Biomechanical testing of quadriceps tendon–patellar bone grafts: an alternative graft source for press-fit anterior cruciate ligament reconstruction?

Introduction: Press-fit fixation of bone-patellar tendon–bone (BPTB) grafts in anterior cruciate ligament (ACL) reconstruction has been analyzed biomechanically in previous studies; however, the use of quadriceps tendon–patellar bone (QTPB) grafts has not been studied so far. It is hypothesized that QTPB grafts provide primary fixation strength comparable to BPTB grafts in press-fit ACL reconstruction with respect to bone plug length and loading angle. Materials and methods: Fifty-two QTPB grafts were harvested from fresh human cadaver knees (mean age 73.3 years) with the length of the patellar bone plug being either 15 mm (Group I) or 25 mm (Group II). The grafts were anchored within fresh porcine femora (mean age 12 months) using a press-fit fixation technique. Forty-eight specimens were loaded to failure at 10 mm/s with varying loading angles of 0°, 30°, and 60° until failure. A microradiographic pre–post-implantation analysis was conducted on four grafts. Results: The biomechanical testing showed a significant difference in the ultimate failure loads comparing Group I (mean 224±79.3 N) to Group II (mean 339±61.4 N), both showing mean ultimate failure loads to increase with rising loading angle. The predominant mode of failure was graft pullout at axial loading and tendon rupture at 60° loading angle. The microradiographic analysis revealed an iatrogenic damage of the bone–tendon junction on the cancellous aspect of the bone plug in all trials, corresponding with the site of impactor placement during implantation. Conclusion: QTPB grafts provide a loading capability comparable to BPTB grafts in press-fit ACL reconstruction. The broad and profound area of quadriceps tendon attachment to the patellar bone plug makes graft implantation demanding.