Johnson & Johnson (NYSE:JNJ) is recalling its DePuy Synthes radial head prosthesis because of the risk of loosening in the component that anchors the implant in the arm’s radius bone.

The entire prosthesis is designed for primary and revision replacement of the radial head, but only the radial stem surgeons insert into the radius is involved in the loosening issue, according to a letter the J&J unit sent to physicians Dec. 30, 2016.

“Based on the currently available data, we believe the cause to be multifactorial (including possible product characteristics, operative and patient factors), but we have not been able to fully characterize these factors. Consequently, we have not been able at this time to issue further instructions to surgeons that might lead to a reduction in issue rate and have decided to remove the DePuy Synthes Radial Head Prosthesis Stem from the global market,” the company wrote.

If the radial stem loosens, the risks include osteolysis, poor joint mechanics, pain, post-operative fracture and soft tissue damage, J&J said.

Patients already implanted with the device should be followed as normal and the device will still be available on request for revision surgeries “in which only the head would be replaced using the evaluation or loaner set programs only,” according to the letter.