SAN FRANCISCO — Intuitive Surgical has tapped Skadden, Arps, Slate, Meagher & Flom partner Allen Ruby to fight an effort by Illinois Union Insurance Co. to void a liability policy it issued the medical device maker earlier this year.

Illinois Union accuses Intuitive of concealing the existence of so-called tolling agreements with plaintiffs lawyers that held injury claims at bay while freezing the statute of limitations. Learning of the agreements dramatically changed the insurer’s risk analysis, because it showed claims accelerating more rapidly than other records indicated, the suit asserts.