▁give ▁them ▁inher ent ▁stability ▁and ▁an ▁almost ▁vac u um ▁effect ▁that ▁keeps ▁the ▁joint ▁surfaces ▁together . ▁ ▁Al ong ▁with ▁the ▁c ran ial ▁cru ci ate ▁lig ament , ▁the ▁other ▁soft ▁t issue ▁structures ▁stabil ising ▁the ▁st if le ▁are ▁the ▁ca ud al ▁cru ci ate ▁lig ament ▁and ▁the ▁two ▁men is ci , ▁all ▁of ▁which ▁are ▁int ra - art icular ▁( with in ▁the ▁joint ), ▁and ▁the ▁two ▁coll ater al ▁lig aments ▁( external ▁to ▁the ▁joint ). ▁ ▁Mus cle ▁tone ▁through ▁the ▁quadr ice ps , ▁ham string ▁and ▁cal f ▁mus cles ▁play ▁a ▁significant ▁role ▁in ▁the ▁forces ▁acting ▁on ▁the ▁joint . ▁ ▁C ran ial ▁cru ci ate ▁lig ament ▁The ▁c ran ial ▁cru ci ate ▁lig ament ▁is ▁composed ▁of ▁two ▁bands , ▁a ▁c ran iom ed ial ▁band ▁and ▁a ▁ca ud ol ater al ▁band . ▁It ▁functions ▁to ▁stop ▁c ran ial ▁( an terior ) ▁movement ▁of ▁the ▁tib ia ▁with ▁respect ▁to ▁the ▁fem ur , ▁hyp ere xt ension ▁of ▁the ▁st if le ▁joint ▁and ▁internal ▁rotation ▁of ▁the ▁tib ia . ▁The ▁c ran ial ▁cru ci ate ▁lig ament ▁is ▁thought ▁to ▁be ▁able ▁to ▁resist ▁a ▁force ▁equivalent ▁to ▁four ▁times ▁the ▁weight ▁of ▁the ▁dog ▁before ▁it ▁ru pt ures , ▁but ▁often ▁the ▁lig ament ▁is ▁weak ened ▁by ▁ar th rit is ▁that ▁is ▁present ▁in ▁the ▁joint