Sometimes an applicant needs to rely on limitations in the preamble to distinguish cited art. But there is no easy way to know whether, at the end of the day, preamble limitations will count (for validity and/or infringement). You may ask - why not just put the limitation in the body and avoid uncertainty if the limitation is needed to distinguish prior art? There are many answers. For example, it could be that the need for the limitation only came to light based on new references cited in a final rejection (and thus moving the limitation to the body would require an RCE). Or new references are only discovered after the patent has issued. Whatever the reason, the issue arises often, including before the PTAB.

A recent example is in SN 14/211,802. Claim 1 is directed to:

1. A regeneration device for annular disc regeneration of a disc, said disc including an outer annulus fibrosus and an inner nucleus pulposus, said device comprising: a trocar having one end including a sharp tip, an opposite end and an inner cavity therebetween; a handle portion attached to the opposite end of the trocar; a plunger mounted to the handle portion; and a catheter having a plurality of ports coupled to the plunger and extended through the inner cavity of the trocar, wherein the plunger is operable to push the catheter through the cavity and out of an opening in the tip of the trocar, said catheter being structurally configured and flexible so that when the catheter extends out of the trocar it bends in a circular manner to be effective to follow along an inside surface of the outer annulus fibrosus.

On appeal, the applicant relied in part on the limitation of the device being "for annular disc regeneration." The Examiner disagreed, asserting that the limitation was merely an intended use and did not limit the structure. The PTAB sided with the Examiner. The Board explained the general issue as follows:

There is "no simple test for determining when a preamble limits claim scope," but rather a determination is made on the facts of each case, in light of the claim and the supporting patent specification. American Med. Sys., Inc. v. Biolitec, Inc., 618 F.3d 1354, 1358 (Fed. Cir. 2010). Case law provides "some general principles to guide that inquiry." Id. "Generally, the preamble does not limit the claims." Georgetown Rail Equip. Co. v. Holland L.P., 867 F.3d 1229, 1236 (Fed. Cir. 2017) (quoting Allen Eng 'g Corp. v. Bartell Indus., Inc., 299 F.3d 1336, 1346 (Fed. Cir. 2002)). For example, "[a] preamble is not a claim limitation if the claim body 'defines a structurally complete invention . . . and uses the preamble only to state a purpose or intended use for the invention." Id. (quoting Rowe v. Dror, 112 F.3d 473, 478 (Fed. Cir. 1997)). Nonetheless, a preamble may be limiting if it recites essential structure or steps; the claim body depends on a preamble phrase for antecedent basis; the preamble is essential to understand limitations or terms in the claim body; or the preamble recites additional structure or steps underscored as important by the specification. Id. at 1236.

Applying those principles to claim 1, we conclude the claim body defines a structurally complete invention, and the claim preamble recitation of "disc regeneration" states only a purpose or intended use for the claimed device. No limitation in the claim body refers back to the "disc regeneration" function recited in the preamble, nor is the claim preamble essential to understanding the claimed device. Appellants do not cite any disclosure(s) in the Specification to support their position that the preamble is limiting. See, e.g., Appeal Br. 11 (discussing Specification generally); Reply Br. 3--4 ( discussing claim construction). Thus, because the "disc regeneration" intended use recited in the preamble of claim 1 is not limiting, the cited prior art need not disclose such functionality.  

So, if you find yourself needing to rely in the preamble, use the guidance above to support your case as best as possible.