In a case involving claims with functional language and means-plus-function limitations, the US Court of Appeals for the Federal Circuit found that the district court erred in its determination that three claim terms were indefinite, but agreed with the district court that a fourth term was not indefinite. Nevro Corp. v. Boston Sci. Corp., Case Nos. 18-2220; -2349 (Fed. Cir. Apr. 9, 2020) (Moore, J.).

Nevro owns patents for improved technologies for high-frequency spinal cord stimulation therapy to alleviate pain, while avoiding side effects associated with conventional stimulation therapies. Several of the asserted claims recite systems and devices in which the stimulation therapy signals are “paresthesia-free,” meaning they do not cause a tingling, pins-and-needles sensation. The district court found the claimed “paresthesia-free” systems and devices to be indefinite because infringement of the claim depends on the effect of the system on the patient, so a skilled person cannot understand the metes and bounds of the claim with reasonable certainty. Nevro appealed.

The Federal Circuit reversed, explaining that the lower court applied the wrong legal standard: “[t]he test for indefiniteness is not whether infringement of the claim must be determined on a case-by-case basis.” The Court further explained that, although “paresthesia-free” is functional claim language, it does not render the claims indefinite because the claims recite specific parameters for systems or devices to generate a “paresthesia-free” signal, and the specification provides sufficiently detailed guidance and examples to allow a skilled artisan to have reasonable certainty as to the claims’ scope. The Court also rejected defendants’ argument that the “claims are indefinite because infringement can only be determined after using the device or performing the method,” stating that “[d]efiniteness does not require that a potential infringer be able to determine ex ante if a particular act infringes the claims.”

Invoking similar logic, the Federal Circuit agreed with the district court that the term “therapy signal” is not indefinite. Defendants had argued that the claims were indefinite because two identical signals might be therapeutic in one patient, but not another. The Court concluded that “the fact that a signal does not provide pain relief in all circumstances does not render the claims indefinite.” The Court found sufficient specificity in the claim language, specification and prosecution history for a skilled artisan to have reasonable certainty as to the metes and bounds of claims reciting this language.

Several claims recite “a signal generator configured to generate a therapy signal,” a term the district court found to be indefinite because the included term “configured to” is amenable to more than one possible construction. The Federal Circuit disagreed, finding that the district court had again applied the wrong legal standard: “[t]he test is not merely whether a claim is susceptible to differing interpretations. Such a test would render nearly every claim term indefinite so long as a party could manufacture a plausible construction.”

Some of the asserted claims recite “a means for generating” a “paresthesia-free” therapy signal, a term both parties agreed is a means-plus-function limitation. The district court found that the claims were indefinite because there was insufficient disclosure of a corresponding structure in the specification, as the specification did not disclose a specific algorithm to provide structure for a computer-implemented invention. The Federal Circuit disagreed, finding that the specification clearly disclosed a signal or pulse generator as the corresponding structure for this limitation, and that disclosure of a specific algorithm is required only where the specification provides merely a general-purpose computer or processor as the corresponding structure.