Rigid Sternal Fixation Improves Postoperative Recovery

INTRODUCTION

Conventionally, the sternum has been closed with stainless steel wires after open heart surgery. In most patients, the stainless steel wire closure is sufficient to provide sternal reapproximation and stability. However, the wire can fracture or may cut through the sternum by excessive coughing or pulmonary toileting, which causes sternal dehiscence, although it is rare. Even if the wire and bone remain intact, the wires may become loose because of the wire cutting into the cortex of the sternum or because of a rolling motion of the sternum due to the respiratory motion of the thorax [1]. Incomplete sternum cooptation may lead to sternal instability, sternal pain, delay in the recovery of the patient’s daily activity, and increased risk of sternal dehiscence and infection. [2, 3]. This sternal instability may occur right after chest closure or weeks after surgery depending on the quality of the sternum, presence of osteoporosis in the sternum, and closure technique. Numerous techniques have been introduced to reduce mechanical stress to the sternum caused by sternal wire circulage [2-6].

Recently, a rigid fixation method using sternal plates was introduced. Rigid fixation requires metal plate and screws to stabilize the sternum. The plate functions as an additional skeletal brace over the sternum to hold the hemisternum together. Compared to the wire closure which is linear and provides a single point of support, rigid fixation provides two-dimensional support using a metal plate. Cadaver study showed that the rigid plate fixation provided better stability of the sternum after median sternotomy than wire circulage [7]. Once the plate is placed on the sternum by screws, the titanium plate will not break. Previous clinical study demonstrated a lower incidence of sternal infection in the group undergoing sternal plating compared that in those receiving conventional sternal wiring [8, 9].

Rigid fixation was introduced at our institution in 2006 and recently has been used more frequently. In this study, we investigated the types of patients more likely to be closed by rigid fixation and analyzed their outcomes in comparison to those whose sternum was closed using wires.

METHODS

RESULTS

A total of 222 patients underwent coronary with or without valve surgery. Among them, 89 patients underwent rigid sternal fixation (group R) and 133 patients underwent conventional closure. These demographics are showed in Table 1. The characteristics of the two groups were different. Univariate analyses showed that patients in group R were younger (62 ± 9 in group R vs 69 ± 11 in group C, p<0.0001), more male dominant (61% vs 49%, p=0.0452), undergone redo-surgery less frequently (2.2% vs 9.0%, p<0.0418). Furthermore, rigid fixation was more often performed in a large patient (body mass index, BMI greater than 30) (58% vs 37%. P=0.0045), more likely performed after coronary artery bypass grafting (71% vs 46%, p=0.0002), less likely to be performed after valve surgery (12% vs 32%, p=0.0002), and more likely to be performed patients with low EuroSCORE (2.6 ± 2.3 vs 4.4 ± 2.7) than group C. Further multivariate analyses showed age less than 65, male sex, and BMI greater than 30 were independent factors favoring the use of ridgid sternal fixation.

Postoperative outcomes are shown in Table 2. Sternal infection was observed in 1 patient (1%) in group R and none in group C. On exploration of this patient with sternal infection, we found the sternum was still intact with the plates; however, the sternocostal cartilage had completely separated from the sternum. There was postoperative bleeding, which was not related to the sternal closure. The patient required emergent sternotomy at bedside. During the exploration the middle part of the plate was able to be cut using a conventional wire cutter without any delay. The sternum was reclosed in the operating room with the Sternalock using different plating configurations.

Intubation time (13 ± 20 hours vs 39 ± 97 hours, p=0.0030), ICU stay (58 ± 40 hours vs 99 ± 119 hours, p=0.0003), and postoperative length of stay (7.0 ± 3.7 days vs 8.4 ± 4.7 days, p<0.0141) were significantly shorter in group R than group C. On univariate analyses, age greater than 65, elevated preoperative creatinine greater than 1.5 mg/dl, heart failure, urgent or emergent status of surgery, valve surgery, and ridgid fixation were identified to be factors influencing the intubation time, ICU stay and postoperative length of stay (Table 3). Multivariate analyses showed ridgid sternal fixation was the single isolated factor affecting both intubation time and ICU stay, although postoperative length of stay was not affected by the method of sternal fixation.

DISCUSSION

Our retrospective study clearly showed that the application of the rigid fixation was clearly biased. Surgeons preferably chose rigid fixation rather than wire circulage if the patient was at high risk for sternal dehiscence especially in obese patients. Obesity is a major risk factor for sternal dehiscence and infection, [11] which may be related to the inability of close the sternum in an adequate manner by conventional wire circulage. Sternal wire may not be strong enough to hold against stress applied to the sternum when a large person coughs. Broken wires are often observed in obese patients. We consider that rigid fixation in obese patients provides better sternal stability than wire circulage. For same reason, patients who wish to go back to work, especially muscular work, as soon as possible after discharge from hospital, may request rigid fixation. The frequent use of rigid fixation in the patients who have undergone CABG could be due to the concern regarding sternal ischemia from the internal mammary artery harvest.

Low risk patients were also closed with Sternalock system in our institution. The sternum of young patients was more frequently closed with rigid fixation and old patients more frequently closed with wires due to high incidence of osteoporosis among elderly patients. For a similar reason, female patients more often underwent wire closure instead of rigid closure. The osteoporotic sternum can not hold the screw to attach the plate. Poor quality of bone is one of the contraindications for Sternalock use. Thus, sternal wire closure was more frequently used instead. Unfortunately, osteoporosis of the sternum is a subjective judgment of the surgeon and the data were not collected in this study.

The thickness of the sternum is important when performing rigid closure using the Sternalock system. The screw size was selected based on the thickness of the sternum. In our practice, surgeons are encouraged to secure the screw into both the anterior and posterior cortex of the sternum. To ensure this, sternal thickness plus 4 mm is our standard for determining screw size. Since the premade screw size ranges from 8 mm to 16 mm, the minimum thickness of the sternum closed with a Sternalock system is 4mm and maximum thickness of the sternum is 14 mm. A screw that is too long may injure the mediastinal structures, although we have not encountered such a complication. On the contrary, a screw that is too short may become loose, eventually migrate to the subcutaneous tissue, and loose the advantage of rigid closure of the sternum. The plate and screws are made of titanium, thus patients the Sternalock plating may safely undergo magnetic resonance imaging study. However, patients with a titanium metal allergy are not considered the Sternalock sternal closure.

Our postoperative results showed low overall complication rates in both groups. There was one sternal infection in the rigid fixation group, requiring removal of the entire plate. Interestingly, despite the infection, stability of the sternum was maintained. There was no sternal dehiscence but dislocation of the sternocostal cartilage was observed. This indicates that rigid fixation can not completely eliminate the risk of the infection.

Regarding postoperative recovery, early extubation and shorter ICU stay in the rigid sternal fixation group was remarkable. Although selected patients were closed with rigid fixation, multivariate analyses showed the rigid fixation was an independent factor that shortened intubation and ICU time. We speculate that the rigid closure provided secure sternal stability and these patients experienced less pain than patients with conventional wire closure. Less pain may result lower narcotics requirement, and may contribute to early extubation in the rigid fixation group. In this study, the pain scores were not collected since this is a subjective measurement and it was difficult to obtain such data in retrospective manner. We consider that better sternal stability provides better sternal comfort, which further contributes to the patient’s early mobilization and shorter recovery time.

A limitation of this study is the non-randomized observational nature of study. The sample size was relatively small to demonstrate any difference in postoperative complication rates, although it was not main purpose of this study. Pain score and the pain medication data were not included study. A prospective randomized study is necessary to identify the true benefit of rigid fixation over conventional wire closure.

SUMMARY

This retrospective study showed rigid sternal fixation was more frequently used in low risk young male patients, or high risk obese patients. Among these selected patients, ridgid sternal fixation was an independent factor contributing to early patient recovery.

REFERENCES