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Ann Thorac Surg 1996;62:512-518
© 1996 The Society of Thoracic Surgeons

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Original Articles: Cardiovascular

Sternal Plating for the Treatment of Sternal Nonunion

Divisions of Cardiothoracic Surgery, Plastic and Maxillofacial Surgery, and Orthopaedic Surgery, Department of Surgery, Duke University Medical Center and Durham Veterans Administration Hospital, Durham, North Carolina

Accepted for publication April 3, 1996.

	Abstract

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Background. Sternal nonunion, defined as sternal pain with clicking, instability, or both for more than 6 months in the absence of infection, is an uncommon complication of median sternotomy. Nonunion is frequently complicated by the presence of multiple transverse fractures, which make simple rewiring inadequate.

Methods. Six patients with debilitating pain secondary to sternal nonunion were treated with the technique of sternal plating between 1989 and 1995.

Results. Sternal plating corrected sternal instability and provided excellent pain relief in all 6 patients. All patients reported an improved quality of life and were able to resume recreational activities. Two patients have had plate removal for late bursa formation. Sternal healing was complete in both instances.

Conclusions. Sternal plating, which is based on the tension-band principle, is an effective treatment of sternal nonunion. The technique is applicable to both simple and complex nonunions. The stainless steel plates resist bending stresses, and the cortical bone resists compressive forces. The technique requires minimal dissection of the posterior sternal border, is not circumferential, and provides secure sternal approximation.

	Introduction

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Sternal wound complications occur in 0.5% to 3% of patients after median sternotomy [1–3]. If unrecognized in the early postoperative period, wire breakage or pull-through results in separation of the bone and leads to a sternal nonunion. We define sternal nonunion as persistent sternal pain accompanied by clicking or grinding and instability for greater than 6 months postoperatively in the absence of infection. Nonunion, with an incidence of less than 1%, is less common than wound infection or mediastinitis [1, 2].

The rate of sternal wound complications is increased by obesity [3, 4], osteoporosis [5], chronic obstructive pulmonary disease [2, 6], and previous irradiation of the chest [7] as well as by factors related to wound healing in general, eg, malnutrition, diabetes, and corticosteroids. In addition to these patient-related factors, operative factors play a role. Technical errors in sternotomy or closure [4, 8, 9], breaks in sterile technique, bilateral internal mammary artery (IMA) harvest [8], and prolonged operative time [3, 4] can contribute to the likelihood of wound breakdown or sternal nonunion. Postoperatively, prolonged ventilatory support, low cardiac output, and the need of closed-chest cardiac massage have been reported to increase the risk of sternal complications [2, 4, 5].

In many cases, nonunion can be treated by debridement and rewiring [7]. Circumferential placement of peristernal wires involves a small but definite risk of injury to saphenous vein and IMA grafts and to the collateral blood supply of the sternum. In many cases, there are complex sternal fractures [4, 10] secondary to wires pulling through the cortical bone [9, 10] or excessive retraction during IMA harvest [11]. Conventional rewiring is inadequate for complex fractures with multiple bone fragments. Many innovative techniques have been proposed to treat these difficult nonunions. One such technique is the Robicsek weave in which bilateral parasternal over-and-under weaves are combined with peristernal wires [10].

Here we propose a classification system for sternal nonunion and present a technique called sternal plating for its treatment. These plates use the tension band principle to provide secure approximation under both static and dynamic loading conditions. Plating does not require extensive deep debridement or circumferential sternal closure and thereby lessens the risk of injury to coronary artery bypass grafts and other vital structures. This technique has resulted in sternal stability with marked improvement in symptoms. All patients treated with this technique have been able to resume recreational activities they had been unable to pursue before repair.

	Material and Methods

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Patient Characteristics
The patients in this report underwent tension-band sternal plating at Duke University Medical Center or the Durham Veterans Administration Hospital between 1989 and 1995 for the treatment of sternal nonunion. There were no instances of superficial wound infection or mediastinitis after the original cardiac procedure. All of the patients were seen with sternal instability and pain, and 4 of the 6 patients were severely limited in their routine activities. The 2 remaining patients had ceased recreational pursuits because of major pain on physical activity.

All 6 patients had undergone median sternotomy for coronary artery bypass grafting. One patient had had concomitant repair of an atrial septal defect. All were men, with a mean age of 61 years (range, 57 to 70 years). Five of the 6 patients had known risk factors for sternal complications. Three had chronic obstructive pulmonary disease, 2 had diabetes mellitus, and 2 were morbidly obese (160 kg and 138 kg). One patient had undergone emergency coronary artery bypass grafting. Bilateral IMA grafts were used in 1 patient, and 4 of the remaining 5 patients had the left IMA harvested. None of the patients were on a regimen of corticosteroids. Two patients had undergone previous attempts to correct the nonunion with rewiring (Table 1).

View larger version (18K): [in this window] [in a new window]   Fig 1. . Paired sternal plates.

View larger version (14K): [in this window] [in a new window]   Fig 2. . Representative sternal computed tomogram with three-dimensional reconstruction. There is complete nonunion with a 1-cm gap between the sternal halves. A transverse fracture is present in the right fourth interspace secondary to wire pull-through. This is an example of a type II nonunion.

View larger version (44K): [in this window] [in a new window]   Fig 3. . Classification system for sternal nonunion. Partial nonunions may or may not lead to bone instability and pain. There are four types of complete nonunions: type I, complete nonunion without transverse fractures; type II, nonunion with a unilateral transverse fracture or fractures; type III, nonunion associated with single or multiple bilateral transverse fractures; and type IV, multiple fractures with missing bone segments.

Reconstruction requires three or four pairs of plates. The plates are selected according to sternal width and depth as determined by the preoperative three-dimensional computed tomographic scan and intraoperative measurements. After the plates are in place, the sternal halves are approximated with a large, pointed reduction device (Fig 4), and the overlapping plates are secured with two to four screws (Fig 5). Stability of the reconstruction is confirmed with manual traction. Two closed-suction drains are placed in the wound and brought out through separate incisions. The incision is closed in three layers. The low profile of the plates allows coverage with skin and subcutaneous tissue; muscle flaps are not necessary.

View larger version (35K): [in this window] [in a new window]   Fig 4. . Sternal halves have been debrided and are approximated with the pointed reduction device in preparation for placement of the plates.

View larger version (46K): [in this window] [in a new window]   Fig 5. . Sternal plates in place and secured with screws. Three or four pairs of plates are sufficient to provide complete sternal stability.

View larger version (16K): [in this window] [in a new window]   Fig 6. . (A) Anteroposterior chest roentgenogram made 1 month after sternal plating showing all plates in good position. (B) Lateral chest roentgenogram showing position of the plates and normal sternal curvature.

	Results

Top Footnotes Abstract Introduction Material and Methods Results Comment References

The types of sternal nonunion in the 6 patients were as follows: type I, 1 patient; type II, 2 patients; type III, 2 patients; and type IV, 1 patient. Sternal fixation was accomplished with three plates in 4 patients and four plates in 2 (mean number of plates, 3.3) (Table 2). The patient with a type IV nonunion required stainless steel reconstruction bars to rebuild the sternal halves prior to plating. Intraoperative cultures were negative in all instances. The sternum was stable in all patients after plating.

All 6 patients had severe pain preoperatively. In 4, the pain continued despite drastic self-imposed limitations on physical activity. All patients reported feelings of depression about the chronic pain. Since undergoing sternal plating, all patients have resumed previously normal activities, including golf, fly-fishing, and yard work, which they had been unable to do prior to sternal fixation. Five of the 6 patients are completely pain free with a mean follow-up of 19.2 months (range, 6 to 71 months). One patient has had intermittent mild sternal discomfort when getting out of a chair but otherwise reports no pain. Another patient reported possible movement of the inferior plate on follow-up 3 months after plating. However, a chest computed tomogram showed good sternal approximation and no evidence of plate displacement. All 6 patients have experienced major improvements in their feelings of depression.

Two patients have had the plates removed for late bursa formation at 6 months and 13 months. In both instances, complete sternal healing had occurred.

Illustrative Case Report
A 61-year-old morbidly obese (138-kg) man with insulin-dependent diabetes mellitus and chronic obstructive pulmonary disease underwent quadruple-vessel coronary artery bypass grafting including a left IMA graft to the left anterior descending coronary artery in June 1988. The operation was uneventful, and the postoperative course was complicated only by atrial fibrillation. Two months postoperatively, a chest roentgenogram revealed a broken wire at the inferior aspect of the sternum, but the sternum was stable at that time. One month later, the patient noted sharp chest pain accompanied by sensations of clicking and grinding in the sternum. Physical examination revealed a tender, grossly unstable sternum.

In January 1989, he underwent sternal debridement and rewiring using the Robicsek weave technique. He did well initially but 9 months postoperatively, he had recurrent chest pain along with a prominent click. The inferior aspect of the sternum was grossly unstable. A chest roentgenogram revealed broken peristernal wires inferiorly with intact parasternal weave wires. The pain eventually became so severe that the patient was confined to bed or to a chair most of the time, and he was unable to sleep through the night. The patient became depressed secondary to the chronic pain and sleep disturbance. Because of the severe disability from the nonunion, he was referred for sternal plating. A preoperative chest computed tomogram with three-dimensional sternal reconstruction revealed a type IV nonunion with bilateral transverse fractures, a free-floating segment of the right hemisternum, and a 1-cm anterior-posterior incongruence.

In February 1990, the patient underwent tension-band sternal plating. Stainless steel reconstruction plates were used to rebuild each half of the sternum by Arbeitsgemeinschaft für Osteosynthesefragen technique. The sternal halves were then approximated using three sternal plates. Postoperatively, a right pleural effusion developed, which resolved after thoracentesis. The remainder of the postoperative course was unremarkable, and he was discharged on the 14th postoperative day. On follow-up examination 3 months later, the patient complained only of intermittent pain when pushing himself out of a chair. He had no other pain, and the sternum was stable. He was able to sleep through the night and participate in physical therapy. The patient has had no recurrence of pain or instability for more than 5 years.

	Comment

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Median sternotomy is used most frequently for cardiac surgical procedures. Sternal nonunion, with a reported incidence of less than 1%, is uncommon [1]. However, the true incidence is probably unknown, with many cases going unrecognized or unreported. Both patient-related and operation-related factors are involved in the pathogenesis of sternal complications. Patient factors include obesity, malnutrition, osteoporosis, diabetes mellitus, corticosteroid use, chronic obstructive pulmonary disease, and history of radiation therapy to the chest [2–7]. Technical errors, prolonged operative time, low cardiac output, and need of prolonged postoperative ventilatory support all increase the probability of wound breakdown [3, 4, 8, 9]. Blood transfusions have been linked to sternal infections [3].

Bilateral IMA harvest also has been reported to be a risk factor [9]. However, prospective evaluation with multivariate analysis has shown that it increases the rate of sternal dehiscence only in diabetics [3]. Although unilateral IMA harvest has been shown to increase the number of sternal fractures, it does not interfere with sternal healing [11]. Proper technique is essential during IMA harvest to protect the collateral blood supply to the sternum. There are three types of collaterals that supply the sternum: sternal/perforating branches of the IMA, sternal/intercostal branches of the IMA, and posterior intercostal arteries [12]. These vessels are more abundant in the upper half of the sternum. Techniques of sternal closure that disrupt these collaterals may prevent bone healing.

If unrecognized in the early postoperative period, sternal disruption may prevent normal bone healing and lead to nonunion. Nonunion is frequently associated with substantial pain, which can be limiting for the patient. Cardiac function and pulmonary function usually are well maintained regardless of whether the sternum is approximated. In fact, it has been demonstrated that after sternal debridement and flap closure for mediastinitis, pulmonary function test results are only mildly abnormal [13, 14]. However, in those patients with unstable and painful sternums, there may be severe impairment.

The principles of managing sternal dehiscence are adequate debridement of avascular tissue and obliteration of dead space. Although most commonly closed with interrupted stainless steel wires, many innovative methods of sternal approximation have been developed both for primary closure and for reclosure. Stainless steel (Parham) bands [6, 15], Mersilene tapes [5, 16], sternal staples [17], and figure-of-eight pericostal sutures [9] have been reported to decrease the incidence of sternal dehiscence. For reclosure, Parham bands, Mersilene tapes, and figure-of-eight sutures necessitate dissection of the posterior table of the sternum with the attendant risks to the underlying right ventricle and bypass grafts. In addition, the circumferential nature of these techniques may endanger collateral vessels. Sternal staples have not been reported for closure of sternal nonunions, but they would not be useful for patients with complex fractures.

Among the techniques suggested for closure of fragile sternums or sternums with multiple fractures are Kirschner wires [10], the Robicsek weave [10], Knodt rods [18], and Association for the Study of Internal Fixation plates in combination with peristernal wires [19]. Association for the Study of Internal Fixation plates are not optimal because they require direct fixation of the plates to the bone with screws, thus making reentry into the chest through the sternotomy extremely difficult. The Robicsek weave has been reported to provide excellent results for patients with complex fractures. However, the continuous over-and-under parasternal weave potentially can disrupt the collateral blood supply to the sternum and thus preclude bone healing.

None of the previously reported methods of sternal closure apply the tension band mechanism. Tension band wiring and plating are used to stabilize bone fractures that are subjected to eccentric or flexural loading forces. These bones have one cortex that is subjected to tension on the convex side, while the concave side is under compression. Fixation of fractures in such bones requires resistance to both the bending and the compressing stresses. Tension band plates are placed on the convex surface of the bone, ie, away from the load axis. When the bone is subjected to a loading force, the plate resists the tensile force, maintaining compression at the near cortex. As the load increases, the plate comes under tension, and the far cortex is dynamically compressed. Thus the plate itself resists the bending stresses, and the bone resists the compressive forces [20]. The sternal plates act as tension bands applied across the anterior table. The anterior table is under static compression. When a load is applied to the sternum, the posterior table is compressed dynamically (Fig 7).

View larger version (31K): [in this window] [in a new window]   Fig 7. . Tension-band sternal plating. (A) The plates apply a compressive force to the anterior table of the sternum (thin arrows) under normal loading conditions. (B) When a distraction force is applied, the anterior table remains fixed in compression. The plate resists the tensile forces and brings the posterior table under dynamic compression (thick arrows). (Inset) Position of the sternal plates.

	Footnotes

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 
Address reprint requests to Dr Levin, Department of Surgery, Duke University Medical Center, Box 3945, Durham, NC 27710.

	References

Top Footnotes Abstract Introduction Material and Methods Results Comment References

 

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This Article Abstract Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Add to Personal Folders Download to citation manager Author home page(s): Steven C. Hendrickson Peter K. Smith Permission Requests Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Hendrickson, S. C. Articles by Levin, L. S. Search for Related Content PubMed PubMed Citation Articles by Hendrickson, S. C. Articles by Levin, L. S.