Sternal force distribution

Background: Median sternotomy is the access of choice in cardiac surgery. Sternal retractors exert significant
forces on the thoracic cage and might cause considerable damage. The aim of this study was to determine the
effects of retractor shape on local force distribution to obtain criteria for retractor design.
Methods: Two types of sternal retractors (straight [SSR] and curved [CSR]) were equipped with force sensors.
Force distribution, total force, and displacement were recorded to a spread width of 10 cm in 18 corpses
(11 males and 7 females; age, 62  12 years). Both retractors were used in alternating sequence in 4 iterations
in every corpse. Data were compared with respect to the different retractor blade shapes.
Results: Maximum total forces for full retraction of both retractors resulted in 349.4  77.9 N.
Force distribution during the first retraction for the cranial/median/caudal part of the sternum was
101.5  43.9/29.1  33.9/63.0  31.4 N for the SSR and 38.7  41.3/80.9  64.5/34.0  25.8 N for the
CSR, respectively. During the 4 spreading cycles, the average force decreased from 224.6  61.3 N in the first
to 110.8  39.8 N in the fourth iteration. The mean total force for the first retraction revealed 226.4  71.9 N for
the CSR and 222.8  52.9 N for the SSR.
Conclusions: The shape of sternal retractors considerably influences the force distribution on the sternal
incision. In the SSR, forces on the cranial and caudal sternum are significantly higher than in the median section,
whereas in the CSR, forces in the median section are highest. (J Thorac Cardiovasc Surg 2013;146:1381-6)

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