Stryker ( SYK) shares dropped 3.5% after hours, despite the fact the medical equipment maker announced earnings that rose more than 40% from last year's levels while easily topping analyst estimates.

Stryker said after the bell Thursday that second-quarter net income came in at $152.7 million, or 37 cents a share, topping the 34-cent analyst estimate and rising 42% from the $107.5 million, or 26 cents a share, of a year ago.

Ahead of the earnings release, shares of the company rose 52 cents, or 1%, to $54.80, but after the earnings announcement, shares dropped $1.92 to $52.85 in extremely thin trading.

Net sales were $1.04 billion, just shy of the $1.06 billion expected by analysts, but up 17% from the year-ago $891.7 million. Domestic sales were $677.2 million, up 19% year over year, while international sales were $365.8 million, up 13% year over year. Excluding the currency effect, however, Styker's international sales were up just 6% in the second quarter.

Sales of the company's orthopedic implants, its main line of business, came in at $630.9 million, up 15%, because of higher shipments of reconstructive, trauma and spine systems. The company's MedSurg Equipment racked up $349.5 million in sales, up 21% from last year, while Physical Therapy Services revenue came in at $62.6 million, up 11% annually.