There are two types of leg length discrepancy, actual and perceived, actual can be checked by physio for you.
​Surgeon if he was doing his job correctly should have checked,
​Procedure, lying on back, on hard table or bench, you must be straight through feet, ankles, knees, hips, shoulders, best way to check is for someone to stand at your feet, and check for you lying straight, then you draw up your knees towards the roof, with ankles as far as you can go towards your bum, keeping your feet flat on the table, again you need someone to check your ankles are even distance to pelvis or bum.
​Only then can you see a leg length difference, looking down your body, knee height is lower leg, and friend or family looking from the side, one kneecap in front of other upper leg difference.
​Other way to check is with a tape measure, on the front of your pelvis near your waist is a prominent point on pelvic bone, end of tape measure there, other point is prominent ankle bone or point inside of ankle, use both points for both legs, physio did mine and came back with 22mm or 3/4 inch difference, that is how I learnt so much about this issue, and surgeon, different one to surgeon who did my surgery, showed me how he measured LLD.
​Percived, - weakness of muscles in and around pelvis, butt crunches are only part of the exercises needed, you also need to be doing clam shell exercise, even if you cannot do it, the fact you are trying exercises the right muscles, the trick is to get advice about how to do it correctly, I was shown by physio, and also how to feel the muscle twitching, even if you cannot lift your leg, the lift comes with time and lots of practice and strengthening of the muscle.
​As the 2nd surgeon told me, in 12 months you will not know your old self, he was right.
​But in my case I do have to wear a shoe lift on my opposite foot as with a lot of research my issues were found to be a natural LLD in lower leg of 10mm and 12mm added when surgeon did hip replacement, only 12mm needed to be corrected as the 10mm natural had been with me my entire life, had grown with it from childhood.
Hopefully this some help for others with LLD.