Manufacturing Defect Claims Under Missouri Law

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Proving that one unit departed from its design—often without the unit, sometimes without an expert, and always against the malfunction doctrine’s limits

The manufacturing-defect claim is the narrowest and, in one sense, the most intuitive theory in products law: it does not attack the manufacturer’s engineering judgment, only its execution. The design is conceded sound; the contention is that this particular unit came off the line wrong—an incomplete weld, a contaminated batch, an omitted fastener—so that it was more dangerous than the thousands of identical units built to the same specification. What makes the theory difficult is evidentiary rather than conceptual. The defective unit is very often consumed or destroyed in the event that injured the plaintiff, and even when it survives, the specific flaw may be invisible without destructive testing. Missouri law answers that difficulty with a robust circumstantial-proof doctrine that lets a jury infer a defect from the fact and circumstances of a malfunction—subject to limits that have hardened noticeably since the State adopted a Daubert expert standard in 2017. This article states the framework, works through the malfunction cases and their boundaries, and turns to how these cases are built and defended.

I. Statutory and Common-Law Basis

A manufacturing-defect claim proceeds under the same “defective condition unreasonably dangerous” prong—section 537.760(3)(a) RSMo—that governs design cases. The statute nowhere uses the phrase “manufacturing defect”; the taxonomy is a judicial gloss on a single statutory cause of action, and both branches are submitted through the same verdict director. The common-law source is Keener v. Dayton Electric Manufacturing Co., 445 S.W.2d 362 (Mo. 1969), which adopted Restatement (Second) § 402A and, with it, the requirement that the product reach the user “without substantial change in the condition in which it is sold,” 445 S.W.2d at 364. That phrase carries double duty in a manufacturing case: it is both a premise of the plaintiff’s affirmative case and the doctrinal seat of the alteration defense. Keener also imported § 402A’s defining feature—liability “although the seller has exercised all possible care”—which is precisely what separates a manufacturing defect from negligence: the manufacturer’s diligence in production is not a defense, because the inquiry is the condition of the product, not the conduct of its maker.

The manufacturing/design line was drawn expressly by the Supreme Court. In Nesselrode v. Executive Beechcraft, Inc., 707 S.W.2d 371, 376 (Mo. banc 1986), the Court described Keener as “a case involving a defect in the manufacturing process rather than a problem associated with the way the product was originally designed,” and located the design branch in Blevins v. Cushman Motors, 551 S.W.2d 602 (Mo. banc 1977). One point of Missouri exceptionalism matters here: the State has not adopted the Restatement (Third) § 2(a) “departs from its intended design” formulation as a discrete element. Missouri retains § 402A and submits “unreasonably dangerous” to the jury undefined, so a Missouri manufacturing-defect plaintiff technically proves a “defective condition unreasonably dangerous,” not a formal specification-deviation element—even though departure from specification is, evidentially, the heart of the proof.

The elements, then, are that the defendant sold the product in the course of its business; that the product was in a defective condition unreasonably dangerous when put to a reasonably anticipated use (for a manufacturing defect, that it deviated from its intended design); that it was used in a manner reasonably anticipated; that the plaintiff was damaged as a direct result; and that the product reached the user without substantial change in its condition.

II. The Circumstantial-Proof (“Malfunction”) Doctrine

The signature of Missouri manufacturing-defect law is that a plaintiff need not produce the specific flaw—or even the product—to reach the jury. A defect, and its causal role, may be inferred from evidence that the product malfunctioned during a reasonably anticipated use, provided other reasonable causes are sufficiently negated. This is Missouri’s analog to the “malfunction theory,” and it is what keeps destroyed-unit cases alive.

The rule-announcing decision is Williams v. Ford Motor Co., 411 S.W.2d 443 (Mo. App. 1966), a power-steering case in which a new Thunderbird’s steering bound and locked four days after delivery, sending the car into a tree. The court held that “the existence of a defect may be inferred, just as negligence may be inferred, from circumstantial evidence,” 411 S.W.2d at 447, so that a jury could conclude a steering defect existed from delivery to impact without the plaintiff identifying the precise failure mechanism. (The frequently cited Williams opinion at 454 S.W.2d 611 (Mo. App. 1970) is the second appeal, principally holding a contributory-negligence instruction improper in strict liability.) The doctrine matured through a line of fire and failure cases. In Winters v. Sears, Roebuck & Co., 554 S.W.2d 565, 569–70 (Mo. App. 1977), a television caught fire, and the court held that “the existence of a defect may be inferred from circumstantial evidence with or without the aid of expert opinion evidence,” and that “some accidents do not ordinarily occur in the absence of a defect and in those situations the inference that a product is defective is permissible”—so long as the plaintiff proceeds “without identifying a specific defect, provided the evidence points reasonably to that conclusion and excludes other reasonable explanations.”

The most-quoted articulation is Klein v. General Electric Co., 714 S.W.2d 896, 900 (Mo. App. 1986), a coffeemaker fire that destroyed the plaintiffs’ home and the unit itself. Holding that “[t]he existence of a defect may be inferred from circumstantial evidence with or without the aid of an expert witness,” the court sustained the verdict where the plaintiffs’ experts had eliminated alternative ignition sources—the very process of elimination that the doctrine demands. Earlier, Lifritz v. Sears, Roebuck & Co., 472 S.W.2d 28, 32 (Mo. App. 1971), had established that “[a]bsolute certainty or positive proof of causation by an expert witness is not required,” and that an opinion of probable cause is substantial evidence; and Brissette v. Milner Chevrolet Co., 479 S.W.2d 176, 182–83 (Mo. App. 1972), held that the mere unavailability of the product—there, a tire—“is a matter going to the weight of the evidence rather than to a complete failure of proof.” Brissette is the case to cite when the accident unit is gone.

Two more authorities complete the affirmative line. The phrase practitioners often attribute to the Supreme Court—that a plaintiff has no burden to prove a specific failure or malfunction—actually originates in Stinson v. E.I. DuPont de Nemours & Co., 904 S.W.2d 428, 431 (Mo. App. 1995), which held the plaintiff “had no burden to establish product failure or malfunction,” the burden being met by proving the product unreasonably dangerous and therefore defective. The Supreme Court’s contribution is Rodriguez v. Suzuki Motor Corp., 996 S.W.2d 47, 65 (Mo. banc 1999), reaffirming that “unreasonable danger” is “an ultimate issue for the jury.” And Gramex Corp. v. Green Supply, Inc., 89 S.W.3d 432, 437 (Mo. banc 2002), holds that even the “substantially unchanged” element may be proved circumstantially, through expert testimony that the defect “would have been in the same form as when it left [the seller’s] hands.” The Eighth Circuit gathered these threads in Sappington v. Skyjack, Inc., 512 F.3d 440, 446 (8th Cir. 2008): a strict-liability claim “may be based solely upon circumstantial evidence and does not require expert testimony,” and the plaintiff “ha[s] no burden to prove a product failure or malfunction.”

III. The Limits of the Inference

The inference is permissive, not automatic, and it collapses in four recurring situations that every defense lawyer should press and every plaintiff should preempt. First, where the harm is a known or inherent characteristic of a product working as designed, nothing “malfunctioned,” and the inference never arises; Rardon v. Falcon Safety Products, Inc., No. 20-6165-CV-SJ-BP (W.D. Mo. June 13, 2023), applying Missouri law to a compressed-gas duster deliberately inhaled, sits at exactly this boundary. Second, the plaintiff must negate other reasonable causes; Winters permits the inference only for accidents that “do not ordinarily occur in the absence of a defect,” and Klein required the elimination of competing ignition sources. Where the causation opinion rests on the expert’s ipse dixit and alternatives are not excluded, the case fails—Menz v. New Holland North America, Inc., 507 F.3d 1107, 1114–15 (8th Cir. 2007) (decades-old tractor; defect claim “mere speculation and conjecture,” with “too great an analytical gap between the data and the opinion proffered,” quoting General Electric Co. v. Joiner, 522 U.S. 136, 146 (1997)). Third, abnormal use or substantial alteration breaks the “substantially unchanged” premise. Fourth, the age and complexity of the product, and a long incident-free service history, weaken the inference that a defect—rather than wear, third-party repair, or use conditions—caused the failure.

IV. Expert Testimony and the 2017 Daubert Standard

Although Missouri permits proof without an expert, most contested manufacturing cases turn on expert causation, and since 2017 that testimony must clear a materially higher bar. Effective August 28, 2017 (L. 2017 H.B. 153), section 490.065.2 RSMo adopted language identical to Federal Rule of Evidence 702: the opinion must help the trier of fact, rest on sufficient facts or data, be the product of reliable principles and methods, and reflect a reliable application of those methods to the facts. Missouri courts accordingly treat Daubert, Kumho Tire, and Joiner as persuasive. The first appellate construction, State ex rel. Gardner v. Wright, 562 S.W.3d 311 (Mo. App. E.D. 2018), stressed that gatekeeping is “flexible” and that “no single factor is necessarily dispositive”—a pro-admissibility gloss. But the strongest products application cuts the other way: Gebhardt v. American Honda Motor Co., 627 S.W.3d 37 (Mo. App. W.D. 2021), affirmed exclusion of a sudden-acceleration causation expert—and summary judgment—where the opinions rested on an untested exemplar drip video, an inapposite recall, and no confirmatory testing, leaving “too great an analytical gap between the data and the opinion proffered.” The lesson for a circumstantial manufacturing case is that the reliability of the expert’s cause-elimination methodology—how competing causes were identified and ruled out—is the point of maximum exposure, and the record must be built with the Daubert motion in mind.

V. The Verdict Director

The manufacturing-defect claim is submitted under MAI 25.04—the same strict-liability product-defect director used for design cases—requiring the jury to find sale in the course of business, a defective condition unreasonably dangerous when put to a reasonably anticipated use, reasonably anticipated use, and damage as a direct result of that condition. There is no separate manufacturing-only instruction and, as in the design case, no paragraph defining “unreasonably dangerous.” The concept is more concrete here, however: a jury rarely struggles to find that a unit built in departure from its own specifications, and more dangerous for it, is unreasonably dangerous. Because MAI is copyrighted and periodically renumbered, confirm the current text and Notes on Use against the official volume before drafting.

VI. Defenses

Alteration and substantial change. Rooted in § 402A(1)(b) and Keener, a material post-sale modification—by the plaintiff, an employer, or a third party—defeats the claim by breaking the causal link between the manufacturer and the injuring condition, and supports an intervening-cause argument. The plaintiff bears the burden to prove the product reached the user substantially unchanged, and may do so circumstantially (Gramex, 89 S.W.3d at 437).

Misuse and reasonably anticipated use. A use the manufacturer could not reasonably anticipate defeats the prima facie case as a failure of an element; a foreseeable but careless use is routed to comparative fault.

Comparative fault—section 537.765. Missouri applies pure comparative fault: “[a]ny fault chargeable to the plaintiff shall diminish proportionately the amount awarded as compensatory damages but shall not bar recovery.” The statute enumerates the exclusive fault categories—failure to use the product as reasonably anticipated; use for an unintended purpose; knowing, voluntary, and unreasonable exposure to a danger; unreasonable failure to appreciate a danger; failure to take the precautions a reasonably careful user would take; and failure to mitigate. Note there is no separate “alteration” category; alteration is handled through the defect and causation elements.

The innocent-seller dismissal—section 537.762. Manufacturing cases routinely name every link in the chain. A defendant whose liability rests solely on its status as a seller may move for dismissal on an affidavit that it knows of no basis for liability other than that status, provided another defendant—including the manufacturer—“from whom total recovery may be had” is properly before the court; the parties get sixty days of discovery, and dismissal is without prejudice and interlocutory. A practice point often missed: the 2019 amendment (S.B. 7) repealed the former subsection that had preserved venue and jurisdiction notwithstanding the seller’s dismissal. By removing that clause, the amendment allows dismissal of a resident retailer to eliminate the in-state anchor—opening the door to removal on diversity or fraudulent-joinder grounds when the only Missouri defendant is the innocent seller. Timing and affidavit requirements were unchanged.

Spoliation. The single-unit manufacturing case lives and dies on the product, so the adverse-inference spoliation doctrine is a two-edged sword. Missouri requires intentional destruction under circumstances showing fraud, deceit, or bad faith—“a desire to suppress the truth”; negligent loss is not spoliation. Schneider v. G. Guilliams, Inc., 976 S.W.2d 522, 527 (Mo. App. E.D. 1998); Brown v. Hamid, 856 S.W.2d 51, 56–57 (Mo. banc 1993). The proponent bears the burden of showing fraudulent intent, and the timing of destruction or repair alone is insufficient (DeGraffenreid v. R.L. Hannah Trucking Co., 80 S.W.3d 866, 873 (Mo. App. W.D. 2002)); the sanction, where it applies, holds the spoliator “to admit that the missing evidence would have been unfavorable to its position” (Marmaduke v. CBL & Associates Management, Inc., 521 S.W.3d 257, 269 (Mo. App. E.D. 2017)). The tension with Brissette is important: mere unavailability of the unit, without bad faith, is weight rather than a bar, so a plaintiff who loses the unit innocently can still reach the jury circumstantially—while a defendant that scraps the accident unit courts the inference, and can wield it offensively against a plaintiff who discarded the unit before inspection.

VII. Limitations

A manufacturing-defect claim for personal injury or property damage falls under Missouri’s five-year limitation, section 516.120(4) RSMo (“any other injury to the person or rights of another, not arising on contract”), with accrual governed by section 516.100—not when the wrong is done, but “when the damage resulting therefrom is sustained and is capable of ascertainment.” The controlling accrual decision, Powel v. Chaminade College Preparatory, Inc., 197 S.W.3d 576 (Mo. banc 2006), makes the test objective: the period begins when the evidence would place a reasonably prudent person on notice of a potentially actionable injury, not when the plaintiff subjectively discovers it—important in latent-injury and toxic-exposure cases. Where the defect causes death, the three-year wrongful-death period of section 537.100 RSMo governs instead, generally running from the death rather than the underlying product injury. Because the choice of theory can move the clock, limitations should be resolved before the petition is framed.

VIII. Building and Defending the Case

Preserve and inspect first. Everything flows from the unit. Issue litigation-hold and preservation letters immediately; photograph and video the unit in situ before anyone handles it; establish and document a chain of custody; and negotiate a written joint-inspection protocol before the unit is touched. Failure exposes the client to the spoliation inference and, on the defense side, forfeits the chance to wield it.

Control destructive testing. Because manufacturing proof often requires teardown, imaging, metallurgy, or sectioning, agree a destructive-testing stipulation: notice to all parties, mutual presence of experts, non-destructive imaging before any cutting, preservation of removed components, and court approval where the unit is irreplaceable. Uncoordinated destructive testing is itself sanctionable spoliation.

Prove departure from specification. Although Missouri imposes no formal “deviation” element, the evidentiary core of the case is showing that the accident unit departed from the manufacturer’s own engineering drawings, tolerances, and quality-control records, and from its sister units. Obtain the design and specification package, statistical-process-control and inspection data, supplier certifications, and—critically—batch, lot, and serial data. A cluster of same-mode failures within a single lot is powerful proof of a manufacturing (as opposed to design) defect, and it does double work by negating alternative causes under Winters and Klein.

When the unit is gone, try the malfunction case. Lean on Klein, Stinson, and Sappington: normal use, plus malfunction, plus exclusion of other reasonable causes, equals a submissible defect without identifying the mechanism, and Brissette keeps the plaintiff in court despite the missing unit. Structure the expert’s opinion as a disciplined differential analysis that affirmatively rules out alternatives, because that is exactly where Menz and Gebhardt defeat weak cases.

Defeating the inference. For the defense, attack each predicate: show the failure is a known or inherent risk of a non-defective product (Rardon); identify un-excluded alternative causes and force the plaintiff’s expert into ipse dixit (Menz); prove substantial post-sale alteration; emphasize age, complexity, and long incident-free use; and mount a rigorous section 490.065 challenge focused on the absence of testing and reliable cause-elimination. Consider the section 537.762 innocent-seller dismissal early—post-2019, it can also destroy the in-state anchor and open removal.

IX. Analytical Tensions

The central tension in modern Missouri manufacturing law is the collision between a plaintiff-friendly substantive rule and an increasingly rigorous evidentiary gate. Missouri law says the plaintiff has no burden to prove a product failure or malfunction and may prove defect circumstantially “with or without” an expert (Stinson; Sappington). Yet the 2017 adoption of Rule 702 in section 490.065.2 imposes Daubert-grade reliability on whatever expert the plaintiff does offer—and contested manufacturing causation almost always needs one. The two doctrines operate at different stages: the “no burden” rule governs substantive sufficiency (what the jury may infer), while section 490.065 governs admissibility (what the jury may hear). The practical effect since 2017 is a quiet narrowing of the malfunction doctrine’s reach—not by changing the substantive rule, but by tightening the screen on the testimony the case depends on, with Gebhardt and Menz on one side and Gardner v. Wright’s “flexible, no single factor dispositive” gloss on the other. The related instructional tension—that Missouri submits manufacturing and design defects on the same undefined “unreasonably dangerous” standard—blurs a distinction that is invisible on the verdict form yet decisive to the evidence, since departure-from-specification proof and risk-utility proof are entirely different enterprises. For the practitioner, the reconciliation is practical: win the case at the evidentiary gate by building an elimination-based expert record that no Joiner gap can swallow, and the generous substantive rule will still be there to carry the inference the rest of the way.

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