The Case of the Nefarious Needle

Some years ago, a lawyer-client presented me with the sharp end of a fractured suture needle and a similar needle still in its packaging. My client was involved in a suit against the manufacturer of the needle.

The Scene of the Crime

The needles are semi-circular, about 2 inches in length. The fracture took place very near the threaded end. My job was to find out the cause of fracture.

The Investigation

I bent the exemplar needle into a sharp "U" and straightened it twice before fracture. The needle was thus very ductile, and brittle fracture was out of the question.

The Scanning Electron Microscope (SEM) combines high magnification with great depth of field, which makes it ideal for fractography. The SEM study showed fracture surfaces on both the subject and exemplar needles to be covered by the fine dimples characteristic of ductile fracture. Analysis of the x-rays emitted under electron irradiation in the SEM showed both needles to be of high chromium, so-called ferritic stainless-steel. This alloy is entirely suitable for suture needles.

There was nothing wrong with the needle material. So why had it fractured? The subject needle had puzzling markings on the inside curvature near the fracture surface as seen in the figure. The longitudinal grooves were introduced during manufacturing to aid in gripping the needle. The battering and resulting cracks seen in the figure had come later. The needle was stressed in tension on the inside diameter during suturing. The cracks were thus in tension and reduced the strength of the needle.

But how did the battering marks arise? I tried to reproduce the battering a number of ways. The exemplar needle was gripped with a hemostat to simulate treatment during suturing. This gripping only caused "scuff marks." I attacked the needle with a three-cornered file and a razor blade. Both treatments resulted in grooves with no resemblance to the batterings. Finally, I put the subject needle on an anvil and struck it sharply with a hammer. The resulting damage bore a striking resemblance to that on the subject needle. (Figures showing these various damages and the ductile fracture surface be viewed online at http://rbi.ims.ca/5384-675.)

The Smoking Gun

I concluded the needle had been struck with something like a hammer. But how and when? It is unthinkable that the damage occurred in the operating room. The needle was shipped in a sealed package, so shipping damage is out. The damage must have occurred prior to packaging.

The needle manufacturer did an in-house failure analysis after my study. It concluded the fracture was caused by excessive force due to a needle holder applied during suturing. The figures in my copy of this report were poor, but the markings from the needle holder bore little resemblance to those on the subject needle. They much more resemble the scuff marks made by the hemostat, which is a very similar device to a needle holder. I cannot conceive of any sort of gripping tool, other than perhaps Vise-Grip-type pliers, giving the observed damage.

My deposition was taken, but the case settled before trial. It is probably fortunate for the defendant company it never had to put its expert on the stand. In-house experts are rarely effective expert witnesses. The individuals may be of high-quality, but are always suspect for being employees of a litigant.