Even as its DePuy unit is trying to recover from its problems with the faulty artificial hips. Johnson is completing its biggest ever acquisition that would reinvigorate its device business. Its $20 billion purchase of Synthes would make the firm a dominant player in a major segment of the medical device market . Systhes, a make of equipment used in trauma surgery, accounts for nearly 50 percent of sales of plates and screws that are used to treat broken bones. The $5.5 billion trauma category grew 8 percent last year, according to estimates by Wells Fargo Securities.