Shares of Alphatec Holdings Inc. plunged to a 52-week low Friday after the spinal device maker said sales are slowing down, and slashed its expectations for the rest of the year.

In morning trading Alphatec shares dove $1.91, or 43.2 percent, to $2.51. Earlier they fell to an annual low of $2.44.

Alphatec reported its results and lowered its revenue forecast after the market closed Thursday. The parent of Alphatec Spine said it lost $3 million, or 4 cents per share, in the second quarter, less than half of last year's loss of $6.3 million, or 13 cents per share. Revenue climbed 55 percent to $45.4 million from $29.4 million, with about half of that growth coming from Scient'x Groupe SA, a French company Alphatec bought in March.

However, analysts had expected a profit of a penny per share and $53.1 million in revenue, according to a Thomson Reuters poll.

Alphatec reported greater expenses related to research, sales, and administration, and also booked restructuring, amortization, and transaction costs. The company said its U.S. revenue grew 11 percent to $29.3 million, and European revenue climbed to $8.9 million from $400,000 a year ago because of the Scient'x deal. Asian revenue doubled to $5.2 million and the company reported $2 million in revenue from other regions.

However, Alphatec noted that growth in spinal device sales in the U.S. and Europe slowed down from their previous levels. Alphatec blamed the slower growth on U.S. price pressure on its core products and the unpredictability of product approvals by the Food and Drug Administration, which makes the timing of products' market release uncertain. It said, however, that it continues is experiencing strong growth in the volume of surgical procedures performed in the U.S.

The company now expects to report $177 million to $182 million in revenue this year, down from a prior forecast of $208 million to $213 million. The new outlook is well below analysts' average forecast of $206.9 million.