8 lines (7 with data), 333 Bytes

AnyVec3 v = r.r - Main.RatModel.Seg.Femur.Cut_Node.r;
AnyVar dist_fact = iffun(eqfun(r.loc,"dist"),1,0);
AnyVar prox_fact = iffun(eqfun(r.loc,"dist"),0,1);
AnyVec3 F_dist = F * dist_fact;
AnyVec3 F_prox = F * prox_fact;
AnyVec3 M_dist = (M - cross(F_dist, v)) * dist_fact;
AnyVec3 M_prox = (M - cross(F_prox, v)) * prox_fact;