Could it be a stress fracture???

Very unlikely...it sounds like muscular and most young girls don't suffer sacral stress fractures unless they're doing extremely high mileage. My advice, it's probably a minor strain from the hill session. Running on it should not make it worse. Don't over stretch it and if it feels bad when running take a few days off. Strains can last for awhile though, I've noticed days off or running didn't change the healing time and sometimes running heals things quicker. Aches and pains are part of running, don't be fooled into thinking everything is a stress fracture. It's usually not.

Thanks that makes me feel so much better! I guess I'm just worried bc the pain is right at my sacroiliac joint- is it possible that I just strained it? If it were a stress fracture, I would probably fail the hop test right?

I get pain there as well. If you have a roller, try and roll it out. Stretch a little, run a little. Sacral stress fractures develop in people with high miles. I'm talking 100miles a week and not known to happen in 15 year olds because you naturally have strong bones. Younger h.s. girls would get stress in the foot or tibia and this is rare because of less mileage. You did say you have low body weight and ammenoreah. Please take care of this, you don't want to develop a sacral fracture years down the road because it will lead to that in your 20's. If you want to run and be healthy take care of yourself. Eat well. The top H.S. runners are strong and powerful, not skinny and weak.

I would say a sacral would hurt all the time and with a hop test. I can't see a 15 year old running enough to develop something like this and as I said, your bones are naturally strong enough at this age.

Thanks for the info, it was very helpful and I'm not as worried anymore. I was only running abt 45 miles a week, so not very high mileage. I am working with a nutritionist to gain some weight and get my period back, so hopefully no stress fractures in the future. Thanks!!

Sacral stress fractures DO happen in young runners. I've seen it. Do yourself a favor and go see a doctor, not some idiot on teh internet.

Also I looked and the exact spot where the pain is there is a small bruise

It's very likely it's nothing more than a tight muscle.

I don't think it is a tight muscle as the muscle itself does not hurt. It's a pain in my bone that hurts to the touch and radiates to my side hip when I walk and lift my leg laterally.

doesn't your own description confirm stress fracture ?

go see a doctor

That sounds like a SF or stress reaction definitely not muscular.

I'm seeing an orthopedist tomorrow morning. If I am able to hop on it though, wouldn't this make an SF unlikely?

I know this is an old post but I felt the need to reply! Thank you for stating this does happen to young runners. My daughter was just diagnosed with a left sacral ala stress fracture. She is 15 and was doing 40 mikes a week during XC season. She is 5’8 130 lb. All of her lab work, bone density scans and hormones were within normal limits. It was solely due to overtraining. That doesn’t always need to be high mileage in the sense some think. It was too much hard runs and workouts without enough rest in between. So to the original poster it definitely can happen to young girls! When in doubt get it checked out my daughter was diagnosed with SI JOINT dysfunction and a muscle strain for a month because no one thought it was suspected in a 15 year old.

if it still persists after a week, go to the orthopedist and ask for an MRI, even if he or she says no