Discussion:
Sternal dehiscence represents one of the major causes of morbidity after cardiac surgery performed through full median sternotomy. The key to the successful management of NISD is early referral to refixation [9]. Time to reoperation for refixation varies in the literature from 10 to 300 days [4,6]. In our study, refixation was performed after a mean time of 49.4±9.5 days following the initial procedure. Surgery for this complication should be performed as soon as possible.
Multiple surgical techniques have been described for reconstructing the anterior chest wall in the treatment of sternal dehiscence, but none of them is yet considered the gold-standard procedure [10]. In our hospital, Robicsek repair is the first method of treatment in NSID after median sternotomy whereas TRNC method is mostly advised for patients with multiple comorbidities. In this study, we compared the surgical results of the TRNC technique in patients with a previously failed Robicsek treatment (group A) and patients who were directly referred for TRNC treatment after a diagnosis of NISD (group B). Moreover, we compared group B with those who underwent Robicsek repair as the first procedure (group C). Our aim was to establish the importance of prioritization of TRNC treatment in high-risk NISD patients.
The potential mechanisms of comorbidities that increase the risk of sternal dehiscence in high-risk patients are as follows: the sternum healing is compromised due to the separating radial forces from the prolonged ventilation and chronic abundant cough in COPD; the sternum bone fragility is induced by the intrinsic pathology in patients >75 years of age, diabetes and severe osteoporosis; and that osteosynthesis is reduced in patients with renal insufficiency, chest irradiation and chronic steroid use. Additional risk factors could include congestive heart failure and peripheral vascular disease, because these patients have particularly compromised peripheral vascularization, which reduces sternal healing [11]. In morbidly obese patients, the lateral stress is increased even more because of their body habitus. Excessive tissue places additional stress on the sternotomy closure, both laterally by the chest wall and inferiorly by the abdominal wall [12]. In our study, there was no significant difference between the groups in terms of comorbidities.
Bilateral internal mammary artery usage interrupts sternal blood flow, which poses a risk for sternal dehiscence. Prolonged retraction of both sternum halves may cause ischemic fields and result in healing problems after long cardio-pulmonary bypass runs, repeated sternal openings, and rewirings. An asymmetric off-center sternotomy and transverse fractures prevent a decent anatomical sternal closure due to disruption of sternochondral joints and sternum halves (Figure 3) [13]. In our study, there was no significant difference between the groups in terms of surgical complications. Both group A and group B consisted of high-risk patients.
The classic technique described by Robicsek et al. relocates and distributes the pressure over the sternum by changing the site of the pressure and providing wider support [8]. The disadvantage of this technique is the need for substernal dissection and the effect on the blood flow to the area. When intercostal arteries are squeezed by the ring formed by steel wires running up-and-down and anterior-posterior around the ribs, a constrictive weave is produced that can disrupt the collateral blood supply to the sternum. This may worsen a pre-existing ischemia, which facilitates bacterial colonization and delays sternal healing. Furthermore, ischemia may cause bone necrosis and additional sternal fragmentation [13,14]. In our study, 260 patients underwent Robicsek repair due to NISD, but 6.1% had still sternal dehiscence afterward (n=16). Out of those 16 patients, 11 cases were high-risk patients and they were referred to TRNC treatment. The success rate of the Robicsek method in the treatment of high risk NISD patients, was 35.3% (6/17). On the other hand, its fail rate was only 2.1% in without high-risk patients (5/243).
The TRNC technique is easier and has a shorter operation time than the Robicsek method. In our study, operative time in group B was significantly shorter compared to group C as expected. The TRNC method is also considered a safer technique because less substernal dissection is needed. TRNCs have shown less risk for tearing the bone than steel wires. Nitinol clips are not integrated into the bone and their thermoreactive characteristics allow them to be removed easily when required [15]. The TRNC technique brings both hemi-sternums together without harming the intercostal structures. Therefore, it does not technically affect sternal blood flow [16]. Many studies have hypothesized that using TRNCs is a superior dehiscence repair method compared to Robicsek method [8,17]. The disadvantage of the TRNC technique is that it is more expensive due to the cost of hardware. The cost of each plate ranges from 90 euro to 100 euro. In our study, we only used TRNCs in high-risk patients and patients with failed Robicsek procedures. We wished to use the TRNC method in each patient with NISD, but its cost prevented us from performing this method on regular basis. After observing several cases of Robicsek repair failure in high-risk patients, most high-risk patients with NISD were directly referred to the thoracic surgery clinic for TRNC treatment.
In our study, we observed that ischemic tissues were more common, the sternum often adhered to the underlying tissue, and sometimes to the myocardium, due to previous Robicsek procedure during TRNC treatment in group A. Since group B had no history of failed a Robicsek method, the surgeon could perform a rapid and less challenging TRNC treatment without additional surgical risks, due to significantly less need for substernal dissection. In our study, we did not perform substernal dissection in group B. Consequently, operation time and operative blood loss in group B was significantly lower compared to group A. Moreover, nonunion rate was significantly lower in group B.
According to various studies, the most commonly reported complications of TRNC treatment are: postoperative pneumonia with an incidence up to 10%, hematoma or seroma formation with an incidence up to 24%, and clip removal due to infection or pain up to 50% [18]. Current sternal dehiscence treatment methods have morbidity rates of 10–25% and mortality rates of 5–47% [19]. Refixation has a high risk of postoperative complications regardless of the chosen treatment method [20]. In our study, although both group A and B consisted of high-risk patients, the postoperative complication rate in group A was significantly higher than in group B (54.5% vs 17.4%). Due to this higher complication rate, hospitalization in group A was also significantly longer compared to that in group B. Postoperative wound complication and pneumonia rates were significantly higher in group A. As a result, an additional operation for refixation and the introduction of an extra session of general anesthesia for patients with additional diseases greatly increased both surgical risks and postoperative complication rates. Fortunately, there was no mortality in either group.
Our study was a single center, retrospective study. We did not include patients with infectious sternal dehiscence due to lack of recorded data. Therefore, we could not come to a general conclusion about the usage of the TRNC system in high-risk patients and were limited to NISD. Due to the small number of patients included in our study, statistical power was low and our ability to examine low-frequency outcomes was limited.
Patients with multiple established factors of sternal dehiscence are high-risk patients for the treatment of NISD. TRNC use in sternal closure of high-risk patients may prevent sternal dehiscence, but it is impractical to use such expensive materials on regular basis. The Robicsek procedure is proven to be an effective method in the treatment of NISD but, in case of its failure, subsequent TRNC treatment might become cumbersome in high-risk patients. In our study; a direct TRNC treatment approach for high-risk patients in the treatment of NISD was superior to the Robicsek method because a previously failed Robicsek procedure caused significantly higher morbidity and additional operative risk in later TRNC treatment of high-risk cases. Ultimately, we speculate that a direct TRNC treatment for NISD is favorable in high-risk patients.
Acknowledgements : English editing by ‘Editage’
Conflict of interest : none
Funding: None