By David Russell, reporter at OptionMonsterNEW YORK -- Stryker ( SYK) pulled back after running hard in January, and now the bulls are looking for more upside. OptionMonster's tracking systems showed the purchase of some 2,100 March 65 calls for 60 cents. Volume was more than triple previous open interest at the strike. Calls lock in the price where investors can buy shares, so they have the potential to generate significant leverage in the event of a rally. But these options also will become worthless if the stock doesn't move by the mid-March expiration. Stryker's shares rose 0.19% to $63.90 Monday and are up 17% so far in 2013. The maker of replacement joints issued a strong preliminary earnings report on Jan. 9, then beat those estimates when final numbers were released two weeks later. Total option volume was twice the daily average in the session, with calls outnumbering puts by a bullish 31-to-1 ratio. Russell has no positions in SYK.