Review of Clancy's article on anterior and posterior cruciate ligament reconstruction in rhesus monkeys

The Classic revisits a landmark paper by Clancy and colleagues ‘Anterior and posterior cruciate ligament reconstruction in rhesus monkeys—a histological, microangiographic and biomechanical analysis’, published in 1981 in the Journal of Bone and Joint Surgery. At that time, this publication offered new and clinically relevant information on the fate of autogenous patellar tendon grafts inserted through bone tunnels for anterior cruciate ligament (ACL) and posterior cruciate ligament (PCL) reconstructions in young adult rhesus monkeys. The microangiographic, histological and biomechanical findings have largely been confirmed by subsequent research work. The findings remain relevant today and go some way to explaining the high failure rates in the first 12 months following reconstructive surgery. Vascularisation of the graft occurred early as well as progressive improvement of the load to failure for the femur-ACL graft-tibia complex under uniaxial tensile testing. Failure occurred in the graft substance and not the attachment sites. The implication is that the improvement with time reflects graft remodelling. The findings illustrate the great potential of a devascularised biological graft that remodels over time. However, despite the capacity to remodel, there remains a clear deficit of the tensile strength and stiffness as compared with the original ACL. The low strength was discussed to be one explanation to the high failure rates with graft ruptures within the first year following reconstruction. This classic publication was the first to demonstrate the process of graft vascularisation, microscopic changes and biomechanical recovery following surgery—all time dependent and imperfect. What is certain is that ‘man’ is a biological creature and that the findings of this study acknowledge this and the wise clinician takes note.