Restructuring charges (Details) (USD $)	3 Months Ended	12 Months Ended					3 Months Ended
	Jun. 30, 2010 2008 plan	Dec. 31, 2010 2009 plan	Dec. 31, 2010 2010 plan	Dec. 31, 2011 Employee severance cost	Dec. 31, 2010 Employee severance cost	Dec. 31, 2010 Employee severance cost 2010 plan	Dec. 31, 2010 Employee severance cost 2010 plan Spine	Dec. 31, 2010 Employee severance cost 2010 plan Orthopedics
Restructuring charges
Recognition of restructuring expenses	$ 3,600,000						$ 400,000	$ 3,200,000
Restructuring charges recorded in selling and marketing expenses			1,600,000
Restructuring charges recorded in general and administrative expenses			2,000,000
Changes in the restructuring liability
Balance at the beginning of the period				1,638,000	1,826,000
Charges under authorized plans		3,550,000				3,550,000
Cash payments				(1,638,000)	(3,738,000)
Balance at the end of the period					$ 1,638,000