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Ann Thorac Surg 2003;75:2009-2010
© 2003 The Society of Thoracic Surgeons

Correspondence

Mechanical comparison of three sternotomy closure techniques using a polyurethane foam sternal model

Aaron R. Casha, MDa, Marilyn Gauci, MDb

a Department of Cardiothoracic Surgery, Castlehill Hospital, 73 Castle Rd, Cottingham, Hull HU16 5JQ, United Kingdom
b Department of Anaesthesia, St. Luke’s Hospital, Guardamangia HillGuardamangia MSD09 Malta

e-mail: aaron{at}casha.fsbusiness.co.uk

To the Editor:

We read with interest the article by Cohen and Griffin [1] on biomechanical testing of three sternotomy closure techniques using a polyurethane foam sternal model. Although we agree that rigid polyurethane foam may simulate cancellous bone, we believe that a polyurethane foam sternal model is an oversimplification and does not simulate adequately the properties of the sternum. The sternum is a cancellous flat bone covered with cortical bone as anterior, posterior, and lateral cortices. The thin cortical shell has important biomechanical properties. Placement of steel wires peristernally makes use of the lateral cortex to offer a significant advantage compared to conventional sternal wire closure. On fatigue testing, the rate of cutting through bone with peristernal wires occurs at one-fifth the rate of conventional interrupted wires [2]. A foam model would not show such a difference. The authors’ model loads the lateral aspect of the sternum, yet the model–device interface simulates cancellous bone not cortical bone. Use of the lateral cortex is the basis of continuous lateral reinforcement (weaving) techniques, eg, Robicsek type closures.

We agree that there is a high degree of interspecimen variability with biological specimens [1], but note that biological material has been used successfully in biomechanical studies of sternal closures [2–4]. The use of a foam sternal model should have been validated against biological material in view of the cortical-trabecular-cortical bone "sandwich" that is the sternum.

McGregor and colleagues’ work on human cadavers shows that sternal motion (and therefore also traction forces) occurred mainly in a lateral direction during simulated Valsalva force and not in anterior-posterior or rostral-caudal directions [5]. However in Cohen and Griffin’s article, statistical significance occurred with dynamic sternal fixation (DSF) plates in yield strength and maximum strength in transverse (rostral-caudal) shear only [1]. Therefore, we do not agree with the authors’ conclusion that closure with DSF plates or stainless steel cables offers important advantages in a clinical setting, since clinically it is lateral distraction that is important and not transverse shear.

References

  1. Cohen D.J., Griffin L.V. A biomechanical comparison of three sternotomy closure techniques. Ann Thorac Surg 2002;73:563-568.[Abstract/Free Full Text]
  2. Casha A.R., Gauci M., Yang L., Saleh M., Kay P.H., Cooper G.J. Fatigue testing median sternotomy closures. Eur J Cardiothorac Surg 2001;19:249-253.[Abstract/Free Full Text]
  3. Cheng W., Cameron D.E., Warden K.E., Fouger J.D., Gott V.L. Biomechanical study of sternal closure techniques. Ann Thorac Surg 1993;55:737-740.[Abstract]
  4. Ozaki W., Buchman S.R., Iannettoni M.D., Frankenburg E.P. Biomechanical study of sternal closure using rigid fixation techniques in human cadavers. Ann Thorac Surg 1998;65:1660-1665.[Abstract/Free Full Text]
  5. McGregor W.E., Trumble D.R., Magovern J.A. Mechanical analysis of midline sternotomy wound closure. J Thorac Cardiovasc Surg 1999;117:1144-1150.[Abstract/Free Full Text]




This Article
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