PULLOUT STRENGTH OF TIBIAL GRAFT FIXATION IN ACL-REPLACEMENT WITH A PATELLAR TENDON GRAFT - INTERFERENCE SCREW VERSUS STAPLE FIXATION IN HUMAN KNEES

The endoscopic single incision technique for ACL reconstruction with a femoral half-tunnel may lead to a graft/tunnel mismatch and subsequen t protrusion of the block from the tibial tunnel. The typical tibial f ixation with an interference screw is not possible in these cases. Fix ation with staples in a bony groove inferior to the tunnel outlet can be used as an alternative technique. Current literature does not provi de biomechanical data of bath fixation techniques in a human model. Th is study was performed to evaluate primary biomechanical parameters of this technique compared to a standard interference screw fixation of the block. 55 fresh-frozen human cadaver knee joints of a younger age (mean age: 44 years) were used. Grafts were harvested from the patella r tendon midportion with bone blocks of 25 mm length and 9 mm width. A 10 mm tibial tunnel was drilled from the anteromedial cortex to the c enter of the tibial insertion of the ACL. 3 different sizes of interfe rence screws (7 x 30, 9 x 20 and 9 x 30 mm) were chosen as a standard control procedure (n = 40). For tibial bone-block fixation the graft w as placed through the tunnel, the screw was then inserted on the cance llous or the cortical surface respectively. 15 knees were used far sta ple fixation. A groove was created inferior to the tunnel outlet with a chisel. The bone block was fixed in this groove with 2 barbed stainl ess steel staples. Tensile testing in both of the groups was carried o ut under axial load parallel to the tibial tunnel in a Zwick-testing-m achine with a Velocity of 1 mm/sec. Dislocation of the graft and stiff ness were calculated at 175 N load. Maximum load to failure using inte rference screws varied between 506 and 758 N. load to failure using st aples was 588 N. Dislocation of the graft ranged between 3.6 and 4.7 m m for interference screw fixation and was 4.2 mm for staples. With bot h fixation techniques, the recorded failure loads were sufficient to w ithstand the graft loads which are to be expected during the rehabilit ation period. Staple fixation of the bone block outside of the tunnel resulted in fixation strength comparable to interference screw fixatio n.