[Biomechanical principles of after-care in replacement of the anterior cruciate ligament].

The patellar tendon graft replacing the anterior cruciate ligament undergoes histomorphological and biomechanical changes. From literature we can estimate a force of 200 N to be a critical limit of graft load after ACL-plasty in humans. The comparison with the graft loads under various conditions provided the following conclusions: Unlimited passive motion of the knee joint can be done without risk. Early weight bearing is possible. Active extension exercise against gravity could damage the graft in the range of 0 to 20 degrees of flexion in some patients. A rehabilitation protocol has to regard these biomechanical principles. In a prospective study 74 patients underwent rehabilitation according to the protocol described. An extension contracture of more than 10 degrees was seen in 9 patients. In all cases it was due to a notch-impingement or a cyclops. One year after operation 57 patients had a follow up. The side to side-difference in anterior drawer measured with a KT-1000-arthrometer was less than 2 mm in 45 patients. Six patients had difference between 2 and 4 mm. In six patients the difference was more than 4 mm.