The Food and Drug Administration has issued a warning letter to orthopedic maker Smith & Nephew PLC over manufacturing problems uncovered at a plant in Germany earlier this year.

Government inspectors visited the company's Tuttlingen, Germany plant in July and cited the company for several quality control problems, according to a warning letter dated Dec. 21. The plant manufactures replacement hip implants.

According to the letter, Smith & Nephew failed to document a number of important production steps, including quality tests and corrections to device parts manufactured at the plant. London-based Smith & Nephew responded to the agency's citations in August, but the FDA's warning letter says that response was inadequate.

The FDA asks the company to respond to its letter within 15 business days, outlining a plan to correct the problems.

Calls placed to Smith & Nephew for comment were not immediately returned.

The FDA regularly issues warning letters to companies that don't follow regulations for manufacturing and marketing drugs, medical devices and other products. The letters are not legally binding, but the FDA can take companies to court if they are ignored.

Shares of Smith & Nephew fell 28 cents to $51.89 in Tuesday afternoon trading.