The ratings of three Medical Devices stocks are down this week, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

Given Imaging’s (NASDAQ:GIVN) rating falls to a D (“sell”) this week, down from C (“hold”) the week prior. Given Imaging has developed a proprietary wireless imaging system that allows a medical professional to examine the gastrointestinal tract. GIVN also rates an F in Portfolio Grader’s specific subcategory of Earnings Surprise. For a full analysis of GIVN stock, visit Portfolio Grader.

Greatbatch’s (NYSE:GB) rating weakens this week, dropping to a D versus last week’s C. Greatbatch develops and manufactures power sources, feedthroughs, and wet tantalum capacitors used in implantable medical devices. The stock gets F’s in Earnings Growth, Earnings Momentum, and Margin Growth.

To get an in-depth look at GB, get Portfolio Grader’s complete analysis of GB stock.

Tornier (NASDAQ:TRNX) ratings are on the decline this week as the company earns an F (“strong sell”). Last week, it received a D (“sell”). Tornier designs, outsources the manufacture of and markets orthopedic products. The stock gets F’s in Earnings Momentum and Earnings Revisions. For more information, get Portfolio Grader’s complete analysis of TRNX stock.

Louis Navellier’s proprietary Portfolio Grader stock ranking system assesses roughly 5,000 companies every week based on a number of fundamental and quantitative measures. Stocks are given a letter grade based on their results — with A being “strong buy,” and F being “strong sell.” Explore the tool here.