Prostaglandin E2 production by the membrane surrounding loose and fixated cemented tibial hemiarthroplasties in the rabbit knee.

Sixteen mature New Zealand female rabbits had cemented, tibial hemiarthroplasty of the right knee (correction of hip) using a stemmed, fluted, titanium-alloyed, condylar type prosthesis. In the fixated prosthetic group (eight rabbits), a 1.5-cm3 doughy bolus of polymethylmethacrylate (PMMA) was used to cement the prosthesis firmly. In the loose group (eight rabbits), the cement was allowed to cure ex vivo on the implant; the prosthesis was then implanted and rotated to ensure that it was loose fitting. Roentgenograms performed postoperatively and at three months were graded for new lucent lines. The implant area was harvested aseptically and cultured during a three-day period, and the cumulative collection of tissue culture supernatants was assayed for prostaglandin E2 (PGE2). The mean cumulative grading of new lucent lines was 0.4 +/- 0.2 (mean +/- SEM) for the fixated prosthetic group and 2.3 +/- 0.5 for the loose prosthetic group. Specimens from the nonloose group produced 8.85 +/- 1.44 ng of PGE2 on the right prosthetic side, and 17.29 +/- 3.72 ng of PGE2 on the left, nonimplanted side. Specimens from the loose prosthesis group produced 52.35 +/- 16.28 ng of PGE2 on the right prosthetic side and 17.29 +/- 3.72 ng of PGE2 on the left, nonimplanted side. Increased PGE2 production relative to fixated prostheses was noted in the membranes surrounding loose prostheses. The left, nonimplanted sides were not statistically different. Roentgenographic and biochemical evidence indicates that a cemented tibial hemiarthroplasty implanted in the rabbit knee can provide a short-term model of arthroplasty loosening.