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”).

ZELTIQ Aesthetics Inc. (NASDAQ:ZLTQ) earns a F (“strong sell”) this week, moving down from last week’s grade of D (“sell”). In Portfolio Grader’s specific subcategories of Equity and Cash Flow, ZLTQ also gets F’s. The stock price has fallen 24.5% over the past month, worse than the 4.8% decrease the Nasdaq has seen over the same period of time. To get an in-depth look at ZLTQ, get Portfolio Grader’s complete analysis of ZLTQ stock.

This week, RTI Biologics (NASDAQ:RTIX) falls to a D (“sell”), worse than last week’s grade of C (“hold”). RTI Biologics processes human and animal musculoskeletal tissues in producing allograft and xenograft implants. The stock price has fallen 6% over the past month. The stock currently has a trailing PE Ratio of 27.90. For a full analysis of RTIX stock, visit Portfolio Grader.

The rating of Staar Surgical (NASDAQ:STAA) declines this week from a D to a F. Staar Surgical develops, manufactures, and markets high margin visual implants that improve a patient’s quality of vision. The stock also gets an F in Earnings Growth. Share prices fell 24% over the past month. The stock’s trailing PE Ratio is 521.00. For more information, get Portfolio Grader’s complete analysis of STAA 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.