United States Court of Appeals
                            For the Eighth Circuit
                        ___________________________

                                No. 19-2637
                        ___________________________

                                 Anthony Markel

                                       Plaintiff - Appellant

                                         v.

  Douglas Technologies Group, Inc., a California corporation, doing business as
                        Douglas Wheel Technologies

                                     Defendant - Appellee
                                  ____________

                    Appeal from United States District Court
                         for the District of Minnesota
                                 ____________

                             Submitted: June 16, 2020
                              Filed: August 6, 2020
                                  ____________

Before KELLY, ERICKSON, and STRAS, Circuit Judges.
                           ____________

ERICKSON, Circuit Judge.

      During the last lap of a flat-track race in Ogilvie, Minnesota, Anthony Markel
was injured after being thrown from his all-terrain vehicle (“ATV”) when its right
rear wheel came off. Markel sued Douglas Technologies Group, Inc. (“DTG”), the
manufacturer of the wheel, seeking redress for his injuries. The district court1 granted
summary judgment in favor of DTG on all of Markel’s claims. Markel appeals. We
have jurisdiction under 28 U.S.C. § 1291, and we affirm.

        While Markel’s complaint alleges five causes of action, including (1) product
liability, (2) negligence, (3) breach of implied warranty, (4) failure to warn, and (5)
post-sale failure to warn, the first three claims merge by operation of law under
Minnesota’s single product-liability theory. Bilotta v. Kelley Co., 

,
623 & n.3 (Minn. 1984); accord Green Plains Otter Tail, LLC v. Pro-Envtl., Inc., 

, 545–46 (8th Cir. 2020) (applying Minnesota law). Markel has abandoned
his post-sale failure-to-warn claim by not including any argument on the issue in his
brief. U.S. ex rel. Ambrosecchia v. Paddock Labs., LLC, 

, 954 (8th Cir.
2017) (“Claims not raised in an opening brief are deemed waived . . . .” (alteration
and quotation marks omitted)).

       We address the two remaining product liability and failure-to-warn claims.
Markel argues that the DTG wheels he was using were not built to withstand the
rigors of flat-track racing; that he had no way of realizing the wheels were inadequate
because they were practically indistinguishable from the sturdier racing wheels sold
by DTG; and that DTG failed to adequately warn that the wheels were not suited for
racing conditions. Markel claims the substandard design and labeling of his DTG
wheels are responsible for the injuries he sustained in his ATV accident.

      We review the district court’s grant of summary judgment de novo, viewing the
evidence in the light most favorable to Markel and affirming only if there is no
genuine issue of material fact such that DTG is entitled to judgment as a matter of
law. Gibson v. Concrete Equip. Co., 

, 1062 (8th Cir. 2020). We


      1
       The Honorable Susan Richard Nelson, United States District Judge for the
District of Minnesota.

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conclude that Markel has failed to provide evidence on an essential element of each
claim, making summary judgment appropriate. See Celotex Corp. v. Catrett, 

, 323 (1986).

        In order to prove his product-liability claim Markel had to show that (1) the
DTG wheels on his ATV were in a defective condition unreasonably dangerous for
their intended use, (2) the defect existed when the wheels left DTG’s control, and (3)
the defect proximately caused Markel’s injuries. 

n.3.
Expert testimony is necessary to get a product-liability claim past summary judgment
when the product at issue and any of its relevant inner workings are beyond the ken
of a lay jury. See Atwater Creamery Co. v. W. Nat’l Mut. Ins. Co., 

,
279 (Minn. 1985); see also Wagner v. Hesston Corp., 

, 761 & n.9 (8th
Cir. 2006) (applying Minnesota law to affirm grant of summary judgment in product-
liability case where there was no admissible expert testimony regarding design defect
in hay baler).

       Markel’s claim depends on an assessment of the appropriate strength and
design of aluminum ATV racing wheels. Such an assessment necessarily involves
complex mathematical and engineering concepts that a lay juror cannot be expected
to understand without the help of an expert. Markel asserts that his expert provided
the requisite background, and in particular an opinion regarding the alleged design
defect in and dangerousness of DTG’s wheel. This contention, however, is belied by
the expert’s report and by the expert’s deposition testimony, in which he specifically
disclaims an opinion as to whether the subject wheel had a design defect that made
it unreasonably dangerous. Summary judgment is appropriate in favor of DTG on
Markel’s product-liability claim.

      To prevail on his failure-to-warn claim Markel must demonstrate that (1) DTG
had a duty to warn, (2) DTG breached its duty by providing an inadequate warning,
and (3) the inadequate warning caused Markel’s injuries. See Balder v. Haley, 399

                                         -3-
N.W.2d 77, 81 (Minn. 1987); Green Plains Otter Tail, 

(applying Minnesota law). The summary-judgment record is completely devoid of
evidence that an inadequate warning caused Markel’s injuries. During a deposition
Markel’s counsel referred to an alleged statement by Markel that he would not have
used the DTG wheels if he had known they were not meant for racing, but this
hearsay cannot on its own save Markel’s failure-to-warn claim. Firemen’s Fund Ins.
Co. v. Thien, 

, 1310 (8th Cir. 1993) (“Inadmissible hearsay evidence
alone may not defeat a summary judgment motion.”). Without any admissible
evidence to support one of the claim’s necessary elements, DTG is entitled to
summary judgment.

      We affirm.
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