Per UA.com,
they are not responsible for "Damage to wheels, feet, extending handles and items of fragile or perishable nature", among other things.
However, I would send a customer care note because that's severe damage. If they still don't offer any help (and tell you you needed to contact the unhelpful airport), I'd contact the Better Business Bureau and see if you can get any help. When I had issues with incorrect mileage charges for award tickets (and many agents unwilling to correct the issue), they corrected the issue within 24 hours of my contacting the BBB.