a rare group of malformations, whose frequency has been reported between 3% and 7% of all craniosynostosis. The clinical diagnosis can be difficult and computed tomography is usually required. Surgical treatment is challenging and staged procedures are performed in up to 80% of patients. The aim of the present study was to determine the reoperation rate and to evaluate the surgical outcomes by measuring intracranial volume (ICV) preoperatively and at follow-up, and comparing it to a control group. Perioperative variables and reoperation rate were recorded. Fifty-one patients presented with a complex pattern of synostosis without a recognizable syndrome (5% of cases of total patients evaluated). Fifteen patients have been treated with spring-assisted surgery, either alone or in combination with a foreheadplasty. The mean follow-up was 6.2 years. The mean preoperative ICV of the patients was smaller, but not significantly, than in the normal population (P = 0.13). Postoperatively, the mean ICV was similar to that of the control group at 1 year (P = 0.92), while at 3 years it was appreciably smaller, although not significantly different (P = 0.06). Five patients (33%) went through a secondary skull expansion for either raised intracranial pressure or cosmetic reasons. Spring-assisted surgery seems to temporarily expand ICV in children with complex synostosis and lower the reoperation rate, thus reducing the need for a second procedure. A longer follow-up would be necessary to further investigate the effects of springs over time.

Anthropometric Outcomes following Fronto-Orbital Advancement for Metopic Synostosis

BACKGROUND

The authors' purpose is to present changes in anthropometric fronto-orbital dimensions after surgical correction of metopic synostosis.

METHODS

The authors retrospectively analyzed craniometric dimensions in older patients with metopic synostosis corrected by fronto-orbital advancement performed by the senior author (J.B.M.). Preoperative and postoperative linear measures (frontal breadth, cranial width, and intercanthal distance) were taken by direct anthropometry. Interdacryon distance and width of the bandeau were also recorded intraoperatively, before and after widening. Follow-up anthropometric values were compared to age- and sex-matched normative data and standard (z) scores were calculated.

RESULTS

Sixteen patients met the inclusion criteria. Syndromic diagnosis was documented in five of 16 patients. Average age at the last postoperative evaluation was 8.9 ± 3.8 years (range, 4 to 16 years). Mean frontal width z-scores decreased postoperatively from 0.82 to -0.32 (p = 0.007), indicating diminished growth in this dimension. The last measured frontal width strongly correlated with the breadth of the bandeau after surgical correction but not with preoperative values. Postoperative mean cranial width diminished significantly to a more normal value. Mean intercanthal distance was normal preoperatively and remained so but was significantly greater in syndromic than in nonsyndromic cases.

CONCLUSIONS

Frontal growth rate is diminished in the coronal plane after fronto-orbital advancement. The authors recommend primary techniques to overcorrect the width of the bandeau and frontal region, including zygomaticosphenoid osteotomies and interpositional cranial bone grafts to advance/widen the lateral orbital rim. Continued evaluation is required to assess whether overcorrection results in normal frontotemporal shape and breadth at skeletal maturity.

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.

Comparison Between Two Different Isolated Craniosynostosis Techniques: Does It Affect Cranial Bone Growth?

INTRODUCTION

Craniosynostosis is a premature closure of a cranial suture. Cranioplasty is indicated to correct skull deformity, relieve increased intracranial pressure, and promote homogenous cranial growth. Different techniques have been adopted to achieve optimal outcomes. Although surgical benefits are widely accepted, this intervention might also affect cranial skeletal growth.

METHODS

The authors conducted a retrospective case-control study including patients operated for isolated metopic or sagittal synostosis. These patients had undergone a computed tomography (CT) scan before surgery and/or at 3 years of age postoperatively. These were operated between 2002 and 2012. Intracranial volume was measured using a MATLAB application. The control group was age and sex-matched individuals who had CT scans for trauma or neurological indications. All results with P value <0.05 were considered statistically significant.

RESULTS

A total of 185 patients were included in the study with a preoperative CT scan (143 sagittal synostosis and 42 metopic synostosis). Postoperatively 160 patients were identified including 103 sagittal synostosis and 57 metopic synostosis. These patients were compared to 414 controls. There was a statistically significant reduction in intracranial volume (ICV) in patients operated for metopic synostosis with both techniques. It also demonstrated a statistically significant difference in ICV in patients with sagittal synostosis operated with Pi-plasty and a nonsignificant difference in ICV in patients operated with strip craniotomy and springs.

CONCLUSION

In conclusion, these measurements of ICV have revealed that extensive cranioplasties for premature craniosynostosis can lead to minor but significant growth restriction and reduced ICV at long-term follow-up.

A functional aesthetic approach to correcting the sequelae of sagittal synostosis

Sagittal synostosis is the most commonly treated form of craniosynostosis exhibiting an incidence of 1:5000 births.(1) Early closure of the sagittal suture is the cause of the classic phenotypic presentation of an elongated head, which is characterized by a narrow and low occiput, a saddle-shaped parietal region, and noticeable frontal bossing. Early surgical intervention is the treatment of choice and surgical options range from simple suture excision to total cranial vault remodeling. Noting that a significant proportion of patients present with limited frontal bossing and asymmetry that is more pronounced in the posterior cranium, the author developed the functional aesthetic approach to reconstruction. This operative technique addresses the changes noted in the posterior two-thirds of the cranial vault, completely correcting the sequelae associated with early closure of the sagittal suture. As an added advantage, the reconstructive paradigm is designed to create a dynamic temporal-occipital component that will activate when a child rests in the supine position. This enhances widening of the posterior cranium thus improving long-term results.

Evidence-based medicine: Craniosynostosis

LEARNING OBJECTIVES

After studying this article, the participant should be able to: (1) Make the appropriate diagnosis for each of the single-sutural synostoses, based on the physical examination. (2) Explain the functional concerns associated with these synostoses and why surgical correction is indicated. (3) Distinguish between the different types of surgical corrections available, the timing for these various interventions, and in what ways these treatments achieve overall management objectives. (4) Identify the basic goals involved in caring for the syndromic synostoses.

SUMMARY

This article provides an overview of the diagnosis and management of infants with craniosynostosis. This review also incorporates some of the treatment philosophies followed at The Craniofacial Center in Dallas, but is not intended to be an exhaustive treatise on the subject. It is designed to serve as a reference point for further in-depth study by review of the reference articles presented. This information base is then used for self-assessment and benchmarking in parts of the Maintenance of Certification process of the American Board of Plastic Surgery.

Parallel angulated frontal bone slat cuts for treatment of metopic synostosis and other frontal skull deformities: the "cathedral dome procedure"

PURPOSE

This study aims to describe a new procedure for the treatment of metopic synostosis and other frontal skull deformities.

METHOD

The procedure comprises a supraorbital bandeau widened with an interpositional graft and rounded laterally to eliminate the acute angle, and parallel angulated slat cuts in the frontal bones. Greenstick fracturing of the medial bases of these slats along a parasagittal hinge line causes fanning of the slats and expansion of the frontal flap both anteriorly and laterally making the forehead contour wider and more rounded. We performed this procedure on six infants (four with severe trigonocephaly from metopic synostosis, one with brachycephaly from bicoronal synostosis, and one with multiple suture synostosis and parietal flattening) for whom only the angulated slat cuts (without bandeau) were used. Each patient had preoperative three-dimensional computed tomography (3D-CT) and postoperative 3D-CT at 1 week, 3 months, and 12 months, to follow the result.

RESULT

The cosmetic improvements are dramatic in eliminating the midfrontal keel, hypotelorism, frontal-lateral retrusion, and temporal hollowing seen in severe metopic synostosis. In coronal synostosis, the procedure corrects the brachycephaly and gives a balanced, well-rounded frontal contour. The end results of the fronto-orbital correction resemble the ribbed dome of a cathedral; hence, the moniker the "cathedral dome procedure". No patient needed a second procedure to fill in cranial defects or recorrect deficient areas.

CONCLUSION

The parallel angulated frontal slat cuts technique (the "cathedral dome procedure") is a straightforward and easily mastered method that reliably produces excellent result for the correction of trigonocephaly and other frontal skull deformities.

The shell technique: bilateral fronto-orbital reshaping in trigonocephaly

The shell technique, used in the Pediatric Neurosurgical Department at the Catholic University, Rome, since the 1990s for the correction of trigonocephaly, is associated to a significant reduction in surgical time and intraoperative blood loss as compared to other procedures, while allowing an adequate remodelling of the bifrontal bone by means of multiple radial osteotomies. The technique does not necessitate the creation of a supraorbital bar, as the supraorbital ridges are modified in situ, further reducing the operative blood loss. In spite of reduced surgical time and manipulation, this procedure ensures aesthetic and functional results comparable to more extensive and complex cranial vault reshaping procedures. The main limitation of this technique is related to the surgical timing, as better results are obtained between 3 and 9 months of age, when the skull bone is still ductile to work with, thus allowing it to be remodelled by greenstick fractures. Moreover, in this age group, the cranial defects that result from the enlargement of the frontal bone flap by means of radial cuts and from the anterior displacement of its lateral portions may benefit from the more effective bone regeneration which characterizes younger children as compared to their older counterparts. A small number of cases showing either persistent hypotelorism or temporal depression have been observed in the post-operative period, although these residual deformities probably depend on a more extensive involvement of the cranial base in the synostotic process in these patients than on the procedure itself.

A review of reconstructive materials for use in craniofacial surgery bone fixation materials, bone substitutes, and distractors

Over the last 40 years, craniofacial surgery, in general, and surgery for craniosynostosis, in particular, has witnessed the introduction of a number of new materials for use in operations involving the cranial vault. Some of these materials have proven quite useful over time, while others have failed to meet their stated objectives. In this review, the more popular implant materials are analyzed, and their relative merits and drawbacks are discussed. Craniofacial surgery in the pediatric population has its own unique limitations, quite different from the adult population and those issues are reviewed as well.

Spring-assisted posterior skull expansion without osteotomies

INTRODUCTION

A posterior flatness of the skull vault can be observed in infants with brachycephaly. Such posterior deformation favours the development of turricephaly which is difficult to correct. To reduce the risk of such deformation, an early posterior skull remodelling has been suggested. Translambdoid springs can be used to allow for a distraction through the patent lambdoid sutures and obtain a progressive increase of the posterior skull volume.

SURGICAL TECHNIQUE

The procedure consists in a posterior scalp elevation, the patient being on a prone position. Springs made of stainless steel wire (1.5 mm in diameter) are bent in a U-type fashion, and strategically positioned across both lambdoid sutures. No drilling is usually necessary, as the lambdoid suture can be gently forced with a subperiosteal elevator in its middle and an indentation can be created with a bony rongeur on each side of the open suture to allow for a self-retention of bayonet-shaped extremity of the spring. Careful attention is addressed to the favoured prone position during the post-operative period. After a delay of 3-6 months, the springs can be removed during a second uneventful procedure, with limited incisions, usually as a preliminary step of the subsequent frontal remodelling.

CONCLUSION

The concept of spring-assisted expansion across patent sutures under 6 months of age was confirmed in our experience (19 cases). Insertion of the springs allowed for immediate distraction across the suture. A posterior remodelling of the skull could be achieved with minimal morbidity allowing to delay safely a radical anterior surgery.

Metopic synostosis

Premature closure of the metopic suture results in a growth restriction of the frontal bones, which leads to a skull malformation known as trigonocephaly. Over the course of recent decades, its incidence has been rising, currently making it the second most common type of craniosynostosis. Treatment consists of a cranioplasty, usually preformed before the age of 1 year. Metopic synostosis is linked with an increased level of neurodevelopmental delays. Theories on the etiology of these delays range from a reduced volume of the anterior cranial fossa to intrinsic malformations of the brain. This paper aims to provide an overview of this entity by giving an update on the epidemiology, etiology, evolution of treatment, follow-up, and neurodevelopment of metopic synostosis.

Biomechanical Analysis of the Effect of Intracranial Pressure on the Orbital Distances in Trigonocephaly

Objective

This biomechanical study aims to elucidate differences in how skulls with trigonocephaly, normal skulls, and postoperative trigonocephalic skulls respond to intracranial pressure and how this affects the orbital distances.

Materials and Methods

For 10 patients with trigonocephaly (8.2 ± 4.5 months), simulation models were produced based on the computed tomographic data of the skulls. These models were categorized as the Trigono group. For each model, a 15-mm Hg pressure was applied to the neurocranium to simulate the intracranial pressure. The interorbital distances expanded in response to the applied pressure. The amount of the change in the orbital distance was calculated using finite element analysis. The same processes were repeated for 10 models simulating normal skulls (the Control group) and postoperative trigonocephalic skulls (the Remodeled group). The changes in the orbital distance were compared among the three groups.

Results

The changes in the orbital distance were significantly smaller for the Trigono group than for the Control group. However, changes were significantly greater for the Remodeled group than for the Control group.

Conclusion

The expansion of interorbital distances in response to the cranial pressure is restricted in skulls with trigonocephaly. This restriction is eliminated by performing remodeling of the skull. These findings explain why spontaneous correction of hypotelorism occurs postoperatively in trigonocephaly.

Surgical treatment of trigonocephaly: technique and long-term results in 48 cases

OBJECT

The authors present their experience in the surgical treatment of metopic synostosis by orbital bandeau remodeling and frontal bone rotation. The pitfalls and advantages of the surgical technique are discussed, along with the long-term clinical results in 48 consecutive cases.

METHODS

Forty-eight consecutive patients in whom trigonocephaly was diagnosed between 1990 and 2009 were treated with frontal bone rotation and frontoorbital bandeau remodeling. Of these patients, 38 (79%) were boys and 10 (21%) were girls. The age at the time of surgical treatment ranged between 4 and 42 months (mean ± SD 11.4 ± 8.7 months). The average follow-up period was 5.5 ± 4.2 years (range 5 months-19 years). The preoperative and latest postoperative photographs of the patients were evaluated for the following features: 1) shape of the forehead; 2) hypotelorism; and 3) temporal depression. Scores of 0, 1, or 2 were assigned for each item: 0 was normal, 1 meant moderate deformity, and 2 denoted severe deformity.

RESULTS

In the early postoperative period, no complications were documented. The average hospitalization period was 4 days. Follow-up radiographs or 3D CT scans were obtained at regular intervals. The mean preoperative scores for the evaluated items were 1.38 ± 0.49 for the shape of the forehead, 1.33 ± 0.48 for hypotelorism, and 1.7 ± 0.46 for the temporal depression. The mean postoperative scores were 0.06 ± 0.24 for the shape of the forehead, 0.21 ± 0.4 for hypotelorism, and 0.67 ± 0.48 for the temporal depression. Overall, the total preoperative score dropped from 4.4 to 0.93 postoperatively (p < 0.05). All the patients were contented with the cosmetic results.

CONCLUSIONS

Early detection and treatment of metopic suture synostosis has a significant, favorable influence on the outcomes. Good understanding of the structural abnormality and the pathophysiological mechanisms of the possible complications is very important for performing proper surgical reconstruction.

Frontobasal suture distraction corrects hypotelorism in metopic synostosis

BACKGROUND

Spring-assisted cranioplasty has been demonstrated to correct hypotelorism associated with metopic synostosis. In addition, the fronto-orbital axis rotates toward a more normal orientation. We postulated that spring-induced shear forces and subsequent displacement across the frontobasal sutures are the primary initial mechanisms for change in cranio-orbital morphology.

METHODS

Sixteen consecutive patients (32 orbits) with trigonocephaly operated on between 1999 and 2004 were studied retrospectively. After frontal remodeling, a spring was placed across the released metopic suture. Preoperative and 6-week postoperative cephalograms were used to measure the relative translation of the medial orbital wall from the midline at fixed vertical distances above and below the frontoethmoidal suture (FES). The vertical height of the spring above the frontonasal suture and the patient's age were analyzed with respect to the increase in bony interorbital distance (BIOD).

RESULTS

There were significant increases in movement of the medial orbital wall above the FES at each measurement point (P < 0.001). There was no significant postoperative movement of the medial orbital wall below the FES at any measurement point. The relative movements above the suture suggest a degree of plastic deformation adjacent to the suture.There was no significant correlation between the age of patient or the height of the spring above the frontonasal suture and the increase in BIOD.

CONCLUSION

Tensile spring forces are transmitted directly to the frontoethmoid suture. Most initial increases in BIOD and altered intraorbital morphology are due to distraction of cranial base sutures rather than plastic deformation.