Synthetic Bone Graft Substitute vs. Autologous Spongiosa in Revision Anterior Cruciate Ligament Reconstruction

\* Study design: Monocentric, prospective, randomised study. Patients who need revision anterior cruciate ligament reconstruction and show a tunnel enlargement of \>10mm will have a first operation filling the tibial/femoral tunnel either with bone graft substitute (Actifuse) or autologous spongiosa. 5 - 6 months after this first operation a CT will be performed to assess the bony consolidation of the former tibial/femoral tunnel. An MRI will be performed to assess vitality of the bone substitute. An osseous biopsy will be taken from the tibial/femoral tunnel at the revision anterior cruciate ligament reconstruction approximately 6 months after bone grafting. Clinical evaluation will be performed 6 weeks, 3 months and 6 months postoperative. At 6 months postoperative additional radiological evaluation and clinical assessment using the SF36 questionnaire will be performed. * Treatment: Either autologous spongiosa or Actifuse (MIS applicator) will be administered by the investigator as a bone graft substitute for tunnel enlargement in patients undergoing revision anterior cruciate ligament reconstruction. * Duration of Participation: The participation of each subject will be approximately 12 months. Each subject will undergo revision anterior cruciate ligament reconstruction approximately 6 months after bone grafting. A biopsy will be taken at this operation. A clinical and radiological follow up is planned for further 6 months. \* Subjects: Male and female patients ≥ 18 years. Approximately 40 patients who undergo revision anterior cruciate ligament reconstruction will be included in the study. Inclusion criteria: Patients in need of revision anterior cruciate ligament reconstruction Exclusion criteria: Infection, wound healing complications