Simple test :
box=Model:Box()
box:SetPosition(0,11,0)
box:SetMass(1)
local shape = Shape:Box(0,0,0, 0,0,0, 1,1,1)
box:SetShape(shape)
box2=box:Instance()
box2:SetPosition(0,12,0)
local joint = Joint:Hinge(0,11.5,0,1,0,0,box,box2,-90,90)
or try : http://www.leadwerks.com/werkspace/files/file/451-ragdoll/
(knees and elbows are hinge joints)