. ▁Ar th rit is ▁inf ers ▁infl amm ation ▁of ▁the ▁joint ; ▁in ▁this ▁condition ▁there ▁is ▁the ▁production ▁of ▁a ▁joint ▁fluid ▁that ▁is ▁less ▁vis c ous ▁and ▁therefore ▁less ▁able ▁to ▁abs orb ▁shock ▁than ▁normal ▁fluid . ▁ ▁J oint ▁fluid ' s ▁other ▁role ▁is ▁to ▁provide ▁nut r ition ▁to ▁the ▁cart il age ▁and ▁the ▁cru ci ate ▁lig aments . ▁The ▁situation ▁is ▁a ▁little ▁like ▁a ▁ch icken - and - eg g ▁scenario : ▁it ▁is ▁usually ▁accepted ▁that ▁the ▁c ran ial ▁cru ci ate ▁lig ament ▁ru pt ures ▁because ▁ar th rit is ▁has ▁caused ▁the ▁lig ament ▁to ▁weak en ▁because ▁of ▁poor ▁joint ▁fluid ▁characteristics , ▁but ▁what ▁causes ▁the ▁ar th rit is ▁in ▁the ▁first ▁place ▁– ▁a ▁partial ▁cru ci ate ▁te ar ? ▁ ▁The ▁situation ▁is ▁dis similar ▁to ▁that ▁seen ▁in ▁human ▁athlet es ▁where ▁over extension ▁of ▁the ▁joint ▁st ret ches ▁the ▁c ran ial ▁cru ci ate ▁lig ament ▁to ▁failure , ▁and ▁replacement ▁of ▁the ▁lig ament ▁with ▁a ▁fas cial ▁prost h esis ▁has ▁a ▁good ▁pro gn osis ▁for ▁return ▁to ▁full ▁function . ▁ ▁Men is ci ▁The ▁men is ci ▁are ▁the ▁other ▁int ra - art icular ▁structures ▁that ▁help ▁to ▁stabil ise ▁the ▁joint ▁and ▁help ▁to ▁dist ribute ▁load ▁even ly ▁across ▁the ▁surfaces ; ▁these ▁are ▁cres cent - sh aped ▁disc s ▁of ▁cart il age ▁facing