Osteochondral mosaicplasty is a popular procedure for the repair of focal lesions of the articular surface. During this procedure, one or more cylindrical osteochondral autografts are press-fit into pre-drilled holes within the articular surface in order to achieve primary graft fixation. Strength of the press-fit created by osteochondral mosaicplasty was examined immediately after and seven days following the procedure in an in-vitro animal model.
Mosaicplasty was performed on five pairs of porcine femurs within one and a half hours of animal sacrifice. Push-in and pull-out strength tests were performed on specimens from one leg immediately following surgery. Indentation tests were also performed to determine cancellous bone modulus used to monitor biomechanical bone viability. The remaining specimens, matched for location in the contralateral leg. were incubated in tissue culture media for seven days prior to performing the same set of mechanical tests. The identical protocol was performed on three pairs of dead porcine femurs to investigate the feasibility of using dead tissue for biomechanical testing.
Press-fit strength of dead tissue declined 55% from an average of 97.6 N to 45.8 N over seven days: however, cancellous bone modulus also declined 55% indicating a loss in biomechanical viability and verifying the necessity of live tissue for the biomechanical testing. Press-fit strength in live tissue decreased 44% over the seven-day period from an average o f 135.7 N to 75.5 N while cancellous bone modulus did not change. These results suggest that initial fixation strength does not represent the minimum load bearing capacity of the graft: rather, press-fit strength declines significantly pricr to the increase in load bearing capacity that occurs with bony ingrowth.
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