Background
SciMed Life Systems held patents on balloon dilatation catheters — medical devices used in angioplasty procedures to open blocked coronary arteries. The catheters contain an inner lumen (a channel) for the guidewire and an outer lumen for the balloon inflation fluid. The two competing lumen designs at issue were: a coaxial design, where the guidewire lumen runs inside the inflation lumen along a common axis; and a dual-lumen or side-by-side design, where the two channels run parallel to each other.
Advanced Cardiovascular Systems (ACS) made a catheter with the dual/side-by-side lumen configuration. SciMed sued for patent infringement, arguing that the claims’ broad language — referring to a “lumen” without specifying coaxial or dual configuration — covered both designs. The district court construed the claims to cover only the coaxial design and granted summary judgment of non-infringement. SciMed appealed.
The key issue was whether claim language that was facially broad could be limited by the patent’s specification when the specification described the invention exclusively in terms of a particular structure.
The Court’s Holding
The Federal Circuit affirmed. Writing for the court, Judge Bryson held that while the claim language itself did not expressly limit the lumen configuration, the patent specification consistently and repeatedly described the invention as having a coaxial lumen structure. Crucially, in several places the specification disparaged or distinguished the dual-lumen design, stating that the dual-lumen approach was a prior art configuration that the invention had improved upon. This constituted a clear disclaimer: SciMed had, through its specification, defined its invention by contrast with the dual-lumen design.
The court reaffirmed the principle that the specification is the single best guide to the meaning of disputed claim terms. Where the specification clearly and consistently defines the invention in terms of a specific feature or structure — especially where it distinguishes or criticizes alternative structures — that definition limits the claims, even if the claim language would be broad enough to cover those alternatives in isolation. A patentee cannot use broad claim language to recapture structures that the specification has disclaimed.
SciMed’s catheters used the coaxial design. ACS’s catheters used the dual-lumen design. Because the claims were properly construed to cover only the coaxial design, ACS did not infringe.
Key Takeaways
- A patent specification that consistently defines the invention in terms of a specific structure limits the claims to that structure, even if the claim language appears broader.
- Statements in the specification disparaging or distinguishing alternative structures constitute disclaimers that narrow claim scope.
- Intrinsic evidence — the patent itself and prosecution history — controls claim construction; broad claim language cannot override clear specification limitations.
- Patentees should draft specifications carefully to avoid inadvertently limiting claims through repeated narrow descriptions of the preferred embodiment.
- This “specification disclaimer” doctrine is now a standard tool in claim construction analysis.
Why It Matters
SciMed established one of the most frequently cited principles in claim construction: when a specification defines the invention in narrow terms, courts will hold the claims to that narrow scope. The case is a cautionary tale for patent drafters. A specification that repeatedly describes the invention as having a particular feature — especially when it criticizes alternatives — can trap the patentee into a narrower claim scope than the literal claim language suggests.
For patent litigants, SciMed remains an important precedent for accused infringers seeking to narrow claim scope using the patent’s own specification language. It also reinforces the primacy of intrinsic evidence in claim construction, a principle that the Federal Circuit has consistently applied in the decades since. The decision exemplifies how the way an inventor describes an invention can be as legally significant as the claims themselves.