Technique Using a Titanium Plate to Reconstruct the Inferior Sternal Cleft in Pentalogy of Cantrell: Lessons From Four Patients

Background By reviewing the outcomes of four patients, we summarize our experience with the strategy of using a titanium plate to reconstruct the inferior sternal cleft in pentalogy of Cantrell (POC). This was a retrospective analysis of 4 patients who visited our department between January 2000 and June 2020 concurrent with POC. All four patients underwent an operation, as well as cardiac ultrasound and thoracoabdominal computed tomography (CT). Cardiac malformations achieved satisfactory correction according to echocardiographs. A titanium plate was used to repair the sternal and supraumbilical abdominal defects. The hospital course, operative data, and outpatient records were reviewed.


Introduction
Pentalogy of Cantrell (POC) is a rare disease that occurs in 5 per million live births and was rst described in 1958 by Cantrell et al. Despite the rarity of POC, most reports of POC are case reports, and only approximately 185 cases have been reported around the world; the largest series of patients was 22, followed by a series of 8 1, 2 . POC is characterized by the presence of ve major malformations: midline supraumbilical abdominal wall defect, lower sternal defect, diaphragmatic pericardial defect, anterior diaphragmatic defect and various congenital abnormalities of the heart 2 . Because of the multiformity of its clinical manifestations and severity of malformations, survival rates are as low as 37% 3 and even 27% 1 according to some reports. Many surgeons are experientially de cient and easily misdiagnose this disease because of its extremely low incidence; to date, most reported cases in the literature have been sporadic. Repair of the inferior sternal cleft has been a hot topic and has attracted much attention, but there has been no consensus of opinions. The biggest challenge is the choice of an appropriate material to repair sternal clefts, and we previously reported on our method 4 . Here, we summarize our experience in successfully treating 4 patients with this complex congenital anomaly and describe the long-term outcomes of reconstruction of the inferior sternal cleft with a titanium plate 4 .

Patients
The Ethics Committee of the Children's Hospital of Chongqing Medical University approved the study protocol. The parents of the patients provided written informed consent.
From January 2000 and June 2020, we enrolled 4 patients in this study: 3 males and 1 females. All were full-term infants. Their weights on admission ranged from 3.4 kg to 7.5 kg, and their ages ranged from 3 months to 6 months. The rst patient showed ventricular septal defect (VSD) and atrial septal defect (ASD); the second patient, who had patent ductus arteriosus (PDA) and ASD, also presented with VSD; the third and fourth patients presented with double-outlet right ventricle (DORV) (subaortic VSD) with pulmonary stenosis (PS); the fourth patient also showed pulmonary valve stenosis, left pulmonary artery stenosis, and persistent left superior vena cava, with collateral circulation; All the patients had partial sternal clefts, and ectopia cordis was incomplete with stable haemodynamics (additional patient characteristics are shown in Table 1). The respiratory and circulatory systems of the 4 patients were all stable. In all 4 patients, ectopia cordis was not obvious (incomplete ectopia cordis) and was covered with loose skin, and only the cardiac apex protruded outside the chest. In these patients, the beating heart could be observed outside the thoracoabdominal or thoracic wall.

Methods
The incision was made through median sternotomy from the angulus sterni to the lower end of the abdominal defect. Then, the hypodermis was separated from the heart. Care was taken during this step not to injure the coronary arteries or diverticulum. The pericardium and diaphragm were explored rst to ascertain the presence of a severe diaphragmatic hernia. The intracardiac anomaly was corrected with standard cardiopulmonary bypass. The heart was pushed back into the thoracic cavity, and the pericardium was closed with an expanded Gore-Tex membrane to protect the heart from titanium. One titanium plate (Autocam Medical, Kentwood, MI, USA) was anchored to the sternum and ribs using 3 − 0 PDS-II or medical silk interrupted sutures (Ethicon, Somerville, NJ, USA) to repair the sternum and chest wall defect 4 monitoring for changes in the heart rate, blood pressure and rhythm.

Results
Sternal clefts can be classi ed into two major forms: partial and complete 5 . All 4 patients had partial sternal clefts; patients 1 and 2 had simple ASD and/or VSD, and both were treated with conventional cardiac surgery. Patients 3 and 4 had DORV (subaortic VSD), mild PS and a mild right ventricular out ow tract; these two patients were treated with DORV correction and dredging of the right ventricular out ow tract. In patient 4, reconstruction of the left pulmonary artery was performed. All four patients underwent a single-stage operation, and in all of these patients, the heart was replaced into the thoracic cavity without causing signi cant haemodynamic changes. A titanium plate was used to repair the defect in the sternal cleft and abdominal wall. In patient 4, low cardiac output syndrome occurred due to the complex cardiac malformation after medical treatment and discharge, but there were no serious postoperative complications. The follow-up period ranged from 9 months to 10 years. No patient developed pectus excavatum, and there were no cases of retrosternal seroma or pneumothorax. In all four patients, the appearance of both the abdominal wall and lower sternum and cardiac function were good. The New York Heart Association function class was I in the patients who underwent an operation. Although the titanium plate was migratory in the second patient and was dislodged at another hospital 3.5 years postoperation, and a breboard was formed in the area of the sternal cleft, the beating heart could not be observed outside the thoracoabdominal or thoracic wall. In the rst patient, the titanium plate was torn with a small ssure at 2 years postoperation( Figure A), but the ssure was not enlarged, and the exterior appearance of the thorax was normal. In the other two patients, the exterior appearance of the thorax was normal, and cardiac function was good.

Discussion
Pentalogy Preoperative assessment should include an echocardiogram, chest radiograph, and computerized tomography (CT) scan with three-dimensional reconstruction illustrating the extent of the bony lesion.
The greatest challenge in repairing these anomalies is the construction of the neosternum; additionally, the sternal cleft may predispose patients to blunt or piercing trauma to the heart. Although many methods for constructing the neosternum have been proposed, none are ideal. The question is what should be used to repair the sternal cleft: autologous tissues or prosthetic materials? Some reports have suggested 8 certain principles for reconstruction of inferior sternal clefts, which include the following: 1) rigid protection of the heart without compression, 2) preferable use of autologous tissue, 3) dynamic reconstruction of the thoracic cage, 4) uncompromised growth, and 5) minimal donor site morbidity.
Autologous tissues are ideal and the rst choice, as accepted by most surgeons 8, 9 . This method has the advantages of reducing the risk of infection and allowing synchronous growth with the body. There have been several excellent reviews describing experience with this approach, such as those by Kim CW 10 and Sabiston 11 , who reported an excellent operative effect. However, these techniques are greatly limited by the size of the defect and corresponding autologous tissues that can be obtained, especially in neonates 8 . Additionally, these therapies all have the common disadvantages of increased surgical trauma and bleeding, and donor site morbidities such as retrosternal seroma and pneumothorax can occur; in addition, they are technically more di cult to perform. In these approaches, ribs and costal cartilage are the most common materials used as autologous tissues to construct the neosternum, but this can cause serious consequences. Research has shown 5, 9 that intraoperative complications occur at a rate of 4% due to pericardial or pleural tears during sternal dissection and that postoperative complications, such as retrosternal seroma and pneumothorax, occur at a rate of 17%. Pectus excavatum is another postoperative complication that occurs in 25% (1/4) of patients.
Many prosthetic materials have been used for sternal cleft reconstruction, such as silicone elastomers and titanium plates 4, 10, 12 . We reported on our previous experience in 2016 4 . In our case, we used a titanium plate to repair the sternal cleft and achieved a good appearance. First, a mould of the abdomenthorax was made according to exact data from three-dimensional chest CT reconstruction. Second, the size of the titanium plate was demarcated on the mould as the defect of the sternum and supraumbilical abdomen. Then, we arched the titanium plate( Figure B) in order to provide more room in the thoracic cavity for the heart, which sometimes resulted in multistage operations because ectopia cordis needed to be avoided. In addition, with the use of a titanium plate, much damage was avoided, i.e., the ribs and costal cartilage remained intact, and the pectorals were not dissociated. Furthermore, this approach reduced the di culty of repairing the thoracoabdominal wall by minimizing the tension of the sutures because the rectus abdominis could be sutured to the lower end of the titanium plate. The merits of titanium plates include stiffness, histocompatibility, resistance to infection and low interference with CT and magnetic resonance imaging 13,14 . Based on our experience, this method is suitable for patients in whom ectopia cordis is not severe and the heart can eventually be repositioned and for patients in whom the area of the sternal cleft is large but ectopia cordis is not severe. While this method is also controversial, the lack of synchronous growth with the body is problematic. The string will be broken, which might be an underlying reason for migration, which is also a serious postoperative complication. In some cases, as in ours, the titanium plate may even need to be removed. In addition, because of lacking synchronous growth, the titanium plate would be torn when xed with steel wire. Other complications, such as psychological problems, are persistent drawbacks, although these de ciencies did not occur in our patients.
At the early stage of our long-term follow-up, no complications occurred, and a good appearance was achieved in all four patients( Figure C and D). We believe this approach is an excellent scheme that can be used to construct the neosternum in the patients with partial sternal clefts. However, with a prolonged follow-up time, complications such as migration and avulsion occurred, and we believe that some improvements should be made to perfect this approach. We analysed the process of this operation and concluded that the most important reason why migration and avulsion occurred was the method of how the titanium plate xed, as we ignored the lack of synchronous growth with the body of the titanium plate. In the rst and second cases, we sutured the titanium plates to the ribs in order to x the titanium plate rmly, and we presume that with the growth of the rib, the titanium plates were torn or the sutures were broken, and then migration or avulsion occurred. In the rest of the cases, we xed the titanium plate to the muscle directly, and no migration or avulsion occurred. A:The titanium plate was torn with a small ssure(red, lled,arrow);B:a titanium plate was tailored;C:Preoperative view;D:Postoperative view.