Addressing the proper construction of the term "backplate," the U.S. Court of Appeals for the Federal Circuit determined that a district court erroneously construed the term to include a tube joint. Laryngeal Mask Co. v. AMBU A/S, Case Nos. 10-1028, -1062 (Fed. Cir., Sept. 21, 2010) (Moore, J.).

Lanryngeal sued AMBU for infringement of a patent directed to laryngeal mask airway devices, which are used to deliver anesthetic gas during surgery and to establish unobstructed airways to patients in emergency situations. The district court construed one claim term "backplate" as "the relatively rigid mask structure surrounded by the cuff and including a tube joint." Based on this construction, the district court determined that AMBU’s accused devices did not have a tube joint and therefore granted summary judgment of non-infringement.

On appeal, Laryngeal argued that the district court improperly read a tube joint limitation into the claims. In support of its position, Laryngeal relied on the fact that the claims did not mention an airway tube, so the claim did not need to clarify how an airway tube would attach to the backplate. Laryngeal also argued that the prosecution history weighed against a tube joint limitation. During the final phase of prosecution, Laryngeal deleted the airway tube and tube joint language from the claims. Because they were deliberately deleted, Laryngeal argued it would be improper to read the limitation back into the claims. AMBU countered that "backplate" is a technical term coined by the inventor. AMBU did not argue that the plain and ordinary meaning of "backplate" includes a tube joint, but rather that the inventor acted as his own lexicographer and defined "backplate" as containing a tube joint. In support of this contention, AMBU relied on the specification statement that "the backplate 52 has a one piece, integral spoon-shape including a bowl 90 and an external tube-joint 92 oriented proximally relative to the bowl." Additionally, AMBU relied on the fact that every figure, embodiment and description of the backplate in the patent shows a backplate separate from an airway tube with a tube joint for connection.

The Federal Circuit, admitting this was a difficult case of claim construction, concluded that backplate should not be construed to include a tube joint. To be his own lexicographer, the Court explained, "a patentee must use a special definition of the term that is clearly stated in the patent specification or file history." Since the specification did not contain such a special definition, the Court concluded that the inventor was not acting as his own lexicographer. The Court also relied on prior art which would inform one of skill of the art to the common meaning of "backplate." It cited two prior art patents disclosing the same inventor that disclosed a backplate. In each of these patents, the backplate did not include a tube joint. Because one skilled in the art would not conclude that backplate must have a tube joint and because the inventor did not act as his own lexicographer, the Federal Circuit found reversed the district court’s judgment for non-infringement.