April 20, 2020
Title 35 USC § 112(b) requires that patent claims particularly point out and distinctly claim the subject matter regarded as the invention. Patent claims often include functional terms that recite a feature by what it does rather than by what it is. On April 9, in Nevro Corp. v. Boston Scientific Corp., the Federal Circuit issued a noteworthy opinion addressing the definiteness of functional language in patent claims.
Nevro sued Boston Scientific, alleging infringement of seven patents directed to high-frequency spinal cord stimulation therapy for inhibiting an individual’s pain. According to Nevro’s patent specifications, conventional spinal cord stimulation systems deliver electrical pulses to generate sensations such as tingling or paresthesia that mask or otherwise alter the patient’s pain. Nevro’s asserted claims were drafted to include systems, devices, and methods that utilize “paresthesia-free” therapy signals.
The district court reviewed the definiteness of several terms used in the patents, including the term “paresthesia-free.” The district court held that the “paresthesia-free” limitations do not render the asserted method claims indefinite because a skilled artisan would be able to quickly determine whether a signal creates paresthesia for any given patient. However, the district court held that similar limitations in the system and device claims are indefinite because infringement of these claims depends on the effect of the system on a patient, and not a parameter of the system or device itself.
On appeal, the Federal Circuit affirmed the finding that the “paresthesia-free” method claims are not indefinite and reversed the finding that the “paresthesia-free” system and device claims are indefinite. The court first rejected the district court’s indefiniteness standard, saying the district court had applied the wrong legal standard. The court explained that the test for indefiniteness is not whether infringement of the claim must be determined on a case-by-case basis, but rather it is simply whether a claim informs those skilled in the art about the scope of the invention with reasonable certainty.
The Federal Circuit then stated that although “paresthesia-free” is a functional term, that does not inherently render it indefinite. In fact, the court noted, functional language can promote definiteness because it helps bound the scope of the claims by specifying the operations that the claimed invention must undertake.
When a claim limitation is defined in purely functional terms, a determination of whether the limitation is sufficiently definite is highly dependent on context such as the disclosure in the specification and the knowledge of a person of ordinary skill in the art. In this regard, the Federal Circuit observed that the specifications of Nevro’s asserted patents provide reasonable certainty about the claimed inventions’ scope. For example, the specifications teach how to generate and deliver paresthesia-free signals with high frequency, low amplitude, and other parameters. As such, the court found the “paresthesia-free” limitations of the system and device claims—in addition to those limitations of the method claims—to be sufficiently definite.
The Federal Circuit also rejected Boston Scientific’s argument that the asserted “paresthesia-free” claims are indefinite on grounds that infringement can only be determined after using the device or performing the method. The court stated, “Definiteness does not require that a potential infringer be able to determine ex ante if a particular act infringes the claims.”
There are number of important takeaways from this case. First, the Federal Circuit reiterates that functional terms are not inherently indefinite, and instead functional terms can actually promote definiteness. Second, the court clarified that the legal standard for determining whether a claim is indefinite does not turn on whether infringement of the claim must be determined on a case-by-case basis. Third, this case highlights the importance of providing detailed guidance and examples in the specification that can provide reasonable certainty about the scope of functional claim language.