A California Court found that the relationship between patent inventors and the alleged infringer did not rise to level of "privity," so as to prevent the infringer from challenging the validity of the patent under the equitable doctrine of assignor estoppel. 


NuVasive sued Alphatec for infringing seven patents on a surgical system. When Alphatec asserted the patents were invalid, NuVasive invoked the equitable doctrine of assignor estoppel, contending that the relationship between Alphatech and the inventors of the patents prevented Alphatec from challenging the validity of the patents.

The court reviewed the facts and whether the doctrine of assignor estoppel prevented a validity challenge.

The NuVasive Decision

Under the doctrine of assignor estoppel, a patent assignor or one with privity with the assignor, cannot later claim the patents are invalid if assignee (the current patent owner) sues them for infringement. The court may apply assignor estoppel at its discretion.

In this case, Patrick Miles and Brian Snider, the inventors of the patents, assigned their rights to the plaintiff NuVasive. Miles and Snider also had various business and employment involvements with Alphatec, the defendant NuVasive accused of infringing the patents.

The court examined whether those involvements created a relationship between the inventors and Alphatec sufficient to constitute "privity" that would prevent Alphatec from challenging the patents under the equitable doctrine of assignor estoppel.

In doing so, the court considered eight factors used in the Shamrock Technologies case: (1) the inventor/assignor's leadership role at the employer; (2) the inventor/assignor's ownership stake in the defendant company; (3) whether the defendant company Alphatec changed course from manufacturing non-infringing goods to infringing activity after the inventor was hired; (4) the inventor/assignor's role in the infringing activities; (5) whether the inventor/assignor was hired to start the infringing operations; (6) whether the decision to manufacture the infringing products was made partly by the inventor/assignor; (7) whether the defendant company Alphatec began manufacturing the accused product shortly after hiring the inventor/assignor; and (8) whether the inventor/assignor was in charge of the infringing operation.

The court found there was no such privity relationship between Alphatech and the first inventor, Mr. Miles, despite Mr. Miles's leadership role at Alphatec and the fact he was recruited to help the company grow. Alphatec began developing and marketing the accused systems and methods in 2014, had a first sale and public surgical use in February 2017, and launched the product in April 2017, all before Mr. Miles joined Alphatec in October 2017. The court also considered a financial investment Mr. Miles made a few months after joining the company, finding that the timing and amount of the investment did not demonstrate he financially enabled the development of the accused system. Further, Mr. Miles was not affiliated with Alphatec when it decided to manufacture the accused system.

The court similarly found no such privity relationship between Alphatech and the second inventor, Mr. Snider. Mr. Snider joined Alphatec in March 2017, after Alphatec begun developing the accused systems and methods, and had a first sale and public surgical use of them. Mr. Snider also invested in Alphatec as part of a placement purchase agreement Alphatec initiated to raise capital, but Mr. Snider's investment, the court found, was not sufficient to show he financially enabled the development or roll out of the accused systems.

Having found that neither Mr. Snider nor Mr. Miles had the requisite involvement with Alphatec to amount to a "privity" relationship, the court held Alphatec could challenge the validity of the patents and was not barred from doing so by the doctrine of assignor estoppel.

Strategy and Conclusion

Whether an accused infringer is prevented from attacking the validity of the patent depends on their roles and relationship with the inventors or other prior assignors of the patents, including the timing of the development, manufacture, and sale of the accused products when compared to the involvement, employment, and financial investment of the assignor. As a result, when developing and selling a product and maintaining invalidity defenses, it can be useful to consider these factors to determine whether, how, and when to become involved with inventors or other owners of relevant patents.

Further Information

 The NuVasive  decision can be found  here.

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