Your best option is to see an Orthopeadist.
Our daughter has a leg length discrpancy of over 2 inches. Looking at your sons legs alone doesn't give you a positive answer of how short one leg is, what looks like good even hip placement to you may not actually be that. When you go to the Ortho they will order X-rays, a CAT scan or MRI to measure the bones and look at the growth plates.
In our daughters case she was a 2 month premature monoamniotic twin with TTTS (she was lucky to be born alive) in the NICU she had a blood clot that compromised her blood flow and in turn the growth plates in her right leg are trying to close early.
If there is a LLD then your options are based on WHAT is causing the discrepancey.
In our case, she has been through 3 surgeries. 1 to fix a patellular dislocation (caused by the same problem as the LLD), the 2nd one to open the femural growth plate up and fix angulation to the leg caused by the growth plate closing. We had a 3rd surgery which was intended to try to open up the growth plate on the tibia & fibula as well as remove a bar on the femural growth plate, then to affix an external fixator. All that was accomplished was the tibial & fibular growth plates being close (ie. no more growth on that part of the leg) and the bar being removed on the femural growth plate (that part of the leg will continue to grow). Due to the prior surgery there wasn't enough bone to attach the fixator so will be applied for growth in a year (when our daughter is 8). She will have 2 surgeries to her tibia & fibula to lengthen that part of her leg, the plan is to have the 1st when she is 8 and the 2nd when she is closer to 13 or 14. If her femur continues to grow then we won't have to lengthen it.
Be proactive, have this looked at immediately so you know exactly what you are dealing with. It's possible if something is causing your sons leg to not grow you can get it fixed NOW so he doesn't develop a bigger LLD.
Had we been warned that the compromised blood flow in the NICU could cause these problems we could have caught it sooner and not have gone through the number of surgeries we have and will continue to go through. If nothing more than for peace of mind... have your son looked at.
Sorry for the novel :o)
i worked for a regular ortho surgeon for a while. people use to bring kids all the time, even tho hes not pediatric.
we had a year and a half boy once. one of his legs was shorter. first the ortho doc, wanted to establish which bone is shorter - hip to knee or knee to ankle. hip xrays showed nothing, which is a good thing. this little boys problem was in the knee to ankle bone ( right leg). the bone was an inch shorter.
the parents were advised of their options - wait and see if anything changes. if no positive changes happen than there are 2 options: wait till the boy reaches a certain age where the healthy leg bone grew enough for him to be average hight at least. than stoppin the growth of the healthy leg, by cutting of a nerve or a muscle (i dont remeber exactly what the cut to stop growth, sorry). and than they just wait for the second (short) leg to catch up.
second option was - im sure u've see this procedure done in with bone growth problems - where they install screws into the bone and slowly stretch it. over few years maybe - eventually the bone becomes as long as the other leg's.
im pretty sure, if it doesnt get better on its own, somethin will have to be done. because he will limp.. (its like you puting on a boot with at least 1 inch heel on one leg, and leaving the other one bearfoot - how long is anyone gona be able to walk like that with one pain?) later causing hip problems and knee problems (in both legs) and back problems.
im not a specialist, im just telling what i have witnesses in my time working for a ortho doctor.
my advise is to see any ortho doctor, to get an opinion of a specialist - bones are bones, kids or adults. he would be able to explain things much better than a physician.
i hope this helps.
good luck