US health care giant Johnson & Johnson announced on Wednesday an agreement on a $21.3-billion takeover of US-Swiss medical technology company Synthes in one of the biggest deals so far this year. The two companies \"announced that they have entered into a definitive agreement whereby Johnson & Johnson will acquire Synthes for 159 Swiss francs per share, or $21.3 billion,\" (15.7 billion euros) they said in a joint statement released on Synthes\'s website. \"The transaction is expected to close during the first half of 2012,\" the companies added. Although the deal has been approved by the boards of Synthes and Johnson & Johnson, it is still subject to approval by shareholders as well as regulatory authorities in the United States and European Union. The transaction would boost the US giant\'s medical equipment business, which made up 40 percent of its 2010 revenues. Synthes, the product of the merger in 1999 of US and Swiss firms, specialises in instruments, implants and biomaterials for use in orthopaedic surgery. It would be grafted on to Johnson\'s own orthopaedic specialist, DePuy. \"DePuy and Synthes together will create the most innovative and comprehensive orthopaedics business in the world,\" said Bill Weldon, chairman and chief executive of Johnson. \"Orthopaedics is a large and growing $37 billion global market and represents an important growth driver for Johnson & Johnson,\" he added. The deal ranks alongside US group Duke Energy\'s $25 billion proposed takeover of rival Progress Energy announced this year and behind telecommunications giant AT&T\'s proposed $39 billion acquisition of US operations of Germany\'s T-Mobile. It would also bring a huge windfall for Synthes chairman Hansjoerg Wyss, who owns about 40 percent of the company. Forbes magazine rated the 76-year-old\'s fortune at $6.4 billion in March, ranking him at 154th on its global rich list. Analysts at Zuercher Kantonalbank (ZKB) expressed surprise at the deal, noting that Wyss had been reluctant to let go until now. \"The price is towards the lower end of the range,\" they said in a note to investors.