Risk factors associated with sternal complication after lung transplantation with transverse sternotomy

Introduction

Background

Sternal wound complications are particularly devastating in lung transplant recipients, with morbidity reported in 8–34% of recipients undergoing transverse sternotomy (1-3). Poor sternal healing can lead to a spectrum of complications, including chronic thoracic pain from malunion that predisposes patients to increased risk of pneumonia and delayed pulmonary rehabilitation and complete dehiscence and deep wound infection that can lead to mediastinitis and death. Moreover, multiple surgical re-exploration, reconstructions, and associated chronic infections can predispose the patient to chronic graft dysfunction. Therefore, optimizing sternal wound healing to prevent sternal dehiscence and infection is paramount.

Rationale and knowledge gap

The risk factors for sternal complications have been well-published in cardiac surgery. The factors such as osteoporosis, diabetes, malnutrition, emphysema, chronic steroid therapy, prolonged mechanical ventilation, and immunosuppressive drugs are various risk factors for sternal dehiscence in cardiac surgery (4,5). However, the risk factors and clinical outcomes of sternal complications after lung transplantation, especially the contemporary experiences, are not well published.

Objective

Therefore, this study aimed to delineate clinical outcomes associated with sternal complications after lung transplant in contemporary experience and to identify the preoperative characteristics, operative factors, and postoperative complications related to sternal dehiscence and infection to prevent sternal complications. We present this article in accordance with the STROBE reporting checklist (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-819/rc).

Methods

Study design

This is a cohort study of adult patients who underwent lung transplantation at Northwestern Memorial Hospital between January 2018 and May 2024. Patients who underwent multiorgan transplants (nine patients) or re-transplant (three patients) were excluded from the study. Only patients who had a dividing sternum were included. A total of 290 patients were included. Data on patient demographics, comorbidities, donor characteristics, preoperative laboratory values, and intraoperative and postoperative outcomes were collected. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was approved by the Institutional Review Board of Northwestern University (Nos. STU00207250 and STU00213616). The need for patient consent for data collection was waived by the institutional review board because this was a retrospective study.

Surgical technique

In Northwestern University Feinberg School of Medicine, the standard surgical approach for bilateral lung transplantation is bilateral transverse thoracosternotomy (commonly referred to as “clamshell incision”), which provides excellent exposure of both hila and mediastinal structures. For single lung transplantation, a lateral thoracotomy is typically employed. However, in selected cases of single lung transplantation, a transverse sternotomy was performed instead of a lateral thoracotomy. This decision was made based on intraoperative considerations, such as the need for better exposure due to complex hilar anatomy, anticipated pleural adhesions, or the need for contralateral inspection or bleeding control.

Management of sternal complications

For sternal infections, aggressive surgical debridement is primarily performed to control the infection. For superficial infections, single wound debridement is often sufficient. However, for deeper wounds and/or significant tissue necrosis and infection, multiple debridements and washouts of the wound are performed until healthy tissues are visible. For deep wound infections with considerable tissue necrosis, vacuum-assisted closure (VAC) is used to help remove excess fluid and facilitate wound healing. This combined approach aimed to optimize wound healing and minimize hospital length of stay.

Definition of complications

Sternum complications

Patients who had sternum dehiscent or infection that required surgical management were considered as sternum complications.

Primary graft dysfunction (PGD)

PGD was defined in accordance with the consensus statements of the International Society for Heart and Lung Transplantation (6). Patients exhibiting no evidence of pulmonary edema on chest radiography were classified as grade 0. In the absence of invasive mechanical ventilation, grading was based on the PaO₂/FiO₂ ratio using criteria analogous to those applied during mechanical ventilation. When PaO₂ measurements were unavailable, the oxygen saturation/FiO₂ ratio served as a substitute. Specifically, grade 1 corresponded to a PaO₂/FiO₂ ratio greater than 300; grade 2 to a ratio between 200 and 300; and grade 3 to a ratio below 200. The lowest PaO₂/FiO₂ ratio recorded within the first 72 hours after transplantation was used for grading. Any patient placed on extracorporeal membrane oxygenation (ECMO) for bilateral pulmonary edema evident on chest radiography was automatically classified as grade 3, whereas patients receiving ECMO in the absence of radiographic pulmonary edema were not included in the grading.

Veno-venous extracorporeal membrane oxygenation (VV ECMO) indication

Patients were managed by a multidisciplinary team following the National Heart, Lung, and Blood Institute ARDS Network guidelines (7). ECMO evaluation was triggered by refractory hypoxemia—defined as PaO₂ <55 mmHg, SpO₂ <88%, or pH <7.2—despite optimized support. Prior to ECMO consideration, patients received lung-protective ventilation (plateau pressure <35 mmHg), neuromuscular blockade, and prone positioning per Extracorporeal Life Support Organization recommendations (8). At Northwestern University Feinberg School of Medicine, both VV and veno-arterial (VA) ECMO cannulations are routinely performed via the femoral vessels. No patients in this cohort required open chest cavity or delayed sternal closure for ECMO initiation.

Acute kidney injury (AKI)

AKI was defined using the Risk, Failure, Loss of kidney function, and the End-stage kidney disease classification (9).

Statistical analysis

Recipient and donor characteristics, preoperative laboratory values, and intra- and postoperative outcomes were compared in lung transplant patients, categorized as with or without sternum complication. The Mann-Whitney U test was used to compare independent, continuous variables between the groups. Fisher’s exact test was used to compare categorical variables, which were reported as numbers and percentages. The Kaplan-Meier test was used to estimate survival, while the log-rank was performed to compare survival between the groups. Odds ratios (ORs) for sternum complication were obtained using a univariate and multivariate logistic regression analysis. Variables with P value less than 0.10 from univariate logistic analysis were included into multivariate logistic analysis.

Statistical significance was set at P<0.05. All statistical analyses were performed using the JMP Pro 17.0.0 software program (SAS Institute Inc.).

Results

Of 290 lung transplant recipients, 33 patients (11.4%) developed sternal complications. Among the 33 patients with sternum complications, most (n=25) experienced infections requiring local surgical debridement, which occurred at a median of 99.0 days post-transplantation (Q1–Q3, 37.5–240.0 days). Three patients required delayed closure with omental or muscle flap procedures, which occurred at a median of 104.0 days (Q1–Q3, 104.0–138.0 days). Non-infectious complications such as wire removal (n = 5) occurred at a median of 126.0 days (Q1–Q3, 51.5–304.0 days). The median time to complication was similar across the groups (P=0.75).

Patient demographics

Table 1 summarizes the characteristics of lung transplant recipients with and without sternum complications. The median age was similar between the two groups, with the no complication group having a median age of 61.0 years (Q1–Q3, 49.0–66.0 years) and the complication group having a median age of 62.0 years (Q1–Q3, 53.0–67.5 years) (P=0.33). The proportion of female patients was significantly lower in the sternum complication group (24.2%) compared to the no-complication group (45.5%) (P=0.02).

Other recipient factors, including body mass index (BMI), body surface area (BSA), smoking history, diabetes, chronic kidney disease (CKD), pre-ECMO use, and waiting list duration, showed no significant differences between the groups. Although hypertension was more common in the sternum complication group (66.7%) compared to the no-complication group (48.3%), this difference did not reach statistical significance (P=0.06). Additionally, bilateral lung transplants were slightly less common in the complication group (75.8%) compared to the no-complication group (87.2%) (P=0.11).

In terms of etiology, both groups showed similar distributions of interstitial lung disease (ILD), chronic obstructive pulmonary disease (COPD), pulmonary arterial hypertension (PAH), and other conditions (P=0.90).

Intra- and postoperative outcomes after lung transplantation

Table 2 details the intra- and postoperative outcomes for lung transplant recipients with and without sternum complications. The median operative time was similar between the two groups, with the no complication group having an operative time of 6.8 hours (Q1–Q3, 5.4–8.1 hours) and the complication group at 6.1 hours (Q1–Q3, 5.5–7.9 hours) (P=0.60). The use of intraoperative blood transfusions, including packed red blood cells (pRBC), fresh frozen plasma (FFP), and platelets (Plt), was comparable between groups, with no significant differences observed.

Postoperative outcomes showed that one-year survival was slightly lower in the sternum complication group (81.8%) compared to the no-complication group (89.5%), but this difference was not statistically significant (P=0.24). None of the deaths within the first year post-transplantation in the sternum complication group were directly attributed to sternal complications. The causes of death were unrelated to wound infection or sternal dehiscence, and no patients in this group developed mediastinitis-related fatality. However, AKI was more prevalent in the sternum complication group (75.8%) compared to the no complication group (47.9%) (P=0.003). There were no significant differences between the groups’ rates of donor-specific antibodies (DSA), PGD grade 3, or dialysis use.

The median ICU stay was 9.0 days for both groups, with no significant difference (P=0.69). Additionally, the median duration on the ventilator post-transplant and the hospital length of stay were similar across the groups. Notably, post-ECMO use and hemodialysis (HD) after discharge were more common in the sternum complication group, with post-ECMO use at 30.3% versus 14.5% (P=0.04) and HD after discharge at 30.3% versus 12.9% (P=0.02), indicating a greater need for these interventions in patients with sternum complications.

Predictor of sternum complications and mortality

Figure 1 shows the overall survival rates for lung transplant recipients with and without sternum complications. Kaplan-Meier survival analysis indicates that patients with sternum complications tend to have lower overall survival rates than those without sternum complications, although this difference was not statistically significant (P=0.28).

Figure 1 Kaplan-Meier analysis of overall survival in lung transplant recipients with and without sternal complications. Kaplan-Meier survival curves comparing patients who developed sternal complications (blue line) and those who did not (red line). No statistically significant difference in overall survival was observed between the groups (log-rank P=0.28). The number of patients at risk at each time point is indicated below the x-axis.

Univariate logistic regression analysis identified several factors associated with the risk of sternum complications after lung transplantation (Table 3). Female patients had a lower risk of sternum complications (OR =0.38; 95% CI: 0.17–0.88; P=0.02). Hypertension was associated with an increased risk of sternum complications (OR =2.15; 95% CI: 1.02–4.76; P=0.05). In terms of postoperative outcomes, AKI was significantly associated with a higher risk of sternum complications (OR =3.40; 95% CI: 1.48–7.83; P=0.004), as were post-ECMO use (OR =2.57; 95% CI: 1.13–5.84; P=0.02) and hemodialysis after discharge (OR =2.92; 95% CI: 1.28–6.69; P=0.01).

Multivariate logistic regression analysis further explored these associations (Table 4). Female gender remained a significant protective factor (OR =0.39; 95% CI: 0.16–0.94; P=0.04). AKI was confirmed as a significant predictor of sternum complications (OR =2.67; 95% CI: 1.08–6.61; P=0.03). Other factors, such as hypertension, bilateral lung transplant, PGD grade 3, post-ECMO use, and hemodialysis after discharge, did not reach statistical significance in the multivariate analysis.

Figure 2 illustrates the survival analysis related to sternum complications. In Figure 2A, Kaplan-Meier analysis shows a significant difference in sternum complication-free survival between male and female patients (P=0.03), with females demonstrating higher survival rates. Figure 2B highlights the impact of AKI on sternum complication-free survival, showing that patients without AKI had significantly better survival compared to those with AKI (P<0.001).

Figure 2 Kaplan-Meier analysis of sternal complication-free survival stratified by gender and AKI. (A) Kaplan-Meier survival curve stratified by gender. Female recipients (blue line) demonstrated significantly higher sternal complication-free survival compared to male recipients (red line) (log-rank P=0.03). (B) Kaplan-Meier survival curve stratified by postoperative AKI. Recipients without AKI (blue line) had significantly higher sternal complication-free survival than those with AKI (red line) (log-rank P<0.001). The number of patients at risk at each time point is shown below the x-axis in each panel. AKI, acute kidney injury.

Discussion

Key findings

Bilateral transverse thoracosternotomy for sequential bilateral lung transplantation (BLTx) offers improved exposure of the hilum, mediastinum, and pleural spaces, but sternal complications are common, with historic data approaching 30–40% (10). Various techniques in closing the transverse sternotomy, such as crossing wires, and closure devices, such as plating or fiber tape, have been described in the literature (11-13). However, no randomized or extensive comparative study exists that closure devices or methods decrease sternal complications. In Northwestern University Feinberg School of Medicine, bilateral transverse sternotomy is typically closed using two single wires, and the sternal complication rate was 11.2%, which appears to be significantly lower than reported in the literature as the historical norm. Our program emphasizes meticulous surgical closing techniques, complete hemostasis, and thorough post-operative wound care, which may contribute to preventing early complications.

Explanations of findings and comparison with results in similar research

Our data showed pre-operative patient factors that are commonly associated with sternal wound infection and dehiscence after heart surgery, such as obesity, diabetes, smoking history, older age, chronic obstructive pulmonary disease, osteoporosis, and chronic kidney failure, were not associated with sternal wound dehiscence and infection in contemporary lung transplant patients (14,15). The vast majority of the complications reported in our study were wound infections/instability that required local debridement more than 3 months after the initial transplantation. The complication’s delayed timing suggests that patient-related factors after discharge, such as the patient’s lifestyle, physical activity, and wound care, might be just as important as perioperative factors in preventing sternal complications. While both men and women can develop sternal wound infections, our study, similar to studies found in the literature, suggests that being a man is an independent predictor for sternal infection and complication. The reason for this is unclear, though males tend to have increased chest circumference and tension on their sternal incision, leading to an increased risk of sternal instability and underlying infection (16). Therefore, structured physical and occupational therapy that educates the patients to avoid tension and stress on the sternum is paramount. In addition to physical therapy, preventive strategies should be further customized based on the identified risk factors. For instance, patients who develop postoperative AKI may benefit from enhanced wound monitoring and nutritional optimization during the postoperative period, as impaired renal function has been linked to delayed tissue repair and increased susceptibility to infection. Educating patients and caregivers about early wound care after discharge may also help in detecting superficial infections early, enabling timely intervention and preventing progression to deep sternal infection. These tailored strategies, particularly for male recipients and those with postoperative complications, may help mitigate the long-term risk of sternal complications after lung transplantation.

The present study demonstrated that postoperative renal dysfunction increases the risk of sternal complications after lung transplantation. Similar findings have been reported after open-heart surgery, where acute renal failure and dialysis were independently associated with sternal wound infection and dehiscence (17,18). It is difficult to know whether acute renal dysfunction directly contributes to poor sternal healing and increases infection or whether it is a reflection of rocky postoperative courses. Still, given most of the sternal complications happened several months after the primary surgery, AKI most likely has directly impaired wound healing. Several mechanisms have been proposed, including AKI causing the formation of uremic toxins that negatively alter wound healing, triggering a systemic inflammation response that further impairs wound healing by affecting the immune system and tissue repair process (19,20).

Strengths and limitations

It is important to note that there was no overall survival difference between the sternum complication group and the no-complication group in our contemporary lung transplantation series. This finding is different from those of historical data, where 1-year mortality associated with deep sternal wound infection approaches up to 35% (21). The observed difference can be attributed to the fact that most of the wound infections in our series were identified early and superficial and managed before becoming deep wound infections and developing mediastinitis. Therefore, it is important to carefully follow the patient post-operatively, even after several months, and intervene early and aggressively to prevent mortality associated with sternal wound complications.

Several limitations exist for this study. The study is retrospective in nature, though data is taken from a prospective database. Thus, like all retrospective studies, our analysis was limited to available data and the fidelity and accuracy of data entered. Moreover, variables that are not captured by the database could have also contributed to the sternal complication. For example, detailed information on preoperative immunosuppressive or corticosteroid use, intraoperative hemodynamic instability, and postoperative use of vasoactive agents in the ICU were not available, limiting our ability to assess their potential influence on sternal wound healing. However, given that the baseline lung etiologies and intraoperative metrics (such as operative time and transfusion requirements) were similar between groups, we believe the impact of these unmeasured variables was likely minimal. Finally, the study is a single institution experience, so the data may not be generalizable as surgical techniques and perioperative management are variable among programs.

Conclusions

This study represents the largest contemporary series of cohorts evaluating the risk factors associated with sternal complications after lung transplantation to date. Sternal complications after lung transplantation were associated with patient factors such as male sex and postoperative complications such as acute renal failures and typically occurred 3 months after the primary surgery. Our study highlighted the importance of customized physical and occupational therapy to prevent stress on the sternum, especially those with high-risk profiles, and careful outpatient follow-up after surgery to prevent and detect signs of infection. Once detected, aggressive and early surgical intervention is recommended in order to avoid deep wound infection and potential mediastinitis.

Acknowledgments

The authors would like to thank Ms. Elena Susan for her administrative assistance in submitting this manuscript. This abstract was previously presented at the 2025 International Society for Heart and Lung Transplantation (ISHLT) Annual Meeting.

Footnote

Reporting Checklist: The authors have completed the STROBE reporting checklist. Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-819/rc

Data Sharing Statement: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-819/dss

Peer Review File: Available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-819/prf

Funding: None.

Conflicts of Interest: All authors have completed the ICMJE uniform disclosure form (available at https://jtd.amegroups.com/article/view/10.21037/jtd-2025-819/coif). The authors have no conflicts of interest to declare.

Ethical Statement: The authors are accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved. The study was conducted in accordance with the Declaration of Helsinki and its subsequent amendments. This study was approved by the Institutional Review Board of Northwestern University (Nos. STU00207250 and STU00213616). The need for patient consent for data collection was waived by the institutional review board because this was a retrospective study.

Open Access Statement: This is an Open Access article distributed in accordance with the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 International License (CC BY-NC-ND 4.0), which permits the non-commercial replication and distribution of the article with the strict proviso that no changes or edits are made and the original work is properly cited (including links to both the formal publication through the relevant DOI and the license). See: https://creativecommons.org/licenses/by-nc-nd/4.0/.

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