In vitro monitoring of rabbit anterior cruciate ligament damage by acoustic emission.

Anterior cruciate ligament (ACL) rupture is a major clinical problem leading to instability and degeneration of the knee joint. The problem is compounded by the limited ability of the ACL to heal when ruptured. The existing knowledge regarding the way the ACL ruptures is limited, and this investigation is an attempt to understand the nature of the ruptures using the rabbit as a model. A total of 16 rabbit tibia-ACL-femur complexes were stretched in tension to complete rupture. Four specimens were stretched to failure at a displacement rate of 0.5 mm/min and 12 specimens at 10 mm/min. Acoustic emission (AE) transducers were placed on both the tibia and the femur, and stress wave signals generated during the tensile test were recorded. Fibre fractures produced the highest amplitude signals with a relatively longer rise time. Other failure modes such as matrix failure and debonding produced lower amplitude signals with shorter rise times. We also noted that few events were recorded during the initial period of tensile loading (the elastic phase). The activity then increased significantly after maximum load was reached. The location information provided by the acoustic emission system was consistent with the final site of rupture. We have shown that AE can be used to characterise ligament damage, with fibre pull-outs and fibre fracture producing the highest signal amplitudes.