Radiographic analysis of Re-Ruptures of reconstructed ACLs - Evaluation of tunnel position as a possible cause of Failure

Objectives: Previous studies detected femoral and / or tibial tunnel malpositioning as possible causes for the failure of an anterior cruciate ligament reconstruction. We investigated various radiological angles and criterias for ACL revision surgery to find possible causes for the failure of the primary reconstructed ACLs based on digital X-ray images. Materials and Methods: 529 ACL revisions after previous reconstruction were carried out between 1993 and 2013, of which we were able to include 100 patients with digital radiographs in our study. We investigated the angles of the femoral and tibial tunnel position in the coronal and sagittal plane. Furthermore we analyzed the entry point on the femur in accordance with the quadrant method described by Bernard and Hertel. We divided into: A) adequate trauma (n = 87) and non-trauma group (n = 13); B) Hamstring (n = 76) and Patella-BTB group (n = 24); C) transtibial (n = 83) and anteromedial group (n = 17). In addition we built subgroups B1/C1 adequate re-trauma or B2/C2 no adequate trauma to analyze whether there were differences in these groups. Results: The trauma group differed significantly from the non-trauma group in the measured angle of the tibial tunnel in the ap radiograph (trauma group 28.4°, non-trauma group 22.67°; p = 0.013). The Hamstring group differed significantly from the BTB group in the measured inclination angle of the femoral tunnel in the ap radiograph (HS group 54.86°, BTB group 62.78°; p = 0.015). There was also a significant difference concerning the tibial tunnel in the ap radiograph (HS group 29.56°, BTB group 21.63°; p = 0.0001). Comparing the two groups for the femoral tunnel placement-techniques we could find significant differences in the femoral ap-radiographs (inclination angle: TT = 59.04°, AM = 45.64°; p = 0.0001). The analysis of the 4 subgroups revealed differences in the tibial ap images: The BTB trauma group had an average of 23.56° relative to the BTB non-trauma group of 16.91° (p=0.013). The HS groups among themselves did not differ significantly, but the HS non-trauma group had a significantly higher angle with 29.38° to 16.91° in the BTB non-trauma group (p = 0.0003). In addition there was a significant difference when comparing the transtibial trauma group with the transtibial non trauma group (TT trauma = 27.66°, TT non trauma = 21.15°; p = 0.017) Conclusion: Overall we could only find a few significant differences in the measured angles and only a few deviations from the values described within the literature. Therefore a real trauma was necessary to rupture the reconstructed ACL in 87%. In 13% we could find a possible cause within the tibial tunnel: the steeper the tibial tunnel was, less trauma was necessary for failure, especially when using the transtibial drilling method or Patella-BTB grafts. However the small sample size limits the results therefore further studies are necessary.