Mechanical Engineering Expert Allowed to Opine on the Design of the Dog Leash

This action arises out of injuries Plaintiff sustained while using a Flexi New Classic medium retractable dog leash (the "Leash").

Defendants' Flexi North America, LLC ("Flexi N.A.") and Petco Animal Supplies Stores, Inc. ("Petco" and, together, "Defendants") filed a motion in limine seeking to preclude the expert report and testimony of Plaintiff's engineering expert, Kristopher J. Seluga, M.S.

Mechanical Engineering Expert Witness

Kristopher Joseph Seluga, M.S. is a licensed professional engineer with bachelor's and master's degrees in mechanical engineering from the Massachusetts Institute of Technology.

Get the full story on challenges to Kristopher Seluga’s expert opinions and testimony with an in-depth Challenge Study.

Discussion by the Court

Seluga's Expert Report

Seluga inspected the Leash, as well as exemplar cord-and tape-style leashes, measured the subject cord at approximately 0.09 inches in diameter and the exemplar tape at approximately 0.44 inches wide, and found that the Leash at issue was functional as designed. As part of his analysis, Seluga constructed a drop-weight apparatus using metal rods wrapped in pig skin to model adjacent fingers. A drop-weight apparatus uses a known suspended mass that is allowed to fall through a measured distance, thereby imposing a sudden dynamic load on the test specimen. Here, Seluga attached forty-four and seventy-pound weights to exemplar leashes and dropped them approximately two to four feet so that he could compare, under controlled loading conditions intended to approximate a dog's sudden pull, whether the cord and tape materials penetrated the pig-skin surrogate. In Seluga's tests, with the exemplar in the locked position, the cord penetrated the pig skin at forty-four pounds, while the tape did not penetrate it at seventy pounds. The forty-four-pound weight corresponded to the Leash's maximum rated dog weight, while the seventy-pound weight reflected Seluga's estimate of Brody's weight based on the available weight and age information. Seluga reported that unlocked leashes did not cut through the skin, even with the 70-pound weight.

Ultimately, Seluga opined, to a reasonable degree of engineering certainty, that the Leash was defectively designed and unreasonably hazardous because its thin cord created a serious laceration and amputation risk. He concluded that technically and economically feasible alternatives — including a tape-style retractable leash or a traditional non-retractable leash — would have significantly reduced or eliminated that risk and, more likely than not, prevented Plaintiff's injuries. Because safer designs were feasible, he considered warnings alone insufficient to address the cord's injury risk. Moreover, because the cord penetrated the simulated skin at the Leash's rated forty-four pound limit, while the tape did not do so at seventy pounds, he concluded that Brody's precise weight was not a significant contributing factor in Dannenfelser's injury.

Motion In Limine to Preclude Seluga

In moving to preclude Seluga's expert opinion, Defendants attack his "drop-weight testing." As described above, in these tests Seluga wrapped an exemplar cord-or tape-style leash around two quarter-inch-diameter brass rods covered with pig skin to simulate fingers, attached a forty-four or seventy-pound weight, and allowed the weight to fall approximately two to four feet. This was intended to imitate a dog unexpectedly pulling on the leash. Defendants challenged the reliability of Seluga's conclusion on the grounds that the apparatus used was developed for this litigation without independent validation or peer review, used brass rather than an accepted bone surrogate, did not measure the force applied in every test, and produced failed or irregular runs involving varying drop heights, knots, and reused or damaged leashes. While Defendants do not claim that an exact recreation of the injury was required, they assert that the testing was not valid as a reliable means of evaluating amputation risk.

Seluga's experiments compared the cord and tape designs rather than attempting to duplicate the accident in every respect. His report describes the exemplary skin, falling weights, drop distances, wrapping conditions, and completed-test results. Seluga observed that the cord penetrated the skin at forty-four pounds, while the tape did not penetrate it at seventy pounds. Moreover, the Seluga Report identifies rods as a surrogate for bone as they have similar strength properties, and not merely as an arbitrary support.

At his deposition, however, Seluga conceded that his testing did not address every aspect and that, for example, he concluded that determining the point at which a finger bone would break was beyond the scope of his testing. To this end, he acknowledged that the rods did not break in any test and that he had not measured the force applied across all tests. Further, the Seluga Report explains that the simulated fingers were rigidly fixed, unlike Plaintiff's movable hand, arm, and body, and Seluga reasoned that this arrangement would produce peak forces as great as those experienced in the accident. He further explained that rigid fixation made the comparison repeatable and, in his view, conservative when evaluating whether the tape would penetrate skin. His relevant inference was that skin penetration is a necessary step toward amputation, so the tape's failure to penetrate the skin under the tested conditions supported his opinion. The Court held that the totality of this testimony on these topics is sufficiently relevant and reliable to submit at trial.

Held

The Court denied Defendants' motion in limine seeking preclusion of the expert report and testimony of Kristopher Seluga.

Key Takeaway

Minor flaws do not render an otherwise reliable opinion inadmissible, while requiring reliability at every step of the analysis.

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