CORTICAL VERSUS CANCELLOUS INTERFERENCE FIXATION FOR BONE-PATELLAR TENDON-BONE GRAFTS

The objective of this study was to evaluate the initial fixation stren gth of a metal interference screw (9 x 25 mm; Arthrex, Naples, FL) wit h respect to its position relative to the bone plug in anterior crucia te ligament reconstruction using a bone-patellar tendon-bone graft. Po rcine lower limbs were used. In group 1 (n = 20) the screw was placed adjacent to the cortex of the bone plug. In group 2 (n = 20) the screw was placed between the cancellous surfaces of the tibial tunnel and t he bone plug. Specimens were loaded to failure using an universal mate rial testing machine. Failure mode was defined by visual analysis of t he specimens after loading. Primary fixation strength was not signific antly different for both groups. Maximum force was 779 +/- 179 N (grou p 1, cortical side) and 743 +/- 143 N (group 2, cancellous side). Ther e was a difference in failure modes. In group 1, testing resulted pred ominantly in tendon ruptures and bone plug fractures (70%). In group 2 , bone plug pullouts were predominant (75%). From these data we conclu de that the position of the screw relative to the bone plug influences failure mode but not the initial fixation strength.