Failure load of patellar tendon grafts at the femoral side: 10- versus 20-mm-bone blocks

The aim of the study was to investigate whether use of short bone blocks is safe in anterior cruciate ligament (ACL) reconstruction. Our hypothesis was that the smaller 10-mm-length bone blocks will fail at lower loads than 20-mm-bone blocks. Ten paired human cadaver knees were randomly assigned to the 10- or 20-mm group (group 1 and 2) and underwent bone–patellar tendon–bone femoral fixation with interference screw. Tensile tests were performed using a tensile testing machine (Instron). Stiffness, failure load and failure mode were recorded. Median stiffness was 72 N/mm (16–103) for 10-mm-bone blocks and 91 N/mm (40–130) for 20-mm-bone blocks. Median failure loads were 402 N (87–546) for 10-mm-long bone block and 456 N (163–636) for 20-mm-bone blocks. There was no statistically significant difference between groups (P = 0.35). All bone–patellar tendon–bone grafts were pulled out of the femoral tunnel with interference screw, due to slippage. We concluded that a 10-mm-long bone block was not significantly weaker than a 20-mm-long bone block. Failure loads of a 10-mm-bone block exceeded loading values at passive and active extension of the knee under normal conditions. Ten millimetre bone blocks offered sufficient fixation strength in ACL reconstruction.