STRUCTURAL CAPACITY OF THE KNEE TO ANTERIOR CRUCIATE LIGAMENT FAILUREDURING QUADRICEPS CONTRACTION - AN IN-VIVO STUDY IN THE RAT

The effect of quadriceps contraction on the structural capacity of the knee joint loaded to anterior cruciate ligament (ACL) failure was stu died in an in vivo rat model. In both knees of 20 rats the joint capsu le and ligaments, except the ACL, were cut and the menisci resected by microsurgery. The rats were randomized to destructive testing of thei r ACLs either by femorotibial distraction or by anterior tibial transl ation at a displacement rate of 2.5 mm s(-1) (60% s(-1)). The knee fle xion during testing was 60 degrees. During loading of the right ACL, q uadriceps contraction was induced by electrical stimulation of the fem oral nerve. As control, the ACL of the left knee was loaded with relax ed quadriceps. The ultimate load for the knee to ACL failure when test ed in tension by femorotibial distraction during quadriceps contractio n was 140% higher than tested with the muscles relaxed (p = 0.0001). E nergy absorption at failure during muscle contraction was 274% higher (p = 0.0001), and the linear stiffness increased by 59% (p = 0.0004). During testing by anterior tibial translation, neither linear stiffnes s nor ultimate load changed significantly, but the energy absorbed at failure was 46% (p = 0.02) higher during quadriceps contraction compar ed to testing with the quadriceps relaxed. These results showed that q uadriceps contraction substantially increased the load carrying capaci ty of the rat knee subject to ACL failure when loaded by femorotibial distraction, but less when it was loaded by anterior tibial translatio n. Copyright (C) 1996 Elsevier Science Ltd.