Effect of Ligament Stiffness on Spinal Loads and Muscle

Abstract

Ligamentsassistmusclesinstabilizingthespinewithinphysiologicalrangesofmotionbylimitingthedisplacements,buttheroleof ligamentsinspinalloadsandmuscleforcedistributionremainsunknown.Thepurposeofthisstudywastoinvestigatetheeffectof differentstiffnessonjointresultantforcesandmuscleforcesindifferentflexedpositions.Forthisstudy,fiveligamentstiffnesssets weredeterminedfromtheliteratureandappliedtoamusculoskeletalspinemodel.Thedimensionsofthemodelwereadjusted accordingtosubjectsintheinvivoexperimentsusedforvalidation,andspinalloadsandmuscleforcesweredeterminedduringflexed positions.Thedifferencesbetweenthespinalloadsduetodifferentligamentstiffnesseswereinsignificant(maximumdifference12%). However,thedifferentligamentstiffnessesshowedastrongeffectonindividualmuscleforces.Amongtheshortmuscles,lumbar multifidiexertedonly65Nwithoutligamentsbuttheforceincreasedupto254Nduetoaddingthemaximumligamentstiffness. However,theloadintheerectorspinaewassignificantlydecreased(30%).Theresultsofthisstudyshowedthatinadditiontolong andsuperficialmuscles,ligamentsalsoplayedanimportantroleinstabilizingthespineinflexedpositions.