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J Thorac Cardiovasc Surg 1995;110:278-279
© 1995 Mosby, Inc.

LETTERS TO THE EDITOR

Treatment of pectus excavatum: Bioabsorbable or metal strut?

Kyoto University
Department of Artificial Organs
53 Kawahara-cho, Shogoin, Sakyo-ku,
Kyoto 606, Japan

Reply to the Editors

The letter in response to our article ¹ states that (1) bioabsorbable material always induces undesirable reactions, unlike metal struts, which offer good biologic tolerance; (2) the desirable stabilization period is often 6 to 8 months; (3) external struts require more extensive dissection; and (4) the cost and availability of poly-L-lactide struts are not clear.

Our answers are as follows:

1. Among a variety of bioabsorbable materials that have been investigated, polylactides are now applied clinically in the form of commercially available surgical suture materials such as Vicryl polyglactin 910 (Ethicon, Inc., Somerville, N.J.) and Dexon polyglycolic acid (Davis & Geck, Danbury, Conn.). One of the peculiar characteristics of polylactides is that their decomposition products are glycolic and lactic acids, which are degraded via the normal metabolic pathway in tissues. In our previous study, we ² clarified the details of polylactide degradation and found that they disappear in tissue without scar formation. Orthopedic devices such as screws and bone plates made from poly-L-lactide are also clinically available. In our clinical study we had to remove broken struts from the surrounding granulation tissue in three patients. However, it is important to emphasize that excessive tissue reactions occurred only with poly-L-lactide plates that were not thick enough to support the underlying severe deformity, and the granulation tissue was thought to be due to mechanical stimulation resulting from sharp fragments of broken struts, rather than a reaction to the polymer itself.
   
2. The fixation time required after surgery is currently the subject of controversy. ^3,4 We believe this depends mainly on the surgical method used and the age of the patient. The investigators gave no details as to the age of the patients, but Fig. 2 suggests that they were young adults or adolescents. In contrast, most of our patients with pectus excavatum undergo surgical treatment before they are 10 years old. We think that a 3-month period of initial mechanical toughness followed by a gradual decrease is sufficient, and our contention is borne out by our clinical experience. Excessively long fixation may disturb the normal growth of the chest and may be detrimental for growing children. In the case of the pull-up method, using a metal strut for adults, 6 to 8 months of fixation may be required.
   
3. The area of dissection is similar to that for the conventional sternal turnover (the deformed area and its margin). We think a similar extent of dissection is necessary for the authors' method, because internal (poststernal) fixation also requires wedge resection of the ribs in their most concave area and because both ends of the metal struts are placed more laterally to the ribs. As Adkins and Gwathmey ⁵ pointed out, the major disadvantage with the use of a strut is the possibility of infection, and the problem with internal fixation is that the strut goes through to the inside of the sternum. In other words, the struts are attached to the pericardium at the center and to the pleura on both sides. Consequently, the risk of mediastinitis ⁶ is considered to be higher because the foreign body is placed behind the longitudinal mediastinotomy. Furthermore, on removal, great care and skill are required to avoid injuring the attached tissues. Several types of conventional metal struts have been designed for placement on the outer surface of the sternum to minimize such risks. ^7,8
   
4. Poly-L-lactide orthopedic devices such as pins, screws, and plates for fixation of bone fractures are now available commercially. Poly-L-lactide plates for treatment of chest deformity are due to appear on the market in the near future. Until then, we can supply them on request. The most important characteristic feature of poly-L-lactide plates is that they can be easily shaped in the operating room according to the thoracic contour of the individual patient.
   

Metallic struts for treatment of chest deformities have a long history since the first reports by Adkins and Gwathmey ⁵ and Paltiaand associates. ⁹ However, metallic stents have several problems:

1. A second operation is required to remove them.
   
2. They sometimes produce pain as a result of shape mismatch, because molding of the metal is not easy.
   
3. It is difficult to fix them to the plastron and the thorax, and they become more difficult to remove when fixed more firmly.
   

In the case of external metallic stents, many fixation points are necessary to pull up the plastron. ^7,8 In this sense, internal struts have an advantage. Poststernal metal struts with ends curving over the outer surface of the ribs on either side were first reported by Jensen, Schmidt, and Garamella ¹⁰ ; their struts had a similar design to those of the authors. If the investigators' struts made it possible to obtain firm fixation as well as easy removal, they would become a good alternative to conventional material. However, the investigators gave no details about how the stent was fixed to the ribs and how many struts were used in a single patient. Absence of these details makes it difficult to evaluate and compare the results with the conventional metallic stent method described previously. ^4,5,7-10

Recently, as computed tomography and magnetic resonance imaging have become routine examination methods in thoracic surgery, large metallic implants tend to be avoided. In this sense also, poly-L-lactide, which does not interfere with postoperative examination, seems promising for clinical application.

References

1. Matsui T, Kitano M, Nakamura T, Shimizu Y, Hyon S-H, Ikada Y. Bioabsorbable struts made from poly-L-lactide and their application for treatment of chest deformity. J THORAC CARDIOVASC SURG 1994;108:162-8.[Abstract/Free Full Text]
   
2. Nakamura T, Hitomi S, Watanabe Y, et al. Bioabsorption of polylactides with different molecular properties. J Biomed Mater Res 1989;23:1115-30.[Medline]
   
3. Bryant LR, Morgan CV. Chest wall pleura, lung, and mediastinum. In: Schwartz SI, ed. Principles of surgery. New York: McGraw-Hill, 1983;636-42.
   
4. Singh SV. The changing trend in surgical reconstruction of pectus excavatum. Thorac Cardiovasc Surg 1981;29:114-8.[Medline]
   
5. Adkins PC, Gwathmey O. Pectus excavatum: an appraisal of surgical treatment. J THORAC CARDIOVASC SURG 1958;36:714-28.
   
6. Serry C, Bleck PC, Najafi H. Sternal wound complications: management and results. J THORAC CARDIOVASC SURG 1980;80:861-70.[Abstract]
   
7. Gotzen L, Dragojevic D. Funnel chest correction by use of AO implants and instruments. Thorac Cardiovasc Surg 1979;27:61-4.[Medline]
   
8. Rehbein F. The use of internal steel struts in the operative correction of funnel chest. J Pediatr Surg 1966;1:80-6.
   
9. Paltia V, Parkkulainen KV, Sulamaa M, Wallgren GR. Operative technique in funnel chest: experiences in 81 cases. Acta Chir Scand 1959;116:90-5.[Medline]
   
10. Jensen NK, Schmidt WR, Garamella JJ. Funnel chest: a new corrective operation. J THORAC CARDIOVASC SURG 1962;43:731-41.
    

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