Zimmer and Stryker - Move Your Hips

Both companies are leaders in orthopedic sector, or more simply they make hips and knees. The global $12B market (5 hips, 6 knees) is fast growing (~10% growth in recent years, except little to no growth in 2009, a lot of it due to strong dollar). Post 2009, market is expected to recover to 10% growth as fatties continue proliferating (from 18% prevalence in 1998 to 25% recently - 5% growth vs 1% population). Overall procedures were growing 6%+, as tech has improved somewhat as well, making the procedure more attractive. Products are getting more competitive though (reflected in no price growth recently vs 10% growth in 2002-2004), and there are share shifts - Zimmer is losing for example. It is trading, on the other hand, pretty cheaply as well - 10x P/E. I can see how multiple can expand to 12-13x + lay a fairly attractive growth profile on top of that, but still, I struggle to see where I can have a differentiated view.