Control of the acute-phase serum amyloid A and C-reactive protein response: comparison of total replacement of the hip and knee.

The acute-phase serum protein response induced by arthroplasty of the knee was compared with that induced by arthroplasty of the hip in patients with rheumatoid arthritis (RA). Total replacement of the knee (n = 13) caused a markedly greater serum amyloid A protein (SAA) (P less than 0.001) and C-reactive protein (CRP) (P less than 0.001) elevation that did total replacement of the hip (n = 13). This effect was not merely due to the use of tourniquet in the knee arthroplasties, since synovectomy of the knee, matched for the duration of the use of tourniquet, induced an SAA response that was significantly lower (P less than 0.001) than that caused by replacement of the knee; the SAA response after knee synovectomy was similar to that after hip arthroplasty. The kinetics and magnitude of the SAA response in patients with reactive amyloidosis were similar to those found in RA patients without amyloidosis. The results show that replacement of the knee is a stronger stimulator of SAA and CRP elevation than replacement of the hip. Thus, total replacement of the knee, possibly due to the performance of the arthroplasty under ischaemic conditions, appears to be more traumatic to the organism than total replacement of the hip.