In a recent District of Massachusetts case, a defendant attempted to use the crucible of summary judgment to invalidate the plaintiff’s body temperature detection patents. But, as shown in the Court’s ruling, sometimes that strategy does not produce the desired results.

Plaintiff Exergen Corp., a manufacturer of human body thermometers, sued Defendant Kaz USA, Inc., alleging that Kaz’s products infringe two of Exergen’s temporal artery temperature detection patents. Kaz subsequently filed a motion for summary judgment of invalidity, arguing that Exergen’s patents are invalid as obvious in view of the prior art—including Exergen’s earlier ’813 patent.

In its motion, Kaz contended that the ’813 patent, which relates to measuring body temperature at the ear, teaches the key elements of the asserted claims and that Exergen was estopped from arguing otherwise based upon positions it took in an earlier litigation involving the ’813 patent. In that earlier case, Exergen alleged that certain temporal artery thermometers similar to Kaz’s infringed claim 7 of the ’813 patent, which is directed to a thermometer for measuring temperature at any “biological surface tissue.” Exergen also claimed that claim 7 of the ’813 patent was enabled by the ’813 specification. As a result, Kaz asserted that Exergen cannot reverse course now and claim that the ’813 patent does not disclose essential elements of the patents asserted against Kaz.

In response, Exergen stated that its position in the earlier case—“that claim 7 of the ’813 patent is both enabled and covers temporal artery thermometers”—and its position here—“that temporal artery thermometers were invented years after the ’813 patent”—are not directly inconsistent and thus, estoppel is not triggered.

The Court sided with Exergen, explaining that after-arising technology—like temporal artery thermometers—can be captured within the scope of the broadly-drafted ’813 patent claims without necessitating the conclusion that “the ’813 patent disclosed the later invention.” Similarly, Judge Stearns found that the earlier jury’s finding of enablement of claim 7 of the ’813 patent “does not conclusively establish that the ’813 patent enabled the making of temporal artery thermometers.”

The Court evaluated the remaining issues regarding the obviousness of Exergen’s patents and found that they are “pertinent questions of fact” sufficient to deny Kaz’s motion for summary judgment of invalidity. The Court determined that certain pieces of prior art suggested ways to take external temperatures at the forehead, while other art did not. And, the Court noted the evidence of secondary considerations of non-obviousness provided by Exergen—such as commercial success, unmet need, and skepticism of those skilled in the art. Thus, Judge Stearns concluded that “it is thus for the jury to decide” the question of obviousness.

The Court’s opinion provides helpful guidance to litigants regarding the nuanced issue of estoppel in the larger context of determining obviousness—particularly when a litigant’s own patents are being used as prior art. Litigants should carefully evaluate the positions they take with respect to these key issues so as to avoid the potential for future pain.

The case is Exergen Corp. v. Kaz USA, Inc., Civil Action No. 13-10628 (D. Mass. August 20, 2015), before Hon. Richard G. Stearns. A copy of the order can be found here.