Blackstone Group L.P. has agreed to buy a stake in China's Xinrong Best Medical Instrument Co, the U.S. private equity firm said in a statement on Tuesday.

Blackstone did not give the size of the stake or other financial details.

A person with direct knowledge of the matter said Blackstone is investing around $100 million in the company, which makes orthopaedic implants. The person declined to be identified as details of the transaction were private.

Boston Consulting Group projects the China orthopaedic implant market to grow to $4.1 billion in 2020 from $1.3 billion in 2013, driven by an ageing population and increasing affordability of treatment.