Bilateral means having both great toes (or both whatevers) done at the same time. So, in this case, it would mean having both great toe joints fused during the same operation. Also as in bilateral bunionectomies (having both bunions removed at same time), bilateral cheilectomies (having both great toes cleaned and shaved at the same time), etc. Bilateral is both as opposed to unilateral which is one (bi= two, uni = one). Get it?