The first bellwether trials over medical devices that are designed to prevent blood clots during surgery have failed to carve out a clear winner, with another trial set to begin next week.

About 9,000 lawsuits allege that various types of inferior vena cava filters, or IVC filters, which doctors implant in patients, have perforated or fractured in their bodies, causing pain and leading to removal surgeries. Among the several device manufacturers listed in the lawsuits, C.R. bard Inc. and Cook Medical Inc. face the largest number of cases, clocking in over 4,000 each.