Analysis of strain distribution in the menial collateral ligament using a photoelastic coating method

The strain distribution over the entire medial collateral ligament (MCL) wa s measured using a photoelastic coating method. This new approach utilized a polyurethane monomer as a photoelastic coating film. The initial experime nts investigating MCL strain measurement showed that this film had a high s ensitivity for strain and good adhesion to the ligament. It was confirmed t hat strain distribution could be obtained qualitatively over the entire lig ament using this method. The mechanism of MCL injury was studied by applyin g this polyurethane coating film to the entire MCL in a femur-MCL-tibia com plex. When simple tension was applied to the complex, strain concentrations were centred at the tibial insertion site, and all the specimens ruptured at the MCL tibial insertion site. With application of a valgus bending mome nt, increased strain was seen in the MCL from the medial femoral condyle to the medial epicondyle, Histological analysis demonstrated midsubstance lig ament ruptures in this same region. For both tests, rupture sites and incre ased strain concentration sites correlated, In addition, an impingement phe nomenon of the MCL on the medial femoral condyle can be seen during applica tion of valgus force, and this phenomenon may explain the higher incidence of MCL injuries on the femoral side seen in the clinical setting. This poly urethane coating method allows for direct and visual measurements, and can qualitatively measure the strain behaviour over the entire MCL surface, Thi s new technique represents a significant improve ment over previous point-b y-point strain measurement methods. (C) 1999 IPEM. Published by Elsevier Sc ience Ltd. All rights reserved.