Funnel chest is a common chest wall deformity in humans, which can be divided into congenital funnel chest and acquired funnel chest, and can be divided into symmetrical and asymmetrical according to the appearance of the deformity. Most patients with funnel chest are asymptomatic or have mild symptoms. In some cases, the deformity is severe enough to affect cardiopulmonary function and development. Older children and adults also suffer from low self-esteem and varying degrees of psychological impairment. It is very unlikely that a funnel chest will heal on its own, and the older the patient, the greater the impairment of cardiopulmonary function and the slower the postoperative recovery. Therefore, surgery is the only effective way to treat funnel chest. In 1998, Nuss1 reported the successful application of minimally invasive surgery to repair funnel chest with good mid-term and long-term results. In recent years. More and more surgeons are applying Nuss surgery to treat funnel chest with continuous technical progress and good early and mid-term results. The understanding of Nuss surgery and the progress of clinical research are reviewed as follows.
1. Common indices of funnel chest deformity
1.1 HI (haller index)
HI is the current international common index to determine the deformity of funnel chest. HI=A/C (A: the maximum transverse longitude of the thorax at the level of the most depressed sternum; C: the distance from the deepest point of the funnel to the front of the spine). In case of asymmetric funnel chest, where the lowest point of depression is not in front of the spine, two horizontal lines are drawn in front of the spine and the lowest point of depression, and the modified CT index is calculated according to the distance between the two lines. The average index for normal people is 2.52, and more than 3.2 can be diagnosed as funnel chest, less than 3.25 for mild, 3.25 to 3.5 for moderate, and more than 3.5 for severe.
1.2 FI (funnel chest index)
FI=(a×b×c)/(A×B×C)(a: longitudinal diameter of funnel chest depression; b: transverse diameter of funnel chest depression; c: depth of funnel chest depression; A: length of sternum; B: transverse diameter of thorax; C: shortest distance from sternal angle to anterior edge of vertebrae), mild: FI<0.2, moderate: 0.3>FI>0.2, severe FI >0.3.
1.3 LVI (1ower vertebral index)
LVI was measured by lateral radiographs of the patient’s chest, LVI = BC/AC (AC: sagittal length from the anterior border of the sternum to the posterior border of the thoracic vertebrae; BC: sagittal length of the corresponding vertebrae). According to Rebeis2 et al, the average value of LVI in normal subjects is 0.21, and in patients with funnel chest, LVI is >0.22, up to 0.54, and the larger the value, the more severe the deformity.
1.4 AI (anthropometric index)
AI=B/A (A: the transverse diameter of the thorax during deep inspiration in the lower 1/3 of the sternum; B: the depth of sternal depression in the same plane as above), the value of AI ranges from 0 to 1, AIR0.12 can be judged as funnel chest, and the larger the value, the higher the degree of deformity.
2.Nuss surgery
2.1 Principle of surgery
NUSS et al. observed that the thorax of patients with chronic obstructive pulmonary disease can change to form a barrel-shaped chest after years of illness, suggesting that even in adults, the thorax has a certain degree of compliance and plasticity. In pediatric patients, the thorax is not yet mature and has greater compliance and plasticity. One or more high-strength curved materials are placed into the sternum of patients with funnel chest to correct the deformed chest wall, and the materials are removed after 2 to 3 years.3 The recommended removal time by Jeffery3 et al. is generally 2 years for patients under 10 years old, 3 years for those between 10 and 12 years old, and 4 years for those over 13 years old.
2.2 Surgical method
The procedure was performed with the assistance of lumpectomy, in the supine position with both upper limbs abducted at 900; the lowest point of the thoracic depression was marked, and a horizontal line was made by extending the mark to select the appropriate rib space position. The distance between the mid-axillary line on both sides via the lowest point of the thoracic depression minus 1 cm is the alternative stent length, and the supporting plate is shaped with a bender; a transverse incision is made between the bilateral anterior axillary line and the mid-axillary line, about 2 cm long. Under direct thoracoscopic view, a penetrator is passed through the thoracic tile at the pre-selected rib space, through the posterior sternal septum to the contralateral chest wall penetration point, and through the subcutaneous tunnel to the contralateral incision. The thick wire was introduced; the thick wire and the support plate were fixed firmly, and the thick wire was pulled and the support plate was bowed backward through the tunnel under thoracoscopic surveillance. Rotate the support plate 1800 so that it is bowed upward and supported behind the sternum, and adjust it so that it is in complete agreement with the curvature of the chest wall; the plate is fixed at two or three points, and the two fixed pieces at both ends are properly fixed with chest wall muscle and fascia encapsulated sutures. The subcutaneous and skin were sutured. Radiographs were taken to observe lung expansion and the presence of pneumothorax.
In non-thoracoscopic assisted surgery, the steps are generally the same, with the difference that the guide is passed through the chest wall from the left side incision (thoracoscopic assisted surgery is usually entered through the right side) so that its curved tip faces upward through the posterior sternal mediastinum to avoid injury to the heart or pericardium, and then passed out through the corresponding intercostal space on the opposite side without the process of chest drainage or venting. The procedure is performed with non-thoracoscopic assistance. The entire surgical operation is performed outside the pleura. The trauma is much smaller and requires the surgeon to be experienced. CT scan is routinely done before surgery to understand the posterior sternal space and anatomical relationship to avoid accidental injury.
3. Indications for surgery and age selection for surgery
3.1 Surgical indications
Most patients with funnel chest are asymptomatic or have mild symptoms before surgery, and the purpose of surgery is to correct the deformity. However, some patients have cardiopulmonary dysfunction or other combined diseases, and the surgery has different degrees of impact on the patient’s cardiopulmonary function and pediatric development. Therefore, the purpose of NUSS surgery is not only to correct the chest wall deformity, but also to consider the improvement of the patient’s postoperative cardiopulmonary function and the growth and development of pediatric patients.
The indications for surgery2 include two or more of the following criteria: (1) Haller index greater than 3.25 on CT. (2) Pulmonary function suggesting restrictive or obstructive airway pathology. (3) Abnormalities such as incomplete right bundle branch block and mitral valve prolapse were found on electrocardiography and echocardiography. (4) Progression of the malformation with a combination of significant symptoms. (5) The deformity in appearance is intolerable to the child, where the history of progressive worsening of the deformity is particularly important. Patients with connective tissue disease (e.g., Marfan syndrome), scoliosis deformity, and allergy to plastic materials are contraindicated. (6) Those with recurrent initial surgery.
Funnel chest is divided into symmetrical and asymmetrical. In imaging, CT is better for funnel chest funnel symmetry estimation.3 Extensively symmetrical funnel chest, especially combined with flat chest, is the best indication for Nuss surgery, because extensively symmetrical funnel chest has no very large angle between the sternum and rib cartilage regardless of age, which facilitates stenting to hold it up. The commonly accepted pathogenesis of asymmetric funnel chest is the unbalanced growth of rib cartilage on both sides of the thorax, which occurs in 1/3 to 1/2 of surgical cases and is usually deeper on the right side, with anterior rotation of the sternum to the right, as the condition worsens. The entire thorax loses its normal shape and shows a severe flat chest or even thoracic dysplasia. Although there are reports of successful Nuss surgery for asymmetric funnel chest with good recent results, Zhang Fuxian et al4 concluded that for severe asymmetric funnel chest, especially in older children, a very large angle between the sternum and the rib cartilage has been formed, which will still cause deformity and asymmetry of the thorax after surgery.
3.2 Age selection for surgery
Currently, the choice of patient age varies from institution to institution and includes individual and social and economic factors. Some experts suggest that the age of surgery should be between 2 and 5 years old, and some experts believe that the optimal age for surgery is between 6 and 12 years old. The current recommended age for surgery is 5 to 20 years old, in which children younger than 12 years old have good flexibility and elasticity of the thorax and better compliance, which facilitates intraoperative operation and postoperative recovery and treatment. The Nuss procedure avoids the possibility of serious complications after the Ravitch procedure because it does not require the removal of rib cartilage and sternal osteotomy. Therefore, age is not an absolute factor, and those with cardiopulmonary dysfunction or symptoms and significant progressive worsening of the deformity may be considered for early surgery to save cardiopulmonary function while correcting the funnel chest deformity. In recent years, Nuss surgery has been widely used in patients of different age levels, including those aged 40 years or older, and a large number of case reports have shown good near- and mid-term results in adults7.
4. Surgical outcome
Nuss surgery outcomes are judged by a combination of factors including postoperative appearance, the physical and psychological impact of the surgery on the patient, the occurrence of postoperative complications, and patient judgment. Overall, the majority of patients reported in the literature had a desirable postoperative appearance, a positive impact on psychological and quality of life, and a good or very good postoperative evaluation by the patient or parents.7 The surgery showed some improvement in cardiac function and very little or no improvement in pulmonary function.
The evaluation criteria for the efficacy of Nuss surgery, (1) excellent: restoration of normal chest wall shape; (2) good: slight concave residue; (3) moderate: moderate concave residue; (4) poor: severe recurrence requiring further treatment. Meeting the requirements of the first 2 criteria is satisfactory. Meeting the latter 2 criteria is unsatisfactory. Zeng Ti et al7 proposed the conditions for assessing the surgical outcome of pediatric funnel chest: (1) chest X-ray showing sternal changes; (2) thoracic appearance effect; (3) satisfaction of the patient and family; (4) degree of thoracic fullness, extension and elasticity. Uemura et al. proposed the criteria for postoperative support plate position: support plate and sternum vertical is excellent, rotation angle less than 450 is good, and rotation up to 900 is poor.
5.Major postoperative complications and prevention
Same as the traditional Ravitch operation, pneumothorax, internal fixation stent displacement, bleeding, allergic reaction, pleural effusion and postoperative infection can occur after Nuss operation.
The most common postoperative complication is pneumothorax, which is asymptomatic in most patients. Routine postoperative radiographs reveal pneumothorax in about 49% of patients, but only about 6% of them require chest tube drainage and recovery in 1 to 2 days. Pneumothorax can be prevented by preoperative bulging of the lung and an external pleural tube at the end of surgery.
Rotation or displacement of the plate was reported more frequently in the early literature, and through continuous improvement in technique, the current incidence is about 5%, with some cases requiring removal of the plate for reoperation. Common methods of fixing the supporting orthopedic plate include adding fixation plates bilaterally, adding fixation plates unilaterally, and tying the supporting plate to the rib without using fixation plates. With the 3-point fixation method, the middle of the support plate is fixed close to the sternum to the rib cartilage on one side, in addition to the existing bilateral fixation.
The orthopedic plate can cause bleeding due to disruption of the intramammary vessels and anterior mediastinum when passing through the sternum. Therefore, thoracoscopy and careful dissection under the sternum can prevent bleeding. Placement of the thoracoscope is possible on both the left and right side; the left side may be safer due to the fact that this access allows for direct visualization and protection of the heart. The plate is placed outside the pleural cavity, so that the separation is performed outside the pleura, reducing the likelihood of injury to the pericardium and the plate is supported by the extrapleural tunnel tissue, making it less likely to shift, slide, or rotate.
Postoperative infection is uncommon in Nuss, with an incidence of 1.2% and 0.7% due to orthopedic plates. Surgical grafts increase the risk of infection and should be removed immediately in the event of infection. In addition, other infections, such as mediastinitis, bacterial pericarditis, and bilateral purulent pleurisy, have been reported in some literature. Strict aseptic practice and antibiotic application can reduce the incidence of post-transplant incisional infections.
Allergic reactions are rarely reported in China, and are relatively common in children after Nuss surgery in Europe and the United States. Nickel allergy is considered the main cause, a typical delayed type IV allergic reaction, with lymphocytes being the key to the patient’s reaction. Rare complications such as recurrence and difficulty in removing the plate have also been reported. With technological advances and continuous improvement of methods, various complications have been significantly reduced compared to earlier applications, and no surgical deaths are currently reported.