IT was a long, fruitful medical marriage that is fast becoming an angry public divorce, one that offers a rare look at a clash between a top-shelf consultant and his corporate patron over patient safety. *snip* In return, Zimmer, an orthopedic implant maker, helped enrich Dr. Berger, portraying him as a master surgeon and paying him more than $8 million over a decade. Those days are gone. Dr. Berger started complaining to Zimmer a while back that one of its artificial-knee models was failing prematurely, and he went public recently with a study that he says proves it.