Mexico presents a challenging course to travelers in wheelchairs or on crutches. At airports, you may encounter steep stairs before finding a well-hidden elevator or escalator -- if one exists. Airlines will often arrange wheelchair assistance to the baggage area. Porters are generally available to help with luggage at airports and large bus stations, once you've cleared baggage claim.
Mexican airports are upgrading their services, but you may still occasionally board from a remote position, meaning you either descend stairs to a bus that ferries you to the plane, which you board by climbing stairs, or you walk across the tarmac to your plane and ascend the stairs. Deplaning presents the same problem in reverse.
Escalators (and there aren't many in the country) are often out of order. Stairs without handrails abound. Few restrooms are equipped for travelers with disabilities; when one is available, access to it may be through a narrow passage that won't accommodate a wheelchair or a person on crutches. Many deluxe hotels (the most expensive) now have rooms with bathrooms designed for people with disabilities. Those traveling on a budget should stick with one-story hotels or hotels with elevators. Even so, there will probably still be obstacles somewhere. Generally speaking, no matter where you are, someone will lend a hand, although you may have to ask for it.