Patients suffering from a rupture of the anterior cruciate ligament (ACL) with instability of the knee joint are treated with an operative ACL-reconstruction: one group of patients with a reconstruction with an autograft tendon (hamstrings), the other group with a reconstruction with an allograft tendon (tibialis posterior). The same surgical technique, the same fixation technique and the same rehabilitation protocol will be used in both groups. Follow-up will be done during 2 years.

Inclusion Criteria:

• isolated rupture of the anterior cruciate ligament with instability of the knee joint
• meniscal tear possible to suture
• partial meniscectomies

Exclusion Criteria:

• chronic laxity (more than 9 months)
• associated collateral laxity (grade III)
• subtotal or total meniscectomy
• infection or inflammatory disease of the knee joint
• large cartilage lesion