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Three Part Question

In [patients undergoing cardiac surgery] is [closure of the sternotomy using standard or figure-of-eight sternal wire closure] the most effective in [preventing sternal dehiscence]?

Clinical Scenario

You are assisting with an aortic valve replacement operation in an 85 year old female. She had a long-standing history of chronic obstructive airway disease and diabetes mellitus. The valve was severely calcified. You successfully excise and replace the valve and you are now asked to close the sternum by the consultant. He states that this patient is high risk for sternal dehiscence and thus you should use the figure-of-eight technique to close the sternum. You agree that this patient is high risk and you close the sternum using this technique but you wonder what evidence there is to support the benefit of this technique in high risk patients.

Search Strategy

Medline 1966-08/03 using the Ovid interface.
[exp sternum OR stern$.mp] AND [exp suture techniques OR exp bone wires OR bone wires.mp OR wire$.mp] AND [exp models, biological OR exp stress, mechanical OR exp surgical wound dehiscence OR dehiscence.mp OR exp mediastinitis OR mediastinitis.mp OR biomechanic$.mp OR sternal union.mp]

Search Outcome

Altogether 111 papers were found seven of which were selected as providing the best evidence. These papers are shown in the table.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Dasika et al, 2003, USA	Sternal replicas composed of a polyurethane foam bone analogue were divided in the midline and reapproximated using three stainless steel wire techniques: six sample wires (6S), six figure-of-eight wires (6F8), seven simple wires (7S) incluiding an extra wire at the lower sternum. Sternal distraction was carried out to a maximum force of 400N	Experimental study	Sternal distraction at 400N at the lower sternum	Seven single wires, 1.64 +/-0.39mm; six sternal wires, 4.92 +/-1.73mm; figure-of-eight wires, 5.1 +/-1.43mm; P=0.003	Wires were placed around not through the sternum models Sternal replicas used rather than true sternal tissue
			Sternal distraction at 400N at the mid sternum	Seven single wires, 1.70 +/-0.47mm; six sternal wires 1.64 +/-0.35mm; figure-of eight wires, 2.09 +/-0.62mm; P=0.174
			Sternal distraction at 400N at the manubrium	Seven single wires, 0.67 +/-0.59mm; six sternal wires 0.73 +/-0.58mm; figure-of eight wires 0.59 +/-0.36mm; P=0.818
Casha, 2001, UK	Sheep sternal model used to test the problem of wire cutting through the sternum by using fatigue testing Standard steel wire closure, peristernal steel wire, trans-sternal figure-of eight closure, polyester and sternal bands sternotomy closure techniques all assessed, in eight pairs of experiments.	Experimental study	Percentage of cut-through on the 150th cycle of loading compared to a reference steel wire closure	Polyester closure 453% (+/-137%); trans-sternal figure-of-eight 232% (+/-35%); sternal wire (this was the reference standard) 100%; peristernal single wire 34% (+/-7%); sternaband 23% (+/-8%)
Losanoff et al, 2002, USA	Single peristernal and pericostal figure-eight were used in 14 fresh cadaveric porcine sterna Technique A four single peristernal wires were used in seven pig sternums. Technique B utilized two pericostal figure-eight wires in seven pig sternums. Lateral separating force applied	Experimental study	Force required to cause sternal or wire fracture	Single peristernal 916.9 +/-170.8N; figure-eight pericostal 651.9 +/-80.7N; P<0.0001	Peristernal closure technique used Only four single or two fig-8 wires used in contrast to human technique of six-eight single or four fig-8
			Did the wire or the sternum fracture when the breaking force was reached	Single peristernal wire 3, Sternum 4 figure-eight pericostal wire 6, Sternum 1
Casha et al, 1999, UK	Tested biomechanical characteristics of five sternotomy closure techniques using a metal sternal model on a materials testing machine Techniques tested: Straight wires, figure-of-eight wires, 'repair' technique (used when a wire breaks), sterna-band, ethibond, multi-twist closure	Experimental study	Rigidity (mean displacement in mm at 20kg force) (this was found to be the tension at which wires begin to untwist)	Multi-twist 0.37mm; straight wires, 0.78mm; figure-of-eight, 1.20mm; sterna-band 1.37mm; repair wires, 5.08mm, ethibond 9.37mm	A bone model was not used to test wires
			Maximum strength at which a wire breaks (maximum force in kg)	Multi-twist 77.1kg; straight wires 98.0kg; figure-of-eight 92.8kg; sterna-band 73.3kg; repair wires 46.0kg; ethibond 58.8kg
			Mathematical model to calculate chest wall forces during coughing in order to determine the force placed upon a sternotomy closure	In a large man the force generated is 150kg or 25 kg across each wire if six wires are used
Casha AR et al, 1999, UK	2000 patients over 10 years undergoing cardiac surgery. Closure of the manubrium and sternum with a trans sternal (6-8) interlocking multitwisted wire technique (No 5 wire)	Retrospective cohort and review	Sternal dehiscence in this cohort	0.5%	Methods of data collection, patient groups, follow-up methodology not described
Murray KD & Pasque MK, 1997, USA	Routine closure of all sternotomy incisions in 86 consecutive patients and an additional 34 high risk patients Six overlapping figure-of-eight wire sutures (No 7 wire), manubial wires are placed trans manubrially but the sternal wires are placed peristernally	Retrospective cohort study	Sternal dehiscence	None reported in this cohort	Methods of data collection, patient groups, follow-up methodology not described Sample size too small to conclude that this technique is low risk
Di Marco Jr RF et al, 1989, UK	978 consecutive patients interlocking figure-of-eight closure of sternum Described a technique where two simple No 5 wires were inserted into the manubrium and then four interlocking figure-of-eight wires were inserted peristernally through consecutive intercostals spaces	Retrospective cohort study	Major sternal wound complications requiring reoperation	9 patients required reoperation including muscle flap closure (0.92% rate)	No control group Follow-up methodology not described Current internationally accepted definition of mediastinitis not used
			Minor wound complications	15 patients had sternal wound complications requiring healing by secondary intention
			Dehiscence or mediastinitis	The authors claimed that in none of the above instances did the patient develop mediastinitis or sternal dehiscence

Comment(s)

Two types of paper were found in this search. Several clinical papers documented the authors' clinical experience of a particular technique, and the remaining papers looked at biomechanical testing of the various sternal wire techniques using ex vivo sternal models. Three clinical papers are presented here. Casha et al (4) described their particular technique of trans-sternal multi-twist wire closure, and stated that over 10 years and 2000 cases their sternal complication rate was 0.5%. Murray et al (2) reported that in 34 high-risk patients and an additional 84 consecutive patients there were no cases of dehiscence or mediastinitis using a figure-of-eight technique. Di Marco et al (1) reported that in 978 patients who had peristernal figure-of-eight wires used to close the sternum, the major sternal complication rate was 0.9%. However, no clinical studies have directly compared one closure technique to another, and thus it is difficult to come to any firm conclusion from the results of these uncontrolled, retrospective cohort studies. In contrast, several well conducted biomechanical studies have been performed. Dasika et al (7) used a polyurethane foam sternal model to compare six simple wires, seven simple wires and six figure-of-eight wires, all placed peristernally. They found that figure-of-eight wires performed similarly to the standard six simple wires and only adding a 7th simple wire reduced the distraction seen at 400N of tension. Losanoff et al (6) directly compared peristernal simple wires with peristernal figure-of-eight wires in a porcine sternal model. They found that the single peristernal wire technique required a higher force to cause failure than the figure-of-eight technique. Casha et al (3) in 1999 studied five techniques of closure using a steel sternal model. They found that the displacement at 20kg of tension was smaller for single wires than figure-of-eight and the breaking strain was similar for both techniques. Casha et al (5) hypothesised that in fact single distraction testing was inferior to repeated cycles of loading which could mimick the clinical phenomenon of sternal cut-through of wires. They used sheep sternums to test a range of techniques and found that trans-sternal figure-of-eight wires performed more poorly than simple wires and peristernal simple wires were considerably superior to either technique in preventing cut-through. It is however, important to note that they did not assess peristernal figure-of-eight wires. None of these clinical or biomechanical studies demonstrated any superiority of the figure-of-eight wire technique over simple wiring, and in fact several of the biomechanical studies suggest that the issue of whether the wire is placed trans-sternally or peristernally may be a more important factor in promoting sternal stability.

Clinical Bottom Line

The figure-of-eight wire technique is not superior to the simple wire technique for closure of the sternum.

References

1. Dasika UK, Trumble DR, Magovern JA. Lower sternal reinforcement improves the stability of sternal closure Ann Thorac Surg 2003;75(5):1618-21.
2. Casha AR, Gauci M, Yang L, et al. Fatigue testing median sternotomy closures. Eur J Cardio-Thorac Surg 2001;19(3):249-53.
3. Losanoff JE, Forest JR, Huff H, et al. Biomechanical porcine model of median sternotomy closure. J Surg Res 2002;107(1):108-12.
4. Casha AR, Yang L, Kay PH, et al. Biomechanical study of median sternotomy closure techniques. Eur J Cardio-Thorac Surg 1999;15(3):365-9.
5. Casha AR, Ashraf SS, Kay PH et al. Routine sternal closure using six overlapping figure-of eight wires. Ann Thorac Surg 1999;16(3):353-5.
6. Murray KD, Pasque MK. Routine sternal closure using six overlapping figure-of-8 wires. Ann Thorac Surg 1997;64(6):1852-4.
7. Di Marco Jr RF, Lee MW, Bekoe S et al. Interlocking figure-of-8 closure of the sternum. Ann Thorac Surg 1989;47(6):927-9.