LIGAMENT CREEP CANNOT BE PREDICTED HORN STRESS-RELAXATION AT LOW-STRESS - A BIOMECHANICAL STUDY OF THE RABBIT MEDIAL COLLATERAL LIGAMENT

In normal daily activity ligaments are probably subjected to repeated loading rather than to repeated deformation. The viscoelastic response to repeated loading is creep; this effect has significance for ligame nt reconstructions. which potentially ''stretch out'' over time. Howev er, most experimental studies have examined the viscoelastic response to repeated deformation. stress relaxation. We hypothesized that the c reep of a ligament could be predicted from its stress-relaxation behav iour. Left and right medial collateral ligaments of eight skeletally m ature rabbits were subjected to either creep or stress-relaxation test ing under comparable conditions. The time-dependent increase in strain (creep) and reduction in load (relaxation) from the tests mere modell ed with use of the quasilinear viscoelastic theory and generalized sta ndard linear solid modelling. Ligaments were found to creep distinctly less than would be predicted from relaxation tests. Although the reas on for this behaviour remains unknown, we speculate that it is due to the progressive recruitment of collagen fibres during creep.