IPR challenges can only be based on prior art patents and printed publications; the PTAB does not have authority to invalidate claims for being indefinite, much as it might want to.  So when a claim is indefinite and therefore cannot be construed, the PTAB can only dismiss the petition.  Sound like a win for the patent owner?  Maybe.  But the district court may be paying attention, and it may not be long before the claim that survived IPR gets killed in court under the indefiniteness roadmap already laid out before the Board.

TLI Communications, for example, had its patent claims invalidated for indefiniteness (and patent-ineligible subject matter) by the district court, in a decision that cited the PTAB’s earlier indefiniteness finding in support of the court’s own analysis.  In Sarif v. Brainlab, the defendants’ expert was able to convince the court to construe means-plus-function claim terms as lacking supporting structure (which makes them indefinite), using the same rationale that had already been demonstrated effective(to provoke an indefiniteness finding, although not to invalidate the claims in IPR) at the PTAB.

Litigation defendants face a tricky decision over indefinite claims in IPR: Attack the claim as indefinite and get your petition thrown out? Or construe the claim for IPR invalidation and appear to concede that the claim is definite?  But the patent owner can still lose either way.