The Penn method measures joint laxity — how much the hip can be distracted from the socket — and expresses it as a number rather than a subjective grade. Because laxity is measurable in a young dog, it can be performed from around sixteen weeks of age, and the result is comparable against a breed-wide distribution rather than being a pass or a fail.
What that buys an owner is time. A puppy whose laxity sits at the tighter end of the range can be treated as an ordinary athletic dog. A puppy whose laxity sits at the looser end is a dog whose weight should be managed tightly from the start, whose long descents and repetitive high-impact work should be deferred, and whose owner should have an orthopaedic conversation at four rather than at eight. None of that reverses genetics. All of it affects when a marginal joint starts hurting.
There are honest caveats. It requires sedation or general anaesthesia and has to be done by a veterinarian certified in the method, so it is not something a general practice can necessarily offer on request. It costs more than a routine visit. And a favourable number is not a guarantee any more than an unfavourable one is a sentence.
But Philadelphia is the one city where the method's home institution is local, the practitioners are comparatively easy to find, and an owner can reasonably expect the conversation to be a familiar one rather than an unusual request. For a breed with hip dysplasia on its documented list, that is a real and specific local advantage.