American Crane Corp. (American) appeals from a final judgment entered in the United States District Court for the Eastern District of Missouri upon a jury verdict finding it liable to Raymond and Charlene Campbell (plaintiffs) under a theory of strict liability for failure to warn. For reversal, American argues (1) the district court erred in refusing to grant its motion for judgment as a matter of law because plaintiffs failed to make a submissible case under Missouri law, (2) the district court abused its discretion in allowing plaintiffs’ counsel to argue material facts not in evidence, and (3) the district court abused its discretion in refusing to grant a new trial because the verdict was against the clear weight of the evidence. For the reasons discussed below, we reverse.
I. BACKGROUND
Raymond and Charlene Campbell filed this strict liability action in Missouri state court in June 1991, two years after Raymond Campbell fell off the boom of a crane manufactured by American Hoist and Derrick in 1980. American is the successor in interest to American Hoist and Derrick. The case was subsequently removed on the basis of diversity. Plaintiffs twice amended their complaint. Their claims originally included negligence, manufacturer’s defect, design defect, and failure to warn. Plaintiffs admit that, at trial, they abandoned all claims except their claim of strict liability for failure to warn.
From approximately 1975 to the present, Raymond Campbell (Campbell) has worked as a crane operator for Winters Brothers Materials Co., which supplies cement, sand, and gravel. As part of his duties, he performed maintenance on the crane, and as part of this maintenance, he periodically (ap*1331proximately once every three months) changed a wire cable which is threaded through the crane’s boom. To perform this task, Campbell would walk the length of the boom, a distance of some ninety feet. Campbell also greased the boom’s sheave (a pulley which guides the cable) approximately twice a week. While greasing the sheave, Campbell frequently walked the length of the boom. On June 18, 1989, Campbell was in the process of replacing a cable on the crane’s boom when a lacing (a structural support beam on the boom) allegedly broke. Campbell fell about twelve feet and sustained back injuries.
After a two-day trial, a jury rendered a verdict in favor of Raymond Campbell, awarding him damages in the amount of $500,000.. The jury also awarded damages to Charlene Campbell in the amount of $20,000 on her related loss of consortium claim. American’s post-trial motions for judgment as a matter of law or new trial were denied by the district court without opinion. Campbell v. American Crane Corp., No. 91-1555-C (E.D.Mo. Apr. 29, 1994) (Order). This appeal followed.
II. DISCUSSION
Under Missouri law, a plaintiff seeking to recover in strict liability for failure to warn must prove that (1) the defendant sold the product in the course of his or her business, (2) the product was unreasonably dangerous at the time of sale when used as reasonably anticipated without knowledge of its characteristics, (3) the defendant did not give an adequate warning of the danger, (4) the product was used in a manner reasonably anticipated, and (5) the plaintiff was damaged as a direct result of the product being sold without an adequate warning. Tune v. Synergy Gas Corp., 883 S.W.2d 10, 13 (Mo.1994) (banc) (Tune); Nesselrode v. Executive Beechcraft, 707 S.W.2d 371, 382 (Mo.1986) (banc) (Nesselrode); see Mo.Rev. Stat. § 537.760 (1995). Further, there are two separate requirements of causation in a failure to warn case: (1) the product for which there was no warning must have caused Campbell’s injuries, and (2) the plaintiff must show that a warning would have altered the behavior of those involved in the accident. Tune, 883 S.W.2d at 14, citing Arnold v. Ingersoll-Rand Co., 834 S.W.2d 192, 194 (Mo.1992) (banc) (Arnold).
American argues inter alia that plaintiffs are barred from recovery as a matter of law because their theory of liability was predicated on the imposition of strict liability for failure to warn of an open and obvious danger. American argues that plaintiffs’ counsel indicated that the danger against which Campbell should have been warned was the potential of falling off the boom. American argues that the danger of falling off the boom is so readily apparent that the product cannot, as a matter of law, be deemed “unreasonably dangerous.”
This ease exemplifies the importance of coherent theories of liability. Throughout the trial, plaintiffs’ counsel presented a number of inconsistent variations on the failure to warn theory which have left us with an opaque record. At certain points, plaintiffs’ counsel appeared to argue that the product was unreasonably dangerous because of the risk that the boom’s lacings welds might develop internal cracks, which could be detected only by sophisticated testing methods. Plaintiffs’ evidence further suggested that their theory of liability was based upon American’s failure to warn of the danger of such internal weld cracks. Moreover, in the present appeal, plaintiffs argue that this was in fact the basis of the claim for damages:
There was more than ample evidence to conclude that at the time it [American] manufactured its crane and put it in the stream of commerce[, American]: (1) knew that users of its crane walked across the boom; (2) knew that the welds attaching the lacings to other structural elements of the boom could crack and that the cracks could go undetected; (3) knew that users of its product might not have either the experience or tools necessary to properly evaluate the sufficiency of the lacings or lacing welds, and that in spite of this knowledge the Appellant failed to effectively communicate, i.e. warn, anticipated users of its product, like Ray Campbell, not to walk across the boom.
*1332Brief for Appellee at 5.1 The position plaintiffs currently maintain on appeal simply does not square with the theory of liability offered at trial.
During a bench conference in which the parties argued over the scope of a particular witness’s testimony, plaintiffs’ counsel made the following statements:
My case, Judge, is that this guy should never be out there regardless of what caused him to fall, whether he slipped and fell or whether a lacing broke. That’s my case.
So the record is clear, my case and it’s always been my case that it doesn’t matter whether the lacing broke or not. My case is and always has been and this is no surprise, that he should never have been up there.
I Trial Tr. 191-192. These statements reveal that plaintiffs were not proceeding on a theory that American was liable for a failure to warn of the internal cracks in the weld. Rather, this theory of liability assumes that the hazard against which American failed to warn was the danger of falling off the boom. Plaintiffs’ counsel reiterated this position in closing argument to the jury:
[American] knew ... that there was a foreseeable risk of someone slipping on the boom of that crane while hauling a piece of heavy cable and I think we can all agree that that’s an obvious and a dangerous practice.
[American’s] argument is if it’s open and obvious, we don’t need to do anything about it. That’s incorrect. Because if it’s open and obvious, [American has] a duty to give [Campbell] an alternative. [American has] a duty to advise [Campbell] of a safe manner to do it [threading wire cable through the boom].
I Trial Tr. 354. Toward the end of closing argument, plaintiffs’ counsel again expressly disavowed reliance on any structural defect or inherently dangerous characteristic, other than the danger of falling off the boom:
The thing that was most likely to happen is that Ray would have slipped and fell. I agree that it’s likely that that weld would have broken, but let’s talk about the weld. I don’t want to talk about it because I don’t think it’s relevant. I don’t think the absence of timbers [structural supports on the boom] is relevant because whether the lacing broke or he slipped — if there is a warning on the side of the crane, we have all seen warnings, stop do not thread boom by walking across, something like that.
I Trial Tr. 360. This argument clearly urged the jury to find that American should be held liable for failing to warn Campbell of the possibility that he may incur injury if he slips and falls while walking on the boom. Now, plaintiffs argue a theory of liability under which they can only recover if the lacing broke because of an internal weld crack.
A careful reading of the entire transcript in the present case reveals the ever-changing characterization of their failure to warn theory. However, we have two clear statements of their trial theory. One comes in the above-quoted bench conference, and the other in plaintiffs’ brief to this court. As noted, in order to make “the record clear,” plaintiffs’ counsel at trial said that their case in no way relied upon a broken lacing. I Trial Tr. 191-192. Presently, however, plaintiffs argue that American was strictly liable for failure to warn because of the danger of internal lacing weld cracks. Of course, if no crack occurred, the requisite causal connection would be lacking because one cannot be liable for failing to warn of a danger which has not been encountered. Thus, it is readily apparent that the trial and appellate theories are inconsistent.
It is a general rule of appellate practice that “a reviewing court will consider a case only on the theory upon which it was tried in the district court.” St. Louis Developmental Disabilities v. Mallory, 767 F.2d 518, 521 (8th Cir.1985), citing Wright v. Newman, 735 F.2d 1073, 1076 (8th Cir.1984). *1333Therefore, we need not consider the strict liability for failure to warn theory that plaintiffs have formulated on this appeal. We review only the theory which plaintiffs submitted below.2
The Missouri Supreme Court has stated that the determinative issue in a strict liability failure to warn case is “whether the information accompanying the product effectively communicates to the consumer or user the dangers that inhere in the product during normal use and the dangerous consequences that can or will result from misuse or abnormal use of the product.” Nesselrode, 707 S.W.2d at 382. However, manufacturers are not required to provide a warning for every potential hazard:
Manufacturers and distributors are not under a duty to provide warnings about dangers which are open and obvious, or which are commonly known. If the user of a product knows or reasonably may be expected to know of a particular danger, strict liability will not result from a failure to warn of that danger.
Grady v. American Optical Corp., 702 S.W.2d 911, 915 (Mo.Ct.App.1985) (citations omitted).
Plaintiffs’ theory, as repeatedly articulated by their counsel at trial, was that Campbell should never have been up on top of the boom because of the danger that he might fall off. Pled as a strict liability failure to warn case, this theory must fail. While we recognize that the issue of the adequacy of Campbell’s knowledge of the risks inherent in the product is normally for the jury to determine, Palmer v. Hobart Corp., 849 S.W.2d 135, 140 (Mo.Ct.App.1993), certainly Campbell, a crane operator with many years of experience, can have reasonably been expected to know of the open and obvious danger that he could fall from the boom. For plaintiffs to recover under their trial theory, we would have to hold American liable for failing to warn Campbell not to walk on the boom because he might fall. Such a warning, however, would in no way provide Campbell with additional knowledge of the inherent characteristics of the crane. See Arnold, 834 S.W.2d at 194 (holding that plaintiffs failure to warn claim should not have been submitted to the jury because the evidence did not indicate that a warning would have imparted additional information). Accordingly, we hold that the district court erred in failing to grant judgment as a matter of law to American.
III. CONCLUSION
For the reasons discussed above, the judgment of the district court is reversed.
. We note that plaintiffs stress the knowledge of American. However, in a strict liability failure to warn context, "liability may be imposed without regard to defendant’s knowledge or conduct.” Nesselrode v. Executive Beechcraft, 707 S.W.2d 371, 383 (Mo.1986) (banc).
. Our opinion should not be read, however, to limit in any way a plaintiff's ability to plead and argue alternative and even inconsistent theories of liability. See generally Fed.R.Civ.P. 8; Mo. Rev.Stat. §§ 509.050 and 509.110 (1986).