An investigation for ten major trusts showed knee implants were sold to one for 634 and 1,109 to another.

Of its key franchises, knee implants rose by 6 per cent, about double the market rate.

This contains hip and knee implants and last year generated revenues of more than $2.2 billion.

Knee implants fell by 47 per cent and hip implants by 27 per cent.

Revenue from knee implants fell 10.6 per cent in the first quarter and hip implants by 8.6 per cent.