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Court revives patent case - Descriptive terms weren’t “indefinite” after all

October / November 2022 IP Newsletter

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Coming up with a new and useful invention is only part of the battle when it comes to obtaining a patent. You also need to choose your words carefully when drafting the application. A recent ruling from the U.S. Court of Appeals for the Federal Circuit highlights one of the most important considerations: what your words communicate to skilled artisans in the relevant field.

Heart of the matter

The patent in question covered a double catheter structure used in the treatment of congestive heart failure. The patent holder sued another medical device maker for infringement.

The trial court determined, among other issues, that the patent’s use of the terms “resilient” and “pliable” rendered the related patent claims indefinite and therefore invalid. The plaintiff appealed this finding.

Diagnostic tools

Federal patent law generally requires that a valid patent include a specification with “one or more claims particularly pointing out and distinctly claiming the subject matter which the applicant regards as his invention.” A patent is indefinite if — when read in light of its specification and prosecution history — it fails to inform skilled artisans in the relevant field about the scope of the invention, with reasonable certainty. In other words, a skilled artisan must be able to determine whether an allegedly infringing product or method infringes the patent.

Patent claims with descriptive words or terms of degrees, such as “resilient” and “pliable,” must provide objective boundaries for skilled artisans. Both the intrinsic record (the patent’s claims, written description and prosecution history) and relevant extrinsic evidence can help identify such boundaries.


In the case at hand, the Federal Circuit found that the intrinsic record and extrinsic evidence sufficiently informed a skilled artisan of the meanings of both “resilience” and “pliable.” Although the terms are broad, the court said, they aren’t uncertain.

For example, the patent refers to “an outer, resilient catheter having shape memory.” The court found this language itself provides guidance on the term’s meaning; numerous related claims further inform the meaning by providing examples of resilient materials that could be used. The written description extends similar guidance, stating that the outer catheter “has sufficient shape memory to return to its original shape when undistorted.”

While the claim language offered less guidance on the meaning of “pliable,” the written description contained numerous examples of a pliable inner catheter, including a “soft material such as silicone.” It further explained that the inner catheter is “extremely flexible and able to conform to various shapes.”

The Federal Circuit concluded that, taken as a whole, the intrinsic record alone disposed of the indefiniteness issues as to the terms “resilient” and “pliable.” The record provided objective boundaries a skilled artisan could apply to determine the scope of the patented claims.

The extrinsic evidence provided further support for this conclusion. The website defines “resilient” as “returning to the original form or position after being bent, compressed or stretched.” It defines “pliable” as “easily bent, flexible; supple.” The court found that these definitions confirm that both terms would have had broad, but understood, meanings to a skilled artisan.

Treat it right

The court’s analysis here offers a strong reminder of the importance of careful patent drafting. Patent claims must meet various requirements, one of which is using terms that provide a skilled artisan in the relevant field the necessary boundaries to determine whether it’s being infringed.