EFFECT OF PRECONDITIONING ON THE VISCOELASTIC RESPONSE OF PRIMATE PATELLAR TENDON

Current techniques for anterior cruciate ligament reconstruction with patellar tendon (PT) allow a measurable tension to be applied to the g raft at the time of fixation. The viscoelastic nature of the PT, howev er, ensures that relaxation will cause the graft tension to decrease o ver time. To better understand this process, a primate model was used to evaluate acute viscoelastic relaxation in the PT. Thirty-five patel la-patellar tendon-tibia (P-PT-T) complexes were harvested from normal primate knees (Cynomolgus monkeys), and were divided into five groups for mechanical comparison. Specimens were subjected to two 10-min rel axation tests separated by a 1-30-min unloaded interval. The first tes t provided baseline relaxation data as well as serving as precondition ing for the second test. Results indicate that preconditioning signifi cantly reduces the tension lost in a graft due to viscoelastic relaxat ion. The effect of preconditioning is reduced with increasing recovery time (the time between preconditioning and the second relaxation test ), but the effect is still significant after 30 min of unloading. No d ifferences were observed in the relaxation behavior of specimens that were cyclicly or isometrically preconditioned, nor were differences ob served between irradiated and nonirradiated specimens. These results s uggest that preconditioning can reduce acute tension loss in a graft d ue to viscoelastic relaxation and that simple isometric preconditionin g is just as effective as cyclic stretching.