This week, the overall grades of three medical devices stocks are lower, according to the Portfolio Grader database. Each of these rates a “D” (“sell”) or “F” overall (“strong sell”).

This week, BIOLASE, Inc. (BIOL) falls to a D (“sell”), worse than last week’s grade of C (“hold”). BIOLASE develops, manufactures, and markets lasers systems for dental and medical applications and procedures in the United States and internationally. In Portfolio Grader’s specific subcategories of Earnings Revisions, Equity and Sales Growth, BIOL also gets an F. As of Jan. 17, 2014, 14.3% of outstanding BIOLASE, Inc. shares were held short. For a full analysis of BIOL stock, visit Portfolio Grader.

Stryker Corporation (SYK) gets weaker ratings this week as last week’s C drops to a D. Stryker produces a variety of products in the medical technology sector. The stock also gets an F in Earnings Growth. The stock’s trailing PE Ratio is 33.60. To get an in-depth look at SYK, get Portfolio Grader’s complete analysis of SYK stock.

Volcano Corporation’s (VOLC) rating falls this week to an F (“strong sell”), down from last week’s D (“sell”). Volcano designs, develops, manufactures and commercializes a suite of intravascular ultrasound (IVUS) and functional measurement (FM) products that enhance the diagnosis and treatment of vascular and structural heart disease. The stock gets F’s in Earnings Growth, Earnings Revisions and Margin Growth. The stock price stands at $21.00, on the rise for the past two days. As of Jan. 17, 2014, 17.7% of outstanding Volcano Corporation shares were held short. For more information, get Portfolio Grader’s complete analysis of VOLC 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.