The failure of synthetic polymeric medical devices - Durability and Reliability of Medical Polymers - page 216

(opening), and she was transferred quickly to theatre where the wound was
restitched by another doctor not involved in the original stitching. He made
the observation that 'all the layers of the wound closure were still present,
but the sheath suture had snapped in the middle'.
The statement claimed that the Vicryl suture had not broken at the knots,
and the knots had not slipped. But the failed suture had been discarded
after the operation, making investigation of the evidence impossible, a not
uncommon problem in medical negligence cases.
9.8.2 Analysis of a new suture
Although the failed suture had been unfortunately lost, equivalent new
sutures were made available for inspection. One of the lengths was strained
to break on a tensometer, by tying a granny knot to form a loop and then
stringing the loop over round supports on the machine. The results of two
tests gave tensile breaking loads of 70 and 58 N for failure strains of 74%
(in free fibre) and 96% (at knot), respectively. There is clearly substantial
variation in strength, depending on the knot, which could be attributed to
slippage and perhaps knot orientation as well. Knots are well known stress
concentrators in ropes and cords, and this also applies to knots in braided
fibre. At the high rate of test, the broken ends showed melting of individual
fibres to form blobs of solidified molten polymer (Fig. 9.39). On the other
hand, the failure loads of about 7 and 5.8 kg are high compared with expected
loads in soft tissue.
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9.39 Fractured test end of Vicryl suture showing fibre melt at tips.