Press-fit fixation technique in anterior cruciate ligament (ACL) reconstruction has recently gained popularity. The objective of this study was to evaluate the initial fixation strength of human patellar tendon-bone (PTB) grafts with respect to bone-plug length and loading angle by using a femoral press-fit fixation technique.

Fourty-eight human PTB-grafts were obtained from 24 fresh frozen cadavers (mean age 72 years). The specimens were randomly assigned to two experimental groups: One with a 15 mm (n=24) and a second with a 25 mm patellar bone plug (n=24). The grafts were implanted to porcine femora in a press-fit fixation technique. Ultimate failure loads were measured at 10 mm/s at varying loading angles of 0, 30 and 60.

Biomechanical testing showed a significant difference of ultimate failure load comparing 15 mm (mean 236 N) to 25 mm (mean 333 N) bone plugs (p=0.015). In both groups, the fixation strength increased with rising loading angles. While axial graft loading exclusively caused plug dislocation, the predominant mode of failure was tendon rupture at 60 loading angle.

It is concluded that bone plug length and loading angle significantly influence the primary stability of PTB press-fit fixation in ACL reconstruction. Based on these findings, we recommend the use of patellar bone plugs with a minimum of 25 mm in length. If graft harvesting occasionally generates a patellar bone plug measuring 15 mm, restrictive postoperative rehabilitation should be advised.