Companies that operate in appealing industries, have little debt, and post net profit margins greater than 20% aren't likely to inflict serious pain in Foolish portfolios. In fact, they may have precisely the opposite effect, as orthopedic implant firm Zimmer Holdings (NYSE:ZMH) seems to demonstrate.

Favorable trends from aging baby boomers appear to support many years of growth in the hip and knee replacement market, not to mention related spine, trauma, and other procedures. Zimmer's second quarter proved no exception, as double-digit knee, extremity, and dental product sales growth contributed to an overall 10% top-line increase.

Growth was strong worldwide, as sales in the Americas improved 9%, a weak dollar more than doubled European growth to 12%, and Asia expanded 11% on a reported basis. Slower growth in costs and share repurchases contributed to a 20% jump in earnings per share, and management expects full-year bottom-line growth of almost 19%.

These results shouldn't surprise Fools familiar with Zimmer, since the company has grown rapidly for many years. With quarterly net margins close to 24%, it's far from showing its age. Strong cash flow generation has given Zimmer plenty of ammo to develop new implant and surgical products, make acquisitions, repurchase shares, and increase cash by $93 million for the first six months of the year.

Zimmer, along with archrivals Stryker (NYSE:SYK), Smith & Nephew (NYSE:SNN), Biomet (NASDAQ:BMET), and the DePuy unit of health-care giant Johnson & Johnson (NYSE:JNJ), are expected to benefit as demographics work in their favor and technology gives their implant products more mass appeal. Any pullback, like the one witnessed about a year ago, will find me implanting more of these names into my portfolio.          

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Fool contributor Ryan Fuhrmann is long shares of Johnson & Johnson, but has no financial interest in any other company mentioned. Feel free to email him with feedback or to discuss any companies mentioned further. Johnson & Johnson is an Income Investor recommendation. The Fool has an ironclad disclosure policy.