Federal Circuit considers means-plus-function claimsOctober 4, 2005

In Cross Medical Products v. Medtronic Sofamor Danek, Inc., a recent decision by the Federal Circuit Court of Appeals, the court mentioned the possibility that it may consider prosecution history estoppel as a bar to the statutory equivalents granted to ‘means-plus-function’ claims under section 112, paragraph 6 of the patent statutes.These types of claims protect the means of performing a function, instead of covering a specific apparatus or step of a method. The scope of a means-plus-function claim extends to the means (typically a part of an apparatus) disclosed in the specification that perform the stated function, as well as things that are equivalent to those described. In order to be equivalent, the so-called ‘function-way-result’ test is typically applied, that is, the alternative structure must perform substantially the same function in substantially the same way to achieve substantially the same result.Additionally, there is a judicially-created doctrine of equivalents that can expand the scope of claims that are not in means-plus-function format. This doctrine has been narrowed over the last decade by a series of decisions holding that statements made between the inventor and the patent office during prosecution of the patent frequently ‘disavow’ equivalents of certain claim terms. This is called prosecution history estoppel. By mentioning that possibility that prosecution history estoppel could potentially apply to equivalents of means-plus-function claims, the Federal Circuit in Cross Medical hinted that it could be inclined to limit the scope of equivalents further, potentially holding that prosecution history estoppel could bar assertion of those equivalents that are expressly permitted by statute.This is a concern for inventors and those who prosecute patent applications. Care should be exercised both in amending means-plus-function claims as well as in the comments made to the patent office regarding such claims in the event the Federal Circuit decides in the future to use the prosecution history to limit the scope of the patent after issued by the patent office.For the complete decision, log on to http://fedcir.gov/opinions/05-1043.pdf